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Thurs Update: The Front Range Forecast: Small showers, mostly dry

In Brief:

Chilly with a few low level showers Friday - a slow warm up after that.

Thursday Update:

A cold front Wednesday night cooled us down for a few days (Figure 2 update). A storm that will hit, mainly, the western slopes, may throw a few rain/snow showers off the mountains over the I-25 folks and out on the plains. The Rockies to the west will appear double sized with the clouds lifting up the west side and evaporating as they descend on the eastern side. Even Estes Park may only see 1/2 to 1 inch of snow.  We slowly warm to over 20F above normal mid-week.  Our next 'possible' chance of snow comes NEXT weekend.

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Figure 2 update: the 10 day graphical forecast from weatherunderground.com

End Thursday update.

Saturday Update:

The snowfall totals for Boulder (Figure 1 update) and Larimer (Figure 2 update) counties show a strong gradient (difference in totals) from locations west of I-25 and those along or east of the interstate. Longmont picked up 5-6 inches pretty uniformly. Boulder received 5-7 inches. Areas west of Ft. Collins and Loveland picked up 8-10 inches while east of I-25, those communities saw 3.5-4.5 inches.  Light snow continued after 7am, so there might end up an additional 1/2 inch or so to some locations.

Not bad for our second winter storm of the season.

figure2u_11252023
Figure 1 update: snow totals as of 7 am Saturday from CoCoRaHS.
figure1u_11252023
Figure 2 update: snow totals as of 7 am Saturday from CoCoRaHS.

End Saturday update.

Winter Storm Warning
Issued: 1:59 PM Nov. 22, 2023 – National Weather Service

...WINTER STORM WARNING IN EFFECT FROM 4 PM THURSDAY TO 5 AM MST
SATURDAY...
* WHAT...Heavy snow expected. Total snow accumulations between 4 and 10 inches.
* WHERE...Fort Collins, Boulder, and the western suburbs of Denver.
* WHEN...From 4 PM Thursday to 5 AM MST Saturday.
* IMPACTS...Travel may become very difficult due to heavy snowfall on roadways, potentially impacting return travel following Thanksgiving.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If you must travel, keep an extra flashlight, food, and water in your vehicle in case of an emergency. The latest road conditions for Colorado can be obtained by  calling 5 1 1 or by going to www.cotrip.org.

Roads will be slick resulting in slow and hazardous travel. Allow extra time to reach your destination.

Forecast Discussion:

Enjoy the unusual warmth today, we are around 20F above normal Wednesday. The cold air begins to invade the state Wednesday PM and then Thursday afternoon.  Temperatures will drop almost 50 degrees by Friday (Figure 1). Typical Colorado Fall weather!

The snow should start around 5-6pm Thanksgiving evening and fall at the highest rate through Friday morning.  Some ongoing snow showers are possible through Saturday morning. This storm is being powered by a large (briefly) cut-off low approaching the state (Figure 2). Moderate to heavy snow will fall on Thursday and Friday evenings (Figure 3 and Figure 4).

With temperatures dropping to the single digits at night, higher snowfall ratios (more like 15:1 or more) are expected. The 10:1 snowfall map is Figure 5 while the 15:1 ratio map is Figure 6.  These ratios mean that 1 inch of rain would be 10 inches of snow (or 15 inches of snow for the colder temperatures).

The weather service is planning on issuing a Winter Storm Watch for snow amounts, cold temperatures, and the higher amount of travel expected around Thanksgiving. I'll post it here when it goes up.

Snowfall Roundup for Longmont:

The GFS 10:1 ratio:  4-6 inches.

The GFS 15:1 ratio: 6-10 inches.

Canadian model:  5-7 inches

NAM 10:1: 3-4 inches

Weatherundrground: 5-6 inches

Weather5280: 4-6 inches

Channel 9 news: 3-5 inches

Channel 7 news: can't find a map yet.

 

figure1_11222023
Figure 1: the 10 day graphical forecast for Longmont from weatherunderground.com
figure1_2_11222023
Figure 2: the 500mb upper air forecast map for Friday morning from the GFS and tropicaltidbits.com
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Figure 3:The forecast surface map for Thursday from the NWS.
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Figure 4:The forecast surface map for Friday from the NWS.
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Figure 5: the 5 day 10:1 ratio snowfall forecast from the GFS and weather5280.com
figure5_11222023
Figure 6: the 5 day 15:1 ratio snowfall forecast from the GFS and weather5280.com

The Longer Range Forecast:

Beyond this storm, we slowly warm to near seasonable temperatures and remain dry to the start of December (Figure 1).


About the Author: John Ensworth

John Ensworth used to work from Longmont as the PI for the NASA through the IGES (The Institute for Global Environmental Strategies). He now teaches technology, algebra, astronomy, meteorology, film school, and Lego robotics to middle/high school.
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Current Weather

Sunny

Sunny

61°F

UV Index
7 High
Pressure
29.96 Rising
Visibility
8 miles
Dewpoint
38 °F
Humidity
43%
Wind
ESE 6 mph
Gust
10.7 mph
Wind Chill
61 °F

Hourly Forecast

Today
12 PM
65°F
Intermittent clouds
Today
1 PM
67°F
Intermittent clouds
Today
2 PM
68°F
Intermittent clouds
Today
3 PM
70°F
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Today
4 PM
67°F
Mostly cloudy w/ t-storms
Today
5 PM
62°F
Intermittent clouds
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6 PM
57°F
Intermittent clouds
Today
7 PM
53°F
Intermittent clouds
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8 PM
50°F
Cloudy
Today
9 PM
47°F
Showers
Today
10 PM
44°F
Cloudy
Today
11 PM
41°F
Cloudy

7 Day Forecast

Partly sunny w/ t-storms

Sunday

70 °F

Very windy; clouds and sun with a thundershower in spots, cooler; winds will be locally damaging


Mostly cloudy w/ showers

Sunday Night

35 °F

Mostly cloudy and colder with a couple of showers; there can be some wet snowflakes mixed in


Partly sunny

Monday

61 °F

Clouds giving way to sun


Clear

Monday Night

32 °F

Clear


Mostly sunny

Tuesday

74 °F

Mostly sunny, pleasant and warmer


Partly cloudy

Tuesday Night

47 °F

Partly cloudy and mild


Partly sunny

Wednesday

78 °F

Partly sunny and warm


Partly cloudy

Wednesday Night

44 °F

Partly cloudy


Mostly sunny

Thursday

75 °F

Sunny to partly cloudy, nice and warm


Rain

Thursday Night

38 °F

Mostly cloudy; a couple of showers in the evening followed by rain and drizzle late


Sunrise and Sunset

Sunrise
6:26 AM
Sunset
7:37 PM

Based on AccuWeather data