038 FXUS65 KBOU 170011 AFDBOUArea Forecast Discussion National Weather Service Denver/Boulder CO 611 PM MDT Tue Sep 16 2025
.KEY MESSAGES...
- Scattered showers and thunderstorms through this evening. A severe storm is possible in the northeast corner.
- Shower/t-storm potential will linger into Wednesday, with cooler conditions through Thursday.
- Drier weather Thursday onward, with warmer temperatures beginning Friday.
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.DISCUSSION /Through Tuesday/... Issued at 242 PM MDT Tue Sep 16 2025
Complicated situation this afternoon, but the main features are the warm moist air ahead of a boundary from Limon to Julesburg. The best moisture/instability/low level convergence is centered right along the state line east of Julesburg and Holyoke and north from there, and we`re seeing storms developing there in the last hour. There`s a zone in between this energy rich air and the cooler air close to the Front Range, west to around Fort Morgan and Limon, that could still support strong storm development with heating this afternoon. The severe threat looks lower in these areas though, and rain cooled air is spreading southward from about I-76 across this zone.
Further west, there may be just enough CAPE to sustain thunderstorms, or perhaps the storms will weaken coming off the mountains, but there should be decent coverage of showers in the late afternoon and evening based on mid level instability and some weak QG forcing. This will diminish by midnight, but the tail end of the lift may still be dragging across the area through the night. There`s a chance of some low cloud/fog development if there is enough clearing or enough rain, but it`s looking like the drying might be substantial enough to keep this out of Denver.
Wednesday we`ll start with cool and relatively drier air. It may take most of the day to generate shower activity, but it will be cool enough aloft that there should eventually be another round of showers and storms. Then there`s some lift from another shortwave dropping south across the plains to keep the threat of showers going overnight. Thursday is a transition day as drier air is moving in, but there will still probably be some diurnal showers.
For Friday and the weekend, we`ll have drier northwest flow as a ridge builds to our west. Temperatures will warm and convection will be at a minimum, though some isolated mountain showers are still possible. Early next week, there will likely be another shortwave dropping somewhere across the plains. It may be enough to bring some cooling for a day or two and a chance of showers, or it may have little effect. Meanwhile, the ridge will likely be building more strongly just to our west so any cooling will probably be temporary.
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.AVIATION /00Z TAFS through 00Z Thursday/... Issued at 555 PM MDT Tue Sep 16 2025
The main line of storms have pushed east of the TAF sites over the past few hours, but can`t rule out another weak storm or shower to pass across the TAF sites through late tonight. Have kept the PROB30 in place to account for this. Additionally, forecast soundings show potential for some low stratus to move into the TAF sites with some light NW flow expected somewhere between the 10-13Z time frame Wednesday morning. Have introduced a TEMPO for the potential of CIGs dropping to around 030 between 12-16Z and beginning to scatter out by around 16-17Z, though confidence is not high at this time. There is enough confidence to add a PROB30 for showers across the TAF sites late tomorrow afternoon, continuing through the evening.
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.BOU WATCHES/WARNINGS/ADVISORIES... None.
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DISCUSSION...Gimmestad AVIATION...Bonner
NWS BOU Office Area Forecast Discussion