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Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – October 5, 2019

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

In Brief:

Our next cold front is headed in this evening to blow your trash cans around around (peak winds after midnight). We cool to the upper then lower 60'sF for the weekend. Down slope flow and a passing ridge take us almost to 80F Tuesday followed by the next front that might send us into the 30'sF for a high Thursday and a chance of our first SNOW for the season. Stay tuned.

Forecast Discussion:

Winds are creating dangerous fire conditions in the mountains Friday afternoon as a deep trough (U shaped purple clouds/moisture to our northwest in Figure 1) approaches. The front this trough pushed through passes later tonight (with a low tracking overhead - Figure 2 and 4 - blue line) and winds will be briefly pretty strong around and after midnight. By Saturday evening, the front is clear of the area with very little precipitation falling in Colorado (Figure 3) at all.

The Longer Range Forecast:

We cool further on Sunday as northerly winds keep draining down (Figure 4). We warm to almost 80F on Tuesday with a passing ridge and down slope flow (not shown, but portrayed in Figure 4).

The really interesting news is SNOW! Figure 4 shows snow Thursday AM and PM and Friday AM. Winds will gust to around 15-20mph and we have a high in the 30'sF IF this holds together. This weather is created by a deep, fast moving trough sweeping the nation (Figure 5). In an earlier run of the GFS, this trough passed as a closed low that created more snow. This run is more of an open wave.

Figure 6 is the same forecast as Figure 7 (they are for snow totals between now and midnight going into Oct 14). The figure 6 forecast was made this morning at midnight and had 1-2 inches of snow falling in Longmont Thur/Fri. Figure 7, made 6 hours later, keeps the snow to the areas just west of town and up into the mountains.

This could certainly end up just being rain showers once the day arrives, or even a merely cloudy day. What is really interesting is this is the day I picked a couple of weeks (or so) ago for Denver's first snow. That would be cool (literally).

Figure 1: the water vapor satellite image (browns/reds are dry air, whites and light grey is moist air, purple/blue is ice and high cloud tops). From the the NWS from Friday PM.
Figure 2: The forecast surface map for midnight Friday into Saturday from NCEP.
Figure 3: The forecast surface map for Saturday evening from NCEP.
Figure 4: the graphical forecast for the next 10 days for Longmont, CO from
Figure 5: The 500mb forecast upper air analysis for Thursday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 6: The forecast rainfall totals for the next 10 days from the GFS and for Colorado made at midnight Friday AM.
Figure 7: The forecast rainfall totals for the next 10 days from the GFS and for Colorado made at Friday 6am.





UV Index
0 Low
30.14 Steady
5 miles
56 °F
SSW 4.3 mph
8.7 mph
Wind Chill
73 °F


Partly sunny w/ t-storms


83 °F

Clouds and sunshine with a thunderstorm in spots late this afternoon

Partly cloudy w/ t-storms

Saturday Night

57 °F

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

Partly sunny w/ t-storms


88 °F

Partly sunny with a shower or thunderstorm around in the afternoon

Partly cloudy w/ t-storms

Sunday Night

59 °F

A shower or thunderstorm around in the evening; otherwise, partly cloudy and mild

Partly sunny w/ t-storms


90 °F

Partly sunny and very warm; a thunderstorm in spots in the afternoon

Intermittent clouds

Monday Night

58 °F

Mild with increasing clouds

Intermittent clouds


89 °F

Very warm with intervals of clouds and sun

Intermittent clouds

Tuesday Night

57 °F

Partly cloudy and mild

Intermittent clouds


86 °F

Periods of clouds and sunshine

Intermittent clouds

Wednesday Night

54 °F

Partly cloudy

Sunrise and Sunset

11:34 AM
2:23 AM

Based on AccuWeather data