The monotony of quiet weather will be interrupted this weekend as a quick-moving storm system brings much colder temperature and light snow to the Metro area on Sunday. We discuss the timing and amounts of our first snow of the month of November.
Northwest flow has kept things on the calm and cool side for the last week or so in Colorado. Today will be no exception. The current atmospheric set-up is shown in the 500 mb map below. A large trough is impacting the Great Lakes and northern Plains region, with cool northwest flow continuing to stream into Colorado. Unfortunately for the skiers, this flow has been lacking moisture most of the week and hasn’t produced much snow at all in the Mountains. Nonetheless, this pattern will translate to quiet and cool conditions across the Front Range both Friday and Saturday. Expect temperatures in the 40’s Friday and 50’s Saturday under mostly sunny skies.
GFS 500 mb vorticity map for Friday
Change arrives Saturday night
As northwest flow persists across the northern Rockies this time of year, it almost becomes inevitable that an embedded disturbance will dive southward and impact our region with wintry weather. This will be the case this weekend as a weak trough digs southward from Canada into Utah and western Colorado by Sunday morning.
GFS 500 mb vorticity map for Sunday morning
We’ve closely been tracking this storm since Tuesday and it has remained steadfast over the last few days in the models. There has been no major changes and this is always nice to see. All signs strongly point to this system bringing a high chance of light snow to the Metro area and nearby Foothills on Sunday, alongside a reinforcing shot of cold air.
The initial and sharp push of cooler air is slated to move into Boulder and Denver around sunset Saturday evening. Both the GFS and NAM models agree closely on this timing. We should see temperatures quickly fall into the 20’s with low clouds developing.
GFS 800 mb temperature and wind forecast for Saturday evening (left) and Sunday morning (right).
After midnight into very early Sunday morning, the atmosphere should moisten-up enough for snow to begin falling. The jet stream will be in a favorable location only for the very beginning of the event. While this jet will help to prevent any freezing drizzle from occurring at the onset, it is poor timing overall. As such, we aren’t too worried about the threat of banded snowfall this time around. The main forcing for Sunday’s snow will be the shallow upslope and modest large-scale lift from the quick-moving trough. Expect a period of light to moderate snowfall lasting about 8 to 16 hours beginning before sunrise Sunday, continuing into the afternoon or evening hours.
This system will be much colder than the Halloween storm, so there’s also no concern about temperatures being too warm. Snow levels will be well below 5000 feet across the entire state.
NAM model-derived snow level forecast for Sunday morning. Below 5000 feet for all of Colorado.
TIMELINE
Saturday: Cool and mostly sunny with highs in the 50’s.
Saturday evening: A strong cold front arrives with temperatures falling into the 20’s and status clouds developing.
Saturday night: Cold with light snow developing after midnight.
Sunday: Overcast with light snowfall continuing through much of the day, ending in late afternoon or evening hours. Highs will remain in the 20’s.
Sunday night: Partly to mostly cloudy skies and temperatures in the teens.
SNOW AMOUNTS
The highest snow totals will be focused across the western Metro area and the Foothills where shallow upslope will have the biggest impact. Models are currently zeroing in on around 0.2″ of liquid in Boulder, with slightly more in the Foothills and about half this amount east of Interstate 25. There is good run-to-run and member-to-member consistency in the ensembles right now on these amounts, which seem more than reasonable.
The one bonus aspect of this storm is the cold air. Temperatures during the day Sunday will be in the 20’s on the Plains and in the teens in the Foothills, with a good growth habitat for dendrites aloft. This should allow for generous snow ratios of 15:1 or higher (fluff!).
All things considered, here is our snowfall forecast for Sunday:
And for the wagering folks out there, we really like the look of the GFS accumulation probabilities…
We’re looking at generally a 2-4″ snow in Boulder, 2-5″ in the Foothills, and 1-3″ elsewhere in the Metro area. Temperatures will be cold, so some roads could become slick during the day Sunday. However, given the daylight and light snowfall rates, we expect road crews should be on top of things. It’s far from a major snow event, but hey, snow is snow!
If anything changes in the next day or so, BoulderCAST will let you know…
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