Area Forecast Discussion
Issued by NWS Billings, MT
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Issued by NWS Billings, MT
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-- Discussion containing changed information from previous version are highlighted. --824 FXUS65 KBYZ 070920 AFDBYZ Area Forecast Discussion National Weather Service Billings MT 320 AM MDT Tue May 7 2024 .DISCUSSION...-- Changed Discussion --Today through Wednesday... Dynamic upper low continues to spin over northwestern South Dakota at this time. Spokes of precipitation were continuously rotating into eastern counties with some isolated lightning while a large band of precipitation was located from the Snowies southeast to the SE corner of Big Horn County. In the meantime...areas of wind continued with the highest gust overnight at Alzada (59 mph). Snow has let up in the Big Horns and the Winter Weather Advisory there was allowed to expire. Ensemble means from the GFS and EC both now generally show the 500 mb low wobbling/spinning over the western Dakotas into tonight. Analysis indicated 700 mb frontogenesis was generating the larger precipitation band across our central zones...a little further west than model proggs had placed it. We have adjusted POPs and QPF for this for the rest of tonight into Tuesday. Generally, more of the same today with considerable precipitation mainly east of Yellowstone county where some areas could see an additional 0.50 or more of liquid today (probability 40-70% in parts of Custer and Rosebud counties) where large scale ascent and trowal effects are strongest. The western areas will see primarily wind again today with gusts 50-65 mph common as a powerful 700 mb wind corridor stretches from Wheatland county to SE MT. Strong winds could also impact areas in the east with local gusts over 50 mph due to the strong pressure gradient associated with the surface low. The 700 mb jet gradually weakens tonight as the upper low slowly fills and begins to drift south. So look for those strong winds to continue into this evening before gradually weakening tonight. No changes to the High Wind Warning thats in place for much of the CWA. As the upper low drifts south tonight into Wednesday the better ascent and frontogenesis will sink south and be aided by low to mid level flow turning more northerly (upslope). Thus, the more efficient precipitation production will shift to areas over and near the north facing slopes of the mountains. Models are suggesting heavy snow along the north/northwest facing slopes with snow levels near 5000 ft tonight as it starts...and climbing Wednesday to around 6500 ft. The snow will continue into Wednesday night and early Thursday. Totals may range well over a foot of snow above 6500 feet by Thu morning in both the northern Big Horns/Beartooths (chance of over a foot of snow as high as 70-90%). Thus we have issued a Winter Storm Watch for the mountains from midnight tonight through Thursday morning. Please see extended discussion below. Highs will be in the mid 40s to lower 50s the next couple of days. Overnight lows in the mid to upper 30s. BT Wednesday night through Tuesday... .KEY MESSAGES... - Precipitation comes to an end Thursday afternoon into evening - Heavy snowfall for the Bighorn and Beartooth mountains. Winter storm watch has been issued - Friday through early next week will be pleasant with temperatures in the 70s with dry conditions Wednesday night into Thursday will see continued precipitation across the region, though with decreasing intensity. WPC clusters show a secondary low spinning of to the west of the main low. The stronger this low is and the farther to the west is stretches, the higher precipitation totals we will see Thursday. This higher precipitation scenario would bring 0.25-0.5 inches of precipitation across much of our west, especially the higher terrain, though this is only favored by 10% of members. The majority of members (90%) have less than 0.25 for this time frame. There is good model agreement that precipitation will come to an end Thursday afternoon into evening. As the low pressure system wraps around and brings moisture, the Bighorn and Beartooth mountains will see heavy snow. 700mb winds will be out of the north leading to north facing slopes being favored for the heaviest snowfall. Currently, these north facing slopes have a 70-90% chance of getting over 1 foot of snow. Snow will start this evening and continue until Thursday afternoon. Breezy to windy conditions may continue Wednesday evening, decreasing throughout the night which will bring calm winds by Thursday morning for the first time in a while. This is reflected in the ECMWF EFI tables which have no significant wind signal for Thursday. Thursday will see a decent pressure gradient set up over the eastern portion of the CWA. This combined with low level lapse rates conducive to mix down, will lead to the return of gusty conditions to locations such as Miles City and Baker where winds could gust into the 20s kts. Friday, there will be a wave moving down from the north which ensemble clusters are agreeing could once again bring breezy conditions to our eastern areas. The farther west this wave is the farther west the strong winds will move impacting more of the region. 30% of models have winds gusting into the 30s as far west as Forsyth. Currently, only areas along the Dakotas border have a chance (20%) of getting a wind gust over 40mph Friday. Friday through the weekend will see ridging return to the region with westerly downsloping on Monday. This will bring the return of temperatures in the 70s with dry conditions. Torgerson-- End Changed Discussion --&& .AVIATION...-- Changed Discussion --Showers and thunderstorms will continue to impact the region over the next 24 hours. Before 21Z today the precipitation will mainly be from Billings and locations to the east. After that the precipitation will pivot and start to impact western areas as well. Winds will remain strong across the region today with widespread gusts in the 40s kts with locations in the western gap areas (K6SO, KLVM, K1KM) seeing gusts into the 50s kts. Tonight around 06Z winds will begin to decrease mainly in our northeast (KMLS, KBHK) while still remaining breezy with gusts in the 20s kts. Torgerson-- End Changed Discussion --&& .PRELIMINARY POINT TEMP/POPS...-- Changed Discussion --Tdy Wed Thu Fri Sat Sun Mon ------------------------------------------------------- BIL 050 039/051 043/060 042/069 045/076 048/079 050/078 4/R 99/R 97/R 11/U 00/U 01/U 12/T LVM 049 036/046 039/056 036/066 040/072 044/075 046/075 3/R 89/O 94/R 10/U 00/U 01/U 12/T HDN 049 037/053 042/062 040/069 040/076 045/080 047/078 9/R 99/R +8/R 21/B 00/U 11/U 12/T MLS 045 039/055 042/062 043/067 044/075 047/078 049/077 9/T 85/R 65/R 11/U 00/U 01/U 11/U 4BQ 044 037/051 040/059 043/064 041/074 046/077 049/077 9/R 76/R 86/R 21/B 00/U 01/U 11/U BHK 047 036/054 037/063 040/065 040/073 044/075 046/075 9/T 75/R 43/R 11/B 01/U 01/U 11/U SHR 052 036/047 038/057 036/064 037/072 042/076 045/075 2/R 58/R +7/R 21/U 01/U 01/U 22/T-- End Changed Discussion --&& .BYZ WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --MT...High Wind Warning remains in effect until midnight MDT tonight FOR ZONES 29>32-34-42-57-138-170-173-235. High Wind Warning remains in effect until 6 PM MDT this evening FOR ZONES 36-37-58. High Wind Warning remains in effect until 6 AM MDT Wednesday FOR ZONES 63-65-66-141-172-228. Winter Storm Watch in effect from late tonight through Thursday morning FOR ZONES 67-68-171. WY...High Wind Warning remains in effect until midnight MDT tonight FOR ZONE 199. Winter Storm Watch in effect from late tonight through Thursday morning FOR ZONE 198.-- End Changed Discussion --&& $$ weather.gov/billings