FXUS65 KBOU 201942 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 142 PM MDT Sun Sep 20 2026 .KEY MESSAGES... - A chance for thunderstorms this afternoon through tonight, mainly over the eastern plains. A few strong to severe storms are possible. - Expect cooler conditions linger Monday, with more limited shower and thunderstorm coverage. - Gradual warming returns Tuesday onwards, with generally isolated precipitation chances each day. && .DISCUSSION /Through Sunday/... Issued at 142 PM MDT Sun Sep 20 2026 It has become unstable over the Palmer Divide and eastern plains with SBCAPE of 400-1000 J/kg. This combined with good shear is expected to produce a few strong to severe thunderstorms. Main area of concern is from the Palmer Divide northeast to Akron to Sterling and eastward. Farther west, subsidence is expected to limit convective activity this afternoon, but this may change this evening. Models have been trending towards scattered to numerous thunderstorms developing over southeast Colorado tonight, after sunset. This activity appears to be triggered by the left exit region of a jet streak moving through. The uncertainty in the forecast is how far north the thunderstorms will develop. The 12Z NAMNest and some of the HRRR runs show storms as far north as the Denver metro area in the 02-04Z time frame. Hail will be the main threat given the steep lapse rates and cooler mid level temperatures. The thunderstorms are expected to continue after midnight over southeast Colorado and then exit the state. Weak riding builds over Colorado Monday bringing dry conditions. Temperatures will be a little cooler than what we have recently seen, but they will be near normal with highs in the mid 70s across northeast Colorado. Models show light precipitation forming over the eastern plains (south of I-76) Monday night. Confidence isn't the highest that we will see rain showers or thunderstorms Monday night, but we have enough moisture and instability for them. If we get enough lift, some showers or storms could develop. The models do show an increasing jet over the area. Therefore, we will include some PoPs in the forecast for this.    A closed low will be over southern Nevada on Monday. It weakens and lifts northeast across Utah and Wyoming Tuesday and Tuesday night in the southwest flow aloft. Best lift with this feature is on track to be later on Tuesday with Tuesday evening seeing the best chance for showers/storms. Temperatures warm with highs in the mid 70s to lower 80s.  On Wednesday, temperatures will be a few degrees warmer with highs in the upper 70s to lower 80s. Chances for showers and thunderstorms look low at this time, but they can't be ruled out with slightly above-normal moisture lingering around.  For Thursday through Sunday, an upper level high will be over Texas and northern Mexico with an upper level trough roughly centered over the Pacific Northwest. This will maintain a southwest flow aloft over the Central Rockies. Models hint at some sort of shortwave trough lifting northward out of the subtropics for Thursday. The timing and location of the trough and its associated precipitation are not agreed upon by the models. However, models are starting to show it will be moist with precipitable water values climbing well above normal reaching 130-180 percent of normal and slightly higher on the GFS. Precipitable water values will stay near or slightly above normal Friday through the weekend. Main chance for showers/storms will be over the mountains, but we could see them spread onto the plains if we get a disturbance or two to help with lift. Temperatures during this period are expected to be slightly above normal, with highs in the upper 70s to lower 80s. Temperatures will be closer to normal on the days with more moisture/cloud cover. && .AVIATION /18Z TAFS through 18Z Monday/... Issued at 1108 AM MDT Sun Sep 20 2026 Expect VFR conditions thru the period. Light and variable winds will gradually become NE in the 19z-20z time period. By 01z winds will become more easterly and then turn more SE by 04z. Overnight winds will go light and variable by 08z. There is a very low chc (5%) of an isold shower at APA and DIA between 03z and 06z. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...BM AVIATION...RPK