277 FXUS65 KBOU 191800 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1200 PM MDT Tue Oct 19 2021 .UPDATE... Issued at 1013 AM MDT Tue Oct 19 2021 Water vapor shows a cut off trough over western Colorado this morning with subtle shortwave troughs embedded within the larger trough. One of these subtle shortwaves is setting up over north-central Colorado which is helping to provide strong QG ascent in southern Wyoming where widespread rain and snow is occurring. On the eastern side of this feature (over the northern foothills and I-25 corridor), there is good 700 mb frontogenesis setting up along with warm air advection. Radar is starting to show a band of precipitation from Elk Mountain to Laramie to Cheyenne in Wyoming. As the day progresses, this band will develop southeastward into Laramie, Weld, and Logan counties in Colorado. High resolution models are showing decent rainfall totals up to a third of an inch just south of the CO/WY border. Therefore, PoPs and QPF were raised to account for the higher confidence that precipitation will fall in those three counties. A couple of the models in the HREF show showers developing this afternoon across the Denver metro. There is some skepticism that these will be anything more than virga especially since the dew points are rather dry. However, PoPs were increased slightly to bring the mention of rain showers into the northwestern Denver suburbs. This chance of rain in the Denver metro will need to be watched since the model trend is certainly towards a higher likelihood that they do happen. && .SHORT TERM...(Today and tonight) Issued at 420 AM MDT Tue Oct 19 2021 An upper level low will arrive in area bringing light snow showers to our mountains zones Tuesday morning. Overall, snowfall accumulations have decreased due to this system becoming weaker and placement of this system does not favor much snowfall due to a northeastward track. Therefore, areas north of I-70 in the mountains will experience slick travel conditions and snowfall totals up to 1.5 inches on the highest peaks. A isolated rain shower cannot be ruled out for the north eastern plains but overall areas outside of the mountains should be fairly dry. Strong subsidence will bring strong low level winds across the CWA with the highest wind gusts of 45 MPH. Most areas will range from 25-30 MPH through Tuesday afternoon. Areas such as the urban corridor, plains, and parts of the foothills will experience partly cloudy skies and cooler afternoon highs in the upper 50s to lower 60s. .LONG TERM...(Wednesday through Monday) Issued at 420 AM MDT Tue Oct 19 2021 WNW flow aloft will develop over the area on Wed and continue into Thu. There will be some mid and high level moisture embedded in the flow, however outside of some clouds, no precip is expected either day. Highs will be near seasonal levels on Wed and then rise to above normal by Thu. For Fri into Sat the flow aloft will become more WSW. Once again there will be some mid and higher level moisture in the flow, however, no precip is expected either day. Meanwhile, with downslope WSW low level flow, highs across nern CO will rise into the lower to mid 70s by Sat. By Sun into Mon the flow aloft will become more southwesterly. The GFS wants to bring in deeper lower level moisture, into portions of the mtns Sun night into Mon, while the ECMWF holds off this moisture until late Mon into Tue. Overall will just mention a chc of precip due to timing differences. As for highs, will trend towards ECMWF Guidance with readings staying well above normal, over nern CO. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1138 AM MDT Tue Oct 19 2021 A few virga showers may create periods where ILS is needed this afternoon. Ceilings should stay at or above 6 kft but the rain below the cloud deck may reduce slantwise visibility. Some of the showers could create brief sporadic winds but overall, winds will be out of the north. This evening, the low pressure system will move out of the area and VFR conditions will return for the rest of the TAF period. Wind speeds will decrease this evening and will be light overnight and tomorrow. && .FIRE WEATHER... Issued at 420 AM MDT Tue Oct 19 2021 A Red Flag Warning is in effect starting 12 PM to 6 PM Tuesday for southern Lincoln county due to low humidity ranging from 14-18 percent and strong low level winds. Areas near the Palmer Divide will trend with the lowest humidity percentages across the region. Gusty winds are expected throughout Tuesday afternoon into early evening. Fire weather concerns will subside by early evening and dry conditions will prevail Tuesday night. && .BOU WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 6 PM MDT this evening for COZ247. && $$ UPDATE...Danielson SHORT TERM...AD LONG TERM...RPK AVIATION...Danielson FIRE WEATHER...AD