778
FXUS65 KBYZ 212108
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
308 PM MDT Tue May 21 2024

.DISCUSSION...
Through Wednesday night...

Upper trough continued to move E through the forecast area per
water vapor imagery. Highest surface-based CAPE was 500 J/kg from
KBIL E and SE. Bulk Effective Shear was less than 30 kt and PWAT`s
were around average. Scattered showers and isolated thunderstorms were
moving across much of the area at 21Z. 20-40% chances of showers
with isolated thunderstorms will continue over the area this
afternoon into early evening. PoPs decrease after 03Z to 20% from
KBIL E and NE. It will then be dry into early Wednesday. As for
snow in the NE Bighorns, web cams showed it was fairly light, with
heavier snow falling S of Burgess Junction. Will keep the Warning
going until 6 PM MDT. Low temps will be a few degrees below
normal.

For Wednesday, weak upper ridging will shift E of the area, while
SW flow and upper diffluence increase over western areas in the
afternoon. Temps will be from the low 60s W to around 70 SE. SREF
did not show much in the way of CAPE, but had greater than 30 kt
of Bulk Effective Shear in the afternoon and evening. Models also
showed breezy conditions for KLVM, so boosted gusts toward the NBM
90th percentile. Cold front will push S through much of the area
in the afternoon. There will be a 20% chance of rain and mountain
snow in the W during the late morning. PoPs then increase from W
to E in the afternoon and evening for areas of rain with some
thunderstorms. There will be rain and snow in the mountains.
Highest PoPs will be W of KBIL at 80-100%. Areas in the far SE
looked dry through the evening as a surface low moves through SE
MT and central/E WY.

PoPs continue to increase for most areas late Wed. night, with
the exception of the far eastern counties where it will remain
dry. Models had upper low centered over NW WY by 12Z Thursday.
Snow levels decrease to 5000-6000` W of KBIL. Precipitation type
will be rain with a few thunderstorms in the lower elevations.
Some snow is possible in the foothills but Red Lodge looks like
rain at this point. There was only a 20% chance of any snow in Red
Lodge. QPF amounts will be highest N and NW of KBIL, and there
was a 30-40% chance of at least a half an inch of precipitation
from Judith Gap to K6S0 to KLVM Wed. night. Snow will start to
pile up in the mountains, especially over the Crazys where up to a
foot is possible over the highest peaks. Continued the Winter
Storm Watch that begins Wed. evening and goes through Thursday
evening. Arthur

Thursday through Tuesday...

The long term will see a split flow northern hemispheric pattern
with a high wave count. This will set the stage for an active long
term with multiple precipitation chances and temperatures swings.
Thursday will start off with an upper wave and deepening low over
Wyoming bringing precipitation. Looking at soundings, there is a
deep moist layer to near 300mb creating a long and skinny
atmospheric profile. This should lead to efficient cold rain
processes with PWAT values near 0.75in. Temperatures Thursday
morning will be in the low to mid 30s across the region with
atmospheric profiles almost entirely below freezing leading to the
possibility of some snow flakes on the ground. Accumulations and
impacts are not expected. Rain will continue to fall until around
09Z Friday as the low moves off to the east and upper level winds
turn more westerly. WPC clusters are in good agreement that much
of the region will receive over 0.5 inches of rain Thursday. NBM
gives most of the region a 30-50% chance of getting over 1 in of
rain with the highest totals being in areas favorable for upslope
with a north wind. During this time, snow levels will generally
be around 6,000 ft. The Beartooth and Bighorn mountains have a
20-40% chance of getting over 1 ft of snow with the Crazys having
a 50-80% chance.

There is more uncertainty in the Sunday system as the clusters
disagree as to how the pattern will look. About 50% of models are
showing a weaker wave with precipitation amounts around 0.25
inches or less and 50% of models showing a stronger wave and
precipitation values 0.3 inches or more. Snow levels will be
closer to 7,000 ft this round with the mountains having a 20-40%
chance for 6 inches of snow.

Temperatures will be cool Thursday with upper troughing keeping
temperatures in the 40s and 50s. Friday and Saturday, shortwave
ridging takes over raising temperatures into the 60s and low 70s.
Sunday will see upper troughing return cooling temperatures back
into the 60s. Monday and Tuesday see the return of upper ridging
and downsloped flow bringing temperatures into the 70s to near 80
for some by Tuesday. Torgerson

&&

.AVIATION...

Isolated to scattered showers with a few thunderstorms will occur
over the area through early evening. Conditions will be MVFR to
IFR in the precipitation. A few showers will linger from KBIL N
and E late in the evening. Areas of mountain obscuration will
decrease through the evening. Expect VFR late tonight into
Wednesday morning, before showers and thunderstorms become more
numerous Wed. afternoon, mainly W of KBIL. MVFR to IFR is expected
in showers and thunderstorms. Mountain obscurations will increase
Wed. afternoon. Arthur

&&

.PRELIMINARY POINT TEMP/POPS...

    Wed     Thu     Fri     Sat     Sun     Mon     Tue
-----------------------------------------------------------
BIL 043/065 042/049 035/065 043/070 045/061 044/072 048/079
    32/R    8+/T    42/R    14/T    66/T    32/R    11/U
LVM 039/061 038/047 032/062 039/064 039/058 039/070 044/077
    27/T    9+/T    33/T    16/T    65/T    21/U    11/U
HDN 040/069 041/052 034/066 041/072 044/064 043/072 045/080
    21/B    6+/T    62/R    12/T    66/T    32/R    11/U
MLS 041/069 043/053 036/062 042/071 047/065 045/071 047/078
    21/B    39/T    62/R    11/B    45/T    42/R    10/U
4BQ 040/070 044/057 035/062 040/071 047/065 044/069 046/077
    21/U    18/T    72/R    11/B    35/T    42/R    11/U
BHK 038/070 040/058 033/060 038/071 043/064 042/068 043/075
    21/U    28/R    72/R    11/B    35/T    33/R    11/U
SHR 035/066 038/053 031/062 037/070 041/061 041/069 042/077
    21/B    49/T    61/U    11/B    45/T    42/T    11/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch in effect from Wednesday evening through
      Thursday evening FOR ZONES 67-68.
WY...Winter Storm Warning remains in effect until 6 PM MDT this
      evening FOR ZONE 198.

&&

$$
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