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625 FXUS65 KBOU 191139 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 539 AM MDT Sat Sep 19 2026 .KEY MESSAGES... - Isolated to scattered showers/t-storms return this afternoon to the mountains and urban corridor. These will become numerous over the plains, where some will be strong to severe through this evening, producing locally heavy rain and hail. - Trending drier Sunday into Monday, although scattered afternoon storms may continue Sunday, particularly along and south of I-70. - Cooler temperatures expected Sunday into Monday, before warmer temperatures return. Next week will bring a few additional opportunities for precipitation, mostly for our mountains, with lesser heavy rain potential. && .DISCUSSION /Through Friday/... Issued at 1243 AM MDT Sat Sep 19 2026 Ongoing showers over the eastern plains early this morning will steadily dissipate as we near sunrise, while moisture will continue feeding into the high country this morning where showers will linger. Despite modestly cooler conditions today (highs will remain below 80F over the plains), we`ll hold onto moderately unstably conditions and ample moisture. The latest forecast soundings indicate bulk shear of 35-50 kts across the majority of the plains this afternoon, which would support another round of numerous thunderstorms, some of which will be strong to severe. Thus far, there isn`t much indication of low stratus this morning, so don`t foresee convective temperatures not being reached. Instability will be exceedingly marginal though for areas roughly along and west of I-25, so the potential for stronger storms and heavier rainfall will be considerably tapered outside of our rural plains. Hail and heavy downpours will be the primary threats from today`s stronger convection. The bulk of the stronger thunderstorms will move out of the plains by late evening. However, with the upper-level trough traversing overhead, we`ll retain potential for overnight showers and weak thunderstorms. Increased PoPs notably for our northern areas in particular. Will additionally need to monitor potential for patchy fog Sunday morning across portions of the lower elevations, especially the South Platte River Valley. Sunday stands to be our coolest day of the week with the passage of the shortwave. If we`re able to clear out morning cloud cover more efficiently, the environment would support renewed scattered showers/t-storms in the afternoon and evening. It`s a big if, with the convective potential being notably lower for the northern half of our forecast area, and best for the Palmer Divide and areas downstream into Lincoln County where it would be easiest to erode any low-level capping. Depending on how quickly the low ejects to our east, isolated to scattered late-day showers and thunderstorms could linger into Monday, but any coverage should be notably reduced relative to previous days. Starting Tuesday, warmer conditions will return as a southwest flow pattern takes hold aloft. An embedded shortwave late Tuesday into Wednesday favors an increase in precipitation potential namely for our mountains, with lesser coverage/more uncertainty for the lower elevations. Regardless, moisture profiles won`t be as robust as those currently being observed, so accumulations should be on the lighter side if we see any. && .AVIATION /12Z TAFS through 12Z Sunday/... Issued at 526 AM MDT Sat Sep 19 2026 As expected, winds have transitioned to light drainage flow at the terminals, which has helped limit stratus development this morning, along with some cloud cover aloft to mitigate radiational fog. Still, some patchy stratus is evident over the Palmer Divide, S/SE of KAPA, however it appears unlikely that this would expand drastically northward to impact KDEN (though stranger things have happened...). In any case, much like the prior update, confidence remains too low for any inclusion in the TAFs. If stratus and fog does migrate over one or more terminals, it should be very brief, lifting shortly after sunrise. Looking ahead at the daytime period, expect a transition to prevailing NE flow by 18-19Z after light and VRB morning winds. Confidence is higher than previous days in afternoon convective potential for KDEN and KAPA, however the potential for stronger TSRA and associated vis restrictions appeared somewhat bullish in preceding forecasts for areas west of I-25 in particular (i.e. KBJC). The current forecast thus continues to reflect this spatial disparity in confidence and/or coverage with a PROB30 for KBJC. Even KAPA and KDEN will likely be on the western fringe of the stronger TSRA potential. Timeframe of impacts remains the same, although have opted to trim the tail end of the TEMPO groups (now ending 00Z) to closer align with the rapid egress of convection to the east which is depicted in the latest guidance. Subsequent impacts should be primarily confined to the NE and SE KDEN gates, though isolated -SHRA may linger for an additional 1-2 hrs in the vicinity. As far as the fog potential for tonight is concerned, still believe there`s a limited threat for any evening impacts given more prevalent drainage flow, so have maintained VFR conditions through ~09Z for the terminals. Thereafter, potential for an incursion of NE flow appears more distinct, and thus too the fog/low stratus potential. Have therefore introduced some lower CIGS for KDEN late in the TAF period, though confidence remains rather moderate. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...BRQ AVIATION...BRQ