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000
FXUS65 KBYZ 210906
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
306 AM MDT Thu Sep 21 2023

.DISCUSSION...

Today through Friday night...

Showers and isolated thunderstorms were moving north through the
area overnight associated with energy rotating around an upper
low, currently centered over eastern Oregon. Expect the energy to
shift north of the area by late this morning into early
afternoon with diminishing shower and thunderstorm chances over
most of the area as a dry slot works in. Shower and thunderstorm
chances increase this evening, becoming more widespread overnight
into Friday, as the aforementioned low tracks east into Idaho, and
eventually northern Wyoming by Friday evening. Energy and
moisture will continue to advect into the area with easterly
upslope flow at the surface and diffluent flow aloft. Instability
over the region will allow for thunderstorms, with the greatest
threat heavy rainfall with gusty winds and small hail.
Temperatures will be cool enough for snowfall over the highest
peaks in the mountains, generally above 9,000 feet.

With regards to rainfall totals through Friday night, current
thinking is that totals could range from 0.50 to 1.50 inches,
with locally higher totals, especially over northwestern areas.
Latest NBM probabilities for a half inch or more of rainfall
through Friday night range from 50-90%, lowest over the southeast,
and highest over the west. Probabilities for an inch or more of
rainfall are around 50-80% over central and western areas,
lowering to around 20-40% over the east. As far as snowfall,
several inches of snow are possible over the highest peaks of the
Beartooth/Absaroka and Bighorn mountains. At this time, the period
with the greatest snowfall potential looks to be Friday night
into Saturday. The Beartooth Highway will likely be affected, and
anticipate needing a Winter Weather Advisory. Plan accordingly if
you have plans to head into the high country over the next few
days.

High temperatures will range from the 50s over the west to the 70s
over the east today with 50s and 60s for Friday. Low temperatures
in the 40s to lower 50s can be expected tonight through Friday
night. STP

Saturday through Wednesday...

Saturday into Saturday night, the upper air low pressure system
will move eastward into the Dakotas with precipitation gradually
tapering off from west to east. During the day Saturday, western
areas such as Livingston and Big Timber will have a 30-50% chance
of rain while southeast MT will have a 60-70% chance of rain. GFS
and ECMWF models both show good forcing for moderate
precipitation likely over south central MT Saturday morning. NBM
shows that the chance of at least 0.25 inches of rain on Saturday
ranges from 10% near Livingston to about 30% around Billings and
Sheridan to 30-50% over southeast MT. Additional snow in the
mountains on Saturday likely will be less than one inch.

In addition to the precipitation, there likely will be gusty
winds over south central MT to Sheridan County, WY on Saturday as
surface pressures rise to the west of the surface low. Winds look
to gust to 20-40 mph in this corridor, strongest in the morning.

Upper ridging will then dominate our weather Sunday through
Tuesday with precipitation-free and warm conditions.

The next chance (20-30%) of precipitation looks to occur around
Wednesday when a fast-moving upper air shortwave trough and
surface cold front move eastward across the area. Precipitation
type will be rain for much of the area but will be snow above
10,000 feet. This front looks to drop temperatures by 10-12
degrees from Tuesday`s expected high temperatures.

High temperatures will generally be in the 60s Saturday, then 70s
Sunday, 70s to lower 80s Monday and Tuesday, and 60s and 70s
Wednesday. RMS

&&

.AVIATION...

Conditions will deteriorate from west to east this morning, with
south central MT ranging from MVFR to LIFR and southeast MT in
MVFR, mainly from low ceilings. Otherwise, rain showers will occur
over most of the area today with a lull in activity southeast of
KBIL from about 12z to 21z today. Thunderstorms are also possible
over southeast MT today then over much of the area tonight.
Mountains southwest to northwest of KBIL will have prevailing
obscuration, while the Bighorn Mountains will have areas of
obscuration. RMS

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Fri     Sat     Sun     Mon     Tue     Wed
-------------------------------------------------------
BIL 064 053/063 050/064 047/074 049/080 050/082 048/070
    4/W 8+/T    96/W    20/U    00/U    00/U    11/B
LVM 056 044/057 041/064 039/072 043/078 046/078 042/069
    8/T 9+/T    84/W    10/B    00/B    01/U    12/W
HDN 071 051/065 047/063 043/074 044/080 045/083 046/072
    3/W 79/T    97/T    31/B    00/U    00/U    11/B
MLS 072 055/065 052/064 050/071 047/077 051/081 051/070
    4/T 89/T    97/T    42/W    10/U    00/U    11/U
4BQ 076 054/068 050/064 048/072 047/079 050/083 050/073
    3/T 68/T    86/T    41/B    00/U    00/U    00/U
BHK 070 051/063 049/064 046/068 045/076 048/078 048/072
    3/T 69/T    97/T    43/W    10/U    00/U    00/U
SHR 070 047/065 044/062 042/073 044/080 046/083 047/071
    3/T 58/T    86/W    31/U    00/U    00/U    01/U

&&

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

&&

$$
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