Area Forecast Discussion
Issued by NWS Billings, MT
Issued by NWS Billings, MT
568 FXUS65 KBYZ 220849 AFDBYZ Area Forecast Discussion National Weather Service Billings MT 249 AM MDT Wed May 22 2024 .DISCUSSION... Today through Thursday night... Deterministic storm tracks have come into good enough agreement to have high confidence in the system bringing widespread moderate to locally heavy rainfall and heavy mountain snow from Wednesday night through Thursday night. Still a big spread on how much precipitation will fall in a given area due to smaller differences in storm track and speed, but even the precipitation reasonable floor is a significant number. Here are the current NBM values for the 25th/75th/Mean and deterministic forecast values. Location Lowest (25%) Highest (75%) Mean NBM Forecast Big Timber 0.69 in 1.45 in 1.10 in 1.13 in Billings 0.62 in 1.63 in 1.16 in 1.34 in Hardin 0.61 in 1.71 in 1.22 in 1.42 in Sheridan 0.40 in 1.39 in 0.96 in 1.17 in Miles City 0.30 in 1.18 in 0.81 in 0.86 in Broadus 0.23 in 0.98 in 0.65 in 1.16 in The forecast values for areas east of Hardin are higher than the mean at this time due to uncertainty on whether the upper low will cut across far SE MT or stay south over NE WY. The Canadian/GFS solutions are further south while the EC cuts the corner. With the GFS/Canadian being ~2/3 of the NBM deterministic, the forecast for these areas is higher than the mean, and in some areas higher than the 75th percentile (in other words, on the high side of available guidance). Snowfall with this system continues to trend higher over area mountains as the storm track has become better defined in a favorable position to generate precipitation in our area. 700 mb temperatures drop to around -8C Thursday as the core of the upper low moves through the area, dropping snow levels down to 5500 feet or so. Dynamic cooling and snowfall rates could push that down to 4000 feet which would bring at least a slight chance for accumulating snow into the higher hills across the area. Current forecast shows 10 to 18 inches being common snow totals across the mountains, with western foothills above 5000 feet (Nye, Red Lodge, Wilsall) in the Trace to 5 inch range. The higher hills over northern Stillwater and Sweet Grass counties are also showing 2 to 5 inches with the aforementioned stronger dynamic cooling where upslope winds are enhanced. The heaviest snowfall/precipitation with this system will start in the west overnight tonight, central and west tomorrow morning, central and east tomorrow afternoo/evening before the system shifts out of the area late Thursday night. Winter Highlites...Upgraded the western mountains to a Winter Storm Warning starting 6pm this evening through Thursday evening. Posted a Winter Storm Watch for the Bighorn and Pryor mountains starting 6am Thursday through 6am Friday. Will likely need additional Winter Weather Advisories for western foothills and valley locations. Will let the next shift take another look at the dynamic cooling influence on the snow levels to make that call. Overall the advisory areas will be mainly for snow on trees/power lines and poor visibility as the roads should stay wet or at worst slushy during this event. Hydrology...Latest stream forecasts not showing a threat for flooding at this time. Cold temperatures aloft should keep the snowpack locked in and the rainfall, while intense for a period of time Thursday, does not look heavy enough to cause any significant flooding issues. That said you can expect ponding of water on roads and in low lying areas, along with rises on small streams and creeks. Those with interests near smaller waterways should move livestock and equipment away from them, as well as out of low lying areas that may hold water as a precaution before precipitation kicks in tonight. Chambers Friday through Wednesday... As the previous system moves out of the region, and shortwave ridging moves in, a slight chance (25-35% over the mountains, 10-20% over the plains) for precipitation will linger into Friday afternoon. Then, Friday evening into early Saturday morning look to remain fairly dry. Energy from the next wave moving into the region is expected to increase the chance of precip for Saturday afternoon through late Sunday. Currently, for locations from Miles City west, there is a 50-60% chance (60-70% over the mountains) of at least 0.25" of precip over the weekend. Mountain snow totals have trended down as the snow level is expected to only briefly drop to 7,000 ft overnight, but otherwise remain above 8,000 ft during the daytime. Currently, there is only around a 20% chance of at least 6" of snow over the mountains. For Monday into midweek, an upper level ridge is expected to build in, bringing mostly dry conditions and a warming trend. Beyond that, the pattern becomes more uncertain, with some models holding on to the ridging and others beginning to move another trough into the region by late Wednesday. Additionally, the models that do bring in a trough vary in strength and placement at this time. High temperatures will be in the mid 60s to low 70s Friday through Saturday, before cooling slightly into the low to mid 60s Sunday. Then, as ridging builds in, highs increase into the 70s Monday and upper 70s to low 80s for Tuesday and Wednesday. Archer && .AVIATION... Showers and isolated thunderstorms will begin to increase late this morning, spreading from west to east through the day and into Thursday morning. Mountains obscurations will also increase. Under pockets of heavy rain, conditions will periodically decrease to MVFR/IFR. Archer && .PRELIMINARY POINT TEMP/POPS... Tdy Thu Fri Sat Sun Mon Tue ------------------------------------------------------- BIL 065 041/049 035/065 042/070 045/063 045/073 048/080 2/R 7+/T 42/R 04/T 66/T 21/U 01/U LVM 059 036/042 033/063 039/064 039/060 039/070 044/079 7/T 9+/T 22/T 17/T 65/R 11/U 01/U HDN 068 041/051 035/067 039/072 044/063 043/073 045/081 2/R 5+/T 61/U 02/T 66/T 31/U 00/U MLS 069 043/054 036/064 041/072 046/064 044/073 047/080 2/R 39/T 62/R 11/B 55/T 31/U 00/U 4BQ 069 042/057 037/064 040/070 044/061 045/071 046/079 1/B 18/T 81/U 01/B 45/T 41/U 00/U BHK 069 041/056 034/062 039/071 043/063 043/070 045/078 1/B 28/R 82/R 01/B 35/T 32/R 10/U SHR 065 038/051 031/062 036/068 041/060 039/070 043/078 1/B 39/T 71/U 01/B 56/T 31/U 00/U && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...Winter Storm Warning in effect from 6 PM this evening to midnight MDT Thursday night FOR ZONES 67-68. Winter Storm Watch in effect from Thursday morning through late Thursday night FOR ZONE 171. WY...Winter Storm Watch in effect from Thursday morning through late Thursday night FOR ZONE 198. && $$ weather.gov/billings