Post Christmas 2018 Storm – Blizzard or Dud?

Why Trying to Predict Snowfall Totals is a Bad Idea

A quick rant… why? Because it helps me feel better, if you just want the storm stuff, skip this section 🙂

I’ve been harping on some folks this week about throwing out snow totals way too far in advance… I probably shouldn’t care. I should probably just move on and forget about it, but the fact of the matter is when people do this it makes them trust meteorologists a bit less each time when it comes out terribly wrong. It frustrates me, I know it shouldn’t but it does!

Case in point, here were the snowfall amounts people were throwing around just a few days ago:

See something like that and it’s pretty easy to think, “wow, we are going to get hit!” One notable agency in Elbert County even latched on the hype and started telling people out here to prepare for a major storm. When I called them on it they got defensive and told me that had reliable forecasts from someone who had been doing this for years. My point here is not to boast or brag, the point here is that where you get your weather from matters… it’s easy to get caught up in the hype, especially with the dry year we’ve had so far. (if that agency is reading this, I’d be happy to work with you in the future for more reliable weather forecasting… if not that’s cool too but I will call you out on bad meteorology…)

This brings me to my final point and I’ll be brief about it…

Don’t believe the hype! We don’t hype stuff at MountainWave Weather; we give you a cool, calm, collected and realistic view of what is going on. Based on sound meteorology and good forecasting… if you need to be worried about a major storm we will let you know in advance. If not, we will give you the details on what to be prepared for or tell you not to worry about it!

Ok, rant over… now to the good stuff!

Latest on the Post Christmas Storm


As of this morning, the storm center is just beginning to move onto the coast in the Pacific Northwest. We can clearly see the trough and associated wind and vorticity profiles in the image above. As we’ve discussed, the track this feature ultimately takes will mean a big difference for snowfall chances in Colorado.

There is still a decent amount of uncertainty between models, originally only the GFS and Euro were in range, but as of this morning the NAM is now picking up on the storm. Unfortunately, the addition of some of the shorter range models hasn’t helped us out a whole lot in regards to what this storm will do.

GFS predicted snowfall through Friday. Remember that image above of 12+ inches? That’s the GFS run from this past Friday…

Euro model predicted snowfall through later this week.

NAM model snowfall accumulation through late this week

So to summarize these models; they’ve all shifted to a lower snowfall solution for the front range of Colorado. While that takes a lot of wind out of our sails for a major storm, we still can’t completely count out a bigger snowfall event. Mainly because our storm still isn’t on shore yet, models don’t have a lot of good data to digest which means we will still see some flip flopping. That being said, it is looking less and less likely we see a major impact storm along Colorado’s front range with each consecutive set of data.

Here’s what the models say for snow for areas along the Palmer Divide as of this morning:

  • GFS
    • 1-3 inches
  • Euro
    • 3-6 inches
  • NAM
    • 2-4 inches

**Keep in mind, these are preliminary numbers and they WILL change as we get more data in on Monday and Tuesday.

WPC snowfall accumulations for the Palmer Divide if everything holds as is today. Again, these will change based on newer data coming in, but it’s always good to have a fuzzy idea of what to expect.


A lot of folks have been asking about when this storm actually hits so they can plan for travel. Right now it looks like most of the snow we see is through Wednesday and early Thursday. There may be a few flurries late Tuesday night but we don’t expect anything major to go on Tuesday night with the data we are seeing now.

If you are travelling to the East of Colorado; we expect much bigger impacts over Northern Kansas and into Nebraska. If you’re driving through those areas be sure to keep an eye on the forecast and be ready to change your route or pull over if things get too hairy.

If you are driving through any of this, please make sure you have a winter survival kit in your car!

We will continue to keep an eye on things… being that it’s Christmas Eve, don’t expect another update tonight unless something really interesting happens. Otherwise we should have an update Christmas morning, stay tuned!

Merry Christmas from us here at Mountain Wave Weather, we wish you and your family a happy and safe holiday!








~John Braddock


Busy Travel Day! Here’s A Quick Weather Update

As we move into the holiday weekend with Christmas only a few days away, a lot of folks are hitting the airport or the roads to get to their Christmas destinations. Depending on where you’re going the weather will be just fine or may be a bit of a headache, even in Colorado there is a mixture of conditions. Here’s a quick update on what to expect if you’re travelling around Colorado or the nation today.

Colorado Weather

A Winter Weather Advisory is in effect for the Northern and Central Mountains of Colorado

If you are travelling into or through the mountains, expect slow travel conditions. A combination of wind and snow will make roads icy and snowpacked through the day Saturday. Expect slow going mainly west of the continental divide on Saturday.

A look at I-70 just West of the Eisenhower Tunnel Saturday morning

Closer to home, the Eastern plains of Colorado will see breezy and partly/mostly cloudy conditions. Snow showers are possible throughout the day but it doesn’t look like it will amount to much (if any) accumulation.

Expect snowfall for the Palmer Divide region over the next 24 hours

So overall, most of the travel difficulties for the state will be in the Northern and Central mountains for Saturday. You shouldn’t run into too many issues along the front range, but keep in mind snowfall amounts are expected to be slightly higher (1-3 inch range) on the far Northeast plains of Colorado into Wyoming and Nebraska.

National Weather

National radar for Saturday morning

Overall it’s not looking too bad for Saturday morning across the U.S. The main areas you’ll find precipitation are across Kansas, Nebraska and Northeastern Colorado. Additionally snow is being reported across North Dakota and the Northeast, none of which seems to be effecting airport operations.

Airport status as of Saturday morning

Most airports checking in with delays this morning are due to traffic… so weather not playing too much of a role.

extExpected 24 hour snow totals across the U.S.Over the next 24 hours the concentration of snow will be in the Pacific Northwest into Washington and Idaho mainly… some areas in Colorado will pick up a bit of snow along with the midwest and Northeast. None of these look like major storms, so delays for airports will probably be mainly around increased traffic.

If you’re driving in and around these areas, be prepared for winter driving conditions. Take it slow and be safe!

Next Week… Major Storm?

500 mb upper air GFS Model for next week

Models are keying in on a potentially large and powerful storm system that would affect the western and central US next week. We won’t go into too many details on this just yet because we don’t have enough information to nail down anything too accurate.

Here’s what you need to know for now:

We will begin to actively monitor this storm and post about it starting sometime on Sunday. We will be watching this very closely as it has the POTENTIAL for a big impact on Colorado. For now, don’t be worried too much about it but keep an eye on reliable weather resources through next week.

Chilly, snowy at Castle Rock Starlighting 2018!

Castle Rock’s Biggest Event of the Year!

If you’re new to Castle Rock or a seasoned veteran of the town, the Starlighting put on by the Castle Rock Chamber of Commerce is definitely an event not to be missed!

The the festivities run from 2PM-7P with the Starlighting Ceremony kicking off promptly at 5PM. Be sure to get there early to enjoy the vendors, food trucks and visit some of the small businesses in the area that often have hot cocoa!

Map for Castle Rock Starlighting 2018

The Weather

As is often the case with Starlighting, it looks chilly this year so be sure to be prepared for that! There is also a good possibility of snow showers on and off through the afternoon and into the evening hours. Doesn’t look like a major storm by any means, mainly the travel impacts we expect are from icy conditions on roads and sidewalks early in the day Saturday and then again into the evening hours.

Let’s look at some models real quick!

Modeled Precipitation


Saturday 1PM precipitation in the area

Saturday 3PM precipitation in the area


Saturday 6PM precipitation in the area

The takeaway; most models are pointing to scattered snow showers throughout the day on Saturday. The model snapshots above show snow showers throughout the afternoon and into the evening hours, keep in mind though any snow that is falling is expected to remain relatively light in intensity.

Modeled Temperatures

Saturday 1PM modeled temperatures

Saturday 3PM modeled temperatures

Saturday 6PM modeled temperatures

The takeaway; it’s going to be chilly throughout the event. We expect temperatures to peak in the mid 20’s by afternoon dropping to low 20’s to upper teens by later in the evening hours. Be sure to dress warm, have hats, gloves and hand-warmers for your family. Another good suggestion is to duck into the small businesses and say hello when it’s getting chilly out, they usually have the heaters cranked up pretty high. It’s also a great chance to meet some new folks!


Be Prepared! Here’s our Castle Rock Starlighting 2018 Checklist!

Enjoy and stay warm everyone!

Be prepared! Sunday Will Be Cold and Snowy Along Palmer Divide

For the past few days we’ve had an idea that a storm would affect the region late Saturday into Sunday but we didn’t think much of it because it really didn’t look like much was there.

Yesterday the storm started to come together a bit better on the models and we saw that snowfall was looking more likely in the area and models continued to bump snowfall totals up ever so slightly. Even still, the meteorology just didn’t support much out of this storm with the data we were seeing at the time… the storm looked to moving too fast, upslope didn’t establish well and like with most storms of this track, moisture was a concern.

Today we’ve seen more data and modeling coming in and a few interesting things have begun to manifest…

A Winter Weather Advisory is in effect from 12AM-4PM Sunday

Snapshot of Nam3K model for Sunday morning

Models overall have shown more support for a bit longer of a duration event, which basically means the storm lingers a bit longer. This is good news if you’re looking to squeeze a little bit more snow out of this storm. The snapshot above for Sunday morning from the Nam3K shows a lot of snow and a lot of energy in the area. Notice the stronger returns along the Palmer Divide, especially in the Douglas County area… this means upslope looks to establish for a time and provided it can stay there long enough, there should be ample time and energy for some snow to stick.

If we take a look at another model, the RAP we see a similar pattern. This is a lower resolution model so it doesn’t have quite the detail as the last, but it’s good that there is some alignment between the two.

RAP model for 9AM Sunday

I’d love to show the HRRR model, but it’s just out of range right now. May be able to show it in a few hours if it is picking up on anything interesting. Stay tuned for that.

What to Expect


I don’t see much happening on Saturday with the current data we are getting… it looks like the largest impact of this storm will come Sunday morning.

  • Light snow possible before midnight, not much accumulation
  • Early Sunday morning snow intensity will pick up
  • Expect heavier snow showers through early morning and late morning on Sunday
  • Some models continue snowfall into the afternoon hours, so be prepared for those conditions if you’re out and about



  • Travel impacts may include slushy and icy roads
  • We expect any travel impacts to be most prevalent on Sunday morning
  • Should snow linger into the afternoon, it may be cold enough for the roads to stay slushy and snowpacked in some areas


Snowfall Totals

Still a bit tricky on this call as models are nearly 50/50 split between two scenarios with this storm. Half of the models have the storm leaving early (remember most of them have done this so far this year) which would result in lower snowfall. The other half show the storm moving through the area slower which would mean we see higher snow totals.

Here’s the results of the two scenarios with our latest data in:

Scenario 1 – Slower Moving Storm… higher snowfall amounts

Scenario 2 – Quicker Moving Storm… lower snowfall amounts

So… still lots of information to chew through and a few questions still remaining. We should get a better idea on snowfall this evening as our higher resolution, short range models come in. Nearly every model is picking up on the snow accumulation as a sure thing for the front range and Palmer Divide… so expect that. The details we still need to sort out will be exactly how many inches of snow we see.

Stay tuned!

10/30/2018 – Tuesday AM Storm Update

Total snowfall accumulation through Wednesday PM 10-31-2018

Expected Snowfall totals for Areas Around the Palmer Divide

Here’s our latest thinking on overall snowfall for areas along the Palmer Divide. Our forecast is largely in line with the NWS forecast, but lower than some of the TV stations have been predicting around here. I still think the ground being so warm will play a part in melting some of the initial snowfall and suppressing snow totals just a bit.

-Castle Rock: 4-8 inches
-Parker: 4-8 inches
-Lone Tree: 3-6 inches
-Kiowa/Elizabeth: 3-6 inches
-Elbert 4-8 inches
-Larkspur: 5-10 inches
-Palmer Lake: 6-12 inches
-Black Forest: 5-10 inches
-Monument: 6-12 inches
-Woodland Park: 7-14 inches

Updated Impacts/Advisories

A Winter Weather Advisory is in effect from Tuesday 12PM through Wednesday 6AM for travel impacts due to snow

Plan on slippery road conditions. The
hazardous conditions could impact the evening commute Tuesday
and the commute Wednesday morning.

See updated Weather Warnings and Advisories for Castle Rock and the surrounding area on our Weather Warnings page.

Look at the first bit of precipitation moving through as of 10:30 AM this morning

  • Impacts
    • Expect tricky travel conditions Tuesday evening, overnight Tuesday and Wednesday mornings
    • Roads will become snow-packed and icy in areas
    • Colder air will be in place Tuesday and Wednesday so be prepared for chilly conditions
  • Timing
    • Scattered snow showers will be possible earlier in the day Tuesday
    • Expect more substantial snow showers to develop later in the Tuesday, through the evening and overnight hours
    • Snow showers will linger through Wednesday morning
    • Snow should clear by mid-day Wednesday
    • Clearing conditions will continue through the day into the evening Wednesday but cold conditions will remain

Halloween Temperatures

Temperatures on Halloween 2018 ~ 4PM

Halloween is going to be chilly, if you have trick-or-treaters going out, be sure to dress warm and watch for remaining ice on the roads and sidewalks. The model above has temperatures generally in the low 30’s to upper 20’s across most of the Palmer Divide around 4PM.

We’ll continue to keep an eye on it and pass along any storm updates as needed on Tuesday. Stay warm!

Shifting to an Unsettled Weather Pattern This Week

Quick Look

Quick look at information regarding timing, impacts and severity for folks who just want the quick information about this storm


  • Expect precipitation to begin mainly as rain on Tuesday morning
  • Models currently have the transition to snowfall occurring in the early to mid morning hours on Tuesday
  • Snow showers continue on and off through the day on Tuesday
  • Tuesday night features the potential for heavier snowfall, especially over the Palmer Divide
  • Snow continues overnight Tuesday until Wednesday morning, models have it wrapping up by Wednesday morning


  • Freezing conditions possible as rain transitions to snow on Tuesday
  • Snowfall could become moderate in intensity Tuesday evening and late Tuesday night

Travel Impacts

  • Expect the possibility of snow-packed and icy roads Tuesday evening and Wednesday morning
  • Biggest impact could come during Tuesday evening rush hour and Wednesday morning rush hour


A Winter Weather Advisory is in effect from Tuesday 12PM through Wednesday 6AM for travel impacts due to snow


Snow should mainly be done by Halloween night but cold temperatures will still remain. If you have friends and family heading out for trick-or-treating dress warm and be prepared for the potential of snow and ice on the roads and sidewalks!



A more detailed look at the weather and mechanics with this storm system

Snowfall is expected mainly across the higher elevations (Palmer Divide) south of Denver and in the foothills and mountains. The elevation you live at will make a huge difference eon how much snow you see accumulate and how far North or South of Denver you are will make a difference too.

Palmer Divide expected snow totals by Wednesday AM


There are some intriguing characteristics to this storm system but it has some similarities to the last one we saw. You may have noticed my snowfall forecast above doesn’t exactly match what you may have seen on some of the TV newscasts. There’s a few reasons for that which I’ll get into below.

The main energy of this storm looks to extend further South than the last, but it still involves an upper level trough sliding in from the North just like the last storm. This will allow the cooler air to move in and provide some of the lift energy to kick off the snowfall.

We can see that pretty clearly as the snow begins to ramp up Tuesday evening… but you’ll notice the jet stream stays over Colorado during this time with Southwesterly flow aloft in the mid and upper levels of the atmosphere.

Tuesday 6PM 500mb model snapshot

Very similar looking to our last storm… and we know that largely the last storm was a “banded” or “jet-induced” snowfall event. This means that some areas saw very good amounts of snow (Fort Collins and Loveland ended up between 6-10 inches) while us along the Palmer Divide ended up in the 1-3 inch range.

I recently read an interesting article about banded snowfall over on SkyView Weather and they had a great image illustrating this:

Great illustration, would love to have an actual article explaining the mechanics behind this type of storm on another day!

All in all, this storm screams “snow bands” to me just like the last so while it is similar to our last storm in that respect, we have to keep an eye on it because the main energy sets up to the South this time instead of the North. This means we could see higher snow totals (bust high) if the snowfall bands set up in just the right spot over the Palmer Divide.

Nam3K Precip type snapshot for Tuesday ~8PM

If we look at one of the models for Tuesday evening you can see some evidence of snowfall banding enhanced by the jet stream as it moves across the state. It shows a pretty strong signal for upslope across the Palmer Divide and heavier rain across the Southeastern portion of the state… very interesting.

There are some things to keep in mind:

  • Models are good at showing the presence of snowfall bands but they are not good at predicting exactly where they will set up
  • This storm is not a slow mover, the best lift will be along the cold front when it first moves through and as the jet transitions across the state. Quick moving storms don’t tend to produce a ton of snow, but jet induced lift can product very intense snowfall accumulation in very isolated spots
  • A surface low setting up in Southeastern Colorado could aid in upslope and instability across the Palmer Divide and front range foothill


Lots of intriguing things going on with this storm, but given the warm temperatures at the ground level, the quickness of this storm and the spottiness of snowfall bands… I’ve aired on the lower snowfall amounts. Please keep in mind, this could change if we start to see drastic uptick in the models and data Monday night.

SREF ensemble expected snowfall for KAPA (Centennial Airport)

The SREF ensembles show a mean of 2.78 inches at Centennial and about 4 at Monument… I expect Castle Rock would end up somewhere in that range (2-4 looks most likely at this time.)

For now, we’ll keep an eye on it and pass along any interesting updates through the day Monday and early Tuesday!

Saturday PM Palmer Divide Storm Update

Not many major changes to what we are seeing tonight based on new data coming in. A lot of the mid and shorter range models are coming in and have dropped snow totals just ever so slightly across the area.

Snow banding is possible so some areas may over perform while others under perform.

As we’ve been saying all along, the way this storm system is moving in (the direction and moisture content) is not conducive to a major snow storm along the front range. The biggest impacts will be the cold temperatures the areas sees on Sunday and into Monday morning.

Still, we can’t discount a few quick bursts of moderate snow overnight tonight and combined with the much colder temperatures could make some areas a bit tricky for travel. The jet stream is overhead and as we’ve seen that can do crazy things to our snow totals for certain areas. Expect some areas to see slick roads overnight into Sunday especially South and West of Denver. The foothills should still see decent amounts of snow so I’d expect the travel conditions to be a bit trickier up that way.

Updated Timing, Impacts and Snowfall Amounts


  • The front is moving through Denver and Southward towards the Palmer Divide as of about 7:30PM
  • Expect precipitation to start as rain but may quickly change over to snow this evening
  • Snow will continue through the night and into the morning hours Sunday
  • Snow looks to end by 12PM on Sunday from the North to South




  • Light to moderate travel impacts across Denver and the Palmer Divide
  • Moderate travel impacts for the foothills and areas of Western Douglas County



  • Temperatures will be below freezing as the front moves through
  • Sunday will see highs in the upper 20’s to low 30’s
  • Sunday night into Monday morning, lows will be in the teens to lower 20’s for most areas. Some areas may even see single digits



  • Castle Rock, Parker, Lone Tree, Castle Pines, Sedalia / Central and Western Palmer Divide
    • 3-6 inch range still looks in play here
  • Southern Palmer Divide (Monument and nearby areas)
    • 2-4 inches looks like the most likely range for these areas
  • Eastern Palmer Divide (Limon, Elizabeth, Elbert)
    • 2-4 inches looks likely in these areas, towards the lower end of that range as  you get East towards Limon


Remember, the Winter Weather Advisory is still in effect from 8PM Saturday through 12PM Sunday for the Palmer Divide! (eastern areas towards Limon excluded)

Any updates I’ll be sure to pass along, also you can ask any questions or pose any thoughts on Facebook.

Stay warm and stay safe everyone!


Cold Blast – Accumulating Snow Coming This Weekend

Click the image for up to date Castle Rock Weather Alerts

Finally Starting to Feel Like Fall

Castle Rock high and low temperatures vs. average since Oct 1, 2018

Temperatures have been running well below normal for the past few days, we haven’t seen average or above average temperatures in Castle Rock since October 5. That’s great news after how warm September was and even better news is that we’ve seen a bit of moisture as well. After the cold temperatures abate a bit on Friday and Saturday another blast of cold air and a chance of snow makes its way into the area. The good news for snow fans is that it looks very likely we will see decent snow accumulation with this weekend’s storm!

Storm Setup and Analysis

Here’s a quick look at conditions on Saturday; a strong trough is expected to dip out of Canada and move into Colorado. Behind this trough is a whole boatload of cold air that has been pooling over Canada for some time now. That means we expect very cold temperatures to accompany this storm system. While this is not a favorable track for large amounts of snow, many models are showing enough moisture for accumulating snow along the front range.

Palmer Divide Weather | Castle Rock Weather | Snow Storm | Snow Totals | Storm Forecast

Estimated snowfall by late Sunday

The image above shows the most likely expected snowfall accumulation through late Sunday (50th percentile or probabilistically the most likely snowfall amount based on data today.) You can see areas along the foothills and areas over the Palmer Divide generally have snowfall totals pegged in the 4-6 inch range.

The SREF ensembles show a 6.42 inch mean at Centennial Airport and a 5.53 inch mean at Monument Hill. Those numbers are pretty consistent with what we see above and with some of the modeling.

GFS expected snowfall Sunday by end of storm

Given the much colder temperatures I say snow accumulation is a good bet if everything else pulls together well. As you can see there is still a bit of discrepancy between some of the models for the snow totals at lower elevations but the overall image is pretty consistent. The foothills and mountain areas stand to see the best snowfall amounts while over the Palmer Divide we will see slightly more than Denver and areas to the North and East.

Speaking of temperatures, they’re going to be downright frigid!


What To Expect

  • Friday and the first half of Saturday will be quite nice with decent temperatures and mostly clear skys.
  • Snow will move in late on Saturday most likely in the evening hours past 4PM
  • Snow will continue overnight saturday into Sunday
  • Snow looks to end by about 12PM on Sunday
  • Extremely cold temperatures will set in Sunday night into Monday morning
  • Expect most areas along the Palmer Divide to see accumulating snow in the 3-6 inch range
  • Largest travel impacts look to be later Saturday night into Sunday morning


Keep the things listed above in mind and know that timing and snow totals still have time to shift. We will have another update as more data comes in!

Stay tuned!


Weather Pattern Change Ahead

After several weeks of well above average temperatures and incredibly dry conditions, it looks like we may finally see a fall weather pattern change on the horizon!

Ridge of Doom is Breaking Down!

For the past several weeks a high pressure ridge has been fairly efficient at keeping warm dry air over Colorado and keeping the storm track away from us. Signs that this is changing are beginning to appear as early as today. 500mb (upper air pattern) shows a trough digging into the Western United States and pushing the ridge responsible for our stagnant weather pattern eastwards.

In simplest terms, this means warm and dry air will dominate the weather pattern for the Eastern U.S. but things in the west will be changing! The trough to our west will finally allow cold air pooling in Alaska and Canada to make its way down to the western and central part of the U.S.

Is Snow in our Near Future?

You’ve no doubt heard the hype already on a lot of weather websites, social media platforms and TV stations; but snow early next week is looking like a sure thing for the mountains of Colorado… and yes the possibility exists even for the front range to see something as well, but as with a lot of these early season storms; the devil is in the details!

GFS Precipitation type and intensity for Sunday 6PM

Looking at some of the longer range (read: less accurate in this time frame) models we see a strong upslope signal showing itself on Sunday and into Monday. The trough should be fairly efficient at bringing cooler air and moisture into the area. But, just like a lot of our “fall/winter” type storms; exactly where and how things set up will make all of the difference.

Don’t get too excited about snow flying around Castle Rock just yet, but this is something to definitely keep an eye on over the next few days. Here’s a few things we will be watching:

  • Cooler and more unsettled pattern for the rest of the week into the weekend is looking very likely
    • Expect cooler temperatures and precipitation Wednesday and again over the weekend
    • Snowfall is not expected along the Palmer Divide for the next 3-4ish days.
  • Weekend has a reinforcing shot of cold air and may be able to tap into decent moisture
    • Where the trough sets up will determine moisture availability and upslope possibility
    • Will the air be cold enough for snow? We think it is a strong possibility but may be too warm for much to stick
    • Timing! Some models shows this stuff cranking by mid-day Saturday while others hold off until later Sunday into Monday

So obviously, still a lot of unanswered questions that need to flesh out in the next few days.

For now, anticipate cool and unsettled weather for the next 5-7 days beginning with a cold front late in the day Wednesday. Be prepared to move sensitive vegetation indoors this weekend and possibility of needing to cover above ground irrigation equipment if it’s not already drained late in the weekend (think Saturday night – Monday night timeframe)

We do not yet have answers on if it will snow (50% probability at this time) and/or what the impacts will be, stay tuned for further updates on that information!

Obligatory Snowfall Model for Late This Weekend

You all know I hate sharing snowfall models this far out… the reason I’m doing it right now is I just want to show you all what models are picking up on as of this morning.

Keep in mind with this image: It is not a forecast, it is very early and preliminary, these numbers WILL change higher or lower as we get more data in and get closer to the storm’s arrival.

GFS total accumulated snowfall from now through Sunday 6PM

This is also why I caution about anyone trying to forecast we definitely will or will not have snow next week. This model was showing 4-8 inches of snow for the Palmer Divide last night and this morning’s run shows 0!


El Nino 101: What is El Nino?

What Is the El Nino Southern Oscillation? (ENSO)

For most people they hear the word “El Nino” and know that it means big shifts in the weather pattern for Colorado (whether from being here long enough or hearing it from the local TV Weather people> But many don’t know exactly what “it” means exactly or the mechanisms behind it.

The El Nino Southern Oscillation is a periodic weakening or reversal of trade winds stretching across the Pacific Ocean from South America to Australia. This allows a redistribution of warm and cold water which in turn affects the atmosphere above the ocean as well. This means big changes in weather patterns for the tropics and subtropics along with areas further North and South.

To measure the El Nino Southern Oscillation sea surface temperatures are monitored in different “Nino” regions. To make a long story short, this area stretches roughly between Australia and South American along the equator; roughly between 120E and 80W lines of longitude and between 0-5 degrees North and South latitude.

There are 3 different “phases” of the El Nino Southern Oscillation that occur based on what the observed sea surface temperatures are for a period of 3 months and I’m sure you’ve often heard about them.


A neutral phase of ENSO means warm water and air is pushed across the ocean towards Australia. Cooler water “upwells” from deep beneath the ocean along the South American coast.

The neutral state is the normal phase of ENSO, it is neither an El Nino or a La nina. In this pattern wind blows from East to West along the Equator pushing warm moist air and warm ocean water across the ocean towards Australia.  As the warmer water at the upper layers of the ocean is pushed away from the coast of South America, cooler water from deeper in the ocean rises to take its place. This is a process called upwelling and is very important to many forms of oceanic life along the coast of South America.

During the neutral phase of ENSO, warmer water tends to flow towards Australia while cooler water upwells of the coast of South America.

It’s also important to note that during a neutral ENSO phase, the trade winds push the warmer water West but this also effects the atmosphere along the equator.  This normal phase of trade winds and high and low pressure  circulation is called the “Walker Circulation.” It’s illustrated in the image above but here’s another to help visualize:

The trade winds that blow across the ocean circle back North and circle around towards North America. This West to East wind over N. America is what influences our storm track across the United States. So as you can imagine, when these trade winds and circulations get disrupted it has big implications for our weather.

So what does that mean for temperature and precipitation patterns for the U.S. during a neutral phase? Basically we’d expect to follow along climate normals through the season. We should see normal temperatures, normal snowfall and normal precipitation through a period of neutral conditions. We know however; this is not always the case as there are other things that can influence our weather.

During neutral conditions the U.S. tends to see colder winters across the Northern and Central United States with drier conditions to the South and close to normal temperatures.

El Nino

The warm phase of ENSO means a weakening or shifting of prevailing  (trade)winds that allows warm water to pool against the South American coast. This can mean a disruption of weather patterns in the Pacific which can in turn influence the weather in the U.S.

When we say an El Nino is setting up or occurring we are referring to the warm phase of ENSO. In this pattern the trade winds pushing from East to West across the equator break down or even reverse in some cases. This allows warmer water to pool against the South American coast while colder water upwells against Australia.

During December 2015 we were seeing one of the strongest El Nino’s recorded. Notice the extremely warm water across the Equator towards South America and the average to below average temperatures near Australia and to the North of Australia.

Sea surface temperatures increase along the South American coast and sea surface temperatures drop in and around Australia. This means areas of increased convection (shower and thunderstorm activity) for South America and less for Australia. It is not uncommon for Australia to see severe drought conditions and South America to see extreme flooding conditions.

During El Nino the weather in the continental U.S. can change too. Due to trade winds and circulations being disrupted, the positioning of high and low pressure systems, along with shifts in the jet stream can cause big changes for our weather. If you’re new to Colorado, you may not know but our bigger snow storms in Denver tend to come during El Nino years, so that’s something to keep an eye on!

El Nino effects on the U.S. largely depend on the strength of the event. During weaker events cooler air stays North and East while warmer conditions manifest during stronger events. Precipitation tends to favor California and southern parts of the U.S. during stronger events while dry conditions tend to show up during weaker events across the Central part of the country.

La Nina

During La Nina, stronger trade winds allow cool water upwelling to spread across the South American coast. The cold water pools and will spread across the Pacific and warmer water stays further West near Australia and New Zealand.

La Nina on the other hand refers to below average sea surface temperatures setting up across the South American Coast reaching further West across the Pacific Ocean. With this pattern the trade winds pushing from East to West across the equator strengthen substantially, which  allows colder water from upwelling to spread out across the ocean to the West of the South American Coast.

As recently as last winter we saw a La Nina event unfolding in the Pacific Ocean. In this image of sea surface temperature anomalies from January 2018 the cooler than normal water can be spreading from the South American coast across the pacific ocean along the equator.

Conditions in a La Nina pattern are basically the opposite of those found within an El nino. Colder water spreads across the ocean towards the West and warmer water stays pooled up against Australia and New Zealand. Just like with an El Nino, this pattern can disrupt normal weather patterns and can mean changes for parts of the U.S.

Just like during an El Nino, ocean and atmospheric circulations get disrupted and have effects on where high and low pressure sets up and even has effect on the jet streams. During La Nina events a lot of convection gets shifted towards Asia and Austrlia, where high pressure across the Eastern Pacific and towards the United States causes shifts in our weather as well.

During La Nina events the overall pattern features a drier and warmer than average Southwest while the Pacific Northwest, Northern tier of the country and the Midwest tend to be a bit cooler and wetter than average.

Quick Summary

I’ll wrap this up with a quick summary because I know this is a long article…

ENSO Neutral

  • Normal oceanic pattern of the El Nino Southern Oscillation. Warmer water is found further West with cooler water from up-welling tending to stay near the South American Coast of the equator.


El Nino

  • The warm phase of the El Nino Southern Oscillation. Weakening or disruption of trade-winds allows warmer than average water to spread across the Pacific Ocean. This warm water can also influence weather systems and atmospheric currents.


La Nina

  • The cold phase of the El Nino Southern Oscillation. Strengthening of trade-winds allows cooler than average water to spread across the Pacific Ocean. This colder than average water can also influence weather systems and atmospheric currents.


How Does ENSO Effect Colorado’s Weather?

This will be coming in our next article… we will deep dive into how shifts in ENSO have effected Colorado’s weather throughout the years and how we can identify patterns to help forecast what this year’s El Nino or Neutral event may be.

I’m putting together that information and will have some pretty nifty graphics and stats, so stay tuned for that in the next week or so!