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FXUS65 KBYZ 270800 AFDBYZ

Area Forecast Discussion National Weather Service Billings MT 200 AM MDT Sat Apr 27 2024

DISCUSSION
Today through Sunday...

Satellite imagery shows an upper low near the 4-corners and an elongated trof axis behind the low extending from southern BC to NV. Deep easterly flow continues to produce some light precip over our far western upslope areas. Dry air/subsidence exist over eastern MT and skies have cleared east of Billings. HRRR is hinting at fog in Fallon & Carter Counties early this morning, and while this is of low confidence, the dewpt depression of only 2F at Baker at 1am gives this some credence, especially as SFC winds will be veering to the northeast.

Focus of precip over the next 24 hours will remain over our far west. Morning precip will be light, but as the upstream trof axis moves slowly to the east and with modest diurnal instability, shower activity will intensify a bit in the afternoon and evening.
Overall, precip amounts should range from 0.10-0.20" at lower elevations to 0.30-0.50" in the mountains. The probability of exceeding a half inch of precip over the high terrain is only 30%.
High elevations will see additional periods of accumulating snowfall, 2-7" today and tonight (mainly above 8kft). Will make no changes to the lingering winter storm warning for the Beartooth- Absaroka and Crazy Mountains, which runs til 6am Sunday.

The easterly flow will shift to westerly tonight as the trof continues to push eastward, and the upper low to our south lifts thru the central plains (i.e. flow thru the northern Rockies becomes zonal). Thus, look for good chances of precip in our west thru tonight, then an eastward shift in shower activity on Sunday as another weak Pacific shortwave moves thru central MT. In terms of t-storms, we are only expecting a few (at most) over/near our southwest mountains this afternoon and again Sunday. There just isn't enough instability (100-200 j/kg of sbcape per HRRR) for much of a risk.

Temperatures will remain seasonable. Look for highs in the upper 50s to mid 60s today and Sunday.

JKL

Sunday evening through Friday...

Models have trended towards a more active and unsettled pattern in the long term forecast. With a wave of energy moving across the state on Monday, precip chances are moderate to high (50-90%) across the area. The mountains and higher elevations will see the higher end of the precip chances, with several inches of accumulations possible through Wednesday. The latest NBM probability of 72 hour snowfall (beginning Monday morning, ending Thursday morning)
exceeding 6 inches, is 60-80% for the Absaroka/Beartooths, 40-60% for the Crazy Mtns, and 25-50% for the Bighorns. As for the lower elevations across the forecast area, precipitation will fall as rain resulting in QPF amounts of 0.1" to 0.4" for the same 72 hour time frame. Wednesday evening into Thursday could potentially see even more precip as some models are showing an upper low over YNP.
As a result, upslope surface flow from the N-E could give the western mountains several more inches of snow. Chances for precip will linger through much of the week with the current forecast depicting 20-40% probabilities.

As a result of continued troughing and waves of energy throughout the week, temperatures have continued to drop in the forecast.
Highs in the 60s to 70F on Monday, dropping into the 50s to 60F Tuesday and Wednesday. A bit of a warmup towards the end of the week with 50s/60s Thursday and Friday.

Lastly, with the wave push Monday into Tuesday, increased winds are anticipated with widespread gusts of 20-40mph possible. The highest gusts are expected to be in the northwestern counties and the far eastern counties.

Matos

AVIATION

Rain showers and mountain snow will remain over the western mountains/foothills today and tonight. Expect local MVFR west of KBIL, and mountains will be mostly obscured. There is a low (20%)
risk of valley fog in far southeast MT thru 15z this morning, possibly impacting KBHK & K97M. JKL

PRELIMINARY POINT TEMP/POPS

Tdy Sun Mon Tue Wed Thu Fri ------------------------------------------------------- BIL 064 043/064 043/066 038/056 034/053 035/059 036/063 1/N 14/W 37/W 73/W 25/W 32/W 14/W LVM 059 039/060 038/059 030/050 028/049 030/056 032/060 6/W 76/T 49/T 74/W 35/W 22/W 25/W HDN 066 041/065 040/069 037/058 034/056 034/060 035/066 1/B 12/W 26/W 83/W 35/W 43/W 23/W MLS 063 038/064 038/068 038/056 035/055 036/059 037/063 0/U 00/B 02/W 73/W 24/W 32/W 12/W 4BQ 061 037/063 038/068 038/058 034/054 035/057 036/063 0/U 00/B 02/W 52/W 23/W 32/W 12/W BHK 059 033/055 032/066 035/053 032/053 032/055 033/060 0/U 01/B 01/U 63/W 23/W 22/W 22/W SHR 062 033/062 037/067 034/057 029/052 031/053 030/061 1/B 03/W 24/W 74/W 35/W 43/W 23/W

BYZ WATCHES/WARNINGS/ADVISORIES
MT...Winter Storm Warning remains in effect until 6 AM MDT Sunday FOR ZONES 67-68.
WY...None.

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