446 FXUS65 KBYZ 211700 AFDBYZ Area Forecast Discussion...Updated National Weather Service Billings MT 1100 AM MDT Mon Jul 21 2025 .KEY MESSAGES... - Scattered afternoon and evening showers and thunderstorms today. Some storms could become severe and produce large hail, strong winds, and heavy rain. - Cooler temperatures (70s and 80s) Tuesday and Wednesday with continued daily chances of showers and thunderstorms. A few thunderstorms could become strong to severe over portions of the area both days. - More typical July weather (warmer and drier) looks to return for Thursday into the weekend. && .UPDATE... Satellite and webcams showed the stratus and fog over southeast MT slowly dissipating this morning. Mid clouds, and light showers/virga were moving in from the southwest ahead of expected convection later today. Diffluent southwest flow over the region will allow the development of showers and thunderstorms, some of them strong to severe this afternoon and evening. Have updated PoPs through tonight to account for latest trends and hi-res guidance. The SPC has expanded the slight risk a bit farther into the southeast for this afternoon and evening, but large hail and strong wind gusts remain the main threats. Keep weather aware if you have any outdoor plans later this afternoon and evening. STP && .DISCUSSION... Today through Tuesday Night... Satellite imagery early this morning shows an area of stratus/fog developing over far south-eastern Montana and northern Wyoming. At this time, observations and webcams indicate most of this is stratus, but as we cool a few more degrees through the early morning hours, additional patchy to areas of fog could develop over the areas mentioned above. After sunrise, expect the stratus/fog to dissipate. Temperatures today will warm into the 80s to lower 90s. By this afternoon and evening, another round of scattered showers and thunderstorms is expected as the flow aloft becomes increasingly diffluent out of the southwest. With good instability (CAPE values around 1000 to 2000 J/kg), deep layer shear (35 to 50 knots), and atmospheric moisture (dew points in the 50s to lower 60s with precipitable water values generally over 1 inch), some thunderstorms could become strong to severe today. With any strong to severe thunderstorm that develops, large hail, strong winds, and heavy rain are the main threats. At this time, the risk for severe weather is greatest over the plains of central and eastern Montana. As far as timing goes, storms look to initiate over/near the mountains early this afternoon before moving northeast over the plains through the afternoon and evening. By late this evening, the severe threat looks to come to an end. As higher pressure and cooler temperatures move into the region tonight, more widespread low clouds and/or fog is possible across much of the area. With this, a few sprinkles are also possible. Tuesday will be a cooler day with highs in the 70s and 80s. With the passage of another shortwave trough and associated cold front, scattered showers and thunderstorms are expected once again during the afternoon and evening, lasting into the night. With good instability (CAPE values around 750 to 1500 J/kg), deep layer shear (35 to 50 knots), and atmospheric moisture (dew points in the 50s to lower 60s with precipitable water values over 1 inch), a few thunderstorms could become strong to severe. With any strong to severe thunderstorms that develops, hail, strong winds, and heavy rain are the main threats once again. Arends Wednesday through Sunday... Low amplitude upper trough tracks across region Wednesday resulting in another round of late day convection and below normal temps over our region. Instability will be a little subdued compared to the earlier days in the week, but a few strong thunderstorms are still possible. Showers associated with this system will dissipate early Thursday morning. Heavy rain is still possible under any stronger thunderstorms given PWATs >1.00 inches from our central to eastern zones. Chance for at least a quarter inch of rain Wednesday ranges from 10% in the west to 50% in the southeast corner of Montana. West to Southwest mid level flow will generally prevail Thursday into the weekend with an influx of drier air...and corresponding decrease in PoPs and less coverage of measurable rainfall, while temps rebound above normal. Temperatures Wednesday will be cooler than normal with highs forecast to be in the upper 70s to lower 80s. Temperatures will gradually trend warmer reaching the mid 90s by the weekend. BT && .AVIATION... Stratus will continue to dissipate over southeast MT this morning. Another round of showers and thunderstorms is expected this afternoon and evening. Some thunderstorms could become severe and produce large hail, erratic winds, and heavy rain. The heavy rain could cause reductions to MVFR or IFR at times. All TAF sites are at risk of TS impacts. Arends/STP && .PRELIMINARY POINT TEMP/POPS... Tdy Tue Wed Thu Fri Sat Sun ------------------------------------------------------- BIL 087 061/083 060/080 058/088 061/093 062/093 062/093 3/T 45/T 64/T 21/U 11/U 11/U 10/U LVM 085 052/081 052/081 049/087 053/090 054/091 053/091 5/T 56/T 54/T 11/U 11/U 11/U 11/U HDN 091 060/084 059/081 056/088 057/093 060/094 061/094 3/T 33/T 74/T 41/U 21/U 11/U 10/U MLS 090 063/084 061/081 059/089 062/094 064/096 064/094 2/T 62/T 63/T 41/U 21/U 11/U 11/U 4BQ 092 066/085 063/080 059/085 062/090 064/093 064/093 3/T 42/T 73/T 61/U 21/U 11/U 11/U BHK 086 061/081 058/078 056/084 058/090 061/090 061/089 2/T 62/T 63/T 51/U 21/U 11/U 21/B SHR 092 057/085 056/081 054/086 055/090 057/093 058/092 3/T 23/T 55/T 52/T 21/U 11/U 10/U && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...None. WY...None. && $$ weather.gov/billings