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Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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430 FXUS65 KBOU 291804 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1204 PM MDT Sat Jun 29 2024 .KEY MESSAGES... - Slightly cooler today, with scattered afternoon thunderstorms returning, strongest and most numerous south of I-70. - Isolated to scattered thunderstorms this weekend, with a few strong to severe storms possible Sunday afternoon and evening. - Decreasing chances for storms through the week, with warm weather persisting. && .UPDATE... Issued at 1017 AM MDT Sat Jun 29 2024 Current satellite imagery shows a cloudy start to the day as a result of a front that moved through last night. Clouds are scattering and thinning out a decent amount across the east plains and the northern tier of the high country is fairly clear this morning. There is a batch of clouds moving through Park County, southern Foothills, and into the urban corridor. With some indications of some breaks in the cloud cover already, clouds will continue to scatter out this morning in those areas. Forecast is on track for a considerably cooler day with temperatures in the low to mid 80s across the plains. It is slowly warming into the upper 60s on the plains, temperatures should recover into the lower 80s this afternoon. Made some minor edits to the precipitation probabilities later today. The higher chances for a shower or storm will be favored mainly along/south of I-70 and across the Palmer Divide and south Denver Metro. && .SHORT TERM /Through tonight/... Issued at 148 AM MDT Sat Jun 29 2024 Temperatures are running approximately 5 to 10 degrees cooler than this time yesterday for all but Summit and Park Counties following the passage of the nocturnal cold front. Although most model guidance remains steadfast in showing the development of a robust yet transient low-level cloud deck around 750mb early this morning, ACARS soundings from DIA show the moistening is, a minimum, delayed. Have thus tapered the extent and persistence of the cloud cover, but will continue to maintain some scattered to broken low clouds through mid morning across much of the urban corridor. In any case, any such obscuration should clear fairly easily later this morning, so will lean toward the warmer end of guidance still, with highs climbing into the low 80`s around the Denver metro, with pockets of upper 70`s for higher elevation areas like the Palmer Divide, high mountain valleys, and Cheyenne Ridge. If cloud cover indeed proves more persistent and extensive, upper 70`s will be more likely for lower elevations highs. Come early to mid afternoon, low-level winds will shift to the southeast in the plains, and south/southwest in the high country, resulting in increased moisture advection with dewpoints progged to climb into the 50`s for lower elevations. The last few days have lacked this southeasterly surface component, and thunderstorm coverage was more isolated across the I-25 corridor as a result. Instability will be rather marginal today and mostly below 500 J/Kg, maximized over the high country and southern tier of our forecast area. The largely southerly low-level flow will provide for some upslope enhancement across Park County and the Palmer Divide this afternoon, hence considerably higher PoPs along/south of I-70 for today. Thunderstorms should then progress eastward into our southern plains in Elbert and Lincoln Counties, where the strongest storms of the day will be favored. With limited shear and somewhat reduced DCAPE, expecting a comparatively lower threat for severe storms, although a stronger storm or two can`t be ruled out completely. Low temperatures tonight will rebound under enhanced warm southeasterly winds, potentially boosted by evening outflows from convection pushing into the SE Colorado plains. && .LONG TERM /Sunday through Friday/... Issued at 148 AM MDT Sat Jun 29 2024 An active weather pattern will likely continue into early next week, before a general trend towards quieter conditions is expected as we approach mid/late week. A plume of above normal moisture (PWATs > 150% of normal) is expected to remain anchored across Colorado, on the western periphery of an expansive ridge across the south central U.S. The mid-level thermal ridge axis is also expected to shift east into the region during the day, which should lead to warmer temperatures across the forecast area Sunday afternoon. The main question for the day is what type of daytime heating/sfc moisture combination we end up with, and how much instability that results in. There should be sufficient deep layer shear across the region, especially later in the day as 500mb flow increases ahead of a weak shortwave trough. HREF again keys on the higher elevations south of I-70, with decreasing PoPs into the plains. The SPC marginal risk area looks sufficient with at least a couple of strong to severe storms possible across most of our forecast area. The previously mentioned upper ridge should shift east and weaken by early next week, with a broad upper trough axis gliding across the northern Rockies Monday into Tuesday. Some moisture should linger across the region, with at least isolated/widely scattered showers and storms during the afternoon hours. The storm threat should shift east of the urban corridor by Wednesday as a dryline sets up across the eastern plains, with considerably drier air working into the high country. Temperatures should remain near or a little above normal during this period. The latter half of the week looks to be dry. Guidance is in reasonably good agreement that a ridge should build across the Pacific coast by Thursday, with a trough axis somewhere over the northern Great Plains. Main question in this period is if a cold front will find a way to push into the region Thursday or Friday. There is quite a bit of spread among individual ensemble members, but this will be worth watching for those with outdoor plans for the holiday weekend. && .AVIATION /18Z TAFS through 18Z Sunday/... Issued at 1204 PM MDT Sat Jun 29 2024 VFR conditions expected for the TAF period. SE to SSE winds this afternoon at 07-11 kts. The highest chances for showers and thunderstorms likely stay south of BJC and just south of DEN. Put in a VCTS for DEN after 22Z. At APA, where it is more likely, there is a TEMPO for TSRA. This will extend through early evening. Collapsing showers and storms may result in brief variable gusty outflows. With most activity to the south and southwest, this may push the more collective outflow from that direction. Enhanced southerly flow expected this evening with a few gusts 25-30kts overnight. Winds become light and variable Sunday morning becoming light N to NNE in the afternoon. There is a chance for scattered showers and thunderstorms in the afternoon (after 21Z). && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Mensch SHORT TERM...Rodriguez LONG TERM...Hiris AVIATION...Mensch