National Weather Service Forecast Discussion |
Thornton Weather Forecast Today's Forecast Story |
467 FXUS65 KBOU 221801 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1201 PM MDT Wed Apr 22 2026 .KEY MESSAGES... - Critical fire weather conditions and potential for rapid wildfire spread today due to gusty winds and very low humidity. Critical conditions expected again on Thursday. - Dry and unseasonably warm weather continues today. Highs will be nearly 20 degrees above normal. - Slight mountain wave amplification to bring strong winds to the higher foothills (mainly above 8,500 feet) Thursday morning. - Pattern change to cooler and unsettled weather by this upcoming weekend. && .DISCUSSION /Through Wednesday/... Issued at 1157 AM MDT Wed Apr 22 2026 Current satellite imagery shows an upper level low over the Pacific northwest trekking east. Increasing southwest flow aloft over Colorado due to this low has led to breezy winds across the mountains and plains this morning. With ACARS soundings showing almost dry adiabatic lapse rates up to ~650 mb, breezy winds have been allowed to mix down to the surface and will likely become more widespread this afternoon as clearing skies and daytime mixing continue. Forecast remains on track for widespread critical fire weather conditions this afternoon and evening as surface observations already show relative humidity values already reaching the single digits in some areas. Outside of fire weather concerns today, our far northeastern plains (Sedgwick and Phillips counties) may see isolated thunderstorms late this afternoon/evening. However, most recent hi-res guidance does indicate the dry line staying east of our forecast area. If any storms were to develop, gusty outflow winds are possible, given decent DCAPE values. Gusty winds are expected to continue overnight tonight and into Thursday. Models seem to be trying to resolve a brief mountain wave for the high elevations due to a 700-mb jet, creating cross-barrier flow of 40-50 kts. This will likely result in winds gusting up to 40- 60 mph across the Front Range mountains and wind prone areas off the Cheyenne Ridge. However, cold air advection will occur right after, which will result in winds turning slight more northwesterly and becoming more bora in nature. with subsidence increasing aloft through the Thursday morning hours, recent hi-res guidance do indicate a brief window where winds gusting up to 40-60 mph could be brought down to the Hwy 93 corridor due to momentum transfer. Despite cooler temperatures on Thursday (highs in the 60s), widespread critical fire weather conditions will return due to gusty winds and minimum RH values between 10-17%. In terms of precipitation on Thursday, isolated mountain snow showers are possible in the afternoon, with a low chance (less than 20% chance) of virga showers for the Palmer Divide and Lincoln county area. By late Thursday afternoon and evening, we will likely get a reprieve of strong winds across the forecast area, as the axis of the upper level trough traverses the region and weaker westerly winds replace the stronger southwest/west. However, by Thursday night and Friday, a 500-mb jet associated with the longwave trough and subsequent low over Canada, will bring breezy winds back to the Front Range mountains. In addition, throughout the day Friday, a developing lee-side trough will create tightening of pressure gradients and allow breezy winds across the plains again. This could bring about another round of elevated-to-critical fire weather conditions. However, a backdoor cold front looks to bring improved RH into at least the northeastern plains, but just how far west it makes it could determine the need for additional fire weather highlights. Confidence remains higher in South Park, the Palmer Divide and our southern plains being the likeliest to see critical fire weather conditions. Will hold off on any fire weather highlights for now, but will continue to monitor the situation. The weather pattern into the weekend will be dominated by the upper level closed low over southern Canada, with westerly flow aloft over the region. Embedded shortwaves in the flow will keep the potential for light precipitation across the forecast area. Sunday continues to look to be the best shot for more widespread and measurable precipitation, due to a more defined shortwave trough pulling in Pacific moisture. As of right now, ensembles are in good agreement of QPF amounts between 0.10" and 0.25" for the plains. Behind this system, ensemble guidance indicates a brief warming trend for Tuesday and possibly Wednesday as a weak upper level ridge tries to build over the Rockies. However, this could be shortlived as models try to hone in on another system by midweek. && .AVIATION /18Z TAFS through 18Z Thursday/... Issued at 1133 AM MDT Wed Apr 22 2026 Models continue to show pretty strong southwesterly winds at DIA into mid afternoon. After 22Z they become more 250-260 in direction. Wind speeds stay pretty strong with gusts 30 to 35 knots. Speeds are expected to decrease somewhat around 03Z this evening. A wind shift to northwesterly winds is progged around 05Z. Speeds weaken overnight. Tomorrow, west and northwesterlies winds dominate. There will be no ceiling issues. && .BOU WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until midnight MDT tonight for COZ214>216- 238>251. Fire Weather Watch from Thursday morning through Thursday evening for COZ214-216-238>251. && $$ DISCUSSION...MAI AVIATION...66