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FXUS65 KBYZ 290258 AFDBYZ

Area Forecast Discussion...Updated National Weather Service Billings MT 858 PM MDT Sun Apr 28 2024

UPDATE

Just a quick update to adjust precipitation chances overnight into tomorrow morning as additional shower activity is expected to develop over the southwest mountains and push northeast overnight. Precipitation amounts will be light (under a tenth of an inch), with snow adding up to less than 4 inches in the highest portions of the Beartooth/Absaroka mountains. Added a mention of fog in for the eastern state line zones. This may be short lived as westerly winds should get in there before sunset which will quickly disperse the low level moisture. Better chances for precipitation arrive for tomorrow afternoon/evening as a stronger disturbance crosses the region. Chambers

DISCUSSION

Tonight through Monday night...

Satellite imagery shows a dynamic low in the central plains and a zonal flow moving thru the PacNW and northern Rockies with embedded weak short waves. The short waves and associated frontogenesis were producing showers over mainly our southern higher terrain (mtns and foothills) today. None of this precip is or will be heavy, and diurnal instability is too bother mentioning "thunder" the rest of the day, though an isolated rumble is not out of the question. Mountains may be picking up a little snow through evening above 8000 ft. Lows tonight will range from lower 30s along the Dakota borders to upper 30s and lower 40s elsewhere.

Westerly downslope winds and pre-frontal warming ahead of a stronger Pacific shortwave will boost temps into the 60-70 degree range for Monday. SW winds will increase (gusts 25-35 mph expected along western foothills). A few showers may spread over our western mountains/foothills and nearby plains in the morning, but the much better chance of showers (30-80%) will be in the afternoon as large scale ascent increases from the west. Dew points in the low-mid 30s will limit instability but sbcapes should reach 100-300 j/kg, so we may see a few weak thundershowers near the front, which isn't expected to reach our west until late afternoon. The cold front/convection combo has the potential to produce gusty winds (up to 45 mph) late in the day, starting in our west of course. Something to watch if you have outdoor plans late Monday afternoon & evening.

Showers will continue to spread east Monday evening with most areas seeing measurable precipitation as favorable jet dynamics target our CWA (Pops from 30% in SE to 90% over mountains and western sections)
After midnight
showers will become less robust and shift east with the better frontogenesis and upper support. While most areas will see precipitation, the chance of seeing a tenth (0.10) of an inch or more of liquid will range from just 10% in the east to 70 percent in the W/NW portions of our CWA for this event.

As for snowfall...snow levels will be over 7500 ft Monday afternoon, falling to about 6500 ft by the end of the event. Our foothills could see some wet snow mixed in, but its more likely only the higher elevations see any snowfall accumulations, generally ranging from 4 to 8 inches over the higher Beartooth peaks.
The Big Horns may see 1 to 4 inches over higher west facing slopes Monday night. BT

Tuesday through Sunday...

For Tuesday, subsidence behind the frontal passage will create dry and windy conditions for the region. Winds in the low/mid levels will mix down, allowing for wind gusts of 35-45 mph Monday night through Tuesday afternoon. The probability of hitting 45 mph is best Tuesday afternoon for north and east of Miles City and along the Dakota borders. PoPs remain limited for the mountains (50%)
with a few inches of snow expected. Wednesday and Thursday, another piece of energy associated with the cyclonic flow to our NE will bring a chance for precip (20-50% chance). More than a quarter inch of rain/SWE is most likely for areas to the west of Billings, especially in the higher terrain. As for mountain snowfall through Friday morning, the Beartooth/Absarokas and Bighorns have about a 40-60% chance of getting 6 inches for the highest peaks with Red Lodge and Story, WY at about a 15% chance.
Ensembles have another piece of energy moving through Friday with possible ridging for the weekend.

High temperatures will be in the 50s through Thursday, 50s/60s Friday-Saturday and 60s/70s Sunday. TS

AVIATION

Isolated to scattered showers will be present through the period.
VFR conditions are expected with MVFR possible under any showers (mainly for KLVM late this evening). Showers will become more widespread tomorrow afternoon and evening moving west to east starting around 21Z and lasting into the overnight. TS/LT

PRELIMINARY POINT TEMP/POPS

Mon Tue Wed Thu Fri Sat Sun ----------------------------------------------------------- BIL 045/066 037/056 035/056 036/057 037/059 036/061 040/071 24/T 72/R 15/O 44/O 24/R 32/R 12/R LVM 038/060 028/049 028/048 030/055 034/055 032/059 038/067 48/T 83/S 36/O 43/O 25/T 22/R 13/R HDN 041/068 037/058 034/058 035/057 034/062 036/064 039/075 33/T 82/R 14/O 55/R 24/R 32/R 11/B MLS 039/066 040/057 035/057 036/055 035/061 036/062 039/072 11/B 71/N 02/R 34/R 12/R 22/R 01/B 4BQ 039/067 040/057 034/058 035/054 033/059 036/059 039/075 01/U 41/N 01/B 34/R 22/R 32/R 00/U BHK 033/066 037/055 032/056 032/052 030/056 031/058 034/068 01/U 42/R 02/R 24/R 12/R 32/R 11/U SHR 037/066 034/056 030/054 031/053 030/059 032/059 036/072 22/R 63/O 24/O 55/O 24/R 32/R 11/B

BYZ WATCHES/WARNINGS/ADVISORIES
MT...None.
WY...None.

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