Area Forecast Discussion
Issued by NWS Billings, MT
Issued by NWS Billings, MT
353 FXUS65 KBYZ 200901 AFDBYZ Area Forecast Discussion National Weather Service Billings MT 301 AM MDT Mon May 20 2024 .DISCUSSION... Monday through Tuesday night... Synoptic Pattern...Upper level low currently over central Idaho will drop into SE Idaho by early evening, then swing east across Wyoming Tuesday before moving into Tuesday night as it opens up and fills. The latest track of this system is a bit further to the north than yesterdays iteration, moving from Rexburg Idaho to halfway between Buffalo and Casper Wyoming and finally into the Rapid City area. Overall this track is favorable for precipitation further north into Montana, and for heavier precipitation along the MT/WY line. QG forcing aloft and H7 frontogenesis increase over western zones this morning and spread east as far as Powder River county this afternoon, working across the rest of the forecast area tonight into Tuesday morning. Low level winds trend easterly today, into the approaching system, enhancing upslope lift into north/east facing foothills/mountain slopes. As the system moves south and then southeast of the area Tuesday winds will turn northwesterly diminishing upslope precipitation enhancement by late Tuesday afternoon. Precipitation...Over the next 48 hours the best chances for picking up over a quarter of an inch of precipitation (40+ percent) will be along and south of an I-90/US-212 line. Probabilities of over a half of an inch of precipitation for north and east facing foothills and mountain slopes are over 60 percent including Red Lodge and Sheridan WY. With the northerly shift of the system even areas as far north as Livingston to Billings to Lame Deer are showing over a 20 percent chance for more than half an inch of precipitation. An isolated thunderstorm is possible embedded in the shower activity this afternoon and again Tuesday afternoon with the instability associated with the cold upper level system and modest daytime heating. Snowfall...With the increase in precipitation comes a corresponding increase in snowfall for the southern mountains. Latest snowfall forecasts show up to 8 to 14 inches for the Beartooth mountains (heaviest on north facing slopes above Red Lodge) and 6 to 12 inches for the Bighorn mountains. Locally heavier accumulations are possible where the upslope winds maximize lift. Highlites...Based on the latest snowfall forecasts, we have upgraded to a Winter Storm Warning for the Beartooth/Absaroka mountains for today through Tuesday morning. Also, we posted a Winter Weather Advisory for the the northeast Bighorn and Pryor mountains for tonight through the day Tuesday. Snow accumulations could exceed 12 inches in isolated portions of the Bighorn mountains above 9000 feet near the Johnson/Sheridan county line, but in the area along US-14 and Burgess Junction accumulations should stay under 12 inches. It is not out of the question that an upgrade to a Winter Storm Warning could be needed at some point with this system for the NE Bighorn mountains. Wednesday...A break in precipitation chances develops Tuesday night as the upper low moves away from the area. The next system begins to influence the weather over western zones by Wednesday night. This system is stronger than the Mon-Tue system and has the potential for heavier and more widespread precipitation. At this point the storm track is still uncertain as the 00z models are tracking a bit further south than yesterdays runs, but have also sped up by about 12 hours. The increase in speed is unusual as closed lows tend to slow down in the models over time, so will need to see a bit more consistency before buying into the latest forecast iteration too much. That said the latest track will bring the potential for precipitation spreading across the forecast area Wednesday afternoon through Wednesday night, though the heaviest precipitation looks to arrive during the day on Thursday. Accumulating snow is advertised for area mountains Wednesday night, generally above 7000 feet. Chambers Thursday through Monday... For Thursday into early Friday, models have continued to trend towards bringing the upper low further north across northern Wyoming, which is a favorable setup for precipitation in our region. As a result, potential precip totals have increased, with a 60-80% chance (highest over the west) of at least 0.25" through Friday and a 40-60% chance (highest over the mountains) of at least 0.5". For the mountains, this translates to a 60% chance of at least 6" of snow and a 30-40% chance of 12" or more over the mountains. Friday afternoon into early Saturday, small scale ridging will build in as the low moves out, bringing a brief period of drying. Then, by Saturday evening, another system moves over the region, renewing the daily chance for precipitation to 30-50% for the weekend. To start next week, strong ridging is expected to build in Monday, leading to warmer and drier conditions next week. High temperatures Thursday and Friday will be in the 50s to mid 60s, increasing to mid 60s to mid 70s Saturday due to the brief ridging. Then, highs will drop back into the 60s for Sunday before a warming trend begins Monday, with highs in the mid 60s to low 70s. Archer && .AVIATION... Scattered showers and isolated thunderstorms will develop over the mountains this morning, spreading as far east as KBIL and KSHR by afternoon. Pockets of heavy rain may periodically reduce conditions to MVFR. Expect mountain obscuration. Archer && .PRELIMINARY POINT TEMP/POPS... Tdy Tue Wed Thu Fri Sat Sun ------------------------------------------------------- BIL 059 042/061 042/068 045/057 039/065 044/071 046/067 5/T 65/T 23/R 58/T 64/T 14/T 44/W LVM 053 035/060 037/062 040/051 036/060 041/066 040/062 6/T 65/T 26/T 79/T 63/T 15/T 44/W HDN 061 042/061 038/070 043/061 038/065 041/074 045/069 3/T 55/R 22/R 48/T 74/T 13/T 44/W MLS 062 043/063 041/071 045/063 040/063 043/073 047/067 1/B 12/R 11/B 36/W 74/W 12/W 33/W 4BQ 059 043/059 039/070 045/066 039/063 042/073 047/069 2/R 65/R 21/U 26/T 74/W 11/U 32/W BHK 062 040/062 038/069 043/066 037/060 040/072 045/068 1/E 12/R 11/U 26/T 74/W 11/B 33/W SHR 056 038/053 034/067 039/060 035/063 038/072 043/067 6/T 88/T 42/R 27/T 74/T 12/T 34/W && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...Winter Storm Warning in effect from 6 AM this morning to noon MDT Tuesday FOR ZONE 67. Winter Weather Advisory in effect from 6 PM this evening to 6 PM MDT Tuesday FOR ZONE 171. WY...Winter Weather Advisory in effect from 6 PM this evening to 6 PM MDT Tuesday FOR ZONE 198. && $$ weather.gov/billings