National Weather Service Forecast Discussion |
Thornton Weather Forecast Today's Forecast Story |
324 FXUS65 KBOU 152340 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 540 PM MDT Wed Oct 15 2025 .KEY MESSAGES... - Isolated evening showers and thunderstorms possible, but a decreasing threat. A few gusts to around 60 mph if a stronger storm develops. - Patchy frost expected for portions of the plains Thursday night/Friday morning, with more widespread freeze anticipated Saturday night for the rural plains. - Cooler and breezy most days through this weekend. Next potential for more widespread precipitation arrives Monday. && .DISCUSSION /Through Wednesday/... Issued at 1254 PM MDT Wed Oct 15 2025 After a morning of dense fog for many locations along and north of I-76, the stratus has finally eroded, not without leaving a swath of notably cooler air in these areas. In the meantime, healthy southerly flow continues to overspread the southern half of our forecast area, with clear skies and the downslope pattern off the Palmer Divide boosting temperatures to around 80F in the warmest locations. This surface warming will allow for modest instability to develop this afternoon (MLCAPE 300-700 J/Kg across the eastern plains). Water vapor imagery already depicts some elevated convection to our east embedded within a moist warm advection layer aloft, and convection should develop over/near the Palmer Divide by mid to late afternoon as we tap into this elevated moisture. Steering flow will remain robust, thus keeping storms moving very quickly, but simultaneously increasing the outflow wind potential with any storms that do develop. A severe storm can`t be ruled out late afternoon or early evening, primarily from the wind threat (the strongest storms could produce localized gusts up to 70 mph) and favoring Lincoln/Washington Counties, but confidence isn`t overly high. For the lower elevations, thunderstorm activity should remain confined to locations south of I-76. Radar shows a well-defined DCVZ boundary currently south of Denver International Airport and, while some northward migration of this boundary can be expected throughout the afternoon, it seems unlikely to cross that I-76 corridor. Come this evening, most areas will stand a chance (20-50%) of seeing some pre-frontal showers as the trough axis and jet max approach. The bulk of the shower activity will be focused over our northern mountains, where light snow could accumulate to around 1" above 9,500 ft by Thursday morning (mainly for the Park and Medicine Bow Ranges). Expect cooler temperatures Thursday following the associated morning cold front, with the change being most pronounced in our mountains (15 to 20 degrees cooler than today). Showers will generally subside by the afternoon, save for perhaps our far northeast corner. With clearing skies and our post-frontal airmass in place, patchy frost will return to portions of the plains, particularly around the South Platte River Valley and in Lincoln County, prompting the issuance of a Frost Advisory for these locations. Seasonal conditions are in store for Friday under weak flow aloft as the trough shears off, with highs in the 60`s for the plains and urban corridor, and 40`s to 50`s for our mountain communities. Saturday`s weather will be influenced by an amplifying trough dipping down from the northern plains. Brushing us to the northeast, it will usher in slightly cooler temperatures once more, including overnight when lows look to fall below freezing for much of the plains. Additionally, breezy conditions will become increasingly widespread. The shortwave would also support at least a chance (~30%) for some light snow showers in our northern mountains during the day. Highly transient ridging will follow suit for Sunday, bringing about 10 degrees of warming and keeping all areas dry. Eyes then turn to Monday, with ensembles highlighting another developing trough over the PacNW approaching the Central Rockies. This feature will give way to our next opportunity for more widespread precipitation, although uncertainty in the track remains particularly notable and could significantly impact precipitation chances. Nonetheless, the airmass should be colder, supporting snow for most of our higher elevations and, if the coldest solutions were to verify, perhaps introduce some wintry precipitation to the lower elevations Monday night into Tuesday. Plenty of time for those details to change still, of course. Finally, will need to monitor the spatial extent of any lingering drier airmass on Monday, which if remaining far enough north, may result in locally critical fire weather conditions for portions of our southern plains Monday as winds strengthen. && .AVIATION /00Z TAFS through 00Z Friday/... Issued at 536 PM MDT Wed Oct 15 2025 VFR is expected to continue through the TAF period. A nearly stationary surface boundary continues to be the focal point of the near term forecast. This boundary currently sits between DEN/CFO and extends towards Parker/Castle Rock (south-southeast of APA). Radar trends suggest this is just beginning to retreat back to the west and could eventually produce wind shifts at DEN/APA by 02-03z. There is also a limited chance of a shower or thunderstorm developing near this boundary, though that potential continues to diminish as we`ve remained mostly capped in the area. Southeast winds behind that boundary will eventually transition to drainage winds later this evening, and should continue into the overnight hours. A gradual clockwise turn to the winds is expected during the day Thursday, with west-northwest gusts likely by the afternoon. && .BOU WATCHES/WARNINGS/ADVISORIES... Frost Advisory from 2 AM to 8 AM MDT Friday for COZ042-043-046. && $$ DISCUSSION...BRQ AVIATION...Hiris