####018006678#### FXUS65 KBYZ 152057 AFDBYZ Area Forecast Discussion National Weather Service Billings MT 257 PM MDT Thu May 15 2025 .KEY MESSAGES... - Very windy along MT/DK border into Friday. Peak wind gusts of 45 to 55 mph, strongest over the higher hills of far eastern Montana. - Unsettled weather continues through the end of the week. In far eastern Montana, band of moderate rainfall is forecast overnight into Friday. Across the rest of the region, isolated to scattered showers and thundershowers are expected each day. - Another high impact precipitation event over the region is anticipated for the start of next week. - Risk of localized heavy rain and associated flooding late Sunday into Monday, mainly around the Big Horns region. && .DISCUSSION... Through Saturday Night... Strong low pressure system over the Dakotas will continue to influence our eastern CWA through Friday morning. Winds will increase tonight over the MT/Dk border area with gusts 45-55 mph expected, possibly a little higher, thanks to a tightening pressure gradient associated with a deepening surface low over the eastern portion of the Dakotas. However, with upper vertical motion over the area, we think winds will remain under our high wind hi-light criteria. The trough axis will swing around through eastern Montana as well tonight bringing rainfall across our eastern border counties. So a wet/windy ride for our eastern border tonight into early Friday. In the meantime, numerous convective showers will prevail across our west and southern sections through this afternoon, winding down after sunset as instability wanes. Some rumbles of thunder are possible, but CAPE is generally low (100-300 J/kg), so strong thunderstorms are not anticipated. A weak flat upper ridge builds in from the west on Friday as the Dakota upper low slowly slides east. So look for lingering light rain along the eastern border Friday to decrease. Pacific moisture in the westerly mid level flow will move into our west and bring an increasing chance of showers (iso/sct) and isolated thunder by late Friday, especially across our SW mountains (Beartooths/Absarokas). As mid level winds back ot the SW Friday night and 500 mb heights rise a bit, precipitation should die off. Saturday/Saturday night...Split upper trough (northern branch over British Columbia coast, southern branch into Nevada) will develop to our west with southwest flow bringing some moisture and perturbations back across our western CWA with some isolated showers spreading east as well Saturday night. Again, some thunder is possible, but CAPE remains under 500 J/kg and forcing is weak, so no strong thunderstorms are anticipated. Look for overnight lows to generally range from upper 30s to mid 40s the next few nights. We may approach the freezing mark along portions of Fallon and Carter Counties Friday night where a brief light frost cannot be ruled out locally (25% chance of dipping below 32F). Daytime highs will be in the 60s at most locations Friday with some 50s still near the Dakota border. Highs on Saturday will be in the 60s to near 70 degrees. As for impact precipitation...At this time, the forecast for Baker, MT has around an additional 0.70 inches of rain for Baker through Friday morning, but there is still a 25 percent chance that they could see over an inch of rain from this whole event. Luckily, soils are drier in this region at this time, so any rain that falls should not be to much of a problem, even if the high end amounts occur. BT Sunday through Wednesday... Ensembles show the next low moving into the Pacific NW coast early Sunday. Low level easterly flow will aid in beneficial precipitation for the region through Monday night. Uncertainty still remains of the exact track of the low and exact precip amounts. There is a 40-60% chance of at least an inch of precip across the region. With instability present Sunday evening, a few thunderstorms are possible with heavy rainfall being a concern given above average atmospheric moisture and low level easterly flow. Heavy rainfall potential will also lead to concern for continued rises on small streams especially with the recent precip. As for mountain snowfall, snow levels will begin around 8-9,000 ft Sunday evening, dropping to around 7,000 ft Monday morning. There is about a 30-40% chance of at least a foot of snowfall in the Beartooth/Absarokas Sunday through Monday night. Additionally, a tight pressure gradient over eastern MT Sunday will allow for breezy winds over SE MT. Some ensembles are depicting lower heights with some energy moving to the north of us late Tuesday into Wednesday, bringing low to moderate precip chances. High temperatures will be in the 50s and 60s Sunday, cooling to the 50s for Monday with 50s/60s for the remainder of the period. TS && .AVIATION... Scattered showers with a few thunderstorms will persist through through the evening. Erratic winds are possible with any showers and thunderstorms with gusts 40-45 kts. Breezy NW winds will persist into the evening, lasting through the day tomorrow for eastern MT (KMLS, KBHK) with the strongest gusts expected to be around sunrise at 40-45 kts. Isolated showers will redevelop into the afternoon Friday. TS && .PRELIMINARY POINT TEMP/POPS... Fri Sat Sun Mon Tue Wed Thu ----------------------------------------------------------- BIL 044/063 044/067 048/065 045/053 043/063 044/067 045/072 33/W 34/T 28/W 98/W 55/W 54/T 23/W LVM 038/061 039/064 044/056 038/053 039/062 039/066 040/069 33/T 44/T 5+/W 97/W 45/W 54/T 23/T HDN 044/063 043/068 049/070 045/053 042/062 042/067 043/073 22/W 23/W 28/W 99/W 66/W 54/T 33/W MLS 047/062 040/067 047/065 043/052 042/059 042/067 044/072 44/W 12/W 36/W 99/W 75/W 44/W 32/W 4BQ 045/058 039/066 046/066 043/050 042/056 042/064 043/070 33/W 21/B 36/W 99/W 75/W 44/W 22/W BHK 038/054 033/063 039/056 038/051 038/058 039/064 040/069 86/W 20/B 35/W 89/W 75/W 33/W 32/W SHR 040/060 038/067 044/069 040/050 038/058 037/064 038/071 32/W 23/T 28/W 99/W 66/W 55/T 23/T && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...None. WY...None. && $$ weather.gov/billings ####018002281#### FXUS65 KMSO 152059 CCA AFDMSO Area Forecast Discussion...CORRECTED National Weather Service Missoula MT 259 PM MDT Thu May 15 2025 .DISCUSSION... KEY MESSAGES: - Friday morning valley fog, followed by showers. - Mild/dry start Saturday morning then increasing showers. - A very wet Sunday with cold/wet backcountry conditions and mountain pass snow. Showers will linger into this evening before tapering off overnight. Valleys that receive late-day rain and partial clearing may see patchy fog Friday morning. However, the next round of showers and increased cloud cover will quickly arrive Friday morning, with precipitation chances increasing through the day. Model guidance continues to support a cool and wet Sunday as a low pressure system tracks through north-central Idaho and western Montana. Snow levels are now forecast to drop to 4,500–5,500 feet, making slushy accumulations increasingly likely across higher terrain and mountain passes. Expected valley rain (25th–75th percentile) totals have increased to: - 0.30 to 0.80 inch for north-central Idaho and Lemhi County - 0.20 to 0.60 inch for western Montana Slushy snow and lowered visibility may lead to slow travel over passes including Lost Trail, Williams Creek Summit, Bannock, Lemhi, Nez Perce, and Gilmore. Patchy fog is possible again Monday morning, with lingering clouds through the day. A gradual warming trend is expected next week, though unsettled conditions may persist through Tuesday. By mid to late week, a southwest flow pattern brings milder temperatures and potential for spring thunderstorms. An upper ridge is forecast to build next weekend, with the NBM showing a 50–75% chance of highs returning to the 80s. && .AVIATION...Showers taper off overnight, but areas of MVFR to IFR due to patchy valley fog are possible Friday morning, especially where skies partially clear. Expect showers to redevelop in the Camas Prairie, Idaho by daybreak and mid- morning in western Montana, with obscured terrain and occasional MVFR ceilings into the afternoon. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$