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711 FXUS65 KBOU 210515 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1115 PM MDT Sat Sep 20 2025 .KEY MESSAGES... - Seasonal temperatures Sunday, with a chance of diurnal showers/storms mainly over the mountains. - Cold front Monday with a good chance of showers late Monday, remaining cool with scattered showers Tuesday. High mountain snow likely Monday night into Tuesday. - Turning warmer and drier again late next week. && .DISCUSSION /Through Saturday/... Issued at 302 PM MDT Sat Sep 20 2025 Current satellite and radar imagery show convection initiating off a boundary over the eastern portion of the Palmer Divide and plains. With the lack of cloud cover allowing instability to build, hail up to 1" and wind gusts up to 60 mph will be the main threats for the strongest storms as they travel east. In addition, scattered high based showers are forming over the Front Range mountains, but are dissipating as they spill onto the adjacent plains due to an overall stable environment. Expect showers and thunderstorms to mostly be confined to the higher terrain this afternoon, with a few of the stronger storms possibly spilling onto the adjacent plains. However, short term CAMs do indicate storms developing off the Cheyenne ridge later this afternoon and traveling across northern/northeastern Colorado. With SPC Mesoanalysis showing MUCAPE ~500 J/kg and steep lapse rates of 9 dg C/km, some of these storms could become sub- severe/severe, with hail up to 1" and outflow winds up to 60 mph. Sunday will be our warmest day of the forecast period, with highs in the low 80s across the plains. With increasing northwest flow aloft ahead of an incoming system, another round of showers/storms are possible mainly for the higher terrain. A few showers may might spill onto the adjacent plains, so have increased PoPs for Sunday. Models are still struggling to grasp the trajectory of the upper level trough that will move into our area late Monday. Short range solutions suggest the system will have a more easterly track, while ensemble solutions like the ECMWF and GEFS have continued to trend with a westerly track. If those solutions verify, we could have more widespread precipitation late Monday and into Tuesday. For now, NBM seems to have a good grasp on PoPs, with increased precipitation chances for the eastern plains Monday night and Tuesday. With cold air advecting into our region, elevations above 10K ft. could see snow. In terms of temperatures, the plains will be in the low-mid 60s on Tuesday, due to a cold front moving through. Wednesday morning, some of the colder spots on the the plains could have frost, but most of the area will be in the low 40s. After the upper level trough departs, a strong ridge will being to build, which will bring temperatures back to seasonal normals by Thursday. && .AVIATION /06Z TAFS through 06Z Monday/... Issued at 1111 PM MDT Sat Sep 20 2025 Winds should gradually become drainage by 07z. By 15z winds will go light W or NW. Winds will then become WNW around 21z thru early Sunday evening. Once again can`t rule out a chc of -shra or an isold tstm by 21z so will keep Prob30 in the Taf. Brief gusty winds up to 30 mph will also be possible with any shower. Ceilings will stay above 12000 feet although aftn showers may drop them down briefly to 9000 ft. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Ideker AVIATION...RPK