Tuesday PM Update: A chance of rain then snow, accumulation possible Wed evening through Fri morning

We hope you all are enjoying the beautiful weather across the region to start this week, as colder and wetter changes are on the way starting tomorrow. The national map today shows a mild pattern in place across much of the country, with chilly weather hanging on across the Great Lakes and mid-Atlantic:

As we discussed in this week's SOTA, our weather starts to change tomorrow as a large cutoff low over the Southwest United States begins pumping moisture into the state in the form of rain and snow:

If we look at the GFS precipitation forecast through Friday, we see precipitation spread out of the Southwest into Colorado, with the heaviest precipitation for the state expected over the Southwest mountains through the end of this week. For Eastern Colorado, totals will be lighter, but a few areas along the urban corridor and immediate plains may see some appreciable moisture, and perhaps even a couple/few inches of snow.

With the heaviest precipitation focus to the southwest, it's not surprising to see this is where most of the NWS hazard alerts are currently issued. From flooding concerns across California, Arizona, and Utah, to heavy higher elevation snow, it'll be an active few days:

For the San Juans, snowfall totals upwards of a foot will be possible if not likely, with totals up to 30" possible for some of the higher peaks.

The GFS shows this well. Heavy mountain snow across the Southwest, some good snow as well for the central mountains, with spottier totals across Northeast Colorado. Some of our precipitation will fall as rain, especially Wednesday. Wednesday night and Thursday precipitation changes to snow everywhere, and a few inches of snow will be possible.

For a broad-brushed look at snowfall potential Wednesday night through Thursday night... Greatest potential for several inches will be across the Western Palmer Divide and up through Boulder County. Areas along and West of I-25 are largely in the 1 - 3" range, with isolated 2 - 6+” totals, with generally just a Trace to 2" to the east:

We can see this reflected in our gamblers. For the urban corridor 1 - 2" is the most likely for all areas. Boulder we see those higher end trailing probabilities indicating at least some potential for several inches of snow.

All the snow may not come all at once. Instead in several waves over the next few days. The initial push of moisture arrives Wednesday morning/midday, and will very likely begin in the form of rain for many lower elevation locations. Another push comes Thursday, which should mostly come in the form of snow, at least along the urban corridor and west. As you can see in the chart below, chilly air arrives Wednesday and sticks with us into Friday. The chance of rain and snow will be in the forecast for several days.

Models differ on who sees their best chance of snow when, as it won't be uniform across the area. The European model has the best chance of snow for the urban corridor coming Thursday afternoon and overnight (with very little tomorrow evening/overnight), while the NAM pulls much of the energy too far south to promote much heavy snow for the northern urban corridor Thursday evening, and instead has a band of heavy snow from Boulder through Fort Collins Wednesday evening.

Cutoff lows aren't generally handled well by models, nor are trailing secondary systems as we see with this one. So we'll keep an on Thursday, but for now lean modest totals overall Wednesday evening through Friday morning for most locations.

So again, probabilistically odds are a Trace to 3" for most locations along the Front Range and adjacent plains. Models indicate banded snowfall may help boost totals in a few location, both Wednesday evening and Thursday evening, but this would likely be more isolated in nature, with totals of 6+” or so through Friday morning should these occur.

Quieter weather will return for the weekend before perhaps another chance of snow early next week. We'll have updates on this forthcoming as we know folks will be watching the weather closely for Thanksgiving week. As it looks today, the best chance for active weather comes Monday evening through Tuesday, with cool but quieter weather forecast by the Euro by Thanksgiving day:

Brendan Heberton

Brendan is founder of Weather5280. He is co-founder of FreshyMap, and develops software for geospatial data analysis and visualization.

Denver, Colorado
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