142
FXUS65 KBYZ 172159
AFDBYZ

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

.UPDATE...
Have cancelled the Severe Thunderstorm Watch for Custer, Powder
River, Fallon and Carter Counties. Roundup of convection which
moved through southeast MT over the past couple hours produced
40-55 mph gusts. This activity has shifted into the Dakotas, and
the air mass in its wake is much cooler and thus with low level
lapse rates not so steep. Nonetheless, the trof axis itself moving
thru central MT will produce more showers and mostly weak t-storms
from west to east over the next several hours. In addition, there
is time for a little warming/destabilizing before sunset. Stay
alert if you have outdoor plans. 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 thunderstorms will spread from west to east
this afternoon and evening. When thunderstorms occur, brief
MVFR/IFR conditions are possible along with gusts up to 45 kts.
Beginning this afternoon, expect gusts up to 45 kts near KLVM,
K6S0 and K1KM. Archer/TS

&&

.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/N    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
    10/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
    50/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/U    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 036/066 039/067 038/055 038/056 036/066 040/061 039/062
    60/U    03/T    36/T    55/T    23/T    46/T    55/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Warning remains in effect until midnight MDT
      tonight FOR ZONES 63-141-172-228.
     Wind Advisory remains in effect until midnight MDT tonight
      FOR ZONES 65-66.
WY...None.

&&

$$
weather.gov/billings