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Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – December 19, 2018

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

Forecast Discussion:

Our first trough is passing and the winds will become pretty extreme Tuesday PM in the mountains and Wednesday everywhere as the nose of the jet stream plows into the state (Figure 2). (I'll push this earlier, on Tuesday, since the NWS has issued a warning for Wednesday.)

HIGH WIND WARNING IN EFFECT FROM 8 AM TO 5 PM MST WEDNESDAY...

The National Weather Service in Denver has issued a High Wind

Warning, which is in effect from 8 AM to 5 PM MST Wednesday. The

High Wind Watch is no longer in effect.

* TIMING...8 AM MST through 5 PM MST.

* WINDS...Northwest winds 30 to 40 MPH with gusts up to 60 MPH

possible.

* IMPACTS...Areas of blowing dust restricting visibility. Strong

crosswinds on highways resulting in hazardous travel for high

profile vehicles. Possible power outages caused by downed power

lines. The strong winds and dry vegetation will result in

elevated fire danger.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A High Wind Warning means a hazardous high wind event is expected

or occurring. Strong winds may lead to property damage. Hazardous

driving conditions due to powerful cross winds will pose a

serious risk for drivers, especially for light weight and

high profile vehicles. Loose outdoor items should be brought

inside or secured properly.

Figure 1 shows the western slope's up-slope flow and snow also created by this jet.

We remain warm through Monday with temperatures in the upper 40's F to 60° F at times. It is normally in the lower 40's F for a high this time of year.

Our previously forecasted snow chance on Wednesday is largely gone (the mountains still get it). Our Saturday snow chances are pretty small as well. We do have a Christmas Day chance of precipitation (but it is small in Longmont). Figure 3 shows that the GFS thinks snow comes very close to Main St. on the west side. That is encouraging. Figure 5 (the GEM) has snow confined to Lyons and westward.

Going further out, there seems to be a real snow "storm" coming the next couple of days after Christmas - Figure 4 gives us 1-3 inches up to the 28th. Figure 6 brings snow just into Longmont by the 28th.

Figure 1: The forecast surface map for Wednesday night. From NCEP.

Figure 2: The 500mb forecast upper air analysis for Wednesday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.

Figure 3: The forecast accumulated snow map from the GFS and weather5280.com for Colorado, through Christmas Day afternoon.

Figure 4: The forecast accumulated snow map from the GFS and weather5280.com for Colorado, through the next 10 days.

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

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

Current Weather

Partly sunny

Partly sunny

60°F

UV Index
9 Very High
Pressure
29.6 Steady
Visibility
9 miles
Dewpoint
21 °F
Humidity
22%
Wind
W 10.2 mph
Gust
22.2 mph
Wind Chill
60 °F

Hourly Forecast

Today
1 PM
59°F
Mostly cloudy
Today
2 PM
60°F
Intermittent clouds
Today
3 PM
62°F
Intermittent clouds
Today
4 PM
60°F
Intermittent clouds
Today
5 PM
58°F
Intermittent clouds
Today
6 PM
56°F
Intermittent clouds
Today
7 PM
54°F
Intermittent clouds
Today
8 PM
51°F
Intermittent clouds
Today
9 PM
48°F
Partly cloudy
Today
10 PM
45°F
Partly cloudy
Today
11 PM
43°F
Partly cloudy
Tomorrow
12 AM
42°F
Mostly clear

7 Day Forecast

Partly sunny w/ showers

Tuesday

62 °F

A couple of brief showers late this morning; windy with times of clouds and sun


Partly cloudy

Tuesday Night

34 °F

Partly cloudy and colder; there can be frost in the normally colder spots


Intermittent clouds

Wednesday

59 °F

Cool with times of clouds and sun


Mostly cloudy w/ showers

Wednesday Night

37 °F

Increasing clouds with a shower in spots late


Partly sunny w/ showers

Thursday

56 °F

Times of clouds and sun with a couple of showers; cool


Partly cloudy

Thursday Night

40 °F

Partly cloudy


Mostly cloudy

Friday

63 °F

Mostly cloudy and warmer


Clear

Friday Night

40 °F

Clear


Mostly sunny

Saturday

74 °F

Mostly sunny, pleasant and warmer


Mostly clear

Saturday Night

43 °F

Mainly clear


Sunrise and Sunset

Sunrise
5:52 AM
Sunset
8:02 PM

Based on AccuWeather data