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Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – December 21, 2018

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

Forecast Discussion:

Welcome to the first day of Winter! It begins at 3:23 p.m. MT today when the sun is at its lowest point in the sky. Days are at about their shortest now, nights at about their longest.

Today's discussion is really an update to yesterday's as we wait for the first trough to bring us some Saturday a.m. and another round of p.m. snow. We'll hit near record heat (low 60's F) today - the record of 66° F set in 2003 is probably not in danger.

It is clear and beautiful for one more day today (Figure 1) - but you can see the front approaching from the northwest. It is knocking on Colorado's door.

You'll see below that this front will drop inches of snow in the mountains again, and spreads a trace to a coating across the Plains (and Longmont) Saturday a.m. and again p.m.

Figure 1: The forecast surface map for Friday PM. From NCEP.

The longer range forecast:

This first front will cool us down a lot. (How could we not cool down? What goes up must come down.) The GFS (Figure 2) spreads 1/10th inch to 1 inch of snow out across the northern I-25 corridor.

For Christmas, the next big trough is rolling towards us (Figure 3). It is looking pretty strong and is expected to dig deep into the desert southwest. This should bring in some snow later on Christmas Day though it is looking less significant than it did yesterday.

Figure 4 is the GEM's idea, and it is very similar to the GFS snowfall idea through Christmas night. More of a trace to maybe an inch, rather than inches of snow.

Still... there is a major change coming with colder temperatures every day for a while and more snow. The next 10 days sees Longmont receive 1-2 inches of snow while the mountains and plains may see up to a foot plus in places. If WeatherBell forecasters are correct, this is the start of a very cold and stormy couple of months (January/February) (overall). More later!

Figure 2: The forecast accumulated snow map from the GFS and weather5280.com for Colorado, through Christmas Eve morning.

Figure 3: The 500mb forecast upper air analysis for Christmas Day evening. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.

Figure 4: The forecast accumulated snow map from the GFS and weather5280.com for Colorado, through Christmas Day night.

Figure 5: The forecast accumulated snow map from the GEM and tropicaltidbits.com for Colorado, through Christmas Day night.

Figure 6: The forecast accumulated snow map from the GFS and weather5280.com for Colorado, through the next 10 days.

Current Weather

Mostly cloudy

Mostly cloudy

36°F

UV Index
0 Low
Pressure
29.83 Rising
Visibility
8 miles
Dewpoint
29 °F
Humidity
76%
Wind
NNE 1.9 mph
Gust
3.8 mph
Wind Chill
37 °F

Hourly Forecast

Today
8 AM
39°F
Mostly cloudy
Today
9 AM
41°F
Intermittent clouds
Today
10 AM
44°F
Intermittent clouds
Today
11 AM
47°F
Intermittent clouds
Today
12 PM
49°F
Intermittent clouds
Today
1 PM
51°F
Intermittent clouds
Today
2 PM
52°F
Intermittent clouds
Today
3 PM
52°F
Intermittent clouds
Today
4 PM
51°F
Intermittent clouds
Today
5 PM
50°F
Intermittent clouds
Today
6 PM
47°F
Mostly cloudy w/ showers
Today
7 PM
44°F
Intermittent clouds

7 Day Forecast

Partly sunny w/ showers

Friday

52 °F

Cooler with sun and clouds; a couple of showers late this afternoon


Showers

Friday Night

34 °F

A couple of showers this evening; otherwise, cloudy


Mostly cloudy

Saturday

60 °F

Mostly cloudy


Intermittent clouds

Saturday Night

34 °F

Partly cloudy


Intermittent clouds

Sunday

62 °F

Periods of clouds and sun


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


Mostly sunny

Tuesday

61 °F

Mostly sunny and milder


Clear

Tuesday Night

29 °F

Clear


Sunrise and Sunset

Sunrise
6:48 AM
Sunset
7:23 PM

Based on AccuWeather data