Following a sunny weekend, Monday will be the first of three stormy days and the first of four possible powder days. Let's get right to the details.

On Monday, the storm will move across Colorado, then on Tuesday, the storm will rapidly strengthen just to the northeast of Colorado. This strengthening system will rotate moisture counter-clockwise around the center of the storm and this moisture will flow into Colorado on Tuesday and Wednesday before waning by Thursday morning.

While there is never 100% forecast model consensus, most of the models are now in good enough agreement that I feel ok about posting the following detailed maps.

Monday

Snowfall will favor the southern mountains due to a flow from the south. Purgatory, Silverton, and Wolf Creek could wind up with 5-10 inches during the day on Monday with the afternoon offering pretty fun powder.

Monday Night

On Monday night, the snowfall will shift to the central and northern mountains with 3-7 inches of snow and possibly more for some northern areas if wrap-around storm energy notches up the totals.

Tuesday

Tuesday morning will offer some powder for the northern and central mountains, and snow will continue throughout the day thanks to a flow from the northwest and west-northwest. The northern mountains should see snow getting deeper through the day and northwest flow can also bring snow to Aspen Highlands, Aspen Mountain, Irwin, and sometimes Monarch, Telluride, and Silverton as well.

Tuesday Night

Tuesday night's weather will be a continuation of the forecast from Tuesday. More northwest flow. More snow.

Wednesday

Wednesday's weather will be a continuation of the forecast from Tuesday and Tuesday night. More northwest flow. More snow, especially in the northern mountains.

Wednesday Night

On Wednesday night, the snow will subside with some more accumulation in the northern mountains.

What could go wrong?

Wind Direction: Subtle changes in the wind direction between north-northwest, northwest, and west-northwest can bring more or less snow to some mountains. However, with a general northwest flow for nearly 48 hours, even some hours of less-than-ideal wind directions shouldn't take away from the forecast for 'a lot of snow' at areas favored by this storm setup.

Moisture/Temperature: We will be right on the edge of the ideal amount of moisture and the ideal temperature to create dendrite snowflakes and fluffy, deep snow accumulation. I am a little worried that we'll have a bit too little moisture and a bit too cold temperatures for the biggest snowflakes at all mountains favored by northwest flow. The ideal temperatures would be a few degrees warmer than what we'll likely see, and this means that some mountains south of I-70 could be slightly favored for fluffy snow due to slightly warmer temperatures, and in the northern mountains, areas that are a little lower in elevation could actually do slightly better.

Total Snowfall

The three maps below show the total snowfall from Monday morning through Wednesday evening. All three models start with somewhat different data but still output roughly the same amount of snow. This agreement leads to increased confidence in the forecast.

These numbers are impressive. And even if these numbers are 30-50% too high, the snowfall totals would still be significant.

Best Powder

Monday: Southern mountains by midday and afternoon.

Tuesday & Wednesday: Northern mountains with refills through the day.

Thursday: Northern mountains in the morning.

Bottom Line

This will be a fun week of snow throughout the state. Enjoy it! Early seasons are not often this good in terms of snow coverage and the number of powder days.

It's likely that Friday, Saturday, and Sunday will be dry.

Then during the December 18-25 timeframe, there are hints of storms showing up in the longer-range models, but overall, our weather pattern will shift so that the center of the storminess is over the central plains of the US, which could leave us in a chilly yet drier pattern with maybe fewer system and moisture-starved storms.

Below is the European ensemble model. Each horizontal line shows one of 51 versions of the model. The colors show the amount of precipitation (green is light, dark green and blue are heavier), and the graphic shows time from left to right for the next 15 days.

And below is the American GEFS ensemble model.

We'll head into the time period of Christmas with a mostly above-average snowpack, though the second half of December is unlikely to be as stormy as the first half.

Thanks for reading!

Joel Gratz

Geography Key

Northern Mountains
Steamboat, Bluebird Backcountry, Granby, Beaver Creek, Vail, Ski Cooper, Copper, Breckenridge, Keystone, Loveland, Arapahoe Basin, Winter Park, Berthoud Pass, Eldora, Rocky Mountain National Park, Cameron Pass

Along the Divide
Loveland, Arapahoe Basin, Winter Park, Berthoud Pass

East of the Divide
Eldora, Echo, Rocky Mountain National Park, Cameron Pass

Central Mountains
Aspen, Sunlight, Monarch, Crested Butte, Irwin, Powderhorn

Southern Mountains
Telluride, Silverton – north side of the southern mountains | Purgatory, Wolf Creek – south side of the southern mountains