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509 FXUS65 KBOU 291151 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 551 AM MDT Tue Sep 29 2026 .KEY MESSAGES... - The threat for heavy rainfall will increase late tonight, continuing through early Thursday. The highest chance for the larger rain amounts will be in our southeastern counties. Uncertainty remains in exact amounts. - Flood Watch in effect for the southern Front Range Foothills, Palmer Divide, and Elbert and Lincoln Counties from late tonight through Thursday morning. - Rain chances decrease late Thursday, leading to warmer and drier conditions for the weekend. && .DISCUSSION /Through Monday/... Issued at 1053 PM MDT Mon Sep 28 2026 As of late this evening, the upper level trough is moving through southern California and Hurricane Polo is nearing the west coast of Baja California. The trough will slowly makes its way across the southeast U.S., eventually absorbing the remnants of Polo on Tuesday. Moisture ahead of and with this system is anomalously high, leading to rain chances for the next few days. Tonight, a weak cold front will move through the area bringing northerly winds and more dense low to mid cloud cover. The northerly winds behind the front could provide enough weak upslope flow along the Palmer and southern Foothills for some light showers throughout the day Tuesday. Temperatures will be slightly cooler behind the front, with temps dropping into the 60s for much of the plains. The main concern for this forecast will be the late Tuesday through mid Thursday time period. The upper level low is forecast to move just south of the four corners region early Wednesday. At the surface a low is forecast to develop just ahead of the trough somewhere in New Mexico. The path of this low is one of the main differences between models, with some taking it northeast into the Texas Panhandle and others take it more north into southeastern Colorado. The location of this low will be very important for our rain chances. If the low tracks closer to the area, our chances for more widespread precip will increase as well as the potential for higher rain totals. If the low tracks more towards the Texas Panhandle and Oklahoma, the larger precip amounts will likely miss our area. I will say, higher resolution models are leaning more towards the surface low moving into southeastern Colorado, which increases our confidence in the higher precip amounts for our southern most counties. However, the northward extent of the heavier rainfall is still very uncertain. Right now, it looks like that northward extent of heavier precip could sit somewhere near Denver, which unfortunately means that the metro is one the area with the highest uncertainty for rain totals. We are starting to get increasingly concerned about the Palmer Divide area in terms of the higher rain totals. If the low does end up moving over SE Colorado, strong northerly winds could provide decent upslope along the Palmer and southern Foothills, which could nudge it towards those higher precip amounts. Because of this we did extend the Flood Watch to include the southern foothills zone. I did consider adding Arapahoe county and Washington county to the Watch as well, but we will wait until confidence increases in the northward extent of the higher rain totals. Areas within the watch are expected to see rainfall totals around 1.5 to 3 inches, with the potential for some areas to see 4+ inches. As of the latest model runs, Denver is sitting at a 50% to 60% chance of seeing at least 1 inch of rain late Tuesday through Thursday, which is slightly higher than what we were seeing yesterday. Snow chances in the higher terrain will peak early Thursday morning as temperatures finally start to cool more aloft. Amounts are still forecast to be on the lower end (a couple inches at most), with snow levels generally around 11,000ft. Rain chances will start to taper off on Thursday as this system moves off to the east. Behind the trough, we`ll see weak ridging start to build over the area this weekend, leading to drier and warmer conditions. Models are showing a cold front moving through the area on Saturday, keeping temperatures slightly cooler and closer to normal for Sunday. && .AVIATION /12Z TAFS through 12Z Wednesday/... Issued at 545 AM MDT Tue Sep 29 2026 Lower ceilings are approaching the terminals from the north along with a shift to northerly winds. KLMO and KFNL are reporting ceilings of ~7000-8000 ft AGL at this hour. The main issue during this TAF period continues to be the ceilings. Once this front pushes through over the next couple of hours, we expect low status for much of the day. KAPA and KBJC look to have the lowest ceilings- approaching 4000 ft AGL. KDEN should see ceilings drop to ~6000 ft AGL this morning and through the early afternoon. We expect ceilings to lower even a bit further for the late evening into Wednesday morning. Winds should stay with a northerly component for most of the day today. Short-term models continue to show little to no rainfall today. Shower chances will only be around 10-20% this afternoon and evening. These solutions seem reasonable given SW flow aloft. Meaningful rain chances start to enter the picture ~8-10z tomorrow morning from south to north. We opted to prevail -SHRA starting at 11z for KDEN, but this timing and/or intensity could need to be adjusted in future updates. Any rain shower could lower ceilings (~2000 ft AGL) and/or visibility (~5 SM), especially with the steadier rainfall expected after 11z. KAPA appears to be the most favored terminal for rainfall on Wednesday. && .BOU WATCHES/WARNINGS/ADVISORIES... Flood Watch from late tonight through Thursday morning for COZ036-041-046-047. && $$ DISCUSSION...AP AVIATION...MV