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.
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