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Update Monday PM: Longmont Weather Forecast: Cool now, cold with rain (and snow?) later

Figure1u_10112021
Figure 1 update: snippet of the 10 day graphical forecast for Longmont from weatherunderground.com

In Brief:

Our first cold front brings cooler weather and small rain chances, a second on Thursday brings better rains and a dusting of snow?

 

Update Monday PM:

Our long anticipated cold front arrives around 2pm on Tuesday (Figure 1 update).  With it comes a small chance of on and off showers along I-25. Things remain cooler after that (below normal) until a short wave arrives on Thursday to bring more showers Thursday into Friday.  We might see around a 10th of an inch or rain or two and a dusting to an inch of snow early Friday AM. Keep looking for your coats!

Figure1u_10112021
Figure 1 update: snippet of the 10 day graphical forecast for Longmont from weatherunderground.com

End Monday PM update.

Forecast Discussion:

A front has passed on Saturday kicking off mountain rains and high elevation snow. Sunday and Monday will be very mild/beautiful (Figure 1). A strong cold front arrives midday Tuesday bringing fall/winter weather to much of the state.

Figure1_10092021
Figure 1: the 10 day graphical forecast from weatherunderground.com for Longmont, CO.

 

The Longer Range Forecast:

 

This storm looked like it might bring the first snow to I-25 communities and the eastern plains. Figure 2 is the forecast for midnight Tuesday/Wednesday made on October 4th.  Figure 3 is the forecast for the same moment made on October 9th.  Precipitation along I-25 is rain now, and there is a strong 'dry slot' pulling into eastern Colorado killing many rain/snow chances. What actually will happen will depend on the position, speed and strength of the upper level low/trough (Figure 4) and the position of the resulting surface low on the plains.

Over the next 6 days, spots in the mountains should get an inch of liquid (Figure 5) while the eastern plains miss out. Snow may fall in Boulder and on the north and west side of Fort Collins, but not much will hit the plains (Figure 6).

What IS notable is how cold it will get.  We should see below freezing temperatures in the pre-dawn hours Tuesday, Wednesday, and Thursday (Figure 7). Go find your favorite coats!

Figure2_10092021
Figure 2: the 6 hour averaged precipitation around midnight Tue/Wed from the GFS and tropicaltidbits.com made Oct 4

 

Figure3_10092021
Figure 3: the 6 hour averaged precipitation around midnight Tue/Wed from the GFS and tropicaltidbits.com made Oct 9

 

Figure4_10092021
Figure 4: the 500mb upper air forecast map for Tuesday noon from the GFS and tropicaltidbits.com

 

Figure5_10092021
Figure 5: the 6 day total precipitation forecast from the GFS and weather5280.com
Figure6_10092021
Figure 6: the 6 day (10:1 ratio) total snowfall forecast from the GFS and weather5280.com
Figure7_10092021
Figure 7: the temperature anomaly (departure from normal) for Wednesday from weather5280.com

 

 

 

 


About the Author: John Ensworth

John Ensworth works from Longmont as the Principle Investigator for the NASA Science Mission Directorate Earth and space science education product review through the IGES (The Institute for Global Environmental Strategies – www.strategies.org).
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Current Weather

Cloudy

Cloudy

44°F

UV Index
0 Low
Pressure
29.94 Steady
Visibility
10 miles
Dewpoint
28 °F
Humidity
53%
Wind
N 0 mph
Gust
4.3 mph
Wind Chill
44 °F

12 Hour Forecast

Today
5 AM
40°F
Intermittent clouds
Today
6 AM
40°F
Intermittent clouds
Today
7 AM
38°F
Intermittent clouds
Today
8 AM
39°F
Partly sunny
Today
9 AM
44°F
Intermittent clouds
Today
10 AM
50°F
Intermittent clouds
Today
11 AM
57°F
Intermittent clouds
Today
12 PM
62°F
Intermittent clouds
Today
1 PM
67°F
Intermittent clouds
Today
2 PM
71°F
Intermittent clouds
Today
3 PM
73°F
Intermittent clouds
Today
4 PM
74°F
Intermittent clouds

7 Day Forecast

Intermittent clouds

Monday

74 °F

Warm with intervals of clouds and sunshine


Mostly clear

Monday Night

44 °F

Clear to partly cloudy


Mostly cloudy

Tuesday

67 °F

Mostly cloudy


Intermittent clouds

Tuesday Night

34 °F

A shower in spots in the evening; otherwise, partly cloudy


Mostly sunny

Wednesday

59 °F

Mostly sunny; much cooler than recent days


Partly cloudy

Wednesday Night

33 °F

Partly cloudy


Mostly sunny

Thursday

63 °F

Mostly sunny


Clear

Thursday Night

36 °F

Clear


Sunny

Friday

69 °F

Pleasant with plenty of sunshine


Clear

Friday Night

39 °F

Clear


Sunrise and Sunset

Sunrise
7:22 AM
Sunset
6:07 PM

Based on AccuWeather data

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