Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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370 FXUS65 KBOU 211812 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1212 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. && .UPDATE... Issued at 1046 AM MDT Fri Jun 21 2024 Current satellite imagery (Day Cloud Phase) shows this morning`s low stratus across the plains/urban corridor scattering out with the morning heating. The low stratus resulted in a cooler morning with temperatures now into the 60s compared to yesterdays 70s/80s around this time for the urban corridor/plains. This puts the forecast on track for a slightly cooler day with highs in the low to upper 80s for those areas. Made some minor adjustments to highs to keep them a touch cooler. Precipitation probabilities seem fairly on track with thunderstorms developing in the mountains/foothills early this afternoon. By mid-afternoon instability builds on the plains and scattered thunderstorms spread eastward. The environment will support some strong to severe storms as well with hail (up to 1.5"), wind, and localized heavy rainfall. Will likely have to keep on eye on boundaries today (already one in Elbert Co.) which could pose a potential landspout risk. && .SHORT TERM /Through tonight/... Issued at 335 AM MDT Fri Jun 21 2024 There should be one more day of showers and thunderstorms along with seasonal temperatures. Radars are showing some weak convection continuing over the CWA this early morning and some over the southwestern quarter of Colorado as well. Models are showing an upper trough over the Great Basin this morning to weaken and move eastward into Colorado by this evening into the overnight hours. The flow aloft will remain southwesterly across the forecast area today and tonight. There is a short period of weak upward synoptic scale energy expected later this afternoon and evening. Models continue to show significant available moisture today into this evening with precipitable water values in the 0.80 to 1.50 inches range. The atmosphere looks to dry out somewhat after 06Z overnight. There is plenty of CAPE progged for the CWA with the highest amounts over the northern border area. Will go with 30-60% pops for the forecast area this afternoon and evening. There will be a few strong storms but the main threat will be heavy rainfall with a flash flooding potential. One good thing is the convection will be moving at 20-30 mph to the northeast. For high temperatures today, readings will be 1-4 C cooler than Thursday highs with mid and upper 80s over the plains a good bet. && .LONG TERM /Saturday through Thursday/... Issued at 246 AM MDT Fri Jun 21 2024 Upper level ridge will intensify over the Central and Southern Rockies this weekend. Highs will top out around 90F on Saturday, and then heat up for Sunday and Monday. For the Urban Corridor and northeast plains highs are expected to reach the mid to upper 90s with a few 100s possible as well. Good chance for heat advisories Sunday and/or Monday. Precipitable water values will be on the low side for convection with three-quarters of an inch across the plains and under a half inch over the higher terrain. The higher terrain may have just enough moisture and instability for weak afternoon showers and thunderstorms through Monday. For the plains, a few weak showers/storms may move off the higher terrain bringing more wind than rain. One exception will be Sunday afternoon/evening over the eastern plains. Southerly winds advect better low level moisture into Lincoln county. This combined with lift from a possible boundary could produce a few afternoon storms. For Tuesday through Thursday, an upper level trough moves across the Northern plains Tuesday. The 00Z operational runs show a cold front from this trough moving through Tuesday morning. Expect temperatures to take a step back with highs in the upper 80s to lower 90s. Seems like the ensemble members are not showing this yet. Some of the guidance that incorporates the ensemble members still show highs in the mid to upper 90s for Tuesday, which seems high. Moisture is still not that great from the models so will keep PoPs on the lower side on Tuesday. Models finally show an increase in moisture for Wednesday and Thursday, so we should see at least scattered showers and storms. && .AVIATION /18Z TAFS through 18Z Saturday/... Issued at 1212 PM MDT Fri Jun 21 2024 Light NNE winds at DEN and NNW winds at BJC/APA become more easterly this afternoon. Scattered thunderstorms develop in the afternoon, mainly after 20Z at the terminals. For the rest of the afternoon, periods of variable gusty winds up to 35 kts, brief heavy rain, and brief lowered ceilings from any close or passing storms. There is still potential for another round of scattered showers/storms 00-04Z, although likely would be lesser in coverage. There is also a low chance of fog/low stratus again for the early morning timeframe (similar to Friday morning) given light winds and residual moisture around. Confidence is low, so not currently being messaged for the 18Z TAF. Light and variable winds become light northerly toward the afternoon Saturday. Can`t rule out an isolated shower, although will likely be high-based resulting in brief variable gusts. && .HYDROLOGY... Issued at 335 PM MDT Thu Jun 20 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. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Mensch SHORT TERM...RJK LONG TERM....Meier AVIATION...Mensch HYDROLOGY....RJK