Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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298 FXUS65 KBOU 212350 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 550 PM MDT Fri Jun 21 2024 .KEY MESSAGES... - Scattered to likely showers and thunderstorms through this evening with heavy rainfall the main threat. Burn scars would be most susceptible to flash flooding. - Hotter and drier this weekend into early next week. && .SHORT TERM /Through Saturday/... Issued at 253 AM MDT Fri Jun 21 2024 Current radar shows scattered thunderstorms developing in the Foothills moving eastward into the adjacent plains. Still some weak capping evident over the central part of the plains with lacking Cu development on satellite and MLCIN < -25 to -50 J/kg on SPC mesoanalysis. Moisture is plentiful this afternoon with surface observations showing dewpoints in the upper 50s/low 60s for the east and northeast plains. Scattered thunderstorms move eastward onto the plains. If it warms or moistens a little more, the cap could break and support more organized convection and a few severe storms. Hail up to 1.5", local heavy rainfall, and gusts to 60 mph possible in the severe storms. The higher chance for seeing a few stronger to severe storms will be closer to northern border where there is slightly higher instability, less of a cap, and more moist. A small percentage of high-res CAMs show potential for another round of showers/storms late evening. However, with lacking agreement among models, it is pretty low confidence. Colorado remains under an upper level ridge on Saturday. Subtle height rises and weak synoptic subsidence build into the region and the plume of above normal moisture shifts south. This will support a drier day than the previous few days. Instability will likely be marginal, if any (< 400 J/kg CAPE). This could support low coverage showers and storms in the afternoon starting on the higher terrain. Based on model soundings, it will be tough for any shower/storm to maintain itself for long once it moves eastward onto the adjacent plains. Profiles show mid-level moisture, but fairly dry at the surface more likely resulting in a brief gust or light shower. High temperatures will be a degree or two warmer than Friday with highs in the upper 80s to around 90 for the urban corridor/plains, 70s for the Foothills, and 50s/60s for the mountains. && .LONG TERM /Saturday night through Thursday/... Issued at 253 PM MDT Fri Jun 21 2024 This entire period will be dominated by an upper level ridge of high pressure stretching across the Central/Southern Rockies and Desert Southwest. There will likely be enough moisture trapped under the ridge for isolated to scattered late day showers and storms, but mostly over the higher terrain. Sunday will feature hotter temperatures as we have light westerly flow aloft and further warm advection. This will support high temperatures pushing into the mid 90s across the I-25 Corridor and plains. Monday will likely be one of the hottest days of the next week, with continued weak downslope flow, warm advection, and a dry airmass. 700 mb temperatures near 19-20C suggest high temperatures will soar into the 95 to 100 degree range across the plains and I-25 Corridor. Initial Heat Risk guidance would suggest a Heat Advisory may be needed for Monday. With just enough moisture and high lapse rates, would expect another round of late day convection with scattered coverage in the mountains, but isolated in the lower elevations with gusty outflow winds the main threat. There is a little uncertainty whether the hot temperatures will stick around into Tuesday and Wednesday or if a little relief occurs with a backdoor cool front. A shortwave moving across the northern U.S. typically brings enough of a push to help. But some models have trended weaker with that wave, but overall we think it should still be enough to bring a couple degrees of cooling. That said, above normal temperatures and highs in the lower 90s are still likely for the plains. Convection could also see a bit of an uptick with the trapped moisture under the ridge combined with slightly better moisture behind the backdoor cool front. Ensembles point to a weak wave or moisture surge from the south on Thursday which could keep more convection in the forecast for another day. Then, hotter and drier conditions may reestablish themselves by Friday under the domination of high pressure. && .AVIATION /00Z TAFS through 00Z Saturday/... Issued at 544 PM MDT Fri Jun 21 2024 VFR through the TAF period. A couple things to note in the near term. A weak outflow boundary is situated near FNL-GXY and is slowly sinking south. This could bring a brief/weak wind shift to DEN/BJC this evening. High-resolution models support this but are also struggling with convection (and the lack of convection) to the north. Similarly, another round of weaker showers is possible later this evening but confidence in this is also pretty low at the time. Will need to watch trends this evening to see if either/both of these features will be more impactful than the current TAF suggests. Quiet weather is expected overnight with generally light drainage flow. Winds will remain weak tomorrow and shift towards the north/northeast in the afternoon. High-based, gusty showers will be possible in the later afternoon hours. Overall coverage looks fairly low at this time. && .HYDROLOGY... Issued at 253 AM MDT Fri Jun 21 2024 There will be a threat of flash flooding with the convection this afternoon and evening. Precipitable water values are quite high and the storms should produce heavy rainfall. However, the thunderstorms will be moving at 20-30 mph to the northeast which will lessen the threat of flooding. The alpine burn scars should be most susceptible to the flash flooding threat as well as areas of training thunderstorms. No threat for flash flooding over the burn areas Saturday. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Mensch LONG TERM...Barjenbruch AVIATION...Hiris HYDROLOGY...Barjenbruch