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Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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858 FXUS65 KBOU 172155 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 355 PM MDT Wed Jul 17 2024 .KEY MESSAGES... - Scattered showers and thunderstorms this afternoon into early this evening with a few strong to severe storms possible. - Thursday will be warm with scattered gusty afternoon storms. - A cool and wet pattern will exist from Friday through Monday. There will be a threat of flash flooding in the burn areas on Friday and Sunday. && .SHORT TERM /Through Thursday evening/... Issued at 319 PM MDT Wed Jul 17 2024 Current radar shows scattered showers and thunderstorms this afternoon over the mountains, foothills, Palmer Divide, and northern Weld County. MLCAPE values range in the 500-1500 j/kg range from west to east. Across the I-25 corridor, shear is on the weaker side keeping storms weaker and capable of brief gusty winds, small hail, and locally heavy rain. Over the eastern plains, shear is more sufficient combined with higher instability (MLCAPE > 1000j/kg) to support a few strong to severe storms. Into early evening, high resolution CAMs show scattered showers and storms pushing east across the plains. A few solutions show a transition into a more linear mode over the far east plains. Given the more favorable severe environment is there, we`ll have to watch for a severe wind,hail threat and if storms slow more, perhaps potential for minor local flood impacts in those areas. RAP mesoanalysis shows DCAPE values >1000j/kg over the east plains support the gusty wind threat. Most activity will have exited to the east by mid-evening. For Thursday, the 500mb ridge centers to the west of Colorado, around the Four Corners region with N/NNW flow aloft over Colorado. Model cross sections/soundings show subtle drying in the low levels and some in the mid-levels from Wednesday. There will be marginal instability around with ample daytime heating; however, limited upper level support for ascent. This will support scattered afternoon showers and thunderstorms lesser in coverage compared to Wednesday with the higher chances over the higher terrain. MLCAPE values 800-1500 j/kg and DCAPE 900-1500 j/kg will support a few stronger storms, capable of strong gusty outflow winds and small hail on the plains. Temperatures trend slightly warmer with less cloud cover and building of the ridge to the west. Highs range in the upper 80s to low 90s across the plains. && .LONG TERM /After midnight Thursday night through Wednesday/... Issued at 319 PM MDT Wed Jul 17 2024 The upper level pattern will be stagnant and quite unusual for July or much of the long term period. A broad upper level trough will move south out of Canada and park itself over the Midwest. 500 mb flow may be northerly for a few days over our forecast area. This will lead to wet and cool weather for the long term period. Getting into specifics, there will be a small shortwave trough that will move across northeast Wyoming through northeast Colorado Friday afternoon. At the surface, there will be a weak cold front that will move trough northeast Colorado along with lowering pressure. The forcing from the trough and cold front will combine to create scattered showers and storms across the area. There will be a concern for flash flooding over the burn areas since there will be upslope flow and good moisture in the area. Across the northeast plains, there will be enough instability for storms to become strong to severe. Since there is organized forcing with the shortwave, these storms may quickly congeal into a line and produce wind gusts up to 60 mph. The primary threat will be east of a line from Fort Morgan to Deer Trail. On Saturday, our forecast area will be under slight subsident flow behind the shortwave that will have moved through the area. The post- cold frontal airmass will have a bit less moisture and will be more capped than Friday. Despite the low level upslope northeasterly flow, the coverage of showers and storms will be limited. Storms will form primarily over the southern foothills as that area is favored with low level northeast winds. On Sunday, there will be another small shortwave trough that will move towards northeast Colorado. At the surface, low level northeasterly flow will increase and moisture will increase as well. There will be widespread showers and thunderstorms over the higher terrain. Some of these storms may train over the same area and there will be a flash flood threat as a result. Storms may also form over the plains but coverage will be lower. By next work week, temperatures aloft will increase and moisture will decrease in the low levels. There will be more stable conditions which will limit coverage of storms. Storms will mostly stay over the higher terrain. By the end of the week, temperatures will rise and there will be less of a threat of storms as a ridge aloft moves overhead. && .AVIATION /18Z TAFS through 18Z Thursday/... Issued at 1209 PM MDT Wed Jul 17 2024 Expect VFR conditions for the TAF period. Light E/SE winds this afternoon, increasing to 7-11 kts mid to late afternoon. Scattered showers and thunderstorms develop this afternoon. Coverage/chances are high enough to include as TEMPO for -TSRA from 20-23Z at BJC/APA and 21-24Z at DEN. Showers and storms may contain gusty outflow winds similar to Tuesday, so included this in the TEMPO for VRB gusts up to 30-40 kts. Winds turn back southerly tonight at 08-12 kts. Winds become light after 14Z, turning NW Thursday morning, eventually settling easterly for the afternoon. There is a low chance (< 25%) for a scattered showers or storm in the afternoon; therefore, not included in the TAF and messaged as a VCSH for now. && .HYDROLOGY... Issued at 319 PM MDT Wed Jul 17 2024 Low level moisture trends downward for Thursday, resulting in lower coverage of showers and thunderstorms. There is little to no threat for flash flooding over the burn areas Thursday. Friday and Sunday will have the best coverage of storms. Some of these storms will produce heavy rainfall and there is potential for training storms. The Cameron Peak will have an elevated threat of flash flooding each day while the other recent burn areas will have a limited threat. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Mensch LONG TERM...Danielson AVIATION...Mensch HYDROLOGY...Mensch/Danielson