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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
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
Figure 5: The forecast rainfall totals for the next 10 days from the GFS and





UV Index
0 Low
30.1 Steady
10 miles
56 °F
N 0 mph
3.4 mph
Wind Chill
72 °F


Partly sunny w/ showers


87 °F

Sunny to partly cloudy and not as hot; a shower in spots late this afternoon

Mostly clear

Monday Night

57 °F

An evening shower in spots; otherwise, mainly clear

Partly sunny


95 °F

Very warm with partial sunshine

Partly cloudy

Tuesday Night

59 °F

Partly cloudy

Partly sunny


95 °F

Partial sunshine


Wednesday Night

60 °F


Partly sunny


96 °F

Partly sunny and very warm

Mostly clear

Thursday Night

65 °F

Mainly clear

Mostly cloudy


97 °F

Very warm with sun followed by clouds

Intermittent clouds

Friday Night

58 °F

Partly cloudy

Sunrise and Sunset

6:08 AM
8:03 PM

Based on AccuWeather data