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812 FXUS65 KBOU 311817 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1217 PM MDT Fri Jul 31 2026 .KEY MESSAGES... - Isolated thunderstorms possible in the afternoon. A few storms could become severe, with strong outflow winds and hail as the main threats. - Heat returns by the weekend, with temperatures reaching up to the 100s on Sunday and Monday. - Heat Advisory for the Urban Corridor and Greeley Sunday afternoon. && .DISCUSSION /Through Thursday/... Issued at 239 AM MDT Fri Jul 31 2026 Current nighttime microphysics RGB satellite product shows low stratus clouds in Nebraska trekking southwest. Guidance does keep the stratus deck from entering Colorado (besides possibly the far northeastern plains) this morning, which will help build a favorable set-up for today`s thunderstorm potential. Isolated showers and thunderstorms are possible this afternoon, with convection initiating in the mountains by late morning/early afternoon before spilling onto the adjacent plains through the early evening. Modeled Skew-T soundings show steep low and mid- level lapse rates, with DCAPE values of 1300-1600 J/kg. This would favor strong-to-severe outflow winds up to 60 mph, particularly for the southern I-25 Corridor and Palmer Divide area where instability will be best. SPC has a Marginal Risk (1/5) for severe storms for that area today. However, any strong storm that develops over the plains has the potential for strong outflow winds as well. While confidence is low, there is also an isolated hail threat with the strongest storms today. One hindrance to today`s storms would be near-surface smoke from wildfires in the northwestern United States. If smoke is able to advect into the plains this afternoon, it could act as a cap for storm development. The upper level ridge will likely restrengthen over the Four Corners region by this weekend, which will bring the return of drier and warmer conditions. Ensemble guidance continues to indicate temperatures reaching near or over 100 F for the Urban Corridor by Sunday. With Heat Risk expecting to get up to 3 (correlating to High Risk for much of the population, especially those sensitive and without effective cooling) have opted in to issue a Heat Advisory for much of the Urban Corridor and the adjacent northern plains (including Greeley where temperatures could reach up to 105 F). Monday will likely see similar temperatures and an additional Heat Advisory may be needed in the next forecast package. We will likely see a reprieve of hot temperatures by Tuesday, as an upper level trough is progged to trek north of Colorado. Ensemble solutions favor temperatures in the mid-to-high 80s for much of the plains. We could also see scattered showers and thunderstorms by midweek, however ensemble guidance does not seem too optimistic about widespread measurable rainfall. Temperatures should climb back to the mid 90s towards the end of the week. && .AVIATION /18Z TAFS through 18Z Saturday/... Issued at 1215 PM MDT Fri Jul 31 2026 Current observations show winds transitioning out of variable and becoming light (< 10 KT) northeast over the Denver metro area. Winds will remain light NE-E through the afternoon until storms begin to develop near the airports at around 20Z-21Z. We have kept the PROB30 for -TSRA for the three airports until 01Z-02Z. However, shower and thunderstorm coverage will be isolated in nature with the primary concerns being lightning and gusty outflows up to 45KT. Winds will return to the usual drainage S/SW drainage flow by 06Z tonight before turning light and variable by mid morning. Model guidance continues to suggest an increase in smoke concentrations from the wildfires in the Pacific Northwest for this afternoon, likely between 21Z and 03Z. Smoke concentrations may increase again for a brief period around 15Z tomorrow morning due to light northerly surface winds. && .BOU WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon Sunday to 9 PM MDT Monday for COZ038>043. && $$ DISCUSSION...MAI AVIATION...AA