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Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – September 18, 2019

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

In Brief:

Our first cold front is moving in to knock 5F off the temperatures and give the western slopes some rain/thundershowers. We'll mainly see increased clouds east of the Rockies with a possible sprinkle. A couple of additional cool fronts will lower us to the 70'sF for highs over the weekend with afternoon showers possible. Next week seems dominated by 70'sF weather for highs and better rain chances.

Forecast Discussion:

Our first cool front is on its way and is kicking off showers over the western counties of Colorado (Figure 1). Down slope flow on this side of the mountains will assure that very little water falls from the sky. By Wednesday morning, the front will be draped down the Front Range into the southeastern parts of the state. A bit more moisture will return behind the front (Figure 2).

The Longer Range Forecast:

Later in the week, a deeper trough starts its trek across the nation (Figure 3). This will kick a couple more cool fronts past us, cooling us to the 70'sF for the weekend. The warmth before the weekend will feel a contribution from that same down slope warming/drying we are experiencing today (Figure 4).

Next week, the trough seems to hold on (or get reinforced) and we stay cool with better rain chances returning (Figure 4). The GFS gives the somewhat dry western and southwestern parts of our state the best rainfall over the next 10 days (Figure 5).

Figure 1: SW US current surface map analysis from Tuesday midday from weatherunderground.com
Figure 2: The forecast surface map for Wednesday AM from NCEP.
Figure 3: The 500mb forecast upper air analysis for Friday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 4: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 5: The forecast rainfall totals for the next 10 days from the GFS and weather5280.com

Current Weather

Mostly clear

Mostly clear

56°F

UV Index
0 Low
Pressure
29.89 Steady
Visibility
8 miles
Dewpoint
45 °F
Humidity
66%
Wind
NNW 4.5 mph
Gust
9.6 mph
Wind Chill
56 °F

Hourly Forecast

Today
1 AM
52°F
Partly cloudy
Today
2 AM
50°F
Mostly clear
Today
3 AM
47°F
Mostly clear
Today
4 AM
45°F
Clear
Today
5 AM
43°F
Mostly clear
Today
6 AM
41°F
Mostly clear
Today
7 AM
45°F
Partly sunny
Today
8 AM
50°F
Partly sunny
Today
9 AM
55°F
Partly sunny
Today
10 AM
62°F
Intermittent clouds
Today
11 AM
66°F
Intermittent clouds
Today
12 PM
70°F
Intermittent clouds

7 Day Forecast

Mostly sunny

Wednesday

75 °F

Mostly sunny, pleasant and warmer


Partly cloudy

Wednesday Night

41 °F

Patchy clouds


Mostly cloudy w/ t-storms

Thursday

75 °F

Turning cloudy, warm; breezy, a thunderstorm around in the afternoon


Thunderstorms

Thursday Night

49 °F

A thunderstorm in spots in the evening; otherwise, considerable cloudiness


Thunderstorms

Friday

70 °F

Mostly cloudy with a couple of thundershowers


Thunderstorms

Friday Night

46 °F

Cloudy with a couple of thundershowers


Rain

Saturday

50 °F

Chilly with periods of rain and a thunderstorm


Rain and snow

Saturday Night

39 °F

Cloudy with rain, mixed with a little snow late


Mostly cloudy

Sunday

59 °F

Mostly cloudy with a stray thundershower in the afternoon


Partly cloudy

Sunday Night

36 °F

Partly cloudy


Sunrise and Sunset

Sunrise
6:08 AM
Sunset
7:49 PM

Based on AccuWeather data