National Weather Service Forecast Discussion |
Thornton Weather Forecast Today's Forecast Story |
830 FXUS65 KBOU 270011 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 611 PM MDT Tue May 26 2026 .KEY MESSAGES... - Today will bring windy conditions to the plains and potential for elevated fire weather conditions in areas that see little/no rain this afternoon. - Higher terrain will see a few rounds of fast moving showers and thunderstorms this afternoon and evening. There is a marginal threat of flooding mainly over the East Troublesome burn scar. - Wednesday appears to be the most active day with more widespread showers and thunderstorm coverage with locally heavy rainfall possible due to slow movement of thunderstorms. - After somewhat of a lull Thursday, thunderstorm potential will increase again Friday through the weekend with a chance of severe thunderstorms over the plains. && .DISCUSSION /Through Tuesday/... Issued at 202 PM MDT Tue May 26 2026 Current water vapor satellite imagery shows a shortwave trough in southwestern U.S. embedded in the flow of an upper level closed lower over the coast of California. Southerly flow aloft over Colorado has allowed mid-level moisture to be advected into the region, with showers now initiating over the mountains. Expect showers and thunderstorms to increase in coverage over the high terrain this afternoon. Modeled Skew-T soundings show a highly saturated environment, with PWAT values between 0.40" and 0.60". With modest instability over the high terrain, some stronger storms could produce heavy rain. However, given the expected fast storm motion, concerns are minimal for flooding at this time, unless we get training. Across the plains, surface observations have shown southeast winds gusting between 30-40 mph this morning. With current ACARs soundings showing relatively steep lapse rates, expect these gusty winds to persist as daytime mixing continues. Overall lack of decent instability across the plains will limit chances for widespread precipitation to occur this afternoon. However, hi-res guidance does indicate potential for a few showers and isolated thunderstorms for the Palmer Divide and I-25 Corridor late afternoon and evening. With DCAPE values projected to reach up to 800-1000 J/kg, gusty outflow winds will be the main threat. The next few days will likely see a blocking pattern set up across the U.S. with the upper level closed low situated over the western U.S. and blocking high over the Great Plains. This will leave Colorado under relatively weak flow aloft between these two features. On Wednesday, global and regional guidance are in good agreement of the aforementioned shortwave trough slowly trekking across the forecast area, providing synoptic lift for a round of showers and thunderstorms for the plains and mountains. Sounding guidance has continued to indicate a warm moist vertical profile, with PWAT values above the 90th percentile. And, given weak flow aloft, storm motion will be slow as evident in hodographs. Thus, localized heavy rain will be the main concern for tomorrow. However, there is also a conditional threat for a landspout to occur if we get a DCVZ and enough sunshine for low-level instability to build. There is still some question if we can get a Denver cyclone to form tomorrow morning, and with the expected incoming cloud cover we might not get enough instability that some models suggest. Showers may continue into the overnight hours of Wednesday night, before gradually ending by sunrise on Thursday morning. Temperatures should rise to the upper 70s across the plains as the upper level shortwave exits the region. With upsloping, we could have another round of showers and thunderstorms mainly for the Front Range mountains and foothills. Given continued weak flow aloft, storms will be slow moving and thus localized heavy rain is possible again. By Friday and into the weekend, ensemble guidance indicates the upper level low over western U.S. weakening and getting absorbed by the flow of the upper level ridge. With continued southeast flow at the surface, low-level moisture will be continuously advected into the region. Soundings show better instability building over the plains, with mid-level flow turning more south/southwesterly resulting in better shear profiles. This will allow better potential for strong to severe storms Friday and particularly Saturday afternoon. Weak southwest flow aloft will dominate the flow pattern Sunday and into the beginning of the week, with an upper level ridge still in place over Central U.S. With low and mid-level moisture still in place, guidance does indicate potential for continued showers and isolated thunderstorms for the forecast area. However, given overall weak flow and forcing, severe threat is very low at this time. && .AVIATION /00Z TAFS through 00Z Thursday/... Issued at 607 PM MDT Tue May 26 2026 Will leave a PROB30 in the TAF for -SHRA this evening as per area radars and high resolution model data. The brisk southeasterly winds are progged to decrease somewhat this evening, with models keeping them with a southeasterly direction all night opposed to true drainage. For Wednesday afternoon`s convection, will go with a PROB30 for -TSRA along with the potential for ceilings down into the BKN-OVC030-040 range from late afternoon into late evening. Cross sections and soundings show ceiling to improve by 06Z Wednesday night. adios && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...MAI AVIATION...66