


Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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249 FXUS65 KBOU 122110 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 310 PM MDT Sat Jul 12 2025 .KEY MESSAGES... - A few strong thunderstorms with locally heavy rain can be expected this afternoon roughly along and south of I-70. - Afternoon showers/thunderstorms to continue most days, albeit with slightly lesser coverage Sunday and Monday. - High temperatures to linger in the 90s across the plains from Sunday through mid-week. && .DISCUSSION /Through Saturday/... Issued at 224 PM MDT Sat Jul 12 2025 This morning`s (Saturday) low clouds have finally scattered out across the forecast area and a Denver Cyclone has developed. Current satellite imagery shows some cumulus starting to build along the higher terrain, with a few weak reflectivity returns starting to show in northern Park/western Jefferson Counties where surface heating has been greatest so far today. With enough instability in place as shown by the 500 to 1000 J/kg of MLCAPE shown in the SPC Meso Analysis, these cumulus are expected to transition into scattered showers and storms by early this afternoon. With a prominent cap in place across the lower elevations as portrayed in the latest ACARS sounding, these showers and storms won`t have much luck of persisting onto the lower elevations where CAPE is far more robust. However, with WNW to NNW steering flow in place, storms that form will have potential to move along the higher terrain where the cap is already broken, and we could see an isolated threat for severe hail and some gusty outflows through the early evening. With the cyclone in place, there is a chance that the convergence zone could aid in breaking the cap along the Palmer Divide and slightly north onto the adjacent plains where the more robust CAPE will be in play, but have kept the greatest PoPs south and west of the urban corridor where guidance continues to portray things staying along and south of I-70 in the mountains and foothills. Light NNW flow aloft will persist into Sunday as the ridge over the southwest remains in place. Instability will increase over the mountains as forecast soundings show SBCAPE reaching 700-800 J/kg and mid-level lapse rates steepening to 9+C/km by the afternoon. This will promote scattered afternoon and evening convection, with showers and storms expected to remain anchored to the higher terrain. Temperatures will return to the 90s across the lower elevations on Sunday and persist there through the first half of the week. Models are fairly consistent for the first half of the week, keeping pulses of afternoon mountain convection each day, becoming more widespread by Tuesday. Some discrepancies with timing of a shortwave trough entering the Pacific Northwest on Tuesday are evident between the ensembles, with the GFS supporting a cooldown on Tuesday/Wednesday, whereas the ECM ens keeps an extra day of 90F+ for the plains, seeing a cooldown for Wednesday/Thursday instead. The NBM seemed like a reasonable solution based on the differences, so little changes were made past Monday for this package. While the timing may be off, the signal is in place that a brief cooldown will occur by mid-week. Past that, ensembles show that the 90s will return and look to stick around across the plains through at least the last week of July. && .AVIATION /18Z TAFS through 18Z Sunday/... Issued at 1129 AM MDT Sat Jul 12 2025 Winds are currently light and vrb across the Denver TAF sites as a Denver Cyclone becomes more developed late this morning. Once the cyclone settles in, winds are expected to have a NNE component before making their way towards the east by ~22Z to 23Z this afternoon for KDEN/KBJC. There are uncertainties with how today will unfold with regards to KAPA as the cyclone may produce a convergence zone over or near the airfield as portrayed in a few hi-res CAMs. This would also allow for a better environment to break the cap that is currently in place as shown in the latest ACARS sounding, and why the PROB30 is in place for TS over KAPA later this afternoon. Or, the convergence zone stays south of KAPA, and winds keep a more NNE component through the afternoon. While there is a small chance (15-20%) that convection develops a little more northward that could impact KDEN, the more likely scenario is that the cyclone helps keep convection to the south, keeping the cap in place. Winds are expected to follow the normal diurnal pattern for the overnight hours tonight through the morning on Sunday. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Bonner AVIATION...Bonner