061 FXUS65 KBOU 190304 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 904 PM MDT Mon Oct 18 2021 .UPDATE... Issued at 853 PM MDT Mon Oct 18 2021 Evident on water vapor imagery, an upper level low gradually pushes eastward into Utah which will eventually enter Colorado tomorrow morning. Radar is starting to show echoes for showers over the northern mountains with little reaching the ground currently. Snow showers will further develop over the mountains after midnight into tomorrow morning followed by another round of showers in the afternoon. Forecast remains on track for light accumulations in the mountains. Breezy W to NW flow expected across NE Colorado Tuesday. With gusts to 25 mph combined with low relative humidities, southern Lincoln County continues to look favorable for near-critical fire weather conditions for a portion of the afternoon. && .SHORT TERM...(This evening through Tuesday) Issued at 242 PM MDT Mon Oct 18 2021 The upper low over the Great Basin this afternoon will move across Utah tonight and should be near the tri-state border of Utah, Wyoming and Colorado early tomorrow morning. QG fields show light synoptic subsidence turning to moderate ascent across northeast Colorado after midnight. Continue to expect a band of precipitation to bring showers to the northern mountains after midnight with the colder mid level air. Forecast accumulations haven't really changed much, most of the mountains should see a trace to 2 inches mainly during the late night hours. The Park Range may see greater accumulations due to better moisture and orographic forcing, generally 2 to 4 inches but 6 to 8 inches possible for the higher peaks. There will be strong southwesterly flow aloft tomorrow as the upper low moves across the central Rocky Mountains near the Wyoming-Colorado border with 100 knot jet winds embedded on its southern side. Temperatures will be much cooler, a few degrees below normal for most of the area. Highs should be in the upper 50s to mid 60s across the lower elevations and 30s and 40s in the high country. There will be a breezy northwesterly to westerly flow across northeast Colorado through the afternoon, with peak gusts reaching 30 to 35 mph in many areas. Showers should increase again Tuesday afternoon, though synoptic scale ascent will start to gradually turn to subsidence as the low moves away to the northeast. Warm downsloping winds should keep the lower elevations mostly dry, except for some isolated rain showers along the Wyoming border. Snowfall will again favor the northern Front Range Mountains and the Park Range, elsewhere accumulations should again be fairly light. .LONG TERM...(Tuesday night through Monday) Issued at 242 PM MDT Mon Oct 18 2021 A cut off trough will be departing our forecast area Tuesday evening. There will be just enough low level moisture left over for a few snow showers to continue across the western slopes of the mountains. Across the northeastern plains, there will be good lapse rates and decent QG ascent which may allow for a couple rain showers to form mainly north of a line from Greeley to Akron. By midnight, the trough will have moved far enough east to essentially end the chance of precipitation in our CWA. There will be some gusty winds across the mountains and northern plains overnight as gusts could reach 30-35 mph. Ridging will develop over the Intermountain West on Wednesday that will last through the beginning of the weekend. There will be a stretch of dry weather with temperatures warming from near normal Wednesday to 5 to 10 degrees above normal Thursday through Saturday. Winds will not be very strong during this period but the dry air will create a few pockets of elevated fire danger across the plains. The upper level flow will become more zonal Saturday night into Sunday as a very weak shortwave trough moves across. There will be very limited moisture with this system and almost no QG ascent so very little, if any, precipitation is expected. By next Monday, a strong trough will move ashore on the California coast and make its way into the Great Basin. Meanwhile, a strong and broad ridge will develop over the eastern two-thirds of the US. For being so far out, there is decent agreement amongst the global ensembles that our forecast area will see strong southwesterly flow in-between these features. This is a classic pattern for high fire danger to develop in our CWA. This period will also see well above normal temperatures. Eventually, the trough will move across our forecast area during the middle of next week bringing a chance of precipitation and lower temperatures. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 615 PM MDT Mon Oct 18 2021 VFR conditions expected to continue through the TAF period. Winds become south to southwest this evening and will remain gusty into the morning hours. The overnight period will be quiet and dry with scattered mid to upper clouds. Similar conditions will persist into Tuesday, as it will be gusty and dry. Most models indicate a period of gusty westerly winds late morning into early afternoon Tuesday with gusts up to 30 kts possible and perhaps slightly higher closer to the Front Range. Confidence decreases with respect to the late afternoon wind pattern with a split in solutions towards either a NW or NNE wind regime. Higher-res guidance indicates a northerly push as a anticyclonic circulation sets up. Timing of this is uncertain, but likely in that 20-00z timeframe. && .FIRE WEATHER... Issued at 242 PM MDT Mon Oct 18 2021 Fire danger will decrease this evening as temperatures fall and humidity improves, though breezy winds are expected to persist through the evening. Tomorrow, there will be elevated fire danger on the plains southeast of the Palmer Divide in the afternoon again as low humidity in the 15 to 20 percent range for a few hours is coincident with persistent breezy winds gusting near 30 mph. Critical fire weather conditions are likely for localized areas and possible for the wider zone if humidity falls lower than forecast. We have maintained the Fire Weather Watch in effect for southern Lincoln County Tuesday from noon through 6 pm. Fire danger will decrease through the evening as humidity improves and winds relax. && .BOU WATCHES/WARNINGS/ADVISORIES... Fire Weather Watch Tuesday afternoon for COZ247. && $$ UPDATE...Mensch SHORT TERM...EJD LONG TERM...Danielson AVIATION...Mensch FIRE WEATHER...EJD