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Thursday Update: Longmont weather forecast: Rapid warm up followed by a Soggy Sunday/Monday

In Brief:

We warm to the 80's on Saturday after our first good Spring storm..  1 to 2 inches of rain Sunday/Monday.

Thursday Update:

Amazing warmth is building. Figure 3 update shows lower to middle 80's F for Friday and Saturday. Watch the grass grow! A front hits around 9pm on Saturday with rain chances picking up around 9am Sunday. Models are giving us around 2 inches of rain from Sunday through Monday (with some showers through Wednesday as well).  Be prepared for more umbrella use as the week begins.  I'll post a full update on Saturday!

 

Figure3u_04292021Figure 3 update: the 10 day graphical forecast for Longmont, CO from weatherunderground.com

 

End Thursday update.

Wednesday Update:

 We got a storm! There were 7 tornadoes in Colorado and 14 hail reports (one not too far to our southeast - Figure 1 update). Longmont also got a good soaking with 2/3rds to almost 1 inch of rainfall.  Boulder saw totals right around 1 inch with 1.5 inches up in the hills above town (Figure 2 update).

We'll keep an eye on it, but after a Saturday high in the mid (to upper?) 80's, we may see another 1.5 inches of rain Sunday through Monday.

Figure1u_04282021Figure 1 update: the severe weather reports from Tuesday from the SPC

 

Figure2u_04282021Figure 2 update: the rainfall reports up to 7am Wednesday from CoCoRaHS.

 

End Wednesday update.

 

Forecast Discussion:

A cold front and follow-up surge of reinforcing air Monday night and Tuesday morning will produce a brief period of thunderstorms around noon Tuesday followed by a prolonged (18 hour) period of up slop rain (Figure 1). The highest chances of rainfall — over an inch up to 1.5 inches — stretch from noon Tuesday to 10 a.m., Wednesday (Figure 2). This is being created by a big trough in the upper atmosphere seen in Figure 3.

 

Figure1_04262021Figure 1: the forecast surface analysis for Tuesday PM from NCEP.

 

Figure2_04262021Figure 2: the 10 day graphical forecast from weatherunderground.com for Longmont, CO.

 

 

Figure3_04262021Figure 3: the 500mb upper air forecast map for Wednesday noon from the GFS and tropicaltidbits.com

 

Coming back, after a long absence, is the Storm Prediction Center, from Norman, OK, severe weather maps —- hello spring! Figure 4 shows the overall chance of severe weather. It puts Longmont and I-25 on the western edge of a Marginal Risk — only a 1 on a scale of 1-5, minimal.  Figure 5 isolates the chance of large damaging hail — we are in the 5% chance of seeing damaging hail within 25 miles. We also have a 5% chance, within 25 miles, of seeing damaging straight-line winds (Figure 6). Figure 7 shows a tiny chance of tornadoes out east of us.

 

Figure4_04262021Figure 4: the risk of severe weather from the Storm Prediction Center, Norman OK for Day 2, Tuesday.

 

Figure5_04262021Figure 5: the risk of severe hail from the Storm Prediction Center, Norman OK for Day 2, Tuesday.

 

Figure6_04262021Figure 6: the risk of severe winds from the Storm Prediction Center, Norman OK for Day 2, Tuesday.

 

Figure7_04262021Figure 7: the risk of tornadoes from the Storm Prediction Center, Norman OK for Day 2, Tuesday.

 

The Longer-Range Forecast:

Things are warming up, so snow — maybe up to 1.5 feet in the mid to higher mountains — will be restricted to elevations above 7,000 feet, mostly (Figure 8).  The weatherunderground model's (Figure 2) latest update gives us 1.3 inches of water, the GFS gives us 1 to 1.25 inches of rainfall (Figure 9). Spring showers are coming.

We break the 80s again with dry weather for the weekend under a big ridge (Figure 2 and Figure 10).  Enjoy that dry wonderful weekend — with grass and flowers growing like crazy.

 

Figure8_04262021Figure 8: the 5 day (10:1 ratio) total snowfall forecast from the GFS and weather5280.com

 

Figure9_04262021Figure 9: the 5 day total rainfall forecast from the GFS and weather5280.com

 

Figure10_04262021Figure 10: the 500mb upper air forecast map for Saturday noon from the GFS and tropicaltidbits.com
Figure 10: the 500mb upper air forecast map for Saturday noon from the GFS and tropicaltidbits.com
Figure 10: the 500mb upper air forecast map for Saturday noon from the GFS and tropicaltidbits.com
Figure 10: the 500mb upper air forecast map for Saturday noon from the GFS and tropicaltidbits.com

 


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

Clear

Clear

77°F

UV Index
0 Low
Pressure
29.65 Steady
Visibility
9 miles
Dewpoint
33 °F
Humidity
20%
Wind
SSW 3.9 mph
Gust
8.6 mph
Wind Chill
77 °F

Hourly Forecast

Today
2 AM
71°F
Clear
Today
3 AM
69°F
Clear
Today
4 AM
67°F
Clear
Today
5 AM
65°F
Clear
Today
6 AM
65°F
Sunny
Today
7 AM
68°F
Sunny
Today
8 AM
74°F
Sunny
Today
9 AM
80°F
Sunny
Today
10 AM
83°F
Sunny
Today
11 AM
86°F
Sunny
Today
12 PM
88°F
Sunny
Today
1 PM
90°F
Mostly sunny

7 Day Forecast

Sunny

Saturday

100 °F

Sunny and hot with the temperature approaching the record of 103 set in 2016; gusty winds, low humidity and dry brush result in a high fire threat


Clear

Saturday Night

65 °F

Clear and mild


Mostly sunny

Sunday

93 °F

Sunny to partly cloudy and not as hot; breezy in the afternoon; gusty winds, low humidity and dry brush result in a high fire threat


Mostly clear

Sunday Night

55 °F

Breezy in the evening; otherwise, mainly clear


Mostly cloudy

Monday

77 °F

Rather cloudy and cooler


Mostly cloudy w/ t-storms

Monday Night

55 °F

A couple of evening showers and a thunderstorm; otherwise, partly to mostly cloudy


Intermittent clouds

Tuesday

80 °F

Intervals of clouds and sunshine with a thunderstorm in parts of the area in the afternoon


Mostly cloudy

Tuesday Night

60 °F

Overcast in the evening; partly cloudy late


Partly sunny w/ t-storms

Wednesday

75 °F

Intervals of clouds and sunshine with a couple of showers and a thunderstorm


Clear

Wednesday Night

54 °F

Clear


Sunrise and Sunset

Sunrise
5:31 AM
Sunset
8:33 PM

Based on AccuWeather data