Spring Blizzard to Hit Denver and Surrounding Suburbs: 3-6″ of Snow and Hazardous Travel Conditions

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Snow accumulation for the Rockies and Plains Regions by Midnight Mountain Time on Thursday Night. Note a reduction in snow along the foothills/west of I-25 due to downslope winds.

Denver is under a blizzard warning beginning tomorrow at noon, which should coincide with the beginning of snowfall that will drop 3-6″ across most of the metro area!

A similar storm system to the one experienced last month will bring high winds, low visibility, and snow to Denver and the front range. Snow will start around noon tomorrow and will continue through noon on Thursday. The highest amounts of snow will be to the east, south, and far west (foothills) of the metro area. This storm is expected to have downslope wind flow that will likely reduce the amount of snow west of I-25 compared to other areas (can be seen above in snowfall totals map).

Remember: A blizzard does not mean that a lot of snow will fall. The definition of a blizzard is a storm with “considerable falling or blowing snow” and winds in excess of 35 mph and visibilities of less than 1/4 mile for at least 3 hours. So, even though snow totals are lighter than the most recent blizzard, travel conditions will still be as hazardous and there is the possibility of wind damage to trees and other objects.

Current DWP Storm Rating: 4/5 – intense: stay at home if possible and ride out with case of beer/couple bottles of wine. Blizzards: for times when you want day-drinking to be socially acceptable.

Updates will be made leading up to and during the storm.

-Andrew

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Blizzard Conditions on Colorado’s Eastern Plains, but Modest Snow in the Metro Area

Screen Shot 2019-03-12 at 9.24.50 PMUpdate on snow totals: Areas east of I-25 are looking at slightly more snow now with accumulations in the 5-10″ range for this storm. Areas west of I-25 and leading up to the foothills will likely see 2-4″ of snow from this storm. The metro area is now under a blizzard warning and strong winds with whiteout conditions will be possible.

Well, the hype train has been in full force with this next weather system as predictions of epic snow have popped up all over the place. Even the famous Frankie MacDonald (I’ve been a big fan for years now) has given his forecast for quite a snow storm for Denver! However, while this storm will be quite powerful, the forecast really doesn’t have much in store for the metro area at this point in time compared to the surrounding areas. In fact, this system looks like a basic spring storm without a whole lot of bells and whistles for the metro area, but we’ll dive into why there has been so much hype and the current forecast a bit ahead. All hype aside, this storm looks to be a good one to bring more moisture to the state and, even though our mountain snowpack is way above average, it’s always better to have too much snow than too little.

As always, I’ll break this up into the following sections to make this a bit easier to read:

  1. Storm Timing
  2. Storm Position (1 Foot of Snow vs. 3-6″)
  3. Snowfall Accumulations
  4. Storm Hazards
  5. National Weather Service Blizzard Warning

Storm Timing

This is a fast moving storm system that will impact Denver and the metro area at a time that is rather uncharacteristic of heavier snowfall. Generally with storm events, we see the passage of a cold front in the afternoon and then snow moving in to the area in late afternoon with the most intense snowfall overnight. This storm is a bit different as snowfall currently looks to begin around mid-morning on Wednesday (8-10am) with rain and continue through late evening with the heaviest snowfall occurring between noon and 5-6pm. As mentioned before, this is a fast moving system and will be out of the area quite quickly once the bulk of the snow has fallen. While we may see some flurries late Wednesday, their accumulation will be minimal.

Storm Position

Screen Shot 2019-03-12 at 9.42.35 PMOne of the reasons that there has been so much uncertainty and a little hype surrounding this storm is that it’s a classic spring upslope snow storm. As such, the position of the low pressure center on the east side of the Rockies is critical to determining which areas will get high amounts of snowfall and the areas that get a few inches. Low pressure systems have winds that rotate around them in an anti-clockwise fashion, which means that any area to the north of the low will be getting winds from the east and any area to the south will get westerly winds (in the northern hemisphere). So, when a low develops on the east side of the Rockies, it generally ends up flinging winds up the eastern slope causing the development of clouds and snow like in the figure to the right. As you might guess, there is an optimal area for upslope winds and a difference in the position of the low can determine the amount of snow you’re getting.

For this storm, two of the main weather models disagree on the position of the low pressure center. The GFS (right below) has the low slightly to the south and east near the Colorado/Oklahoma border, which puts the front range under the influence of winds from the north that won’t have much of an upslope component. The NAM (left below) has the low more to the northwest, which would give us a bit more moisture from the east and allow for bigger Denver snow. So far, it looks like the NAM is the outlier and that the low will be closed to the GFS’ position, which means that Denver likely won’t be seeing more than a foot of snow, but there is still some time for the forecasts to come in line with each other and for the low to develop in a location with more of an upslope component.

 

 

Snowfall Accumulations

Currently, it’s looking like Denver and the front range will be in a bit of a dead-zone for snow with higher amounts in just about every direction. Currently, it’s looking like areas west of I-25 will get 2-4″ of snowfall and areas to the east of I-25 will get between 5-10″ of snow with locally higher amounts of up to 14″ in some places. The large gradient in snowfall totals is from east to west Denver is primarily due to the storm moving out of the area and causing westerly downslope winds that will reduce precipitation in areas along the foothills. There’s still plenty of time for the forecast to shift, which means that final snowfall totals likely won’t come out until later this afternoon/evening. So check back.

Storm Hazards

This storm will be relatively warm with temperatures only barely dipping below freezing, which means that it will likely start off as rain and continue as wet/heavy snow. Assuming periods of heavy snow on already wet roads, slushy nonsense will be likely and driving may become problematic. The afternoon commute will probably be even worse and working at home may be a good idea to avoid the chaos. Now, the biggest threat out east is blowing snow in intense winds and this is where the blizzard comes into play. While most areas out east will see anywhere from 6-12″ of snowfall, wind speeds could be as high as 75 mph, which will result in near whiteout conditions and is the reason that blizzard warnings have been issued (blizzards aren’t actually defined by big snow accumulations). Winds will also be blustery in the metro area with speeds in the mid 20s to low 40s. So, avoid travel if at all possible on Wednesday.

Thanks for reading!

-Andrew

National Weather Service Blizzard Warning

...Blizzard expected to develop over portions of northeast
Colorado Wednesday afternoon and Wednesday night...

.Heavy snow and very strong winds will develop over most of
northeast Colorado Wednesday afternoon and Wednesday night.
Blizzard conditions are likely to develop along and east of the
I- 25 Corridor where the heaviest snow is expected to fall. Power
outages and wind damage will also be possible as winds gust to
between 60 and 70 mph will be possible.

West of the I-25 Urban Corridor, heavy snow and gusty winds will
also be possible, with significant travel impacts. Rain is
expected to develop Tuesday night, and then change to snow late
Wednesday morning and may become heavy at times with wind gusts
from 40 to 60 mph.

Mountain areas will also see more accumulating snowfall during
this period.

Denver-Greeley-
Including the cities of Aurora, Brighton, City of Denver,
Denver International Airport, Highlands Ranch, Littleton, Parker,
Eaton, Fort Lupton, Greeley, and Roggen
1055 AM MDT Tue Mar 12 2019

...BLIZZARD WARNING IN EFFECT FROM 10 AM WEDNESDAY TO MIDNIGHT
MDT WEDNESDAY NIGHT...

* WHAT...Blizzard conditions expected. Total snow accumulations of
  5 to 8 inches expected. Winds gusting as high as 60 mph.

* WHERE...Denver and Greeley.

* WHEN...From 10 AM Wednesday to midnight MDT Wednesday night.

* ADDITIONAL DETAILS...Plan on slippery road conditions. Areas of
  blowing snow will reduce visibility to near zero at times. The
  hazardous conditions will impact the evening commute. Very
  strong winds could cause extensive tree damage.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Blizzard Warning means severe winter weather conditions are
expected or occurring. Falling and blowing snow with strong winds
and poor visibilities are likely. This will lead to whiteout
conditions, making travel extremely dangerous. Do not travel. If
you must travel, have a winter survival kit with you. If you get
stranded, stay with your vehicle.

Snow and Colder Temperatures to Impact Denver Saturday Night into Sunday

Snowman

Surveying his kingdom in the Snowy Mountains of Australia, the snowman contemplates what his life would be like in Colorado.

It’s that time of the year, we’ve had some cool temperatures and seen a few flakes of snow fall, but it has been relatively light to this point. This looks to change later today and tomorrow when a cold front will move into the region that will bring snow and a large drop in temperatures! A big unknown, however, is how much of this snow will actually stick to the ground after it has fallen. Regardless of the final accumulations, it’s time to brush up on your snowball technique, fire up Netflix, and break out the Irish Hot Chocolate (especially if you’re going to the Broncos game) because snow and cold is on the way!

As always, the forecast will be broken into a few different parts to make it a bit easier to read. It will be structured as such-

  1. Timing and Details of the Weather System
  2. Expected Snowfall Amounts and Accumulation*
  3. Potential Impacts

Timing and Details of the Weather System

CODNEXLAB-GOES16-regional-northcentral-14-12_37Z-20181013_map_-100-1n-10-100

GOES-16 Longwave infrared satellite imagery of the high plains. Warmer cloud temperatures (lower altitude) are in whites and purples/pinks, colder cloud temperatures (higher clouds) are in blues and greens. State outlines are in light blue.

 

Cloud cover from a cold front can be seen developing near the Wyoming/Montana border and moving south towards Colorado (Above Satellite Image Gif). It’s expected to arrive late Saturday afternoon with a nearly a 30 degree drop in temperature in the metro area! This front will change our dominant wind direction from easterly (due to the counterclockwise winds of a Low pressure system centered on the CO/NM border) to northerly that will funnel plenty of cold air into the state from up north. A chance of rain will follow the passing of the cold front and rain should persist around the area until late this evening/early tonight when it should switch to snow. Snow will continue overnight with the heaviest snow falling between midnight and 6am on Sunday morning. Snow will continue through most of Sunday and will eventually reduce to flurries on Sunday afternoon/evening.

Expected Snowfall Amounts and Accumulation

A bit of theory about forecasting snow-

I’m guessing that you probably noticed the asterisk next to this section when I outlined the forecast structure, right? Of course you did, you’re smart. The reason why that asterisk exists in next to the title of this section is because we normally discuss snow storms in terms of accumulated snow on the ground. While this is the most relevant for most people, it isn’t actually the best measure of the amount of snow that will be coming from a storm system. Warm ground temperatures, very dry air, and wind can all alter how much falling snow actually accumulates on the ground. This is particularly true in Autumn and Spring when air temperatures (and subsequent ground temperatures) can fluctuate from very warm to relatively cold in short periods of time. So, the amount of accumulation on the ground could be substantially less than what actually fell.

snow-energy-balance

A graphic snowing sources of energy for a snowpack. We’re only concerned with the ground heat flux for this forecast, but the other information is nice to have as well. Credit: Wasatch Weather Weenies

With the our little excursion into snow/atmospheric energy in our minds, it’s important to note that this system will be coming through after a day with high temperatures in the low to mid-60s. This means that, even though the ground will begin to cool once the cold front comes through, it may still be warm enough to melt initial snowfall. Now, this will depend on a number of factors with the largest being the amount of rain that falls before the snow. Rain is much better at cooling down the surface better than simple swings in temperature. So, if we get enough rain to cover everything relatively well, we’ll probably see most of the snowfall accumulate on the ground. If there is little to no rain, we could see the initial snowfall melt when it hits the ground due to the warm ground temperatures. Anyway, on to with the totals!

Snowfall totals of 2-4″ are expected around the metro area with slightly higher amounts to the west/south and slightly lower amounts to the east. Boulder along with Castle Rock and their surrounding suburbs can expect 3-6″.

Potential Impacts

Roads will be icy late on Saturday and during Sunday. Windchills are expected to be in the teens during the day on Sunday. Make sure that you have an emergency kit in your car if you plan on traveling.

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The National Weather Service has issued a Winter Weather Advisory that can be seen below. Please note that my expected accumulations are slightly lower than theirs. As always, please feel free to ask any questions that you may have. Thank you for reading!

Including the cities of Fort Collins, Hereford, Loveland, Nunn,
Arvada, Boulder, Golden, Lakewood, Longmont, Aurora, Brighton,
City of Denver, Denver International Airport, Highlands Ranch,
Littleton, Parker, Castle Rock, Elbert, Fondis, Kiowa, Larkspur,
Eaton, Fort Lupton, Greeley, and Roggen
343 AM MDT Sat Oct 13 2018

...WINTER WEATHER ADVISORY NOW IN EFFECT FROM 8 PM THIS EVENING
TO NOON MDT SUNDAY...

* WHAT...Rain and snow showers will develop this evening, then
  turn to all snow overnight tonight. Total snow accumulations of
  3 to 6 inches expected by midday Sunday.

* WHERE...Fort Collins, Boulder and the western suburbs of
  Denver, Denver, Castle Rock and Greeley.

* WHEN...From 8 PM this evening to noon MDT Sunday.
. latest high tendency
* ADDITIONAL DETAILS...Plan on icy and slippery road conditions.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Winter Weather Advisory for snow means periods of snow will
cause primarily travel difficulties. Expect snow covered roads
and limited visibilities, and use caution while driving.

The latest road conditions for the state you are calling from can
be obtained by calling 5 1 1.

Afternoon Thunderstorm Forecast and Monitoring 6/18


Updates (see original forecast below)-

Thunderstorms have developed along the foothills to the west of Boulder and Longmont. Storms look to be intensifying quickly and one report of pea-sized hail has already been made from the storm northwest of Nederland.

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Thunderstorm Position and Intensity at 4:45pm


THIS AFTERNOON’S THUNDERSTORM FORECAST-

A few thunderstorms are in the forecast for this afternoon and evening!

Denver will see a few thunderstorms, but severe storm development should stay far to the east/northeast of the metro area. Thunderstorms should begin to build around town over the next couple hours and will move to the northeast fairly quickly.

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Expected Storm Position and Intensity at 8pm from 20Z HRRR Model Run

Severe Storm Risk- Current models are showing severe storms developing east of DIA and E-470 (picture) with storms continuing to develop and eventually tracking along I-76. Threats from these storms will be large hail, damaging winds, and possibly a tornado.

As always, feel free to ask any questions that you might have.

Severe Storms Possible Along Front Range on Friday

understanding_categoriesSevere storms with damaging hail, wind, and a slight possibility of a small tornado are in the forecast! These storms will be the beginning of what will be a soggy and cool weekend that will have Denver’s high temperatures dipping into the mid-50s. While these storms will have the potential to cause damage, current forecasts suggest that the danger should be minimal. The Storm Prediction Center currently has the front range in a Marginal Thunderstorm Risk and areas to the east, such as Aurora, in a Slight Thunderstorm Risk.

Forecast

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NAMNEST Simulated Reflectivity (estimated storm position and intensity) at 4pm Local Denver Time

 

A small lee-side low pressure will develop tomorrow in along the Colorado/New Mexico border that will allow for increased transport of moisture and instability to the front range. All models are currently showing thunderstorm activity around the Denver metro area tomorrow that will start in the early to mid-afternoon. The positioning of the storms (as usual) is fairly hard to predict, but the models are agreeing on the overall intensity of the storms. The GFS has things pushed a bit further east and has the primary wave of storms over eastern Denver and Aurora, whereas the NAM and 3k NAM have the storms developing right along the foothills. I’m inclined to agree with the NAM models at this time as orographic forcing and the boundaries created by the mountains always play an important role in storm development.

Timing

Storms will begin developing in early to mid-afternoon (~2-3pm) and will begin moving eastward. This means that there is a high likelihood that there will be storms occurring during rush hour and that it may be a better idea to wait to commute if a storm is nearby. Storm intensities should begin decreasing in the evening and areas of light to moderate rain could occur overnight. The times with the most intense storms should be from 3-7pm.

Threats

microburst_schematic_nubilt.jpg

Primary threats from these storms will be hail and strong winds. Current vertical profiles in the area show a very wet atmosphere high and a drier atmosphere at the surface. This has the potential to create damaging wind events as the rain aloft falls into the drier air beneath it, absorbs heat and evaporates, and then the cooler air around it accelerates towards the ground (cold air is heavy and sinks! Heat rises!). These may or may not be seen as microbursts. While a small tornado is not out of the question, the needed wind shear and helicity don’t look to provide a favorable environment for development.

As always, thanks for reading and let me know if you have any questions! I’ll update when new information is available.

Cheers!

Andrew

Upslope Storm to Bring 4-8″ of Snowfall to Denver Metro Area

Update: Models have diverged slightly in maximum snowfall totals with
some predicting a bit less and one predicting a bit more. I'm staying 
in the center at the original 4-8", which I think is realistic. The
Short Range Ensemble Forecast (SREF) model has upped its totals, but
it tends to get a bit crazy with its accumulations as we approach
major events. So, we'll stick with the others that are generally 
agreeing on the position of the system and the precipitation that we
can expect. With that being said, focal points for this storm such as
the foothills, Palmer Divide, and higher mountain terrain could see
amounts a bit higher in the 6-12" range with localized amounts even 
a bit higher.

Greetings! After what seems like years, we finally have an exciting winter storm that will be coming through the Denver and Front Range regions!

ermahgerdWith very low seasonal snowfall accumulations leading into this weekend, we need to embrace our wonderfully overdue moisture-brining storm! However, this storm has a bit more in store for us than just snowfall. We’ll see a decent drop in temperature with this system and that could contribute to freezing drizzle before the snow starts. So, this could definitely end up as a a fairly impactful and, at times, dangerous storm.

We’ll break down the forecast like this:

  • National Weather Service Winter Storm Watch
  • Storm Timing and Development
  • Expected Accumulations and Threats

National Weather Service Winter Storm Watch

...WINTER STORM WARNING IN EFFECT FROM MIDNIGHT TONIGHT TO 5PM MST
SUNDAY AFTERNOON THAT INCLUDES FORT COLLINS, BOULDER, DENVER, AND 
GREELEY. HEAVY SNOW POSSIBLE. PLAN ON DIFFICULT TRAVEL CONDITIONS 
REDUCTIONS IN VISIBILITY ARE POSSIBLE DUE TO BLOWING SNOW. TRAVEL 
WILL BE IMPACTED SUNDAY MORNING AND INTO THE AFTERNOON HOURS. 
PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Winter Storm Warning means significant amounts of snow, sleet
and ice are expected. This will make travel very hazardous or
impossible. The latest road conditions for the state you are
calling from can be obtained by calling 5 1 1.

Storm Timing and Development

Screen Shot 2018-01-20 at 10.30.11 PM

GOES Infrared Satellite Imagery at 5:22 am MST

Currently, clouds related to the current system can be seen in the image above draped over northeastern Colorado into Utah and Nevada and down into Arizona. Cloud cover will continue to increase and will move eastward during the day today and we should start seeing heavy coverage around the area in mid- to late-afternoon.

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Forecasted Mean Sea Level Pressure and Temperature at the surface at 5pm Mountain Time on Saturday

The low pressure system that is currently sitting in eastern Colorado will continue to strengthen and will center itself over southeastern Colorado near the Oklahoma panhandle late Saturday night into Sunday morning before moving eastward Sunday afternoon. As it progresses, we will notice temperatures that will cool off beginning at 2pm when winds should shift from easterly/northeasterly to predominantly northerly. Temperatures will fall from the upper 40s on Saturday until daybreak on Sunday when a slight increase during the day will occur. Lows over night are expected to be in the low 20s and highs for Sunday will be in the mid- to upper 20s.

Precipitation is expected to start in the region around midnight on Saturday/early Sunday morning. Currently, the precipitation is expected to start off as freezing drizzle or freezing rain because of the relatively warm temperatures that will exist until late Saturday night. The freezing drizzle should turn to snow quickly and snow will remain dominant until the storm system moves out on Sunday afternoon.

You’ll notice that the low pressure system in the image above (black lines) looks particularly circular and has a good position for creating snowfall for Denver. But, there are a couple ingredients missing for that blizzard that everyone wants. First, this is a relatively dry system with minimal moisture input which will limit the amount of snow that we get. Another reason that we won’t see feet of snow is that the storm system will move out of the area too quickly. We really need a blocking pattern (holds weather pattern still-ish for a while) to really give us those storms that last days and give us heavy dumps of snow. We’re just not going to get that out of this one, unfortunately.

Expected Accumulations and Threats

The Global Forecast System (GFS), North American Mesoscale(NAM), Short Range Ensemble Forecast (SREF) models all agree on the Denver metro area getting between 4-8″ of accumulation for this system. As this is an upslope event, meaning that the winds will be coming from the east/northeast and will travel “up-slope” when they hit the mountains, I expect the largest accumulations to be along the western foothills and south along the Palmer Divide in areas like Castle Rock and Highlands Ranch. It will be important to monitor the latest model output as the High Resolution Rapid Refresh (HRRR) model comes into range and begins to create snowfall predictions as well.

The biggest concerns with this storm will be the freezing drizzle falling early and occasionally heavy snow. If freezing drizzle builds up on the ground and a layer of snow is combined with it, roads will be very icy and dangerous on Sunday morning. However, current thoughts are that the impact from freezing drizzle will be minimum due to the short period that it will fall. Driving conditions will be hazardous when the icy and snow-packed roads are combined with reduced visibility from heavy and blowing snow. Avoiding travel is a good idea if it is non-essential.

I will update this post as new model runs come out and new information becomes available.

Thanks for reading!

-Andrew

Snow to Return to Denver Tonight and Tomorrow

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After a long absence, snow will arrive overnight tonight in the Denver area and along the front range. For some, this is a welcome departure from the hot summer temperatures that we have experienced. Others aren’t so excited about the arrival of the cold and fluffy white stuff. Regardless of your feelings about it, snow will be here and we will actually be receiving quite a bit of it!

As always, the forecast will be broken down into a few different parts and they are as follows-

  1. National Weather Service Winter Storm Warning
  2. Storm Timing
  3. Accumulation Totals

 

National Weather Service Winter Storm Warning

...WINTER STORM WARNING REMAINS IN EFFECT FROM MIDNIGHT TONIGHT
TO 3 PM MDT MONDAY...

* WHAT...Heavy snow expected. Some secondary roads and bridges
  and overpasses may become snow or slush covered. Plan on slow
  and hazardous travel conditions, including during the morning
  commute on Monday.
* WHERE...Fort Collins, Boulder, Denver and Castle Rock.
* WHEN...Midnight to 3 PM Monday.
* ADDITIONAL DETAILS...Scattered power outages may occur due to
  heavy wet snow accumulating on trees still bearing their
  leaves.

Storm Timing

Cold air is now funneling into Colorado following the passage of a recent cold front and rain will be arriving in the metro area late this evening. Current winds are from the northeast and are helping to bring some moisture into the area, but will transition to northerly winds as time passes. Rain will continue until shortly after midnight when it will transition to snow and will remain as snow through Monday afternoon. The most intense snowfall should occur immediately after the transition to snow and mid-morning from approximately 7-10am. So, give yourself some additional time for your morning commute because it is looking to be a sloppy one!

Accumulation Totals

hrrr_sner

HRRR Forecasted Snow Totals Through Monday at 3pm

This is shaping up to be a weak upslope storm which means that accumulation totals will be highest in the western parts of the metro area. Accumulations will be between 4-8″ with the slightly higher amounts falling near Boulder and east of the Denver area. While 4-8″ is a fairly substantial amount of snow, the soil and ground temperature is warm enough to melt most of it once it hits the ground. However, neighborhoods and side roads will probably have some light snow accumulation and slush. This will be a moisture laden and heavy snow that will have the possibility of breaking tree branches that have leaves.

As always, let me know if you have any questions!

Thank you for reading!

-Andrew