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533 FXUS65 KBOU 210621 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1221 AM MDT Mon Sep 21 2026 .KEY MESSAGES... - Cooler conditions continue Monday, with more limited shower and thunderstorm coverage. - Gradual warming returns Tuesday, with generally isolated precipitation chances each day. && .DISCUSSION /Through Sunday/... Issued at 1215 AM MDT Mon Sep 21 2026 Current radar imagery shows a few strong thunderstorms lingering over Elbert and Lincoln counties as well as a couple of weak showers over the northern Colorado plains. Any storm that is able to strengthen over the next hour or two will be able to produce large hail and torrential rainfall. However, we believe the severe thunderstorm threat to be nearing its end for the night as mesoanalysis shows an overworked atmosphere and decreasing CAPE. Areas of patchy fog will likely develop due to the low level moisture left over from today`s convection and small dewpoint depressions. Monday afternoon looks to be fairly quiet as a weak ridge builds over Colorado and subsidence gives way to mostly sunny skies. Temperatures will remain slightly cooler than normal, with afternoon highs mainly in the low 70s at low elevations, and 50s-60s for the mountains. Model guidance suggests a weak shortwave grazing southeast Colorado Monday night as well as an increase in wind speeds at the 700mb level. Given the slightly above normal moisture already in the environment, few sprinkles over the plains cannot be ruled out late Monday night into Tuesday morning. The upper level ridge tracks east and flow aloft turns southwesterly on Tuesday. At least a few isolated showers seem possible over the high terrain due to the slight uptick in monsoonal moisture, with the plains remaining dry. One point of uncertainty for Tuesday is that model guidance suggests breezy southerly winds over eastern Colorado/western Kansas which could lead to a richer atmosphere for storm development, although instability should remain fairly limited. A disturbance will track north from New Mexico onto Colorado on Wednesday, which will bring a better chance for showers and storms over the eastern Colorado plains in the late afternoon and evening. The mountains will see an increase in shower activity Wednesday afternoon as well, but it remains unclear whether any showers from the foothills would survive and make their way onto the Denver metro or if low level moisture will be transported west enough. Moisture will generally remain above normal through the entire forecast period, and models have been consistent in bringing precipitable water values that are at least 150% of normal to the region Wednesday through Friday. However, given the cooler temperatures expected to be in place, lifting mechanisms will be needed for meaningful rainfall to come to fruition. && .AVIATION /06Z TAFS through 06Z Tuesday/... Issued at 1110 PM MDT Sun Sep 20 2026 VFR conditions are favored to prevail for the majority of the TAF period. We are seeing come patchy CIGS of 050-070, although these should gradually scatter out in the coming hours. With recent precipitation, there`s a slim chance of patchy fog/low stratus early morning, but generally 15% or less, and primarily for KAPA. At this juncture, will continue to exclude from TAFs. Current convective activity should continue to remain due east of the metro, though may clip the 5 mi vicinity of KDEN through 07-08Z. Associated weak outflows look to shift winds briefly to the NE for the first 1-2 hrs of the TAF period, before lighter and more VRB flow settles in. On Monday, expect generally east flow to develop by midday, with a clockwise veering towards drainage flow in the evening. This drainage could be robust for KDEN and possible KAPA, with speeds of 10-15 kts after ~08Z Tue. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...AA AVIATION...BRQ