Saturday March 26 Winter Storm Update

Snow continues at this hour for the Castle Rock area and for areas South into Colorado Springs. This storm is mainly affecting these areas and is not doing a whole lot for Denver or suburbs immediately South of Denver.

A 9:30AM look at the radar shows the narrow areas of light to moderate snow:

radar_3-26-2016 9-35-21 AM

Air temperatures overnight remained relatively warm which means a good portion of this snowfall has melted. 3-6 inches was my forecast yesterday and this still looks to be on track. Roads were a bit slick this morning when I was out and about but are recovering as temperatures continue to warm slightly.

This morning there is a slight bit of wind out of the North so we are getting just enough of a windchill to make it feel quite cold out. Be sure to bundle up before heading out anywhere as it will remain chilly today with high temperatures only projected to reach the lower 30’s.

windchill_wind3-26-2016 9-36-33 AM

Many areas around Castle Rock are showing light winds out of the NNE and wind chill temperatures in the teens.

The Rest of Saturday

The bulk of models have light snow continuing through the morning with most of it tapering off by about noon.

Forecast radar at 12PM (HRRR)

Forecast radar at 12PM (HRRR)

Expect the light snow to end by late morning or into early afternoon at some point. Accumulations today will be light as additional snowfall will have a difficult time overcoming melting. Expect maybe another inch or two if you are in the Castle Rock area on top of what you already have this morning.

HRRR predicts light accumulation for Palmer Divide the rest of Saturday

HRRR predicts light accumulation for Palmer Divide the rest of Saturday

Easter Sunday

The good news is the current storm will scoot out of here pretty quickly and a high pressure ridge will begin to build behind it meaning warmer and drier air will make its way into the state as early as Sunday. It will still be a bit chilly during the day, high temperature is expected to reach right around 50 degrees but a bit of wind may make it feel a bit cooler than that.

WinterWxStory_EasterForecastt

Weather looks to be quiet through late Tuesday so we won’t have a whole lot of posts up on Sunday. Monday we will begin taking a look at our next storm system and chance for snow.

Have a great weekend everyone!

 

Afternoon Update

This will be a very short post folks as I have not seen big changes to this forecast. I will start off this post by saying I don’t agree with the National Weather Service’s prediction of 5-10 inches for the Castle Rock area. I’m sticking with 3-6, but believe even that may be high, if I’m wrong and they are right I will gladly post a big picture of a crow tomorrow and eat the entire thing…

 

This is a huge reason why I’m not with the NWS on this storm; every model except the GFS takes a lot of the precipitation south of Castle Rock. I’m not saying we don’t get any snow, but anything over 6 inches is a long shot.

3-25-2016 4-03-00 PM

Snowfall accumulation probabilities for Denver and Castle Rock

Castle Rock is in the blue, you can see anything over 6 inches of accumulation is about a 20% chance of happening. The last storm was a long shot too and proved a lot of us wrong so keep in mind, it is March and anything can happen. Sometimes mother nature likes to beat the odds, in this case it looks possible but very unlikely.

Maybe I’ll be humbled again? Tune in tomorrow to see!

Final Forecast/Impacts

wwadv_03252016

A Winter Weather Advisory has been issued for the Castle Rock area and points East and South. A Winter Weather Advisory is issued when periods of heavy snow make for difficult travel conditions. I have no doubt we will see some bands of moderate to heavy snow through the night but this storm may already be winding down by morning to early afternoon. Also, as I stated above, I think the 5-10 inch range for Castle Rock  is quite overdone.

For snowfall I’m staying put on my forecast based on data I’ve seen so far. This could still change later tonight but I see no reason to change with data I’ve received today.

Castle Rock: 3-6 inches

Palmer Divide South (Larkspur, Monument…) : 5-10 inches

Denver: 0-2 inches

Expect:

  • Some bands of moderate to heavy snowfall at times

  • Winds at 15-25mph will cause minor snow drifting

  • Roads will become icy and snow packed through periods of heavier snow

  • Travel may become difficult at times earlier on Saturday

 

At the risk of repeating myself too much, I probably won’t post again ahead of this storm  unless the forecast changes drastically tonight. I will most likely have a post up Saturday morning with coverage of how the storm is going, but not much else tonight unless things change.

The snowfall amounts and impacts above remain the same as of right now.

Hope everyone has a great Friday night and stay warm and be safe if out and about this evening.

 

Friday/Saturday Winter Storm Update

A quick update on where we are this morning with regards to our projected winter storm scheduled to arrive Friday afternoon and into Saturday morning.

Model Guidance

If you click through each model below, you will see a lot of uncertainty still remains about this storm. It does not look to be a major storm like we saw Wednesday and while I know we’ve said that before, the dynamics if this storm system are very different from the last. The way it is moving into Colorado, the energy is has and the track and speed are all working against it. Every model has it moving out of the state very quickly so even if it sets up in a favorable position, it may not linger long enough to dump heavy snow along the front range.

03252016_GFS_21ZSAT

GFS snowfall by Saturday PM

03252016_HRRR_04ZSAT

HRRR snowfall by Saturday PM

NAM snowfall by Saturday PM

NAM snowfall by Saturday PM

NAM4K snowfall by Saturday PM

NAM4K snowfall by Saturday PM

Since all of these models (minus the HRRR) were terrible with the last storm, we can take a look at the one that nailed it pretty early on. The MLSP part of the EURO gives us a glimpse of where it believes the storm system will set up after it moves across the Rockies.

03252016_EMCWF_00ZSAT_2

If the EURO verifies again with the positioning of the storm, it has the main energy too far South to affect areas North of the Palmer Divide much. The big question is will areas along the divide get much if any snow out of this or will the storm be too far South so that down sloping kills snowfall along the divide?

Uncertainty Remains

What do you do when half the models tell you we get snow and half don’t? We look around for a few other clues…

The SREF ensembles are a good way to look a bit closer at what many different models may be picking up on. Unfortunately, the don’t run these for the town of Castle Rock itself, but they do have one for Centennial Airport and one for Monument. I generally take a look at both of these and average the result out:

Centennial Airport snowfall ensemble: 2.72 inches

Centennial Airport snowfall ensemble: 2.72 inches

Monument Hill snowfall ensemble = 4.18 inches

Monument Hill snowfall ensemble = 4.18 inches

If you average both together and take that amount for Castle Rock you get a total of 3.45 inches. That falls in my initial forecast range of 3-6 for Castle Rock, albeit on the lower end. This may mean I shift my forecast downwards at some point on Friday if I see no change in the models.

Keep an Eye on Forecast Changes Friday Afternoon

I’m not sold at all on this storm system at this point. There are many things working against it and most models have the main energy going too far South to be any major affect on the Castle Rock area. I’m not entirely sure the Winter Storm Watch will stand in the end. Admittedly, even the NWS has mentioned this:

THE GFS IS THE ONLY MODEL
SHOWING HEAVY SNOW IN THE SRN FOOTHILLS AND PALMER DIVIDE AREA WHILE
THE OTHER MODELS KEEP THE THREAT FOR HEAVY SNOW FURTHER SOUTH OVER
SRN CO.  AT THIS POINT CONFIDENCE IS NOT HIGH AS TO WHAT TO DO WITH
THE WATCH SO WILL LET IT RIDE AND SEE IF THERE IS BETTER CONSENSUS
WITH THE LATE MORNING RUNS.


The key words in this statement: AT THIS POINT CONFIDENCE IS NOT HIGH

Forecast

At this point, I’m sticking to my forecast much like the NWS and awaiting further data through the day on Friday. For this storm, it’s best to be prepared for the impacts Saturday morning but realize that this storm may not do a whole lot. I can see dropping snow totals especially for Denver and Castle Rock this afternoon unless the models start to flip.

Castle Rock: 3-6 inches

Palmer Divide South (Larkspur, Monument…) : 5-10 inches

Denver: 0-2 inches

Stay tuned for any updates today, if we see a major shift in model guidance I will update accordingly.

 

Getting Ready for Round 2. Winter Storm Watch Issued…

I warned earlier this week that our Wednesday storm was just the first in a series of storms to affect our area.

This afternoon, the National Weather Service issued a Winter Storm Watch in anticipation of our next storm.

WinterStormWatch_3-24-2016 4-14-19 PM

Note: This watch includes Palmer Divide Cities such as Castle Rock, Elbert, Kiowa, Larkspur, Monument… it does not include areas North of Castle Rock at this time (including Parker, Lone Tree, Denver…)

See Also: Current Colorado Weather Watches/Warnings/Advisories

Impacts

  • Moderate to Heavy snowfall

  • Winds at 15-25mph will cause minor snow drifting

  • Roads will become icy and snow packed through periods of heavier snow

  • Travel may become difficult at times on Saturday

 

Snowfall Forecast

This looks to be another tricky storm. Like this past storm, models are picking up on some pretty decent snowfall but can’t agree who is going to get it. Right now, I can do a preliminary forecast for snowfall, but as always expect this to change through the day Friday.

Castle Rock: 3-6 inches

Palmer Divide South (Larkspur, Monument…) : 5-10 inches

Denver: 0-2 inches

**Keep in mind this is preliminary today, this forecast may change upwards or downwards based on the data I see throughout the day Friday.

Synopsis

Here we go again, another storm that is 50/50, on the verge of being nothing or something significant just like this past storm on Wednesday.

There are a few things that this storm will lack that the other one had.

If we compare the look of the storm (and I’ll use the Euro to illustrate this) we can see it is nowhere near as organized as the blizzard was.

Euro model low positioning Tuesday night

This was the low position forecast for our blizzard on Wednesday

Euro_03242016_21ZSat_MSLP

Forecast storm position for Saturday’s storm

 

You can notice some differences in the two images above:

  • Blizzard storm positioning and strength
    • Notice the tightly wound low sitting over Eastern Colorado. This “closed low” as we call it is generally the sign of a stronger storm system. It has colder air to work with and a lot more energy and moisture
  • Saturday’s storm positioning and strength
    • The main energy of the storm stays well North of Colorado
    • We are only getting snow because there is a smaller disturbance the sets up to the South of the main storm
    • This means we are seeing a weaker storm overall but still has potential

The next storm system will also lack the strong winds (although we will see decent winds in the 15-25 mph range) and is projected to move very quickly.

Interestingly enough, here’s a look at snowfall models:

GFS projected snowfall by Saturday PM

GFS projected snowfall by Saturday PM

NAM projected snowfall by Saturday PM

NAM projected snowfall by Saturday PM

So I’ve said this before, but pretty open and shut case right? Models tend to zero in on a range of 2-6 inches of total snowfall, but then comes the Nam4K, a higher resolution and shorter range model:

Nam4k projected snowfall by Saturday PM

Nam4k projected snowfall by Saturday PM

Ugh! This model keeps the bulk of the snowfall south of the Palmer Divide. If this model were to verify, we would see maybe an inch at most.

Summary

There are not a lot of similarities between this storm and the blizzard we have on Wednesday save for one; it is March in Colorado and these things have a way of wreaking havoc on meteorologists.

My advice; keep an eye on weather updates through the day Friday and be prepared for a nasty day South of Denver on Saturday. Know the impacts (stated above) and realize this is another 50/50 storm that has potential to do a lot or nothing at all.

See Also: Recap of Spring Blizzard March 23, 2016

Keep an eye out for updates from us late Friday night in case this thing does what the last storm did and starts to go nuts at midnight. I’ll be up late posting any forecast changes.

To all of you who gave me feedback about my coverage, I really appreciate it!

 

Spring Blizzard 2016 Storm Recap

Wednesday’s snowstorm looked to be just another quick hit and run type of storm, dropping maybe 4-8 inches and scooting out very quickly. By late Tuesday night and into Wednesday morning, things began to change very suddenly, model runs coming in at midnight slowed the storm system down, changed the track and cranked forecast snow totals through the roof! Today I have a look at how this storm evolved, how it played out once it got over Colorado and how it fooled even the most experienced meteorologists up until the last few hours.

Storm Total Snowfall Accumulation

I’ve provided a couple of maps detailing specifics with snowfall accumulation. Keep in mind, the drifting and blowing snow can leave drifts over 2-3 feet, these numbers do not reflect things like that because they are not accurate measurements. For instance, if I go in my backyard and measure the biggest drift, I would see 30 inches of snow, but a drift is just where snow has piled up from the wind. The NWS has a specific protocol for measuring actual snowfall amounts that does not include drifting, when I use this I got 16.8 inches of snow total.

Official reported snowfall across the metro area for Weds March 23, 2016

Official reported snowfall across the metro area for Weds March 23, 2016 (click on the image to see the larger version)

NWS preliminary snowfall map

NWS preliminary snowfall map

Storm Evolution

This storm through a lot of folks for a loop, even experienced meteorologists had a tough time forecasting this. March snowstorms are notoriously some of the most difficult weather systems to forecast for Colorado, mainly because of their unpredictability. There are a ton of factors that go into making a big snow storm like this and the ingredients have to align just right otherwise we get nothing.

As I go through how this storm evolved, keep an eye out. There are little details that this could become a major storm that nearly every meteorologist missed in Colorado (msyself included.) I’ll put these little clues in blue text.

Tuesday Morning

I had posted early Tuesday about a new Winter Storm watch being issued for the front range of Colorado. I took a look at the models and saw an interesting but somewhat unimpressive looking storm system:

 

NAM Radar forecast Weds AM

NAM Radar forecast Weds AM

NAM total snowfall forecast by Weds evening

NAM total snowfall forecast by Weds evening

NAM 4K Radar forecast for Weds AM (Higher resolution model)

NAM 4K Radar forecast for Weds AM (Higher resolution model)

NAM 4K total snowfall forecast by Weds evening

NAM 4K total snowfall forecast by Weds evening

GFS surface winds Weds morning

GFS surface winds Weds morning

GFS_snowfall_03222016_00ZThurs

GFS total snowfall forecast by Weds evening

Many of the models accurately tracked the system moving over the mountains, getting shredded up a bit but then re-organizing somewhere over Eastern Colorado. Nearly all of these models predicted the Low to reorganize in Eastern Colorado or Northwest Kansas. Basically, this storm had potential to bring us good snow, but the models indicated it would re-strengthen and move quickly off to the East.

At one point I posted this graphic from the Euro model:

Euro model low positioning Tuesday night

Euro model low positioning Tuesday night

I even made a remark: “… then along comes the EURO model. This model has been extremely accurate this year, much more so than some of the American and Canadian models.”

The Euro showed the storm system setting up in a much more favorable position and with much lower speed. This model had been telling us this for nearly 3 days…wow.

Tuesday Afternoon

The afternoon model runs showed us more of the same. Snowfall totals stayed right in the 4-8 inch range but many showed a pronounced dry slot over the front range foothills. This is a clear signal for downslope flow, which dries out the atmosphere and can erode snowfall quickly.

NAM_03222016_Thurs00Z

I think these model runs were the main reason many of us didn’t pull the trigger and up snowfall totals, there were serious questions about who got how much snow. We knew because of the modeling that some areas were going to get dumped on, but Denver and the front range foothills didn’t look to be the place.

03232016_snowstormimpacts

As of Tuesday afternoon, the high impact areas were the Palmer Divide (mainly East of Castle Rock) and Northeastern Colorado. We had the areas along the front range as a big  yellow question mark, the potential for a big storm was definitely. Based on the data we saw at the time though, it was still 50/50.

Midnight Wednesday

8198034682_7ce18d5294_z

This is when we began to get the first inkling that something big was about to happen. I posted an updated around 1AM with news that every model run across the board had shifted the positioning of the storm and thus cranked up total snowfall quite significantly.

HRRR snowfall accumulation forecast by Weds PM

HRRR snowfall accumulation forecast by Weds PM

I am very hesitant to jump on board the Blizzard bandwagon based on one model run, but in this case it was such a resounding jump by nearly every single model. That plus, the Euro had been picking up on this for days, all the other models had been jumping up and down but were now migrating towards the solution the Euro had been telling us for days now.

Initially I had forecast 4-8 inches, I now jumped my forecast to 6-12 inches based on modeling data and looking at observations and possible dynamics. The models cranked up snowfall, but in the end were still short at this time, as was I with snowfall predictions.

Wednesday Throughout the Day (Storm Arrival)

At this point we knew we were in for a doozy, consecutive model runs had pumped up snowfall accumulation. What caught everyone off guard though I think was, if you left to go to the office early Wednesday morning the roads were not that bad.

Many of us had mentioned it may be worth staying home or delaying your commute because the heaviest stuff, based on modeling would not fall until 6AM-12PM. This caused a lot of people to be out and stuck when the worst of the storm hit.

radar_look_03232016_11am

In the end the storm system re-organized over Eastern Colorado and stalled out. This allowed it to wrap moisture around into Colorado and strengthened up slope enough where we saw some intense bands of snow migrating through the area for most of the day. Again, no models picked up on this at all until midnight Wednesday, except the Euro which was forecasting this as early as Monday night.

The storm finally began moving out Wednesday evening and off to the Northeast to cause some havoc. It left behind closed roads, stranded cars and snowplows by the boatload in ditches.

Wrapping it All Up

As significant as this storm was, it was not by Denver standards a “big blizzard”

Biggest Denver Snowstorms (1881-Present)

Snowfall (Inches)

Dates

45.7

Dec 1-5, 1913

31.8

Mar 17-19, 2003

30.4

Nov 2-4, 1946

23.8

Dec 24, 1982

23.0

Apr 23, 1885

22.7

Oct 20-23, 1906

21.9

Oct 24-25, 1997

21.5

Nov 26-27, 1983

20.7

Dec 20-21, 2006

19.3

Jan 29-31, 1883

19.0

Apr 24-25, 1935

18.7

Mar 5-6, 1983

18.5

Mar 20-22, 1944

18.2

Apr 17-19, 1920

18.0

Mar 19-20, 1907

18.0

Mar 31-Apr 1, 1891

17.7

Nov 19-21, 1979

17.3

Apr 2, 1957

16.9

Mar 20-21, 1952

16.8

Apr 20-22, 1933

16.5

Sep 26-28, 1936

16.0

Oct 3-5, 1969

15.9

Feb 2-4, 2012

15.8

Apr 26-27, 1972

If you look at the top 25 blizzards in Denver, Colorado history, this one doesn’t even make the top 25 list.

The snowfall is not what made this a significant storm, I think that was more the combination of snow and wind. We saw gusts upwards of 50mph through the day yesterday and it was this that caused the roads to deteriorate very quickly.

Grading Ourselves

I’m usually my toughest critic when it comes to weather forecasting, but despite the fact that this storm busted way high for snowfall, I think we did a good job communicating the possible impacts.

When we post weather updates we try to communicate more the impacts than the snowfall totals, because that is what will ruin your day if you are out and about. By Tuesday afternoon these were the impacts I communicated:

Heavy snowfall, strong winds up to 50mph, hazardous road conditions especially Wednesday morning. 

By Wednesday at Midnight:

  • Heavy snowfall

  • Strong winds up to 60mph, sustained 30-40mph

  • Hazardous road conditions (morning commute may not be too bad yet but as snow falls throughout the day road conditions will deteriorate)

So while the snowfall forecast fell well short, the impacts were certainly there.

B

I give our coverage on this event a B. I think we did a decent job communicating that this storm will make Wednesday very rough. The only tricky part is that by the time we knew snowfall was going to be a bigger issue, my post missed many folks as they were already asleep. Still, I don’t like to start hyping up a storm until I have facts that warrant it.

For those of you following along with my clues, you will notice that one model in particular is mentioned in every clue. The Euro model. This model was upgraded recently and in the past some models have really struggled to re-align after a big upgrade. The Euro in this case, was predicting this storm would be significant as early as Monday night.

A lot of meteorologists glossed over the Euro I believe for 2 reasons:

  1. The upgrade, this was the first big storm it was forecasting since its upgrade so we were a bit hesitant about its solution
  2. Out of all the models we look at, this was the only one predicting this type of storm. We often call this an outlier and basing your entire forecast on an outlying model can burn you bad!

For those of you who get updates from me through E-mail or Facebook I’d like to know:

  • The amount of posts

    • Too many, too little, just right?

  • Coverage

    • Would you like to see more or less of something I discuss?

Feedback is greatly appreciated!

 

Stay tuned for a post later today about our next storm system, hitting very, very soon!

 

Snowfall Totals and Storm Update

Latest Look at Snow Totals Around the Area

11am_SNOWFALL_03232016

This update is as of 11AM, the snow is coming down pretty fast and furious so these may be higher by now.

The storm continues this afternoon and will continue throughout the afternoon but should begin to lighten up by the evening hours.

The latest look at the radar shows:

radar_look_03232016_11am

You can see the pink gradients, this shows heavier bands of snow in and around the Denver area. We are also seeing moderate to heavy snow fall in Castle Rock as those bands of heavy snow will continue to slide South and East so expect more snow in the hours to come.

HRRR radar forecast as of 6PM

HRRR radar forecast as of 6PM

Taking a look at our short term models, they show snow through about 6-7pm. The heaviest stuff will probably begin to lighten up by the afternoon to early evening hours with lighter snow lingering through 6-7pm. The shot above from the HRRR shows the storm energy leaving the state and pulling the snow with it.

The Rest of the Afternoon

  • Moderate/Heavy snowfall through the afternoon into the evening

  • Strong winds up to 60mph, sustained 30-40mph

  • Hazardous road conditions (some roads are already closed)

  • Strongest impacts will be felt along the Palmer Divide the rest of the afternoon 

    • This means you guys in Parker, Castle Rock, Elizabeth, Franktown, Kiowa, Limon…
  • Power outages may continue to be an issue throughout the day

  • Traction laws are in effect for I-25 (means your car needs snow tires/chains, trucks need chains)

  • TRAVEL IS NOT RECOMMENDED THIS AFTERNOON

 

Stay tuned, I’m still tracking this storm!

 

March 2016 Blizzard in Full Effect

If you were up late enough last night for my 1AM post you noticed I started using the ‘B’ word in my posts. I’m usually cautious to start calling storms full-fledged blizzards, but that is exactly what we are now looking at. The computer models were sluggish with upping snow totals all day yesterday and then the models late last night began upping snow totals drastically.

See Also: 1AM Blizzard Update (Models Crank Up the Snow)

The Latest

For all intents and purposes this storm remains on track to be a major spring snow storm.

NAm4k total snowfall accumulation by Weds PM

NAm4k total snowfall accumulation by Weds PM

HRRR total snowfall accumulation forecast by Weds PM

HRRR total snowfall accumulation forecast by Weds PM

The models this morning are pretty consistent with what we saw late last night. The storm track shifted slightly southward enough to bring  good snowfall to the front range of Colorado.

Snowfall Forecast

Castle Rock: 7-14 inches

Palmer Divide (Eastern Douglas County and Elbert County towards Limon) : 8-16 inches

Denver: 6-12 inches

Impacts

We are already seeing these impacts

  • Heavy snowfall

  • Strong winds up to 60mph, sustained 30-40mph

  • Hazardous road conditions (expect road conditions to deteriorate through the day with improvement in the late evening hours)

  • Strongest impacts will be felt East of Castle Rock into Elbert County.

  • Road closures will be likely in some areas

  • Power outages have been reported

  • Traction laws are in effect for I-25 (means your car needs snow tires/chains, trucks need chains)

I’ll be continuing to track this system throughout the day. Expect snowfall to come to an end late this afternoon and improving conditions by tomorrow.

At this time I would not recommend driving if you absolutely don’t have to. Stay home, enjoy a movie!

 

Blizzard Update as of 1AM

For the night owls still up, I have a quick update on the latest status of the storm set to impact the front range of Colorado. For everyone else, no worries as I’ll have another update Wednesday morning.

The Latest

In a nutshell, models across the entire spectrum have significantly increased snowfall accumulations. I am usually very hesitant to jump on increases based on one set of model runs, we can see these flip-flop the other way on the very next run. Overall though, this is a very convincing set of models as far as how they all agree on a higher snowfall amount. With that in mind I’m increasing my snowfall forecast in and around the Castle Rock area. I’ll look to the morning’s models to see if this stays on track or if I need to adjust downward again (or maybe even upward, depending on the data)

Here’s a quick look at the latest models for snowfall accumulation

NAM snowfall forecast by Weds PM

NAM snowfall forecast by Weds PM

HRRR snowfall accumulation forecast by Weds PM

HRRR snowfall accumulation forecast by Weds PM

As we get closer to the storm, I begin to look at some of the better short range forecast models. The HRRR especially (bottom image) is quite good at picking out finer details and overall trends.

As with any analysis of the weather, I don’t simply look at one model or one set of circumstances, the EURO’s positioning of the low has been very consistent for 3 days now. When a lot of models dismissed this snowfall event, the EURO held fast. The latest look at this model show the Low setting up in a very favorable position for heavy snowfall along the front range.

EuroMSLP_03232016_weds20z

Updated Castle Rock/Palmer Divide Forecast

Castle Rock West of I-25: 6-12 inches

Castle Rock East of I-25: 7-14 inches

Palmer Divide (Eastern Douglas County and Elbert County towards Limon) : 8-16 inches

Denver:4-8 inches

 

You’ll notice my totals are slightly lower than model guidance shown above. Mainly this is because down-slope may still play a bit of a factor for some areas, though it is much less prevalent on the latest models. The other reason is that warmer temperatures (especially at lower elevations) may cause some significant melting before the snow sticks.

Impacts Remain the Same

  • Heavy snowfall

  • Strong winds up to 60mph, sustained 30-40mph

  • Hazardous road conditions (morning commute may not be too bad yet but as snow falls throughout the day road conditions will deteriorate)

  • Strongest impacts will be felt East of Castle Rock into Elbert County.

I’ll have further updates Wednesday morning with a look at new model data and if the storm still looks on track at that time. Stay tuned for further details!

 

Wednesday (3/23/16) Snowstorm Update

Thought I’d post a quick update on how the storm looks with the latest data in; in short, I see no reason to change the forecast at this point. There are still some major questions about this storm as far as the Denver area and even the Western Palmer Divide.

Here’s a quick look at the areas and impacts we are watching closely this afternoon:

03232016_snowstormimpacts

The Yellow Area (Includes Castle Rock Denver, Parker, Longmont, Boulder, Fort Collins…)

  • This is the area of greatest uncertainty now. Folks before you jump on the media hype train that the local TV news stations have started up, understand that the areas in yellow have equal chances of seeing 1-3 inches or 6-12 inches.
  • Uncertainty is extremely high because every model shows a dry slot of air in this area that could result in much less snowfall than anticipated. Downslope could kill snowfall in these areas.

The Orange Area (Includes Elizabeth, Kiowa, Limon, Flagler…)

  • These areas look certain to get heavy snowfall and strong winds during the period on Wednesday
  • Travel in these areas may become very difficult, if you plan on travelling in these areas consider postponing if possible.

The Red Area (Includes Strasburg, Woodrow, Last Chance…)

  • At this time the area in red looks to be the most severely impacted
  • Blizzard conditions will be possible, heavy snow and winds up to 50mph may cause some roads to close.

Bottom Line

Keep a close eye on the weather forecasts this afternoon and into this evening. If you are travelling in the red or orange areas tomorrow you need to keep a close eye on the situation.

For us in and around Castle Rock, the forecast still stands:

Preliminary snowfall forecast for the Castle Rock area: 4-8 Inches

Main Impacts: Heavy snowfall, strong winds up to 50mph, hazardous road conditions especially Wednesday morning. Strongest impacts will be felt East of Castle Rock into Elbert County.

**Keep in mind this is preliminary today, this forecast may change upwards or downwards based on the data I see throughout the day Tuesday.

But understand there is still a high degree of uncertainty for areas in and around Castle Rock. These areas could receive big snow if the up-slope cooperates, but right now models are latching onto down-sloping winds which would eliminate a lot of moisture for snowfall. The tricky part is, it is very difficult to forecast how much down-slope erodes the storm and where.

NAM_03222016_Thurs00Z

I’ve highlighted the areas in yellow that stand the most chance of having this storm bust. This means those areas could equally see little to no snow accumulation from this storm depending on a lot of variables that set up on Wednesday morning.

NAM4K_03222016_Thurs00Z

The latest NAM 4k is also picking up on a pronounced dry slot due to down-sloping.

Keep an eye on the weather forecasts this afternoon, I expect the NWS to start pulling the trigger and upgrading some of these Watches to Warnings soon. We’ll keep a close eye on it and expect at least a couple more posts about this storm today as more data comes in.

As always, thank you all for reading, liking and sharing, if you have any questions please don’t hesitate to ask on our Facebook page!

 

**Winter Storm Watch Issued** Next Storm Begins to Organize to the West

The National Weather Service in Denver has issued a ***Winter Storm Watch*** for some areas of the front range of Colorado for 4AM Wednesday morning through 6PM Wednesday night. This storm echoes a lot of the last storm system to move through in the fact that it will not be a major, city-crippling blizzard, but it does look to be significant enough to cause quite a few headaches throughout the day on Wednesday. Here’s the latest as of this morning:

Impacts

  • Heavier snowfall between 6AM and Noon on Wednesday
  • Winds will be strong starting Tuesday afternoon and continue through the day Wednesday
    • Expected sustained winds of 25-35mph with gusts up to 50mph
    • This could cause blowing and drifting of any snow that falls. Areas East of Castle Rock towards the plains will have the highest threat of blizzard like conditions
  • Roads will become icy and snow-packed with the heavier snow on Wednesday. Roads to the east on the plains may become impassible with drifting snow
  • Wednesday morning commute looks rough, the evening commute may be dicey as well depending on how long the snow lingers around during the day

See Also: Current Colorado Weather Watches/Warnings/Advisories

Expected Snowfall for Castle Rock Area

I’ve held off on snowfall totals through the day Monday as models were having a tough time pinning down where the heaviest snow will fall. It looks like that is still the situation with the latest models, but in any case here is what they show as of this morning:

 

NAM Radar forecast Weds AM

NAM Radar forecast Weds AM

NAM total snowfall forecast by Weds evening

NAM total snowfall forecast by Weds evening

NAM 4K Radar forecast for Weds AM (Higher resolution model)

NAM 4K Radar forecast for Weds AM (Higher resolution model)

NAM 4K total snowfall forecast by Weds evening

NAM 4K total snowfall forecast by Weds evening

GFS surface winds Weds morning

GFS surface winds Weds morning

GFS_snowfall_03222016_00ZThurs

GFS total snowfall forecast by Weds evening

**I put the GFS last because it’s the model I trust least in the winter season

You can see that every model is bringing snowfall to our area to some degree. The NAM and Euro (not shown) models have been much more consistent this year with predicting winter storms so I tend to stick with them first and give the GFS just a passing glance.

One big concern I have about total snowfall is that in the NAM models above, there is a pronounced dry slot against the foothills and Western Douglas County. This is a signal consistent with down-sloping winds, winds like this tend to dry the atmosphere and could impact how much snow we get. You’ll notice the bulls eye is not over Castle Rock proper, but just to our immediate East, especially in Elbert County. The NWS has a snowfall range of 4-8 inches, which I tend to agree with but have serious concerns about down-slope flow killing our snow accumulation as you move West. If this signal verifies, expect my snowfall forecast to drop drastically at some point on Tuesday, however if the storm track shifts more favorably, the 6-12 inch range may not be out of the question.

I know at first glance the 4-8 inch range contradicts the NAM pretty sharply, however I’m not looking at just one model. Given the data I’ve seen across the entire spectrum of model products that I use, some do indeed show the higher snowfall pusing further West, hence why I agree with the 4-8 inch range at this time.

My preliminary snowfall forecast for the Castle Rock area: 4-8 Inches

Main Impacts: Heavy snowfall, strong winds up to 50mph, hazardous road conditions especially Wednesday morning

**Keep in mind this is preliminary today, this forecast may change upwards or downwards based on the data I see throughout the day Tuesday.

Stay tuned to Mountain Wave Weather throughout the day Tuesday, I will have several updates regarding this storm and will post as new data comes in and the forecast either begins to verify or change.

Synopsis

For the weather nerds more interested in the science of this storm I usually throw in this section to talk more technically about the storm setup.

NAM 4K Radar forecast for Weds AM (Higher resolution model)

NAM 4K Radar forecast for Weds AM (Higher resolution model)

Model guidance has a strong low pressure system crossing the Rockies of Colorado today. As often the case with these types of storms, the mountains tend to shred the energy as the storm system crosses the divide. What becomes important to us is where the energy re-strengthens; the NAM 4k shows the low re-developing over Northwest Kansas into Wednesday morning. The positioning here will be important as any shift could have big implications for how much show we get along the front range.

The low will usher in colder air overnight Tuesday and into Wednesday and as it does so, it will wrap moisture back around the Western side of the storm system.

NAM 4K

NAM 4K snowfall forecast

This is shown quite well on all models with snowfall taking a heavier track across Eastern Colorado, Northeastern Colorado and into Nebraska. I think those areas will have the biggest impact from this storm.

Upslope Vs. Downslope will Make or Break This Storm

classic-downslope-event

In weather we all know that upslope causes rising air and thus moisture on windward side of the mountains. The leeward side is punctuated by sinking air, this causes it to compress and warm and it moves down the slopes and generally dries out the atmosphere. This is an important thing to know for Colorado as it can dictate our weather quite frequently.

Let’s look at the  NAM4K snowfall model:

NAM 4K

NAM 4K

Notice the bulk of the snowfall falls across the Eastern plains and there is a noticeable lack of snow right along the front range. This is a strong down-slope signal and it shows up pretty clearly here. What I’ll be watching for in Tuesday’s model runs is does that dry spot disappear or intensify. This is ultimately going to depend on where the models think the Low will set up over Kansas. If it should back off to the West a bit or South, up-slope flow will enhance along the front range and we will get more snow.

Should the low shift North or East, we will see stronger down-slope along the front range which means our snowfall accumulation could greatly diminish. As is often the case with these snow storms in Colorado, it’s all about location, location, location!

The National Weather Service’s latest statement echoes this concern:

AT THIS TIME AS MODELS ARE STILL NOT LOCKING ON TO A STEADY SOLUTION OF THE HEAVIER SNOW…WITH THE LATEST GFS DOUBLING ITS AMOUNTS OF QPF NEAR THE FRONT RANGE WHILE THE NAM MOVED THE HEAVIER PRECIP EAST OVER THE EASTERN PLAINS. ONE COMMON FEATURE IS THE DOWNSLOPING SIGNATURE ALONG THE FOOTHILLS AND NORTHERN FRONT RANGE URBAN AREAS AS NORTHWEST FLOW WILL DOWNSLOPE OUT. THE QUESTION IS HOW MUCH AS IT DOES LOOK LIKE THERE WILL BE A SMALL WINDOW WHERE WINDS UP THROUGH MOUNTAIN TOP MAY TURN UPSLOPE BETWEEN SUNRISE AND NOON.

For what it’s worth, here was a look at the SREF ensembles this morning for snowfall at Centennial Airport:

SREF_0322_2016

You can see the mean is right in that 4-8 inch range, so I’m sticking with that for the western Palmer Divide area (Castle Rock, Parker, Monument, etc…)

It should be interesting to see how this storm develops with so much inconsistency between the major models. I expect the forecast to change drastically at some point on Tuesday with either much more snow than anticipated or a total collapse of this system from down-sloping and we’ll be looking at a dusting at best. This is why weather is so interesting, every storm is different!