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Update 12/14 5pm: Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – December 14-15, 2019

This content was originally published by the Longmont Observer and is licensed under a Creative Commons license.

In Brief:

We are in the middle of our four day heavy snow event (now and then) up in the mountains. Some spots will see 1 to 3 feet up there. We'll see a chance of showers (snow at night and probably rain midday Saturday) then snow showers getting heaver Sunday afternoon and night. Still only 1-3 inches are likely in Longmont (with only a dusting still a possibility). We start next week cold and dry and slowly warm up with no next-storm in sight.

Update 12/14 5pm:

Oh oh, down-slope flow looks like it is going to spoil our snow-fun (and the jet dynamics/storm is passing far to the south of Longmont and NE Colorado). First, the HRRR through Sunday 6am gives us a dusting to a coating of snow overnight (Figure 1 update). Both the GFS (Figure 2 update) and the NAM (not shown) don't show snow accumulation for Sunday night as previously expected. We are trending towards no snow this weekend. An inch or so of snow is still always possible if things shift a bit, but less likely now.

For fun, I'm still watching Christmas Day on the GFS, and the snow moves in late Christmas Day into the 26th IF this pans out. Don't place bets or change plans on this forecast yet - it is just for fun (it is still just too far out).

End Update 12/14 5pm.

Forecast Discussion:

Our first surge of cool air has swept over the state (cold front). There was a chilly north wind Friday night. The front will remain south of the state with short waves passing the state now and then through the weekend. The main even for the I-25 corridor will be Sunday afternoon and evening (after Figure 1) - north of Denver, it should only be a few inches. If the European model is right (not shown) Denver might get 3-6 inches of snow. More likely Denver will see 2-4 inches.

The weatherunderground model doesn't print measurable snow amounts for Longmont, but does show a chance of showers all weekend with the better chance of snow Sunday and Sunday night (Figure 2).

Snowfall Roundup:

Weatherunderground is a trace of snow to a coating (??). Figure 2.
The NAM finally brought snow to town but has us in the 0.5-1 inch belt. Figure 3.
The GFS is still more bullish with 3-4 inches. Figure 4.
The GEM has been the most excitable all along, but is at 2-3 inches. Figure 5.

The Longer Range Forecast:

The snow tapers off early Monday morning (Figure 2). There might be icy and slick spots on your Monday commute. We are barely above freezing Sunday through Tuesday then we warm to near 50F by next week.

Super far-off fantasy Christmas Forecast:

We are still too far away for models to be reliable, but the GFS has a present for the White Christmas folks tonight. Figure 6 shows (completely different than all earlier forecasts we've looked at) a big up slope snow making monster for Christmas afternoon. Again, we'll see!

Figure 1: The forecast surface map for Sunday morning from NCEP.
Figure 2: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 3: 10:1 (snow to liquid) snowfall totals through Monday morning from the NAM and weather5280com for Colorado made Friday afternoon.
Figure 3: 10:1 (snow to liquid) snowfall totals through Monday morning from the GFS and weather5280com for Colorado made Friday afternoon.
Figure 5: 10:1 (snow to liquid) snowfall totals through Monday morning from the GEM and tropicaltidbits. com for Colorado made Monday afternoon.
Figure 6: The 6 hour precipitation type forecast for Christmas Day evening from the GFS from tropicaltidbits.com

Current Weather

Cloudy

Cloudy

48°F

UV Index
0 Low
Pressure
29.77 Steady
Visibility
8 miles
Dewpoint
27 °F
Humidity
44%
Wind
SE 2.8 mph
Gust
6 mph
Wind Chill
47 °F

Hourly Forecast

Today
1 AM
45°F
Cloudy
Today
2 AM
43°F
Intermittent clouds
Today
3 AM
40°F
Intermittent clouds
Today
4 AM
38°F
Intermittent clouds
Today
5 AM
36°F
Intermittent clouds
Today
6 AM
34°F
Intermittent clouds
Today
7 AM
36°F
Intermittent clouds
Today
8 AM
38°F
Intermittent clouds
Today
9 AM
41°F
Intermittent clouds
Today
10 AM
44°F
Intermittent clouds
Today
11 AM
47°F
Intermittent clouds
Today
12 PM
50°F
Intermittent clouds

7 Day Forecast

Partly sunny

Thursday

65 °F

Partly sunny


Intermittent clouds

Thursday Night

34 °F

A shower in spots late this evening; otherwise, partly cloudy


Partly sunny w/ showers

Friday

53 °F

Cooler with times of clouds and sun; a couple of showers late in the afternoon


Showers

Friday Night

33 °F

A couple of showers in the evening; otherwise, cloudy


Mostly cloudy

Saturday

60 °F

Mostly cloudy


Intermittent clouds

Saturday Night

36 °F

Partly cloudy


Intermittent clouds

Sunday

62 °F

Times of sun and clouds


Mostly cloudy

Sunday Night

33 °F

Becoming cloudy


Showers

Monday

52 °F

Cloudy and cooler with occasional rain; windy in the afternoon


Intermittent clouds

Monday Night

29 °F

Windy in the evening; partly cloudy


Sunrise and Sunset

Sunrise
6:50 AM
Sunset
7:22 PM

Based on AccuWeather data