Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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897 FXUS65 KBOU 180927 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 327 AM MDT Wed Sep 18 2024 .KEY MESSAGES... - Dry and warm through Friday with elevated fire weather conditions. - Cooler temperatures this weekend with good chances (30-60%) for rain, and accumulating snow in the Front Range mountains. && .SHORT TERM /Through Tonight/... Issued at 326 AM MDT Wed Sep 18 2024 A subsident southwest flow aloft will prevail today behind yesterday`s storm system. Weak ridging in the southwest flow aloft will move over the state tonight and into Thursday. The airmass dries out with mostly clear skies expected today and tonight. Relative humidities fall into the lower teens today to elevate the fire danger, but wind speeds here are expected to be less than 25 mph. Breezy conditions are expected over the higher terrain with southwest winds gusting to 25 to 35 mph. In these areas relative humidities will be in the upper teens and more so in the 20s. It will be another warm day for this time of year with highs in the lower to mid 80s over northeast Colorado. For tonight, winds decrease with the ridging moving overhead. Low temperatures will be chilly due to the dry airmass, light winds, and clear skies. Most of northeast Colorado is expected to fall into the 40s with the mountains valley expected to dip below freezing (upper 20s to lower 30s). && .LONG TERM /Thursday through Tuesday/... Issued at 326 AM MDT Wed Sep 18 2024 Zonal flow will continue over northeastern Colorado as an upper level ridge begins to transition eastward. Cross sections indicate a relatively dry airmass Thursday which will lead to limited precipitation over the region. With above normal temperatures and the transition of upper level systems increasing pressure gradients, low level southerly winds increase along the Palmer Divide, Lincoln county and parts of the urban corridor. Although winds remain below red flag warning criteria, near critical fire weather conditions are possible Thursday afternoon for the areas listed above. Additionally, similar conditions are possible Friday afternoon. The combination of daytime heating, weak mid-level moisture, and QG ascent could lead to isolated chances of a high based storm or two along the higher elevations Friday afternoon. Thus decided to keep low (10-20%) chances through Friday evening. The next upper level trough arrives early Saturday morning. Both GFS and ECMWF continues to display an abundance of QPF over our area. No major changes from ensembles as Denver QPF ranges from 0.30-2.50 inches. Given that models have better agreement on the trough axis placement providing a brief window of upslope flow, it isn`t out of the question parts of the urban corridor could receive up to a half an inch or higher with this system. The flash flood threat increases over recent burn areas this weekend. There is still lingering uncertainty in the speed of this system which could affect our precipitation amounts. It is likely by Saturday evening, the entire region should receive scattered to numerous showers and storms. Also there is high confidence this weekend`s afternoon temperatures will become cooler. In fact, 700-850mb temperatures drop near 2-4C across the CWA which should result in mid 60s to low 70s for the lower elevations. Higher elevations cool significantly between 40-56 but areas above 11k should remain cold enough for a few inches of light snow through Sunday. By early next week, ensembles have been persistent keeping near normal temperatures therefore decided to decrease NBM highs both Monday and Tuesday afternoon. && .AVIATION /06Z TAFS through 06Z Thursday/... Issued at 1142 PM MDT Tue Sep 17 2024 VFR to prevail through Wednesday under mostly clear skies. Southerly drainage winds to prevail into Wednesday morning with south to southwest winds continuing to at least 18Z. A Denver Cyclone forms and likely brings northeast to east winds to the Denver area after 19Z. The northeasterly winds continue through 00Z Thursday and then become a southerly drainage direction after sunset (02Z). && .FIRE WEATHER... Issued at 326 AM MDT Wed Sep 18 2024 Southwest flow will bring dry weather to the area today. Relative humidities fall into the lower teens this afternoon across the plains. It will be somewhat breezy across the plains, mainly south of I-70 where gusts of 15 to 25 mph are expected. Over the higher terrain, southwest winds will be a little stronger with gusts of 25 to 35 mph. Relative humidities over the higher terrain will range from the upper teens to mid 20s. Relative humidities drop near 11-17 percent for the Palmer Divide, Lincoln county and parts of the urban corridor both Thursday and Friday afternoon. Winds remain below warning criteria thus leading to near critical fire weather conditions. There is a greater threat of near critical fire weather conditions Friday afternoon as southerly winds may increase. Will continue to monitor. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Meier LONG TERM...AD AVIATION...Meier FIRE WEATHER...Meier/AD