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1 am update: Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – August 4-6, 2019

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

In Brief:

Upper atmospheric high pressure and dry air keeps things quiet on Saturday. Moisture in place and a shifting of the high center allows for afternoon storms and seasonable high temperatures for many days to come.

1am update 8/6:

A bunch of work and home stuff crowded out the forecast discussion today (8//6) but the story is pretty simple. The high that either blocks the moisture and convection or pumps it into the state is in a no-so-great location for storms Tuesday and (somewhat) on into Wednesday. After that it does drift to the southeast of Colorado again. Moisture will return Thursday-Saturday (at least) and short waves will be able to interact with this moisture to really kick off some better thunderstorm coverage Thursday +. More later!

End 1am udpate.

Forecast Discussion:

There is quite a big blob of tropical moisture over the southwest U.S., (Figure 1) but the high has wobbled over Colorado Saturday which will keep things quiet except for a few isolated thunderstorms up in the mountains and on the Palmer Divide (Figure 2). For Sunday, the high center drifts to Arizona which will allow some afternoon storms to form and drift east off the mountains.

The Longer Range Forecast:

Little changes in the longer range - you can watch the animation of the 500mb pattern and the closed set of circles that is the high (like a mountain with lines of equal elevation) drift this way and that around the southwestern U.S. over the next 5 days (Figure 3). The upper atmospheric relative humidity gives an indication of the moisture flow around this high - the animation in Figure 4 shows blobs of moisture getting pulled into the circulation. Because of this, we'll see varying amounts of afternoon convection over the next 10 days with peak activity occurring when the high is more distant or to the southeast of us, and when the higher moisture values are in place at the time of maximum daytime heating (Figure 5).

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 Weather Channel from Satruday.
Figure 2: The 500mb forecast upper air analysis for Friday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 3: Animation of the GFS 500mb pattern and anomaly for the next 5 days from
Figure 4: Animation of the GFS upper air moisture representation for the next 5 days from
Figure 5: the graphical forecast for the next 10 days for Longmont, CO from





UV Index
0 Low
30.33 Steady
10 miles
47 °F
W 3.5 mph
3.9 mph
Wind Chill
62 °F


Mostly sunny


94 °F

Mostly sunny and very warm; air quality will be unhealthy for sensitive groups

Mostly clear

Saturday Night

60 °F

Mainly clear; air quality will be unhealthy for sensitive groups

Partly sunny w/ t-storms


98 °F

Very warm with partial sunshine; a shower or thunderstorm in spots in the afternoon

Partly cloudy w/ t-storms

Sunday Night

65 °F

A shower or thunderstorm in spots in the evening; otherwise, mainly clear and mild

Partly sunny


96 °F

Remaining very warm with some sun

Mostly clear

Monday Night

58 °F

Mainly clear

Partly sunny


88 °F

Not as hot with sun and some clouds

Partly cloudy w/ t-storms

Tuesday Night

58 °F

A couple of thunderstorms around in the evening; otherwise, patchy clouds

Partly sunny


88 °F

Beautiful with sunshine and some clouds

Mostly clear

Wednesday Night

57 °F

Clear to partly cloudy

Sunrise and Sunset

11:41 AM
2:30 AM

Based on AccuWeather data