533 FXUS65 KBYZ 120441 AFDBYZ Area Forecast Discussion National Weather Service Billings MT 1041 PM MDT Sun Aug 11 2019 .UPDATE... The Tornado Watch 571 has been cancelled for Rosebud, Treasure, and Big Horn Counties in Montana, and Sheridan County in Wyoming, but remains in effect for CARTER, CUSTER, FALLON, and POWDER RIVER COUNTIES in Montana until Midnight. Gilstad && .SHORT TERM...valid for Mon and Tue... A strong late-season upper low and trough is situated over northern Idaho and western Montana this afternoon. This is resulting in a diffluent southwest flow aloft across south central and southeast Montana and northern Wyoming. A low-level easterly flow continues to keep dewpoints high, especially for this time of year, in the 50s to lower 60s. In addition, soundings show a decent shear profile as a strong jet streak moves overhead. As a result, widespread severe thunderstorms are expected this afternoon through the evening. Large hail and damaging winds will be likely with any thunderstorm through this evening. There is also plenty of moisture in the upper levels so thunderstorms will produce very heavy rain resulting in a flash flood threat. This is more in line with a June pattern than a mid August day. As a result, a severe thunderstorm watch is in effect until 7 PM for Park, Sweet Grass, and Wheatland Counties and a tornado watch until 9 PM for all the remaining counties in our forecast area. Monday and Tuesday will see a dry zonal flow across the forecast area. Winds Monday will be quite gusty from the west and northwest. Temperatures will be cooler Monday with middle 70s to lower 80s with slightly cooler readings on Tuesday. Afternoon humidities will remain fairly high in the 25 to 35 percent range so we are not anticipating any fire weather highlights. Hooley .LONG TERM...valid for Wed...Thu...Fri...Sat...Sun... Broad ridging midweek for mostly dry and seasonable conditions becomes more unsettled by weeks end as upper level low pressure moves into the Pacific Northwest. Does not look to have quite as much moisture associated with it as the previous system with the strongest energy moving northwest of the area. Given the present track looks to be more of a mixing downslope producer with some shower and thunderstorm activity favoring eastern Montana on the eastern side of the surface trough. Not expecting significant moisture through the period with temperatures rising to above normal next weekend. borsum && .AVIATION... Relatively low cloud bases today due to unseasonably high moisture across the region though stratus has eroded. Thunderstorm activity expected through this afternoon and early evening with storms producing hail...heavy rain and large hail. Strongest storms will produce brief IFR conditions. Drying conditions expected by late evening. borsum && .PRELIMINARY POINT TEMP/POPS... Mon Tue Wed Thu Fri Sat Sun ----------------------------------------------------------- BIL 057/082 055/084 057/090 060/088 058/083 056/084 057/088 51/N 00/U 11/U 13/T 53/R 32/T 10/U LVM 048/077 046/081 049/085 051/082 049/076 046/080 048/084 50/N 00/U 11/B 36/T 74/T 31/U 11/U HDN 056/081 052/081 055/089 059/088 057/083 054/083 055/087 61/N 00/U 00/U 12/R 43/R 31/B 10/U MLS 059/078 053/076 054/085 061/086 059/083 056/081 056/086 81/N 10/U 01/B 22/R 43/R 31/B 11/U 4BQ 057/079 053/077 054/085 059/088 057/083 054/081 055/085 71/N 00/U 11/U 12/T 33/R 42/T 21/U BHK 057/076 052/073 051/082 056/084 057/082 054/080 054/083 92/T 10/B 01/U 32/T 42/R 31/B 21/U SHR 053/080 050/081 052/087 056/088 055/083 052/082 052/086 40/U 01/U 11/U 12/R 43/T 42/T 11/U && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...Tornado Watch 571 in effect until midnight MDT tonight FOR ZONES 32-33-36-37. Flash Flood Watch in effect until 6 AM MDT Monday FOR ZONE 37. WY...None. && $$ weather.gov/billings