ForecastLast Gasps of Summer; Fairly Wet Friday-SaturdayStorm potential this week increases ahead of a system to our west. This will bring a weak cold front later Friday, and more widespread rain and snow in the high country from Friday to Saturday.
- Increasing afternoon storm potential this week.
- Low pressure system impacts Colorado on Friday, bringing more widespread rain/snow to western and northern Colorado.
- In the high country, there could be precipitation on Friday and Saturday mornings.
- The Sangres will largely miss out on this moisture.
- Weak cold front later Friday. 5-10 degrees colder by Saturday.
- A few inches of snow are possible for the high peaks, especially by Sunday morning.
- System clears out by next week, but temperatures don't look to rebound much.
Lightning Risk Grids
This week looks to be the last gasp of summer. After Thursday, there are no decent chances in the medium term forecast for 80 degree temperatures in Denver, and by next week, we're not seeing significant thunderstorm coverage in the mountains.
That's not to say we can't see such conditions later in October (temperature records indicate that Denver has seen highs in the 80s every day in October except October 31st), but it doesn't look likely to happen over the next couple weeks.
This will be the last week in which we post our afternoon thunderstorm outlook products. Colorado saw zero lightning fatalities this year, which is notable since this year featured more storms than average across much of the high country.
September has been warmer than average across Colorado (and the entirety of the western United States).
The cooldown on the horizon will take us a little closer to average, but overall we should still be on the warmer side.
Currently, high pressure to the south is keeping warmer air in the region and also drawing subtropical moisture in to the Four Corners region. This moisture will gradually push east over the course of this week, increasing the risk for afternoon thundershowers.
High pressure will break down over the next few days as a closed low over the Pacific Northwest lifts eastward. The warmest temperatures of the week will come on Thursday and early Friday, ahead of a cold front associated with this system. This front is pretty minor and will only knock temperatures back by 5-10 degrees from later on Friday and into Saturday.
Friday looks to feature the best storm coverage across the state as dynamic lift head of the closed low taps into robust moisture. The largest impacts are expected in western and northern Colorado.
Models lean towards this low pressure system stalling out, which would continue to advect moisture into Colorado with southwesterly flow.
Saturday would again be fairly wet in western and northern Colorado.
This precipitation is driven by synoptic-scale processes and thus not limited to afternoon convection. We're expecting Friday and Saturday mornings to feature decent rain coverage across parts of Colorado's high country. The afternoons will feature more convective activity, with stratiform clouds giving way to thunderstorms.
Due to the position of the jet, it's likely that the Sangres will miss out on much of this precipitation.
Temperatures will dip to near/below freezing above 12,000ft. during the nighttime hours. Expect a coating of snow on the high peaks as we progress into the weekend.
The above table may be conservative if comparing to the Euro model, which has 1-5" of snow across most of Colorado's higher peaks by Sunday.
We'll keep our eye on that snow potential. For now, the big takeaways are the increasing afternoon thunderstorm threat through Friday, and the chance for widespread, cool rain/snow in western and northern Colorado on Friday morning and Saturday morning.
Models are more uncertain for Sunday, but there's a good chance for some afternoon showers across the high country as well. Overall, things will be on the wetter side for much of the mountains (except the Sangres) until next week.
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