Severe Weather Saturday for Colorado

I mentioned a couple days ago about the evolving severe weather threat along the front range setting up for today and it looks very possible that some areas will see it along the front range.

The latest Storm Prediction Center general outlook:

spc_05072016

The Castle Rock area has been moved out of the slight risk area this morning and into the marginal risk area. I’ll explain why I think this is a bit later.

Categorical risks are also out (percentage probability of seeing a type of severe weather within the risk area):

spcHAIL_05072016

A decent risk for hail exists today over Northeastern Colorado. The main risk area is at 15% while Castle Rock is in the 5% risk area. Hail is very possible today but not all areas along the Palmer Divide will see severe sized hail. If you live in any of these areas, keep an eye out for strong storms building and moving your way.

spcTOR_05072016

The highest risk of tornadoes will be in Northeastern Colorado today. I don’t see a strong chance for tornadoes for us along the Palmer Divide but we are included in the 2% chance area so the possibility exists of seeing them in and around the area today. I would be surprised to see at least a funnel cloud or two for us closer to home.

Severe Weather Threats

  • Strong to severe thunderstorms will produce gusty winds
  • Hail will be possible, sizes will be larger with areas that experience severe storms
  • Dangerous lightning will be likely with severe storms. 
  • There is a small tornado threat, mainly for areas Northeast of Denver, however some models suggest a brief timeframe where they are possible along the Palmer Divide

Timing

  • Storms will begin to initiate as early as 11AM-12PM along the foothills and Palmer Divide
  • Main severe threat along the Palmer Divide looks to be between 11AM-3PM
  • Storms will generally move in a Northerly or North-Northeasterly direction
  • By afternoon and into the evening hours, severe storms will transition mainly into Northeastern Colorado

Impacts

  • Hail could be large enough to cause damage in some areas
  • Lightning will be a big threat to people outdoors caught without shelter
  • There is a slight chance for tornadoes

 

Synopsis

A surface low building over Colorado will transition to the Southeaster areas of the state this morning. This will allow winds to turn Southeasterly bringing in moisture and enhancing upslope flow along the Front Range of Colorado. The terrain in and around Denver will veer these winds Northerly and Northwesterly at the surface.

05072016_HRRR_700mbwinds

This is a classical setup for a pattern we call the Denver Convergence Vorticity Zone or “Denver Cyclone.” These winds will loop around the metro area and as they turn Northwesterly they will crash into the winds from the Southeast along a line from the Palmer Divide, DIA and up into Northeastern Colorado. This area will see intense areas of lift and possible vorticity (spinning motion in the atmosphere.)

Storms that form and move along this boundary area have a chance of becoming severe and combined with the enhanced lift and vorticity, they will have a chance of large and a slight chance of funnel clouds and tornadoes.

The best chance as per model guidance for severe weather along the Palmer Divide is earlier in the day, 11AM-3PM time frame. Storms should begin to form in the area between 11AM-1PM.

If we look at the supercell parameter around 1pm we see:

This graphic shows the supercell parameter compsite. It is a measure of how favorable ingredients in the atmosphere are for severe storms. It does not gaurantee storms in these areas, just shows how favorable conditions are for any that do form to become severe.

This graphic shows the supercell parameter composite. It is a measure of how favorable ingredients in the atmosphere are for severe storms. It does not guarantee storms in these areas, just shows how favorable conditions are for any that do form to become severe.

3PM composite forecast

3PM composite forecast

By around 3pm or so, the main threat will move off to the Northeast. This environment is much more favorable with more heat and moisture to work with. We expect storms across the Northeast plains to get quite nasty through the afternoon and evening hours.

Summary

If you live along the Palmer Divide, be prepared for severe weather to initiate as early as 12PM. The most favorable window of severe weather looks to occur between 12-3PM along the Palmer Divide, after that time the atmosphere looks to stabilize and any additional storms will have difficulty forming.

Expect the possibility of hail (in some cases larger) and a slight chance of a funnel cloud or tornado. Today will not be a widespread, damaging severe outbreak, in fact many areas will see no severe weather at all.

While we appreciate you following us for weather coverage, we are not a great source for real-time weather warnings. I do not issue my own tornado warnings or severe storm warnings, I’m generally out chasing these so I don’t always catch the stuff going on close to home. If I am online and see something building along the Palmer Divide I will relay that information if I can.

Otherwise, I suggest following local TV News stations (my favorites are listed) or the NWS:

I’ll have any updates if necessary, but for today be safe and keep an eye on the sky. These things will pop up very, very quickly and if you are outdoors they will most likely have lightning. Stay weather aware!

 

Severe Weather Threat Possible for Colorado Saturday

A severe weather threat continues to evolve for Eastern and Northeastern Colorado on Saturday this weekend. This is something we will keep a close eye on through the next day or two and at this time it appears Denver and surrounding suburbs will be included in this threat.

day3otlk_0730_05052016

Day 3 RiskArea (sq. mi.)Area Pop.Some Larger Population Centers in Risk Area
SLIGHT59,5892,483,388Denver, CO…Aurora, CO…Thornton, CO…Westminster, CO…Highlands Ranch, CO…Castle Rock, CO
MARGINAL206,8579,033,185Kansas City, MO…Colorado Springs, CO…Lincoln, NE…Lubbock, TX…Amarillo, TX…

The current Storm Prediction Center outlook calls for a slight risk for severe weather across East Central, Northeastern Colorado and Western Kansas. Folks living in these areas will need to keep a close eye on the sky Saturday especially in the afternoon hours and especially if you are outdoors or plan to be during this time period.

Severe Weather Threats

  • Strong to severe thunderstorms will produce gusty winds

  • Hail will be possible, sizes will be larger with areas that experience severe storms

  • Dangerous lightning will be likely with severe storms. 

  • There is a small tornado threat, mainly for areas East and Northeast of Denver

Timing

  • Severe weather will be possible Friday night with the passage of a cold front 

  • Saturday will be the primary severe weather threat

  • Storms are expected to form over the mountains and foothills by early afternoon and move East

  • By afternoon and into the evening hours, severe storms will linger in the area, moving Eastward as we get later in the day

Impacts

  • Hail could be large enough to cause damage in some areas

  • Lightning will be a big threat to people outdoors caught without shelter

  • There is a slight chance for tornadoes

Synopsis

700mb.conus_05052016

A strong cold front will move through the area late Friday night. This may initially touch off a few strong thunderstorms late Friday but the main threat will establish behind the front on Saturday as the winds become Southeasterly and an up-slope setup establishes along the Colorado front range.

As the low moves into Southeastern Colorado, moisture will increase along the front range setting up a sharp dryline just South and East of Denver.

sfcrh.us_c.satby3pm_05052016png

This dryline will be the initial area of concern for severe thunderstorm initiation.

The overall setup looks very interesting to me, the profile of where the CAPE (convective available potential energy, how much lift and energy for severe storms over a certain area) fits a very similar pattern that we see in Colorado for severe weather events.

The Denver Convergence Vorticity Zone (DCVZ) is a phenomena we see in Colorado during severe weather season where upslope winds from the Southeast wrap around Denver and turn Northwesterly. This causes the winds to converge East and Northeast of Denver in a line. This convergence boundary is the focus for severe storms and tornadoes.

Credit: http://www.theweatherprediction.com/

Credit: http://www.theweatherprediction.com/

 

When you look at the CAPE profiles you see this:

sbcape.us_cbysat3pm_05052016

The red arrows in the image above point to an area of CAPE, lift in the atmosphere caused most likely be a DCVZ setup. We would expect these areas to be closely watched for the biggest storms.

Interestingly, there is a tornado threat that shows up on the models as well…

SigTor Parameter

SigTor Parameter

For this image, the higher the number the better the conditions for significant tornadoes. A threat does establish along that boundary zone for many on Saturday including Denver, Douglas, Arapahoe and Weld counties, but the number is overall relatively low. Still given that information, we cannot rule out the possibility of tornadoes.

As we move through the day into the evening the threat intensifies but shifts East.

stp.us_cbySat6PM_05052106

Summary

Not all areas will see severe weather on Saturday, the SPC outlooks mentions slight risk because storms will be initially very spotty. However, those areas that do end up under these storms should be prepared. Large hail, deadly lightning and strong winds will be the primary threats most experience with these storms. That being said, given the information I outlined above, tornadoes cannot be ruled out either.

If you have plans on Saturday, please keep an eye on the sky for these storms. If you see them building and moving over your area, be prepared to take shelter if needed. Have a severe weather plan in place!

We will continue to monitor this setup through the next few days, stay tuned!

 

A Look Back at April 2016 (Castle Rock Climate Summary)

April 2016 finished as the second month in a row with below average temperatures and well above average snow. Continuing the trend we saw in March, we experienced swings of warm weather followed by a couple of large, cold, wet storm systems that allowed our snowfall to finish way above average!

Below is a recap of what I recorded at my weather station on the North side of the Meadows in Castle Rock. These are not official measurements so may differ what the NWS has recorded ( their measurements for Castle Rock come from Centennial Airport)

If you are at all curious about how January – March went so far this year, you can see that data at the link below. I post results of each month’s weather data after the last day of each month.

See also: January 2016 – March 2016 Castle Rock Climate Summary

Apr2016_cs_title_banner

apr2016_cs_datasheet

Summary

There were some concerns about our strong El Nino pattern breaking down too quickly through March and all but eliminating our chances for a wet spring. March and now April 2016 delivered in a big way for moisture in Colorado and much of it in snowfall. Normally we see higher than average temperatures in an El Nino spring accompanying the higher than average precipitation, but April 2016 was the second month in a row with below average temperatures and well above average snowfall.

Apr2016_hightempchart

First we look at the temperatures. I saw a lot of similarities between March and April 2016. The front half of the month started out relatively warm and quiet while the second half of the month saw much below average temperatures as a series of storm systems moved through.

This helped April 2016 finish 1.07 degrees below average when combining daytime and nighttime temperatures (daily mean)

As is often the case in El Nino spring months, it was very, very soggy! The colder temperatures (again this was unusual for an El Nino spring month) ensured that a large amount of the precipitation that fell came down as snow.

In fact, April 2016 finished way above average in terms of snowfall.

Apr2016_snowvsaveraget

April is our third snowiest month and one of the wettest months of the entire year. It is not uncommon to see Aprils with large amounts of snowfall. April 2016 finished a staggering 16.8 inches over the normal monthly average for snowfall! To say it was a snowy month is an understatement but surprisingly didn’t crack one of the top snowiest Aprils in history. This was a snowy April, but we have had much snowier April’s in the past!

As if we needed any more proof of how soggy April was, here’s a look at collected precipitation and days they were collected. You can see we saw big numbers in the second half of the month pretty consistently.

Apr2016_precip

Speaking of which, this year Castle Rock has seen a large amount of snow!

apr2016_cs_snowgraphic

The city is only one good storm or maybe 2 smaller storms from seeing the most snowfall recorded in a single season in history. The previous amount was set in the early 80’s (folks who’ve been here awhile will remember the infamous 1982-1983 season accompanied by the Christmas Blizzard of ’82!) I took a look at a lot of stations along the Palmer Divide and foothills and many locations are very close to breaking their snowfall record too. Will we make it? Time will tell!

May 2016 Outlook

The CPC predicts a better chance of cooler and wetter than average weather through the month of May.

cpc_temps_may2016

Given the “troughiness” of the weather pattern (lots of storms projected to move through, generally every week or week and half or so) I can definitely see this being the case. Although I would consider this unusual to what we normally see in May during an El Nino year. I took a quick look at the GFS going out a ways and saw that while we do get some decently warm days here and there, every week or so a big storm system moves through and cools things back down. I saw no indication of strong ridges building in the first half of May, meaning temps will most likely be at or below average the first part of the month.

cpc_precip_may2016

The precipitation outlooks coincides quite well with what we are predicting above. Troughs continually moving out of the West (either Northwest or Southwest) will most likely mean we see at least a few soggy, multi-day storm systems through the month of May.

In short, we expect temperatures in May 2016 to be at or below average and precipitation to be slightly above average overall.

Weekend to Remain Unsettled, Big Warm Up On the Way!

For the folks asking where spring has been lately… it’s here! Spring is usually our wettest time of the year in Colorado and when you see average to below average temperatures a lot of that falls as snow. The last few days have been quite typical days for what we would expect in spring for Colorado.

Saturday – Sunday Will Be Cold, Wet and Unsettled

There are a couple of things going on today that are keeping the snow around, despite the fact the main storm system is well off to our East.

4-30-2016 2-07-31 PM

The main center of low pressure from our storm system is in Southeast Nebraska today, but it is still quite a large system and is pushing a ton of moisture around itself. In most circumstances this moisture would not make it back to Colorado but a disturbance parked over the mountains is helping to pull that moisture back into the state and continuing to enhance upslope along the front range enough for snow to fall.

Because of all these mechanisms working together, we are still seeing spotty snow showers along the front range including those of us South of Denver.

4-30-2016 1-58-48 PM

Radar snapshot as of 2PM today. Still lingering spotty snow showers in the area

This pair of systems is not moving all that quickly and many models have it staying with us through the day Sunday as well.

Monday – Wednesday, Beginning of the Warm Up

The Monday through Wednesday time period begins a slight warm up as the troughs move to the East and allow the air to warm a bit. I don’t see it getting super warm as no ridge has built in and won’t be transporting a lot of warm air into the state. Monday and Tuesday high temperatures look to be in the mid to upper 50’s for most higher elevation locations South of Denver.

850t_anom.conus_05042016

Wednesday the temperatures will be markedly higher with most locations in the upper 60’s to low 70’s and this is where the ball will start rolling on spring-like temperatures to end the week. Notice that big blob of warm air to our Northwest!

Thursday – Saturday, Cranking up the Heat!

By Thursday we see that warm air filtering down into Colorado.

850t_anom.conus_05062016

Some locations along the front range could see high temperatures in the 80’s Thursday and Friday. I think locations South of Denver along the Palmer Divide will struggle to reach 80 on Thursday but may have a chance for Friday. Unfortunately the warmth will be a bit short lived as another storm begins building to our West and begins to affect us as early as Saturday.

We will have to keep a close eye on the next storm system as we’ve seen with the last few how much precipitation they have been bringing into Colorado. The good news is that it doesn’t look like there is any snow with our next storm system but it is still early yet.

Thanks for visiting and reading everyone, enjoyed the comments and interactions through this latest storm. I will have a storm re-cap up in the next day or two with a look at how this storm did and snow totals. Have a great Saturday!

 

Spring Storm Update (April 29-30, 2016)

The snow started later than anticipated for much of us last night but now appears to have arrived. We had a good idea that this storm would be nothing like our blizzard a couple weeks ago, but we didn’t expect it to dwindle out as much as it has. There are a couple of things we are seeing this morning that are working against this storm, keeping that in mind, we will still see snow accumulate with this thing, just probalby not quite as much.

Updated Forecast

Despite the late start, we will see an increase in snow through the rest of the day. Snow showers along the Palmer Divide and areas South and East will have the best chance of accumulating snow. Temperatures will remain warm enough so that many areas at lower elevations won’t accumulate much.

Due to the late start of the snow and the increased temperatures during the daytime, I’d expect most roads will remain wet in Castle Rock and points North. Points to the South (higher elevations of the Palmer Divide) may see some accumulation on roads. At this time, it looks like most areas will have minimal travel impacts from this storm, would not be surprised to see the Winter Weather Advisory cancelled early.

In the forecast I’ve adjusted snow totals down slightly, there is still possibility totals hit the original forecast amount, but because of melting and compacting I don’t think those amounts will quite accumulate on the ground.

Area Snowfall Amounts

  • Castle Rock: 4-8 inches

  • Palmer Divide South (Larkspur, Monument…) : 6-12 inches

  • Western Douglas County Foothills: Spots of 8-16 inches, locally up to 20 inches

  • Denver: 2-4 inches

Timing

  • Snow showers will continue to spread on Friday morning 

  • Upslope increases through the day and snow lingers

  • Most models have the heavier snow bands moving out by Friday evening

  • Weather will remain unsettled with chances of rain and snow through the weekend but any additional accumulation will be minor

Impacts

  • Will remain mainly wet in lower elevation areas including Denver and Castle Rock. Some areas South of town in higher elevations may see some accumulation on streets, but overall travel impact with this storm is looking minimal.

Storm Synopsis

This storm has been very tricky to forecast, mainly because you have models telling you one thing, while mother nature is going another way.

Even this morning, models are particularly bearish on snowfall, but we are noticing some issues with this storms ability to organize and create decent upslope.

GFS snowfall predicted by 3PM Saturday

GFS snowfall predicted by 3PM Saturday

NAM snowfall predicted by 3PM Saturday

NAM snowfall predicted by 3PM Saturday

Nam4K snowfall predicted by 3PM Saturday

Nam4K snowfall predicted by 3PM Saturday

You’ll notice the NAM models have backed off of snowfall quite a bit from their runs yesterday. They also show a pronounced drier slot right along the front range foothills and Palmer Divide. This is a signal of downslope and could be a reason we had such a tough time getting snow going last night.

All in all, I don’t think the models have a great grasp on temperatures as they have consistently predicted lower temperatures than what have been observed. This seems to be a struggle for computer modeling on these late season spring snow storms.

When we look at a few other data sources we get confirmation on a few of these theories:

GOES_4-29-2016 8-46-31 AM

The GOES sattellite image above shows the low and its associated energy. When the storm doesn’t organize well it has a hard time pulling moisture in from the Gulf and creating upslope along the front range of Colorado. We saw hints of this last night and while its getting better organized now, it is moving off to the East quickly so the biggest impacts may be felt in Eastern Colorado and points further East.

The last bit of data we can look at is what is called a Skew-T diagram. These are created by NWS offices launching a balloon every 12 hours, for Denver it is 6AM and 6PM. We can also look at models for forecasted Skew-T’s. These diagrams give us an excellent idea of what winds, temperature and moisture are like at different heights of the atmosphere.

HRRRSkew4-29-2016 8-53-38 AM

There are a few things we can gather from this image:

  • Temperatures at the surface are much warmer than originally forecast. This could be due to downsloping and the fact the atmosphere is so saturated. The more moisture in the atmosphere, the longer it takes to cool down.
  • Weak and shallow upslope caused by weak winds out of the South-Southeast. We need stronger upslope at the surface combined with better upslope higher in the atmosphere for good snowfall.
  • There is a band of Southwesterly winds not too far above the surface, this is downslope and causes that level of the atmosphere to dry and kill upslope

So as you can see, there are quite a few things working against this storm to be a major snowfall producer. Latest modeling shows conditions getting better, but at this point the storm is beginning to move East. By loosing our snowfall last night and early this morning, we may not see the originally forecast totals.

 

I’ll bee keeping an eye on this storm today and will have any updates or changes up on facebook or the website.

 

***Winter Weather Advisory Issued*** (April 28-30,2016)

The Winter Storm Watch that was originally issued along the Palmer Divide has been upgraded to a Winter Weather Advisory.

Latest Update on Winter Weather Watches/Warnings/Advisories

ww_04282016_1PM

**Winter Weather Advisory In Effect**

Timing

WINTER WEATHER ADVISORY IN EFFECT FROM 6 PM THIS EVENING TO MIDNIGHT MDT FRIDAY NIGHT

Cities/Areas Included

CASTLE ROCK…ELBERT…FONDIS…KIOWA… LARKSPUR

Snowfall

ANYWHERE FROM 6 TO 12 INCHES BY LATE FRIDAY EVENING.

Impacts

WET HEAVY SNOW ACCUMULATING ON BRANCHES AND POWER LINES COULD LEAD TO TREE DAMAGE AND POWER OUTAGES. ROADS MAY BECOME SLUSHY AND POSSIBLY SNOW COVERED TONIGHT AND AGAIN FRIDAY EVENING. DUE TO THE HIGHER SUN ANGLE THIS TIME OF YEAR ROADS AND HIGHWAYS MAY NOT SEE MUCH IF ANY SNOW ACCUMULATION DURING THE DAYLIGHT HOURS ON FRIDAY.

A WINTER WEATHER ADVISORY FOR SNOW MEANS THAT PERIODS OF SNOW WILL CAUSE PRIMARILY TRAVEL DIFFICULTIES. BE PREPARED FOR SNOW COVERED ROADS OVERNIGHT AND LIMITED VISIBILITIES. SLOW DOWN AND USE CAUTION WHILE DRIVING.

**Winter Storm Warning In Effect**

Timing

THE NATIONAL WEATHER SERVICE IN DENVER HAS ISSUED A WINTER STORM WARNING FOR SNOW…WHICH IS IN EFFECT FROM 6 PM THIS EVENING TO MIDNIGHT MDT FRIDAY NIGHT. THE WINTER STORM WATCH IS NO LONGER IN EFFECT.

Cities/Areas Included

CAMERON PASS… LARAMIE AND MEDICINE BOW MOUNTAINS…RABBIT EARS RANGE… ROCKY MOUNTAIN NATIONAL PARK…WILLOW CREEK PASS… BERTHOUD PASS…BRECKENRIDGE…EAST SLOPES MOSQUITO RANGE… EAST SLOPES SOUTHERN GORE RANGE…EISENHOWER TUNNEL… INDIAN PEAKS…KENOSHA MOUNTAINS…MOUNT EVANS… WILLIAMS FORK MOUNTAINS…WINTER PARK…ESTES PARK…GLENDEVEY… NEDERLAND…RED FEATHER LAKES…BAILEY…CENTRAL CITY… EVERGREEN…GEORGETOWN…IDAHO SPRINGS…WESTCREEK…FAIRPLAY… HARTSEL…LAKE GEORGE…SOUTH PARK

Snowfall

GENERALLY 10 TO 20 INCHES. FAVORED UPSLOPE AREAS EAST OF THE CONTINENTAL DIVIDE WILL SEE THE MOST SNOW… WITH TOTALS PERHAPS APPROACHING TWO FEET.

Impacts

ACCUMULATING SNOW ON BRANCHES AND POWER LINES COULD LEAD TO TREE DAMAGE AND POWER OUTAGES. ROADS WILL AT LEAST GET SLUSHY THURSDAY NIGHT AND FRIDAY NIGHT BUT DUE TO THE HIGH SUN ANGLE DURING THE DAY ON FRIDAY THEY MAY NOT EXPERIENCE A LOT OF ACCUMULATION DURING THE DAYLIGHT HOURS.

A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW… SLEET AND ICE ARE EXPECTED OR OCCURRING. TRAVEL IS LIKELY TO BE SEVERELY IMPACTED.

Forecast Update

Everything else looks on track about this storm so far.

See Also: Morning Forecast Update for Thursday April 28, 2016

The SREF continues to climb this afternoon with the ensemble forecast for snowfall. This morning we were sitting at an average of 11.83 inches of accumulation between all models.

This afternoon we are at 14.07 inches as a mean. I think this may be a bit overdone based on temperatures but does give me higher confidence in the 8-12 inch range for Castle Rock.

SREF_sno_05022016_00Z We’ll keep an eye on it for any changes into this evening.

Stay tuned!

 

Spring Storm to Bring Significant Snowfall South and West of Denver (April 28-April 30, 2016)

Models have been predicting snow all week but the biggest question we were waiting for confirmation on was; how much cold air actually makes it in and where does that put the snow line down to? Based on model updates late last night and into this morning, we are predicting colder air to filter in than originally anticipated with this storm meaning the snow line will move downward in elevation.

With that information, the NWS has upgraded Winter Storm Watches along the foothills to Warnings and issued new watches that include the rest of the Palmer Divide. Warning details, forecast updates and model guidance are all updated below.

Current Winter Weather Watches/Warnings/Advisories

ww_04282016_8AM

**Winter Storm Watch In Effect**

Timing

THE NATIONAL WEATHER SERVICE IN DENVER HAS ISSUED A WINTER STORM
WATCH...WHICH IS IN EFFECT FROM THIS EVENING THROUGH FRIDAY
EVENING.

Cities/Areas Included

CASTLE ROCK...ELBERT...FONDIS...KIOWA...
LARKSPUR

Snowfall

6 TO 12 INCHES ARE EXPECTED BY LATE FRIDAY
EVENING.

Impacts

ACCUMULATING SNOW ON BRANCHES AND POWER LINES COULD
LEAD TO TREE DAMAGE AND POWER OUTAGES. ROADS WILL GET SLUSHY OR
SNOW PACKED TONIGHT AND FRIDAY NIGHT. HOWEVER...DUE TO THE HIGH
SUN ANGLE DURING THE DAY ON FRIDAY HIGHWAYS MAY NOT EXPERIENCE
AS MUCH SNOW ACCUMULATION DURING THE DAYLIGHT HOURS.
A WINTER STORM WATCH MEANS THERE IS A POTENTIAL FOR SIGNIFICANT
SNOW...SLEET...OR ICE ACCUMULATIONS THAT MAY IMPACT TRAVEL.
CONTINUE TO MONITOR THE LATEST FORECASTS.
**Winter Storm Warning In Effect**

Timing

THE NATIONAL WEATHER SERVICE IN DENVER HAS ISSUED A WINTER STORM
WARNING FOR SNOW...WHICH IS IN EFFECT FROM 6 PM THIS EVENING TO
MIDNIGHT MDT FRIDAY NIGHT. THE WINTER STORM WATCH IS NO LONGER IN
EFFECT.

Cities/Areas Included

CAMERON PASS...
LARAMIE AND MEDICINE BOW MOUNTAINS...RABBIT EARS RANGE...
ROCKY MOUNTAIN NATIONAL PARK...WILLOW CREEK PASS...
BERTHOUD PASS...BRECKENRIDGE...EAST SLOPES MOSQUITO RANGE...
EAST SLOPES SOUTHERN GORE RANGE...EISENHOWER TUNNEL...
INDIAN PEAKS...KENOSHA MOUNTAINS...MOUNT EVANS...
WILLIAMS FORK MOUNTAINS...WINTER PARK...ESTES PARK...GLENDEVEY...
NEDERLAND...RED FEATHER LAKES...BAILEY...CENTRAL CITY...
EVERGREEN...GEORGETOWN...IDAHO SPRINGS...WESTCREEK...FAIRPLAY...
HARTSEL...LAKE GEORGE...SOUTH PARK

Snowfall

GENERALLY 10 TO 20 INCHES. FAVORED UPSLOPE
AREAS EAST OF THE CONTINENTAL DIVIDE WILL SEE THE MOST SNOW...
WITH TOTALS PERHAPS APPROACHING TWO FEET.

Impacts

ACCUMULATING SNOW ON BRANCHES AND POWER LINES COULD
LEAD TO TREE DAMAGE AND POWER OUTAGES. ROADS WILL AT LEAST GET
SLUSHY THURSDAY NIGHT AND FRIDAY NIGHT BUT DUE TO THE HIGH SUN
ANGLE DURING THE DAY ON FRIDAY THEY MAY NOT EXPERIENCE A LOT OF
ACCUMULATION DURING THE DAYLIGHT HOURS.
A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW... SLEET
AND ICE ARE EXPECTED OR OCCURRING. TRAVEL IS LIKELY TO BE SEVERELY
IMPACTED.

Forecast

Expect a cool and cloudy Thursday with highs only reaching the mid 40’s in Castle Rock and most places along the Palmer Divide. Rain tonight will transition into snow through early Friday morning. Friday looks to be the biggest impact day, snow will continue and accumulate all day into Friday night and possibly early Saturday morning.

Area Snowfall Amounts

  • Castle Rock: 8-12 inches

  • Palmer Divide South (Larkspur, Monument…) : 10-20 inches

  • Western Douglas County Foothills: Spots of 10-20 inches

  • Denver: 3-6 inches

Timing

  • Rain showers will begin Thursday and last on and off through the day. 

  • Rain will transition into snow later on Thursday

  • By Thursday night into Friday snow will fall and begin to accumulate

  • Best chances of snow is late Thursday, all day Friday and into Saturday morning. Lighter snow will linger on Saturday – Sunday

  • Impacts

    • Heavy snow will stress budding or trees with leaves on them. Keep an eye on those branches and be prepared to shake them off frequently to prevent damage

    • Heavy snow may accumulate on power lines causing power outages in areas

    • Road conditions may get slushy and snow-packed in some areas. Due to the warmer daytime temperatures and higher angle of sunlight, travel may become tricky in some areas but not all areas will see bad road conditions.

Latest Model Guidance

 

 

GFS (Long Range Model)

Storm Total Accumulation by Saturday April 30, 2016 6:00PM

The GFS agrees on snowfall with colder air filtering
in behind this storm system. Because of that
it has jumped on board for significant snow up
and down the urban corridor.

Using 10:1 Ratio: 10-12 inches of snow

 

NAM (Medium Range Model)

Storm Total Accumulation by Saturday April 30, 2016 6:00PM

The NAM shows slightly lesser accumulation than
the GFS, however it is on board with significant
snow accumulation up and down the front range.
Its overall range of snow accumulation is
consistent with other models

Using 10:1 Ratio: 8-10 inches of snow

 

NAM4K (Short-Medium Range High Resolution Model)

Storm Total Accumulation by Saturday April 30, 2016 12:00PM

The NAM 4K’s range doesn’t quite encompass
the entire storm yet but is consistent with other
models in range to snowfall

Using 10:1 Ratio: 9-12 inches of snow

 

SREF Ensemble (Short Range Model Ensemble)

Storm Total Accumulation by Saturday April 30, 2016 12:00PM

The SREF is a combination of a bunch of model
runs. It generally has a better accuracy level
than just looking a single model (GFS,NAM,etc…)

The SREF Ensemble has been slowly
but consistently pushing snowfall totals
upwards over each run. It has settled just a
tad below the one foot mark as of this morning
(Accumulation as an average between all
short range models): 11.83 Inches

**Please note, the snowfall forecast ranges are looking at data for the Castle Rock area.

 

Summary

This spring storm is loaded with moisture and just like the last, temperatures will play a huge part on how much snowfall accumulates. The biggest impact to travel looks to be Friday and possibly Saturday morning, so keep that in mind if you are commuting in on Friday or out and about on Saturday.

This storm will not trap you in your house for days, so I honestly don’t think a grocery store run is necessary as long as you have food for Friday and Saturday. Most likely, roads will be slushy but passable and clearing on Saturday by late morning.

I will be keeping a close eye on that watch area and will relay any information in forecast change or warning upgrades throughout the day today. Stay tuned!

 

Tracking This Week’s Possible Snow Storm (April 28-30, 2016)

Model guidance is continuing to suggest a very wet and soggy storm system to affect the area later this week and into this weekend. While this storm shows a lot of similarities to our blizzard we had just a couple of weeks ago there are some big differences as well. This storm is showing no signs we need to go raid the grocery stores as of this time.

  • Similarities
    • This storm has a ton of moisture, just like the last one it taps into gulf moisture and spins this into the state giving us ample up slope to produce precipitation
    • It is very slow moving. Many models have the affects of this storm being felt from Thursday this week into Tuesday next week
  • Differences
    • This storm looks to have trouble tapping into colder air form the North. This means more precip may fall as rain and snow may take longer to accumulate, diminishing overall totals
    • Because of the first point, temperatures will remain warmer overall. A single degree warmer or colder makes a huge difference in the spring-type storms
    • The storm track is slightly further South meaning we would see the best snow further South. Areas along the Palmer Divide and into Springs will see the most moisture, but elevation will play a key role in snowfall amounts

Model Guidance on Snowfall as of This Morning

(Again, not official forecasts. These are just a look at models at this time)

 

 

GFS (Long Range Model)

Storm Total Accumulation by Saturday April 30, 2016 12:00PM

The GFS shows snowfall along the front range
Thursday night into Friday and possibly
lingering into Friday. The amount shown
uses a 10:1 ratio but warm temperatures may
cut this amount down.

Using 10:1 Ratio: 3-6 inches of snow
Using 5:1 Ratio: 1-3 inches of snow

 

NAM (Medium Range Model)

Storm Total Accumulation by Saturday April 30, 2016 12:00PM

The NAM shows lesser snow accumulation
possibly due to a warmer atmosphere or
storms in the East robbing us of moisture and
dampening our upslope.

Using 10:1 Ratio: 1-3 inches of snow
Using 5:1 Ratio: 0-2 inches of snow

 

NAM4K (Short-Medium Range High Resolution Model)

Storm Total Accumulation by Friday April 29, 2016 12:00PM

The NAM 4K’s range only goes through Friday
noon at this point. It shows some of the finer
details with the storm and shows similar totals
to the other 2 models.

Using 10:1 Ratio: 1-3 inches of snow
Using 5:1 Ratio: 0-2 inches of snow

 

SREF Ensemble (Short Range Model Ensemble)

Storm Total Accumulation by Saturday April 30, 2016 6:00PM

The SREF is a combination of a bunch of model
runs. It generally has a better accuracy level
than just looking a single model (GFS,NAM,etc…)

This model shows a solution more in line with the
GFS and shows slightly higher snowfall
accumulation along the Palmer Divide
Predicted Snowfall (as an average between all
short range models): 6.17 Inches

 

Current Winter Weather Watches/Warnings/Advisories

WW_04272016_11AM_2

This watch does not include Central or Eastern Douglas County as of this time. Castle Rock is not included.

**Winter Storm Watch In Effect**

Timing

WINTER STORM WATCH IN EFFECT FROM THURSDAY EVENING THROUGH
FRIDAY EVENING

Cities/Areas Included

CAMERON PASS...
LARAMIE AND MEDICINE BOW MOUNTAINS...RABBIT EARS RANGE...
ROCKY MOUNTAIN NATIONAL PARK...WILLOW CREEK PASS...
BERTHOUD PASS...BRECKENRIDGE...EAST SLOPES MOSQUITO RANGE...
EAST SLOPES SOUTHERN GORE RANGE...EISENHOWER TUNNEL...
INDIAN PEAKS...KENOSHA MOUNTAINS...MOUNT EVANS...
WILLIAMS FORK MOUNTAINS...WINTER PARK...ESTES PARK...GLENDEVEY...
NEDERLAND...RED FEATHER LAKES...BAILEY...CENTRAL CITY...
EVERGREEN...GEORGETOWN...IDAHO SPRINGS...WESTCREEK...FAIRPLAY...
HARTSEL...LAKE GEORGE...SOUTH PARK

Snowfall

GENERALLY 10 TO 20 INCHES. FAVORED UPSLOPE
AREAS EAST OF THE CONTINENTAL DIVIDE WILL SEE THE MOST SNOW...
WITH TOTALS PERHAPS APPROACHING TWO FEET.

Impacts

ACCUMULATING SNOW ON BRANCHES AND POWER LINES COULD
LEAD TO TREE DAMAGE AND POWER OUTAGES. ROADS WILL AT LEAST GET
SLUSHY THURSDAY NIGHT AND FRIDAY NIGHT BUT DUE TO THE HIGH SUN
ANGLE DURING THE DAY ON FRIDAY THEY MAY NOT EXPERIENCE A LOT OF
ACCUMULATION DURING THE DAYLIGHT HOURS.

Summary

At this time there is no reason to panic with this storm. With what we are seeing now it looks like it will at worst be an inconvenience for folks below 7,000 feet in elevation on Friday and possibly Saturday. This storm does not look like it will produce the type of snowfall that will trap you in your house so no reason to run on the grocery stores.

We will continue to keep an eye on the forecast and relay any changes in forecast through the day Wednesday and Thursday regarding higher or lower snowfall amounts. Stay tuned!

 

Unsettled Stormy Week to End April

A series of weather systems will move through this week keeping our weather cloudy, cool and wet with decent chances of thunderstorms and even chances of snow, especially for areas along the Palmer Divide.

Tuesday April 26

HRRR_TuesApr27_2pmRun

Forecast radar as of 3PM

The first our disturbances began to move through on Monday night, touching off a few thunderstorms late into the evening and into Tuesday morning with the passage of a cold front. Because of this front, temperatures along the front range will struggle to hit 60 degrees.

Thunderstorms will become likely, especially for areas South of Denver in the afternoon hours. While we are not expecting severe weather, we cannot rule out the possibility of a strong or severe storm along the Palmer Divide. The greatest chances of thunderstorms based on modeling is between 2pm-6pm.

Chance of Snow?

There is the possibility of snow Tuesday night. As temperatures cool into the low 30’s during the overnight hours, precipitation falling as rain may mix with snow. Some models show accumulating snow and some do not, but anything that falls will melt quickly. Along the Palmer Divide, some of the Western areas will see some snow accumulation while most other areas will see anywhere from 0-2 inches.

Castle Rock can expect 0-2 inches, but will vary greatly depending on elevation and which areas see precipitation. So all in all, not a major snow producer.

GFS predicted snowfall by Weds AM

GFS predicted snowfall by Weds AM

Wednesday April 27 – Friday April 29

Wednesday will be a bit of a transition period between storm systems.

NAM_mlsp_04272016_18Z

Predicted surface-mid level winds on Wednesday. Note the tail end of the jet over Colorado, this means breezy/windy conditions will be likely

As the last storm system departs Colorado will find itself on the tail end. This will mean dry but cool weather, it should also be quite breezy as well. High temperatures will once again be in the 50’s to near 60 but skies should be mostly clear through the day.

By Thursday and Friday we see more energy and moisture move into the area.

NAM_radref_04292016_00Z

Predicted radar image from Thursday evening, moisture streams in from the South combined with the energy behind a cold front will mean thunderstorms are possible

Severe weather is not anticipated at this point but expect rain and thunderstorms behind the initial front moving through Thursday evening/night. By Friday, expect much cooler temperatures in the 40’s with rain showers throughout the day. There is also still some question between models as to whether snow starts falling on the Thursday-Friday time-frame instead of the Saturday – Sunday time-frame.

Saturday April 30 – Sunday May 1

As of this posting snowfall is looking likely during this time-frame, especially South of Denver. Models are picking up on some decent snow totals along the Palmer Divide and foothills as of this morning’s runs.

Here’s what we are seeing so far (Please Note: this is not an official forecast, just a look at what models are predicting at this time!)

For the Castle Rock Area:

  • GFS
    • 8-12 inches total accumulation
    • GFS_sno_04302016_06Z
  • NAM
    • 6-10 inches total accumulation
    • NAM_sno_04292016_12Z
  • SREF Ensemble
    • 4-6 inches total accumulation
    • srefsnowfall04262016

Summary

There is still a ton of uncertainty with the snow chances later this week and into the weekend. Most models across the board are predicting some type of snowfall accumulation but they can’t agree on what time it gets here. Some models have snow falling as early as Thursday night along the Palmer Divide, others don’t have any until Saturday. This is another one of those, “too early to call” situations, but that being said I will be watching the models very closely the rest of this week.

Plan for

  • Snowfall likely later this week into the weekend
    • Snowfall accumulations cannot yet be determined, so if you here forecast amounts yet take them with a huge grain of salt.
  • Snowfall accumulations look less than our blizzard at this time, but could be significant enough to impact travel

Stay tuned with us throughout the week as we will have updates when the models give us a better clue as to this storm’s behavior.

 

Unsettled Weather May Continue into May

After a cold a snowy weekend, followed by a very unsettled and cool first half of the week; we are finally looking forward to some nicer weather over the next few days!

Thursday-Sunday (This Weekend)

euro_fri4222016

A ridge of high pressure will begin to build on Thursday allowing warmer and drier air to filter into the state from the South. This will mean that we are in for some sunny and warm days for at least a little while.

euro_850mbtempanomly_04242016

As we move into Saturday and Sunday the high pressure ridge and associated blob of warm air hangs around the central U.S. For Colorado, I would not be surprised to see some locations in Eastern Colorado flirting with high temperatures in the 80’s at some point. This warm stretch should definitely help rid us of any remaining snow.

Monday April 25 – Tuesday April 26 Time frame (Storm #1)

euro_500mb_04262016

The Euro signals a change during this time period but at this time is not predicting a major snow storm, or even a major storm in general for Colorado. There are a few reasons why detailed in the image above:

  • This low pressure system is much less organized. It moves out of the due west, getting shredded by the mountains as it crosses the divide and re-organizes over Northeast Colorado. This storm track does not usually produce big precip. storms for us along the front range.
  • The positioning of the low once it re-forms is too far North so that decent upslope is not established for a decent amount of time.
  • Due to the weaker nature of the storm, it looks to have trouble tapping into cooler air from the North. This means any precip we do get would most likely fall as rain.

At this time, this storm looks more likely to drop rain rather than snow and doesn’t look to drop a lot of precipitation in general We’ll keep an eye out for any forecast changes

Friday April 29 – Monday May 2 Time frame (Storm #2)

This is still a long way out and on the very edge of our long range model’s ability to forecast so there is a ton of time for this to change either way, but thought it was worth mentioning as it has caught my eye.

If we look at the very edge of the long range Euro and GFS we see a situation that sets up like this:

500mb_euro_thurs04282016

As we move into later in the day on Thursday April 28, we see a strong low pressure trough carving out in the Western United States. This low looks decently organized on most models at this point and is expected to take a more Southerly track before turning Northeast and moving into Southeastern Colorado. This is important because the storm will not get shredded nearly as much crossing the Southern mountains and has a decent chance of retaining more energy.

By Friday we see an interesting setup:

500mb_euro_fri04292016

There’s a few reasons this jumps out at me but there are questions with it too.

  • The low pressure system remains well organized as it moves into Southeastern Colorado
    • This position usually gives the front range decent upslope and moisture
  • A blocking high pressure system sets up to our East
    • This is the same type of feature that stalled out the low and dumped snow over Eastern Colorado with our big April snowstorm last week
    • If the low stalls out over the Southeast part of the state it means we will see a longer period of upslope flow, enhancing whatever preciptation may fall
  • Questions
    • Being this far out, this setup still needs to be take with a huge grain of salt. Models aren’t terribly accurate this far away, especially on the edge of their range.
    • Does the cold air get cut off by the ridge to our West or East? If so, precipitation will most likely be rain.

This setup certainly looks similar to our big snowstorm last week, but don’t take it to the bank just yet. Suffice to say, we will keep a close eye on it as we get into next week and pass along any forecast changes.

In the meantime, enjoy the warm and dry weather we get this weekend, it will be an excellent time to get out and about. Happy Thursday!