Colorado Weather Forecast | July 15 —18, 2021

Thunderstorms remain a concern into the weekend as moisture looks to stick around.

A surge of monsoonal moisture and some dynamical forcing from a shortwave has made today wet and stormy across most of Colorado, starting with the San Juans early this morning. Radar over the past 12 hours show widespread precipitation across the state, which is now starting to step off the high terrain and onto the plains:

Note that radar cannot see most of the central and southern San Juans — you can assume there’s been a hefty push of precipitation there as well.

This widespread stratiform precipitation successfully inhibited the development of stronger storms and lightning in the morning and early afternoon, but a line of thunderstorms did eventually pop up in northwestern Colorado where it has been sunnier and warmer. These thunderstorms have pushed southeast over the course of the afternoon.

In our last forecast we described Thursday to Friday as likely being somewhat stormy in the mountains, with a drying trend into the weekend — with a lot of uncertainty. The uncertainty has reared its head, and models have been trending to slightly more zonal flow over the United States, which looks to be just enough of a difference to keep drier air from pushing into Colorado on Saturday. Instead, moisture and thus thunderstorms look to remain in the forecast through Sunday.

Consider the forecast the GFS issued this afternoon for Sunday (brown colors = drier)…

…compared to what we were looking at on Monday morning.

The Sunday forecast difference is a little subtle, but it reflects the amount of moisture that is sticking around from now and through Saturday. It finally starts to get pushed out by Sunday, but there will be enough around to cause lightning concerns especially near the Divide.

Conversely, we’re seeing a little more dry air working its way into the state on the backside of our current disturbance, keeping Thursday’s thunderstorm potential a little lower than we last forecasted.

With all that in mind, here’s how some major 14ers are looking in terms of thunderstorm potential:

Thursday features the lowest thunderstorm potential, with highest chances near the Divide, Sangres, and San Juans. Friday and Saturday look the most active, with isolated-scattered thunderstorm chances for most of the mountains and scattered thunderstorms along the Divide, in the San Juans, and in the Sangres. Sunday’s thunderstorm potential drops again, with the highest chances along the Divide and in the Sangres.

We would expect smoke to remain a concern through the weekend as anticyclonic flow pulls it in from the wildfires in Idaho, Montana, and Oregon.

Header image: @kmcdonphoto

Forecast by
Thomas Horner (Twitter: @thomaschorner)

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