422
FXUS65 KBYZ 180232
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
832 PM MDT Fri May 17 2024

.UPDATE...
Winds along the western foothills (w/ the exception of a lone
convective 58mph gust at the western Livingston DOT at 715pm)
have remainder under 58 mph and have cancelled the wind highlights
in this area.

Mesoanalysis shows a 90kt H3 jet nosing into south central MT
which continues to provide modest ascent and produce a few light
showers over our west as of 8pm. This activity is finally showing
signs of ending, but up to this point the ascent definitely worked
against the wind potential. Showers are most numerous east of
Billings but the amount of lightning has scaled back quite a bit
over the past 1-2 hours. Post-frontal surface temps have fallen to
the upper 40s to mid 50s most places, so the air mass has
stabilized significantly. Showers and a few embedded weak t-storms
will taper off from west to east over the next several hours,
ending in our far east by approximately 08z.

Of note is the Wicked Ck Raws temp down to 34F, at an elevation
of 7600 feet. Western mountains are seeing just a bit of snow as
the precip diminishes.

After a cool night tonight (lows in mid 30s to lower 40s), look
for dry conditions Saturday with highs in the 60s.

JKL

&&

.DISCUSSION...
Through Saturday night...

Severe Thunderstorm Watch has been issue for Carter, Fallon,
Custer and Powder River Counties through 02Z tonight. Main threats
are damaging winds in excess of 60 mph, heavy rainfall and small
hail. Also cannot rule out gusty winds or small hail with any
thunderstorms over the area through this evening. There was 40-50
kt of Bulk Effective Shear moving E through the central zones
into the E. MUCAPE/Surface CAPE was running 500-1000 J/kg over
most of the forecast area. First cold front had sagged S through
much of the area and was entering Sheridan to Carter Counties at
20Z. A second front will move into the western zones in the next
hour or so. SPS was issued earlier for storms in Big Horn County,
and latest SPS was over Custer County for a fast moving cluster of
storms with gusty winds and small hail. Isolated to scattered
showers were behind the cluster over the rest of the area.

WSW flow was over the area with energy moving through the flow. A
stronger shortwave will move in behind the second front through
tonight. Used the CAMS for PoPs through tonight. PoPs will be
50-70% E of KBIL through 06Z, then PoPs decrease markedly
overnight. Will continue wind highlights as winds have been
increasing in the western zones this afternoon. KLVM has reach 52
mph thus far.

Saturday still looked dry under westerly flow. It will be breezy
and have blended gusts with NBM 90th percentile. Temps will be
near normal. SW flow moves overhead Sat. night and a cold front
will push SE into the area ahead of the next shortwave. Models
were in decent agreement with 20-30% PoPs W of KBIL overnight,
although soundings looked fairly dry. Lows will be in the upper
30s to mid 40s. A mix of rain/snow is not out of the question over
KLVM/foothills due to lower dewpoints, but just have rain in there
for now. Arthur

Sunday through Friday...

Sunday into Monday, ensembles have a shortwave trough moving into
western MT, increasing chances for precip. Currently the chance
for a quarter inch of rain/melted snow is best for the mountains
and foothills, with about a 40-60% chance, decreasing north and
east to around 20% for eastern MT. With snow levels predicted to
drop down to around 6000 ft Sunday night, the foothills could see
a rain/snow mix. The mountains will likely pick up a few inches of
snow. As this low tracks southeast on Tuesday, most of the energy
will stay over WY, allowing for mild and dry conditions. Dry
conditions will continue into Wednesday as brief ridging builds in
behind troughing. Ensembles then have another round of troughing
moving through early Thursday into Friday, but are in some
disagreement on the behavior of this low. Chances for
precipitation increase across the region to 40-70% Thursday with a
40-60% chance Friday.

High temperatures will generally be in the upper 50s to low 70s
through the period. TS

&&

.AVIATION...

Scattered showers and a few weak thunderstorms will move eastward
and diminish over the next several hours. Post-frontal W-NW winds
will remain gusty while gradually decreasing thru the night.
Expect evening gusts of 30-45 knots decreasing to 20-30 knots
overnight. Areas east of KBIL could see local/brief MVFR this
evening, otherwise VFR will prevail tonight and Saturday. JKL

&&

.PRELIMINARY POINT TEMP/POPS...

    Sat     Sun     Mon     Tue     Wed     Thu     Fri
-----------------------------------------------------------
BIL 042/067 044/062 040/060 041/062 042/067 045/059 042/063
    40/U    15/R    45/R    23/R    14/T    57/R    55/T
LVM 035/066 041/058 035/057 036/061 039/063 040/057 039/061
    20/N    28/T    47/T    34/T    16/T    68/T    55/T
HDN 039/067 041/066 039/060 040/062 040/069 044/062 042/065
    70/U    13/R    44/R    23/R    13/T    46/R    55/R
MLS 042/065 042/068 042/060 039/061 041/067 044/062 042/062
    60/N    11/B    32/R    12/R    12/R    34/R    44/R
4BQ 042/065 042/070 043/060 041/059 041/068 043/062 042/062
    60/N    01/B    33/R    23/R    22/R    24/R    44/R
BHK 039/063 039/070 040/061 037/059 037/065 040/060 038/059
    70/N    11/B    42/R    12/R    12/R    24/R    44/R
SHR 037/066 039/067 038/055 038/056 036/066 040/061 039/062
    60/U    03/T    36/T    55/T    23/T    46/T    55/T

&&

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

&&

$$
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