029
FXUS65 KBYZ 202130
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
330 PM MDT Mon May 20 2024

.DISCUSSION...
Tonight through Tuesday night...

Upper trough from W MT into ID was sending energy NE through the
forecast area this afternoon. Jet energy was also moving through
the trough, contributing to the lift. Best PWATs were in the SE at
.5-.6 inches. Not much CAPE or shear is expected into the evening,
but there were steep lapse rates especially in the W. There have
been some isolated thunderstorms in the W, with scattered showers
W and central moving E.

The upper trough will swing through the area through Tuesday.
PWATs will climb in the SE due to a Gulf fetch, reaching .5-.75
inches. Snow levels remain above 6000` through Tuesday evening.
Mountains still look to receive heavy snowfall, especially the NE
Bighorns where the EFI had .8-.9 in the southern portion of the NE
Bighorns 00z Tue-00Z Wed, showing higher than the model climate
for snowfall. Up to 16 inches are forecast, with highest amounts
in the southern part of the mountains from 00Z tonight through 00Z
Wednesday. Thus have upgraded the Advisory to a Winter Storm
Warning. For the Beartooths/Absarokas, continued the Warning
through 18Z Tuesday with highest amounts expected in the highest
elevations where Beartooth Highway clearing operations were
taking place. Thus this Warning was for impacts as well as snow
amounts for up to 14 inches through Tuesday morning. Elsewhere,
PoPs for showers and isolated evening thunderstorms will be from
Rosebud County W this evening, then highest PoPs (70-90%) will be
over S. Big Horn and Sheridan Counties for the rest of the night
into early Tuesday. Lows will be in the low 30s to low 40s.
Scattered showers and thunderstorms will be over areas from KBIL W
Tue. afternoon, as well as over S and SE parts of the area. PoPs
will be from 30% in KBIL to the 40s and 50s W of KBIL. Temps will
be several degrees below normal.

Zonal flow/weak ridging moves over the area Tue. night with
quickly decreasing PoPs. Lows will be a little higher than they
will be tonight. Arthur

Wednesday through Monday...

Ensembles and cluster analysis remain consistent in progging an
upper low to lift into and cross the region Wednesday night into
Thursday, exiting the east by early Friday. While confidence
continues to increase in the overall pattern, uncertainty remains
in the exact track of the low, as any shift north or south would
affect precipitation amounts, along with temperatures. That would
then affect snow levels and amounts as well. Currently the low is
progged to slide across the MT/WY border and lift north and east
into southeast MT on Thursday, moving into the Dakotas by early
Friday. At this time, Thursday has the best precipitation
potential, with precipitation chances ranging from 60-90%. Latest
NBM probabilities show a 50-90% chance (highest over the west) of
at least 0.25" through Friday and a 40-80% chance (highest over
the Crazy Mountains into central zones) of at least 0.5". For the
mountains, this translates to a 60% chance or greater of at least
6" of snow.

Shortwave ridging builds in for the second half of Friday and
Saturday, before another potential low pressure system is progged
to move through the region on Sunday. High pressure then looks to
build over the area starting Monday. Temperatures are currently
forecast to range from the 50s to upper 60s on Wednesday, cooling
into the 40s to 60s on Thursday. Highs in the 50s and 60s on
Friday, warm into the 60s and 70s for Saturday through Monday. STP

&&

.AVIATION...

Scattered to numerous showers with isolated thunderstorms will
affect the area this evening with MVFR/IFR conditions. Chances for
showers will move S of KLVM to KBIL to KMLS overnight with
MVFR/IFR conditions. Expect areas to widespread mountain
obscurations. Scattered showers and afternoon showers and
thunderstorms continue for Tuesday with MVFR/IFR conditions and
areas to widespread mountain obscurations. Arthur

&&

.PRELIMINARY POINT TEMP/POPS...

    Tue     Wed     Thu     Fri     Sat     Sun     Mon
-----------------------------------------------------------
BIL 042/062 042/067 044/052 038/066 045/072 044/066 046/070
    65/T    12/W    69/T    52/W    14/T    54/W    22/W
LVM 034/061 038/061 039/050 035/063 041/063 038/062 040/068
    55/T    16/T    99/T    42/T    16/T    54/W    22/W
HDN 042/062 037/070 043/056 036/068 042/076 043/067 044/070
    63/T    11/B    49/T    62/W    13/T    54/W    32/W
MLS 042/063 040/070 045/060 037/063 043/074 045/066 045/070
    11/B    11/B    27/T    62/W    11/B    43/W    22/W
4BQ 043/060 038/070 044/065 038/064 042/076 045/066 044/068
    44/W    11/U    16/T    62/W    01/U    33/W    32/W
BHK 040/063 037/070 042/062 035/061 039/073 043/064 042/067
    12/W    01/U    17/T    63/W    11/U    33/W    22/W
SHR 038/055 033/067 039/057 033/064 038/074 040/065 040/067
    99/T    21/B    37/T    62/W    12/W    44/W    32/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning in effect until noon MDT Tuesday FOR
      ZONE 67.
     Winter Storm Warning in effect until 6 PM MDT Tuesday FOR
      ZONE 171.
 WY...Winter Storm Warning in effect until 6 PM MDT Tuesday FOR
      ZONE 198.

&&

$$
weather.gov/billings