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899 FXUS65 KBOU 140544 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1144 PM MDT Sun Sep 13 2026 .KEY MESSAGES... - Isolated to scattered showers overnight, along with a couple thunderstorms in the mountains. - Unsettled pattern this week, but plenty of uncertainty with regard to daily precipitation chances. - Cooler weather arriving for Tuesday. Temperatures average around seasonal normals for latter half of the week. && .DISCUSSION /Through Sunday/... Issued at 252 PM MDT Sun Sep 13 2026 It is mostly sunny across the low elevations of Colorado, and consequently, much warmer that it was around this time yesterday with temperature readings at Denver International Airport in the low 90s. Cloud cover is increasing over the mountains, and a few showers have already developed over the Park and Front Range. Weak upper level ridging moving onto the Northern Plains has begun to turn flow aloft a tad more southwesterly, which will help advect monsoonal moisture into the region. For the rest of the afternoon and evening, scattered showers and thunderstorms will be able to produce gusty winds up to 40-50 mph. The best dry microburst potential will be over the Denver metro and I-25 corridor, where hot afternoon temperatures (low 90s) and surface dewpoints in the 40s will yield DCAPE values 1200-1500 J/kg. Although we expect shower activity over the plains to cease by around 9PM this evening, multiple rounds of showers will continue over the mountains in the overnight hours as mid-level moisture continues to increase. A stray shower over the Denver metro cannot be ruled out Monday morning. However, we do not expect this rainfall to amount to more than a trace. An upper-level trough will track through Montana through the day on Monday, flattening out as it progresses east, and in turn shifting upper-level flow to the west-southwest. Near cross-barrier flow will make for a breezy day in the mountains, with sporadic gusts up to 50 mph over the highest peaks and ridges. Weak downsloping and daytime mixing may also lead to periods of gusty westerly winds (20-30 mph) for the foothills and western Denver metro. Another round of showers will be possible over the east Colorado plains Monday afternoon, between 2pm and 7pm. Uncertainty remains regarding how the synoptic pattern will evolve this week, and thus, how the rainfall chances will play out each day. A cold front will move through the region in the very early morning hours of Tuesday, bringing cooler air and a layer of stratus that will likely persist through most of the day. Temperatures on Tuesday will be cooler than normal, with afternoon highs only reaching into the 70s at low elevations, and 50s-60s for the mountains. Moisture Tuesday afternoon now looks less promising than it did yesterday due to slightly more zonal mid-level flow. However, there will likely still be enough moisture around for scattered showers over the high terrain and some isolated showers over the plains. Weak ridging returns on Wednesday and temperatures will be back to near-seasonal. Although warmer temperatures will lead to better instability for convective development, questions remain regarding how much moisture will be available for the plains. Therefore, the better shower chances will likely reside over the mountains and Palmer Divide. Daily chances for precipitation now appear to continue through the weekend. However, there is considerable uncertainty regarding the development and timing of a few shortwaves Friday through Sunday. Long-range ensembles are trending drier for next week, although precipitable water means will remain near the climatological average. && .AVIATION /06Z TAFS through 06Z Tuesday/... Issued at 1144 PM MDT Sun Sep 13 2026 One last surge of outflow winds had moved through KDEN, which is a brief shift to W-NW and then VRB through 07Z, before settling into fairly normal S-SW winds overnight. For Monday, an upper level disturbance is on track to produce a chance of weak showers in the morning, with the best time frame being 12Z-16Z. Aviation impacts are expected to be minimal with ceilings well above 6000 feet and generally light winds.Confidence is low regarding the wind direction after 16Z Monday. The HRRR model continues to show gusty west winds up to 25 knots while most other models show weak winds with different directions. We think west winds are likely (>70% chance) at least after the passage of the weak disturbance Monday morning, but the direction becomes unclear after 18-20Z. We may just end up VRB so we opted for VRB in the afternoon for now. Also, while the chance of showers is limited due to lack of instability, it will still be quite warm with high DCAPE. As a result, we`ll keep the PROB30 with VRB G30kts in the TAFS for the 21Z-01Z period. Cold front will arrive after 06Z Tuesday, which would bring a low threat (20% chance) of stratus impacts for the Tuesday morning rush. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...AA AVIATION...20