Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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686 FXUS65 KBOU 202115 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 315 PM MDT Thu Jun 20 2024 .KEY MESSAGES... - Scattered showers and thunderstorms through Friday evening. A few storms could be strong to severe, and also produce locally heavy rain. Burn scars would be most susceptible to flood risk. - Hotter and drier this weekend into early next week. Potential for heat impacts starting Monday, but some relief toward Wednesday. && .SHORT TERM /Through Friday/... Issued at 1053 AM MDT Thu Jun 20 2024 Current radar trends show scattered thunderstorms continuing to initiate off of the higher terrain then moving northeastward across the adjacent plains this afternoon. While sub-severe storms are more likely as activity continues to spread onto the plains, still can`t rule out a few severe storms within the moist, unstable environment. Most storms will yield brief heavy rainfall, gusty winds up to 50 mph, and small hail. Within any of the severe storms, hail up to 1.5" and severe wind are possible. With boundaries present, can`t rule out landspouts initially on the plains as well. Storms continue to move eastward onto the plains this evening. Some CAMs models continue to show potential for another round or two of lower coverage showers and storms mainly in the early evening to midnight timeframe. There isn`t a ton of agreement among the high-res suite of models, so this remains lower confidence still. Friday, the region stays under a weak upper level ridge. The ridge will gradually slide eastward inducing WSW flow aloft while transporting in a plume of above normal moisture (140-170% of normal). The region remains under weak synoptic ascent to provide additional support for scattered showers/thunderstorms in the afternoon/early evening. MLCAPE values build into the 500-1000 J/kg range. High-resolution guidance highlights an area mainly north of a line from Denver to Fort Morgan and through the northeast corner for potential for a few severe storms with higher probabilities for CAPE >500 J/kg and 0-6km bulk shear >30kts. With above normal moisture around, localized heavy rainfall will be a threat again Friday. Soundings indicate potential for drier air to remain in the lower levels which would reduce a higher coverage heavy rain threat. Temperatures will be a degree or two cooler than Thursday with highs in the mid to upper 80s for the plains, 70s in the foothills, and 50s/60s for the mountains. && .LONG TERM /Friday night through Thursday/... Issued at 230 PM MDT Thu Jun 20 2024 The more active weather pattern of late will taper down late Friday evening and overnight as a shortwave pushes east across the area. There are now indications the shortwave and weak synoptic support will be a little faster, adding to shower/storm coverage into Friday evening. A couple stronger storms would still be possible into the evening hours, with locally heavy rain and isolated severe storm threat. Then, subsidence builds in from west to east after midnight, effectively taking most convection with it. Saturday will then feature drier weather with less and weaker convection. Temperatures will also be warming as the drier airmass takes hold. The trend to hotter temperatures will continue through Sunday and Monday as an upper level ridge builds over the Central and Southern Rockies. We see high temperatures pushing into the mid to upper 90s on the plains and I-25 Corridor, with a couple spots near 100. Thus, we may need Heat Advisories for a good chunk of the plains/I-25 Corridor by Monday as the heat load builds. We`ll be on the northern fringe of moisture, so still expect a few high based showers and storms each afternoon and evening, with the mountains and Palmer Divide area seeing the main chance. For Tuesday and Wednesday, there are a couple signs of change in a few of the ensemble members showing a stronger shortwave moving across the northern U.S., pushing a backdoor cold front across the High Plains. Typically, these types of waves eventually result in some cooling across the northeast plains, so hopefully some heat relief is in the cards by midweek and more than what the current National Blend of Models would suggest. A backdoor front would also support a little uptick in the chance of thunderstorms each afternoon and evening. && .AVIATION /00Z TAFS through 00Z Friday/... Issued at 1216 PM MDT Thu Jun 20 2024 Enhanced southerly winds expected this afternoon with gust 20-25kts. Scattered thunderstorms develop and move eastward this afternoon, mainly in the 20-00z timeframe. Any nearby or passing thunderstorms may bring variable gusty winds up to 40kts, potentially closer to 45kts in any stronger storms. Heavy rain may also bring brief reductions in visiblity/ceilings for short periods. After 00z, there is a chance for another round of loewr coverage showers or stormss through midnight. Friday, light and variable winds in the morning become easet in the afternoon. Scattered thunderstorms develop in the afternoon around the terminals. && .HYDROLOGY... Issued at 230 PM MDT Thu Jun 20 2024 An increase in atmospheric water content will bring increased shower and storm coverage and more intense rainfall. Rainfall efficiency will grow, as warm cloud depths increase to 4,000-5,000 ft, rather impressive for this time of year. NAEFS shows precipitable water (PW) increasing to 1-2 standardized anomalies, and greater than that on the western slope (due to this earlier than climatological arrival of the subtropical moisture plume). Storm motions should move along at a decent clip of 20-25 mph, although a Bunkers right mover could be closer to 15 mph. Stronger storms would be capable of producing 1-1.5 inches of rain in 30-40 minutes. Overall, burn scars would be most susceptible to any flooding threat, although we couldn`t rule out some minor urban/street flooding if we got a stronger storm in a metro area, && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Mensch LONG TERM...Barjenbruch AVIATION...Mensch HYDROLOGY...Barjenbruch