661 FXUS65 KBOU 171609 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1009 AM MDT Fri Sep 17 2021 .UPDATE... Issued at 1000 AM MDT Fri Sep 17 2021 Cloud cover is currently over much of the I-25 corridor and plains this morning after a cold front came through last night. This cloud cover has kept temperatures below forecast and will continue to do so through the rest of the day. Highs were lowered roughly 3 degrees across that same area as the clouds are not expected to clear until around midday. This will be the first day since August 21 that Denver will have a daily average temperature below normal. No other changes were made to the forecast as fire danger will stay below Red Flag criteria. && .SHORT TERM...(Today and tonight) Issued at 314 AM MDT Fri Sep 17 2021 Strong surface cold front continues to sweep southward across Eastern Colorado and will be through Lincoln county shortly. Gusts of 30-45 mph have been common along and behind the front. Expect winds to slowly decrease through early this morning with the strongest winds remaining across Lincoln county until 9 am or so. Behind the front, expecting some stratus to develop across the plains through the rest of the night and continue into the early morning hours. Currently, satellite imagery showing areas of low clouds developing across Southern Wyoming and just now across Douglas and Elbert counties. Still unclear how extensive the stratus will become but latest model solutions keep most the low clouds east of the Interstate 25 corridor with the exception of Douglas county and southern portions of Denver. Mainly a dry and subsident airmass will be over Northern Colorado today and tonight. The big impact will be the cooler temperatures expected today over northeast Colorado. Strong low level inversions will be keep temperatures 15 to 20 degrees cooler over yesterday with readings only in the pleasant 70s. Too stable for any showers or thunderstorms today. High pressure ridge will slowly build through tonight with weakening westerly flow aloft. .LONG TERM...(Saturday through Thursday) Issued at 314 AM MDT Fri Sep 17 2021 A warm, dry airmass will be in place through the weekend. Saturday, temperatures will already be well above normal again with highs back in the upper 80s and lower 90s across the plains and 70s and 80s in the high country. There may be enough energy and moisture ahead of a shortwave approaching from the southwest for some isolated, high-based storms over the high terrain Saturday afternoon through Saturday night. Models show precipitable water values increase from around 0.2 inches or less on Saturday morning up to around 0.5 inches Saturday evening, but forecast soundings show dry lower levels and deep mixing to around 550 to 500 mb. This suggests that storms will bring mainly gusty winds and very little precipitation. The lower elevations should remain clear of storms. Sunday, temperatures will remain similarly warm across the area, maybe a few degrees cooler but still well above normal. The shortwave will cross the Central Rockies and exit to the northeast, while a deeper trough approaches from the Pacific Northwest. Models are showing a band of mid level vorticity and moisture Sunday afternoon but also warm advection and stability aloft which would limit development. The high terrain may see isolated to scattered storms and showers Sunday afternoon through Sunday night, but expect mostly gusty winds and very little precipitation again. Models remain in good agreement about the progression of the trough, which should be moving over the central and northern Rockies Sunday night and Monday morning. It will push a cold front across northeast Colorado Monday morning, which will bring temperatures down to the lower 70s across the plains and 40s and 50s in the high country. The trough is expected to move quickly, with the axis already moving over Colorado by Monday afternoon, meaning any impacts will likely be brief and limited. Continue to expected scattered showers and light precipitation, this time affecting both the high country and plains. There might even be some flurries in the high country, and very light snowfall on the higher peaks of the mountains Monday night and Tuesday morning. The trough will be exiting east early Tuesday and skies will clear, though highs will remain well below normal. There is still much less certainty in the synoptic situation behind the trough in the latter half of the upcoming week. Generally it looks like brief and mild ridging ahead of another trough from the Pacific Northwest, but models disagree significantly about the timing and intensity. The GFS and Canadian are showing shortwave troughs approaching at different speeds, while the ECM is currently showing a cutoff low off the west coast. So, generally expect warmer and drier conditions as heights rise Wednesday and Thursday, with clear skies and near normal to slightly warmer temperatures, before another system maybe Friday. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1000 AM MDT Fri Sep 17 2021 Ceilings of around 25 kft will continue until roughly 18z at DEN this morning. Clouds are beginning to erode from southwest to northeast so BJC and APA will see clouds clear around 17z. VFR conditions will develop for the rest of the TAF period. Winds will pick up a southeasterly direction this afternoon before going to drainage this evening. && .FIRE WEATHER... Issued at 314 AM MDT Fri Sep 17 2021 Still expect elevated fire danger across the high mountain valleys this afternoon but decided to cancel the fire weather watch for the mountain valleys of Jackson and Grand counties. Humidities will certainly be under 15 percent but wind speeds rather marginal for red flag conditions and only expect a few hours of gusts up to 30 mph over Jackson county. Fire danger will remain elevated Saturday due to persistently low afternoon minimum humidities and breezy winds across much of the area. The greatest concern is for North Park, where maximum gusts are expected to approach 30 mph while humidity is just over the critical threshold of 15 percent briefly during the afternoon. Fire danger will be mitigated by higher humidity Sunday through about mid week, then in the latter half of the week by lighter winds. && .HYDROLOGY... Issued at 314 AM MDT Fri Sep 17 2021 No flash flood threat through tonight with dry and stable airmass. Saturday and Sunday, isolated high-based storms should bring only light precipitation and a very low threat of burn area flooding. Monday, scattered storms are expected to produce still light precipitation and the flooding threat will remain low. Dry conditions will set back in Tuesday. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Danielson SHORT TERM...Entrekin LONG TERM...EJD AVIATION...Danielson FIRE WEATHER...Entrekin/EJD HYDROLOGY...Entrekin/EJD