Plaincast — the National Weather Service forecast, decoded into plain English

Messages

Very warm today with only isolated high based showers/virga late this afternoon and evening.

Slight increase in shower/storm coverage this weekend. Cooler Saturday, then warmer Sunday.

Unsettled pattern next week, with multiple cold fronts expected to bring a few more noticeable cooldowns.

Discussion

Zonal flow aloft will strengthen today, bringing a stronger downslope component and thus a bit more warming. We expect highs to reach 90F or more over most of the plains and I-25 Corridor. To offset that, there is some mid/upper level moisture evident on satellite and radar now reaching northern Utah. This will continue to push east today, resulting in enough for scattered virga, isolated high based showers, and even a lone weak storm. The main threat of any light precipitation would be over the northern mountains this afternoon, spreading to the northern plains this evening, but even there coverage would be sparse. Any high based showers/virga would support gusty outflow winds to 40 mph given increasing environmental flow and DCAPE increasing to 800-1200 J/kg.

For tonight, a cold front pushes south across the High Plains and through northeast Colorado late tonight into early Saturday morning. This will lead to cooler temperatures (near normal) for Saturday. While moisture levels increase slightly, considerable uncertainty exists for afternoon and evening shower/storm coverage due to thermal profiles. For the most part, we don't think we'll reach convective temperatures over the plains but still can't rule out a few late day showers and storms spilling eastward from the higher terrain due to mid level instability and moisture.

Sunday will likely feature a return to much above normal temperatures. model output statistics guidance suggest highs pushing into the mid 90s for metro Denver and the I-25 Urban Corridor. That may be a bit aggressive as there is some guidance (not surprisingly) slowing the redevelopment of lee troughing and erosion of low level moisture. The record for Denver on the 13th is 96F set in 2018, 1990, and 1895, but at this point it appears we'll most likely stay a couple degrees shy of that. With regard to convection, isolated showers and storms will be high based and relatively weak. However, if a storm or two can break the cap over the northeast plains they could certainly tap into higher MLCAPE and become severe.

As discussed yesterday, the cooldown for Monday appears to be tempered as the next cold front/upper trough has been delayed slightly. However, there is still high confidence in more significant cooling for Tuesday behind a moderately strong early (meteorological) autumn cold front. While daily uncertainties exist about the degree of cooling, there is modest agreement we'll settle into highs in the 70s (and 30-40% chance of 60s) for the plains and I-25 Corridor. A brief warmup is possible for Wednesday before yet another front arrives Thursday. Ensembles are in decent agreement holding a plume of mid/upper level moisture and higher than normal climatological precipitable water over us. Thus, we should have daily chances of showers and storms most of the days this upcoming week.