862
FXUS65 KBYZ 170937
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
337 AM MDT Tue Sep 17 2024

.DISCUSSION...

Today through Wednesday night...

An upper level low currently over the Great Basin area is
forecasted to track northeast into south-central MT. This dynamic
system will bring strong to severe thunderstorms today, strong
winds Wednesday and heavy rainfall through Wednesday night.

Starting with the severe threat for today, SPC has highlighted
much of central and eastern MT in a slight risk (2/5) for severe
weather with much of south-central and southeast MT in a marginal
risk (1/5). The main threats will be large hail and wind gusts up
to 65 mph with the time frame of 1-9 pm. Given the strong
dynamics of this system as well as the increased moisture, there
is confidence in the potential for thunderstorms and heavy
rainfall. One factor that could limit the strength of these
thunderstorms is the lower CAPE values (generally 750 J/kg or
less). The likely reason for this is the potential for cloud cover
and isolated rain showers ahead of the better forcing. Take
caution if you have outdoor plans and make sure you have a way to
receive warnings. Tuesday evening, a band of low level winds
(associated with showers and potential thunderstorms) will move
south to north across SE MT bringing gusts of 40-50 mph down to
the surface. In addition, conditions will be warm, dry and breezy
ahead of this stronger push of wind, so take care to not cause a
spark!

Into Wednesday, as the low moves over central and eastern MT, a
tight pressure gradient will give way to strong winds. Highest
winds are currently expected to be at Big Timber up through
Harlowton and eastward through Golden Valley and southwest
Yellowstone counties. These areas have at least a 50% chance of
seeing gusts of 58 mph or greater. With this, a High Wind Watch
has been issued. Given the changing nature of the track of this
low, areas may need to be removed or added, so make sure to watch
the forecast in the coming day.

With regards to heavy rainfall and rainfall totals in general, the
dynamic nature and increased moisture (150-200% above average)
will bring beneficial rain for much of the region. However, again,
the ever changing track of the low has created uncertainty in
what locations will see the highest amounts. At this time, areas
Rosebud Co. and west have a 50-80% chance of getting at least an
inch through Wednesday night. Areas north of I-90 from Livingston
to Forsyth have a 20-50% chance (increasing northward) of getting
at least two inches of rain.

For snowfall, snow levels are expected to drop to around 9,500 ft.
There is about a 40-70% chance of getting at least 6 inches in the
Crazy and Beartooth/Absaroka mountains through Wednesday night.
The Beartooth Pass has around a 60% chance of getting at least an
inch of snow. Monitor the forecast if you have plans in the high
country.

High temperatures today will be in the low 70s west to low 90s
east. Cooler conditions are expected across the region with highs
in the 60s to low 70s. TS


Thursday through Monday...

Upper low will weaken and depart quickly to the northeast
Thursday. Some light showers may linger in the morning near Miles
City & Baker, but otherwise this will be a dry day w/ breezy W-NW
gradually diminishing. There may be enough diurnal instability
for some late day showers over the Beartooth-Absarokas.

Friday through Monday will be characterized by W-NW flow and what
looks to be a series of fast-moving Pacific shortwaves. There
remains plenty of uncertainty regarding the timing and strength of
these waves, and a wide spread of QPF is shown in the ensembles,
along with a fair spread in temperatures. Until this can be
worked out, a forecast of slight (20%) pops and near to slightly
cooler than normal temps will suffice for this period of time. If
there is a sharper wave it would be cold enough to produce some
high elevation snow...so something to think about if you have
outdoor plans in the mountains this weekend. Temperatures thru
the extended period look to range from the mid 60s to mid 70s, for
now.

JKL

&&

.AVIATION...

VFR will prevail across the region through the morning. A dynamic
weather system will bring a high chance (60-90%) of multiple
rounds of showers and thunderstorms this afternoon & evening.
Storms will move south to north and could produce localized strong
wind gusts in excess of 40 knots, along with brief heavy rain and
local MVFR conditions. Showers (some heavy) will be widespread
tonight, resulting in areas of MVFR. The Beartooth-Absaroka and
Crazy Mountains will become obscured, with rain changing to snow
above 10kft late tonight. Finally, a deepening low pressure system
over eastern MT tonight will produce strengthening west winds
along the western foothills (KLVM-K6S0-KHWQ) between 06-12z.

TS POTENTIAL TIMES TODAY:
KBIL 21-04Z
KLVM 18-06Z
KMLS 22-07Z
KSHR 18-03Z

JKL

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Wed     Thu     Fri     Sat     Sun     Mon
-------------------------------------------------------
BIL 080 052/062 054/073 050/076 047/068 046/070 047/070
    3/T 89/T    61/N    01/B    21/B    22/W    22/W
LVM 071 045/060 045/071 042/073 040/068 041/069 041/068
    9/T 99/W    71/B    02/W    22/W    23/W    33/W
HDN 083 050/062 051/074 046/077 044/068 044/070 044/071
    2/T 88/T    71/B    01/U    21/B    22/W    22/W
MLS 088 054/064 054/071 048/076 046/066 045/069 045/068
    2/W 87/T    62/W    01/U    21/B    22/W    22/W
4BQ 089 051/065 054/072 047/078 046/067 045/070 043/068
    2/W 75/W    41/N    01/U    22/W    22/W    21/B
BHK 090 051/069 051/071 046/077 044/067 042/068 041/068
    2/W 85/W    42/W    01/U    11/B    22/W    22/W
SHR 083 045/071 048/074 042/078 042/068 041/073 040/071
    4/T 55/W    41/B    01/U    22/W    23/W    22/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Watch in effect from Wednesday morning through
      Wednesday evening FOR ZONES 34-42-63-68-141-172-228-235.
WY...None.

&&

$$
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