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Update 7:30am: Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – July 20, 2019

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

In Brief:

Big changes, in the form of a strong cold front, will begin Saturday morning with continued cool air flow coming in from the northeast. This flow will also create up slope rain and storm chances along a front stalled over the area through Monday. After that we remain in the upper 80's for the week with storm chances in the afternoon. No more near 100F for a while.

7:30am Update:

Not much has changed in the forecast overnight. We still have a Marginal Risk (1 on a scale of 1-5) with the primary risk being damaging thunderstorm winds and large hail (Figure 1 update). The NWS did mention that a tornado could briefly form as well.

The weatherunderground model gives us 0.4-0.5 inch of rain tonight (with rain chances increasing quickly around 1pm). The GFS gives us about 0.5 inch of water by Sunday AM. Rain chances picks up again Sunday afternoon and overnight into Monday with significant accumulations expected again. Watch for these details in tomorrow's forecast discussion.

Figure 1 update: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Saturday for Saturday.

End 7:30am update.

Forecast Discussion:

With near 100F temperatures for a few days (it looks like 101F for Thursday and 100F on Friday), a cold front that will enter the state Saturday morning will give us immediate relief. We drop to the upper 80'sF today and the upper 70'sF for Sunday. Wow!

This front will lie along the Front Range foothills and Palmer Divide (south of Denver) - Figure 1. Up slope flow will make rain easier to form and the front will trigger thunderstorms at times (Figure 2). There is a Marginal Risk of severe weather Saturday for the Front Range communities and mountain locations for gusty, damaging winds (not shown).

The Longer Range Forecast:

Weatherunderground.com (Figure 2) gives us between 0.75 inch and 1 inch of precipitation through Monday (with an increase in rain chances in the afternoons). The GFS shows over 1.5 inches of precipitation over the next 5 days for all regions from Colorado Springs up to Cheyenne and northward. This run has a (most likely fictitious) bullseye over 3-4 inches near Longmont.

My camper had a wheel bearing burn out on I25 today so my 2 hour commute from camping took almost 8 hours. We'll look deeper into this dramatic weather change on Saturday (after I get some sleep).

Figure 1: The forecast surface map for Saturday night from NCEP.
Figure 2: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 3: the forecast accumulated precipitation map from the GFS and weather5280.com for Colorado, for the next 5 days.

Current Weather

Mostly cloudy

Mostly cloudy

51°F

UV Index
0 Low
Pressure
29.77 Steady
Visibility
8 miles
Dewpoint
25 °F
Humidity
37%
Wind
SW 3.2 mph
Gust
7 mph
Wind Chill
51 °F

Hourly Forecast

Tomorrow
12 AM
45°F
Showers
Tomorrow
1 AM
43°F
Intermittent clouds
Tomorrow
2 AM
41°F
Intermittent clouds
Tomorrow
3 AM
39°F
Intermittent clouds
Tomorrow
4 AM
37°F
Intermittent clouds
Tomorrow
5 AM
36°F
Intermittent clouds
Tomorrow
6 AM
34°F
Intermittent clouds
Tomorrow
7 AM
35°F
Intermittent clouds
Tomorrow
8 AM
38°F
Intermittent clouds
Tomorrow
9 AM
41°F
Intermittent clouds
Tomorrow
10 AM
44°F
Intermittent clouds
Tomorrow
11 AM
47°F
Intermittent clouds

7 Day Forecast

Partly sunny

Thursday

65 °F

Partly sunny


Intermittent clouds

Thursday Night

34 °F

A shower in spots late this evening; otherwise, partly cloudy


Partly sunny w/ showers

Friday

53 °F

Cooler with times of clouds and sun; a couple of showers late in the afternoon


Showers

Friday Night

33 °F

A couple of showers in the evening; otherwise, cloudy


Mostly cloudy

Saturday

60 °F

Mostly cloudy


Intermittent clouds

Saturday Night

36 °F

Partly cloudy


Intermittent clouds

Sunday

62 °F

Times of sun and clouds


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


Sunrise and Sunset

Sunrise
6:50 AM
Sunset
7:22 PM

Based on AccuWeather data