FXUS65 KBYZ 200656 AFDBYZ Area Forecast Discussion National Weather Service Billings MT 1256 AM MDT Wed May 20 2026 .KEY MESSAGES... - Scattered showers and thunderstorms this afternoon and evening; main risks are small hail, erratic wind gusts and localized moderate rainfall. - Cool and wet weather system brings widespread rain and snow in the mountains above 7000 feet, tonight through Thursday. - Over a half inch of precip is expected along southern mountains and foothills (>75% chance). North aspects of southern mountains will see 6" or more of snowfall (80% chance). The opening of the Beartooth Highway on Friday may be impacted. - Warming trend Friday through early next week. && .DISCUSSION... Through next Tuesday... Water vapor imagery shows a distinct shortwave dropping thru BC/AB in northerly flow aloft, downstream of a strong upper level ridge off the Pacific coast. This wave is expected to form a weak mid level low as it reaches southern AB tomorrow, and is our primary weather-maker over the next 36hrs. This begins with increased t-storm potential this afternoon and evening, with high res models suggesting development beginning in our W/NW around noon (early start per the increasing synoptic scale ascent). Instability is very modest (100-400 j/kg) but the tall/skinny cape w/ relatively low freezing levels should support small hail, along with erratic wind gusts and localized moderate rainfall. Heads up to those w/ outdoor plans in the evening. A cold front arrives from the north in the late afternoon (pre- frontal temps should reach the 60s to low 70s) and the diurnal convection will evolve to a precip event tonight thru Thursday. As energy digs thru western MT into southeast ID, upslope N=NE winds will deepen and thus precip will become most widespread over our southern upslope areas, gradually shifting eastward thru the day tomorrow. Chances of at least 0.50" of rain are high in these upslope areas (>75%) but even Billings-Hardin could see a half inch (50% chance). Lesser amounts will fall over the north and east of Rosebud County (0.05-0.25"). Will need to monitor for a potential axis of enhanced frontogenesis as the trof pivots to our west, which along with the upsloping could produce over an inch of precip on the north aspects of the Beartooths/Pryors/northern Bighorns...and among these areas latest models show western Big Horn County has the greatest potential. In addition to the precip, snow will fall above 7kft with several inches of accumulation in the aforementioned upslope areas. The Beartooth Hwy is scheduled to open Friday but there may be some plowing needed first. Lower elevation high temps Thursday will be cool (upper 40s and 50s) but expect a return to the 60s Friday as the system exits and is replaced by rising heights. One final note, as the synoptic forcing shifts east Thursday there should be enough instability for the development of scattered diurnal showers on the back side of the trof. Friday through the weekend will trend warmer and be mostly dry, but there may be enough weak shortwave activity thru the backed zonal flow for isolated diurnal convection, at least over the mountains. Look for temps back to the 70s Saturday and into the low-mid 80s Sunday. The first half of next week will see the next Pacific trof begin to move inland in some fashion. Cluster analyses show high spread in potential solutions with this trof, ranging from an open wave across the northern Rockies to a deep low forming over the SW CONUS. Impossible to determine at this time, but generally speaking look for a warm start to the next work week (80s) then modest cooling and increasing chances of showers/t-storms per the advancing trof. If another dynamic low forms to our SW/W it may allow for a push of plains moisture and greater instability for potential t-storms. Something to monitor. JKL .AVIATION... VFR will prevail through the first half of today with mid clouds on the increase from an approaching weather system. An associated cold front will drop through the area this afternoon and evening bringing increasing chances for showers and weak thunderstorms. Wind gusts up to 25 kts are possible with the frontal passage, and thunderstorms will be capable of gusty and erratic winds to 30 kts, small hail and brief downpours. MVFR conditions are possible with the showers/thunderstorms, with showers becoming more prominent this evening, spreading east overnight. Mountains will become obscured this afternoon and evening due to rain/snow. STP && .PRELIMINARY POINT TEMP/POPS... Tdy Thu Fri Sat Sun Mon Tue ------------------------------------------------------- BIL 068 043/056 039/069 045/079 051/085 053/089 054/082 4/T +8/T 10/U 00/U 00/U 01/U 12/T LVM 063 036/054 032/067 040/076 046/081 048/084 048/074 4/T +8/T 10/B 00/U 11/U 22/T 15/T HDN 070 041/057 037/071 040/079 046/085 049/089 051/083 2/T 99/T 10/U 00/U 00/U 00/U 12/T MLS 072 044/062 040/069 042/078 048/084 051/090 055/086 2/T 66/W 21/U 00/U 00/U 00/U 11/N 4BQ 071 042/058 040/066 041/076 047/083 051/089 056/086 2/T 26/T 52/W 00/U 00/U 00/U 01/N BHK 072 038/065 038/066 038/076 047/083 050/088 055/086 2/T 36/T 63/W 10/U 00/U 00/U 01/N SHR 067 038/049 033/064 035/073 040/081 043/087 045/082 2/T 2+/T 51/U 01/U 01/U 00/U 02/T && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...None. WY...None. && $$ weather.gov/billings