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394 FXUS65 KBOU 202007 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 207 PM MDT Mon Jul 20 2026 .KEY MESSAGES... - Storm coverage and intensity increases through Wednesday and Thursday as monsoonal moisture moves into the region. Storms from Tuesday onward will be capable of producing locally heavy rainfall, and some threat of flash flooding. - Hottest day of the summer today, then just slight cooling through Thursday. Return to hot weather is likely this coming weekend. - Storm coverage expected to decrease again by Friday into this upcoming weekend, although mountain areas should see at least scattered storm coverage each afternoon and evening. && .DISCUSSION /Through Monday/... Issued at 206 PM MDT Mon Jul 20 2026 Temperatures have soared early today with weak inversions and further warming aloft. We`ll be pushing 100F or a bit more across most of the plains and I-25 Corridor through late this afternoon, before finally some slight relief arrives over the next few days. The Heat Advisory for the I-25 Urban Corridor through Weld county will be allowed to expire at 9 pm this evening. Scattered storms were developing in the northern mountains as expected this afternoon. While the majority of the storms stay in the high country, isolated high based convection with gusty winds and light rain may also spill onto the plains into this evening as the hot temperatures help break the cap. For Tuesday, the upper level high directly overhead will elongate and shift to the southeast. This will allow for a slight bump in monsoonal moisture as flow aloft turns light southerly. The moisture bump would be much greater, however, if it wasn`t for the current dry punch into southern Colorado seen in the waver vapor imagery. A "cool" front will back into Colorado late tonight and early Tuesday morning. This will support a slight increase of low level moisture over the plains as well. Precipitable water (PW) values still increase to 150-175% of normal over the higher terrain, so locally heavy rainfall will be possible. The main threat of any flooding would be over the most severe portions of the 2020 burn scars and the 2024 Alexander burn scar, given an inch of rain would be possible in 30 minutes from the strongest storms. The best chance of storms on the plains would be late in the day and especially in the evening as east/southeast low level flow continues to support low level moisture advection into slow moving storms. Given the very warm temperatures, these will likely be outflow dominated so any heavier rain may be relatively short- lived, but there is an opportunity for more balanced storms and locally heavy rain especially if they persist later into the evening. The greatest risk for locally heavy rainfall and any threat of flash flooding will enter the picture for Wednesday and Thursday. PW values are still forecast to reach the daily maxes for this time of year, with ensemble averages generally pointing to 1.3-1.4 inches along the I-25 Corridor, and 150-200% above normal across the entire forecast area. That`s the common ingredient for heavy rainfall potential for both days, but each day will also have their own characteristics that may be more/less favorable for heavy rain. On Wednesday, we`ll have very slow storm motions, but rather shallow warm cloud depth less than 3,000 feet. On Thursday, warm cloud depths are forecast to increase to ~5,000 feet, but storm motions will also be faster as mean wind/storm motions are forecast to increase to 20-25 mph. At the same time, instability grows slightly on Thursday so storms may be more organized and intense (heavy rain but not much hail). We`ll also have to watch the timing of a shortwave expected for Thursday. The GFS remains slightly faster, while the EC is slightly slower and would be favorably timed with peak daytime heating and convection. Whatever the case, both days would at least have a couple ingredients favorable for flash flooding, so we`ll monitor that closely over the next couple days before issuing any Flood Watches for flash flooding. Looking ahead to Friday and the weekend, there is more agreement now that we`ll be drying and stabilizing. This would focus mostly on the plains with less storm coverage (mainly isolated near the higher terrain), while mountain areas should be able to hold onto more moisture and instability under the ridge. After a brief respite from the heat and near normal temperatures Thursday, hot weather will likely return with highs pushing back to the 95-100 degree range across the plains and I-25 Corridor, with potentially another Heat Advisory by next Sunday. && .AVIATION /18Z TAFS through 18Z Tuesday/... Issued at 1138 AM MDT Mon Jul 20 2026 VFR conditions expected through the TAF period. Easterly winds are currently setting in place at all terminals and will likely continue throughout the afternoon before shifting more southeast. With the plume of the monsoon moisture slowly shifting east into Colorado, there are increasing chances for showers along the I-25 Corridor late this afternoon/evening. However, there is high uncertainty with exactly where the showers will occur. For this reason have kept the PROB30 in the TAF. Most likely, all airports would see gusty outflow winds from surrounding showers, rather than any showers impacting the terminals. PROB30 currently ends at 04Z, however there could be gusty outflows through 06Z. Drainage flow expected overnight. A `cool` front will arrive sometime between 10Z-14Z which will bring northerly winds, with speeds generally between 10-15 kts. Another round of showers and thunderstorms are possible tomorrow, however models indicate another late show (starting as early as 23Z) so have kept it out of the TAF for now. Will likely need to introduce a PROB30 in the next TAF issuance. && .BOU WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 9 PM MDT this evening for COZ038>040-043. && $$ DISCUSSION...Barjenbruch AVIATION...MAI