098
FXUS65 KBYZ 060949
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
349 AM MDT Mon May 6 2024

.DISCUSSION...
Today through Tuesday night...

A powerful storm system currently moving into Wyoming from Utah
will track E/NE today and settle into the western Dakotas by
evening. Models are in slightly better agreement and are each
drifting the closed low a little further west on Tuesday (The GFS
more so). The main change from previous forecasts is that the
band of precipitation generated by the negatively tilted trough
today is initiated further west this morning under strong
difluence/divergent flow. This means much better chance of
rainfall for the Billings vicinity today and nearby areas to the
south and east. Due to strong west/northwest wind developing and
the strong dynamics involved, look for a sharp edge to the
moderate/heavy precipitation with downsloping limiting precip in
our western foothills and nearby plains. The upper low wraps up
and strengthens this evening in NW South Dakota which will keep
the potential for strong winds going overnight...especially in our
western zones where we have a high wind warning in place. The
high winds may extend a further out east and southeast tonight and
Tuesday as the upper low pivots west with an impressive corridor
of 700 mb winds from the Snowies to the Black Hills. Trowal
effects around the system will produce mixing and strong upward
motion which models suggest will produce a strong band of
precipitation over portions of our CWA.

Where this band sets up Tuesday is uncertain as its placement is
very sensitive to the exact position of the upper low. For now the
best chance of moderate/heavy rainfall is from Yellowstone County
eastward on Tuesday. Rainfall and upward motion may also limit
the strength of wind gusts over our central/eastern zones Tuesday.
However, this is not a system we are accustomed to, and the
dynamics may still generate high winds to the surface. For now we
will hold on to the High Wind Watch, but start it at midnight
tonight, while the High Wind Warning for the foothills still looks
reasonable. We will need to monitor southeast Montana as well as
its close proximity to the surface low and the 700 mb wind max
setting up just over head late tonight into Tuesday may lead to
gusts 50-60 mph in the Powder River/Carter County area, especially
n higher hills, though again it may be fighting rainfall/upward
motion limiting this potential. We will add a High Wind Watch to
Powder River. Southern Rosebud and Carter Counties from 6 PM this
evening to 6 Pm Tuesday.

As far as snowfall goes the western mountains are still expected
to see limited accumulation in the high country for the short term
period with less than 6 inches of snow for the Beartooth/Crazy
mountains, though strong wind gusts will still make conditions
difficult for those working on the Beartooth Pass. Winter weather
advisory for the Bighorn mountains continues where around 4 to 8
inches of snow is expected to fall from early this morning into
the evening hours, mainly on west facing slopes. Winds will be
strong at times in this area as well, so those planning to head up
to the Bighorns should be prepared for snow and blowing snow
issues.

Please keep up to date on the latest forecasts which will likely
be adjusted as this weather event unfolds. BT


Wednesday through Monday...

.KEY MESSAGES...

- Long duration weather system continues Wednesday/Thursday
  bringing significant rain, strong winds, and high elevation snow

- Friday through the weekend will likely see ridging return
  bringing warmer temperatures and dry conditions

There is still stubborn model and ensemble disagreement in the
placement of the surface low pressure system leading to
uncertainty in the long term forecast. Looking at WPC clusters
the GFS still wants to keep the low farther to the west bringing
more precipitation to TFXs CWA and significantly lower
precipitation totals for locations in our east. Currently this
solutions has a 40% chance of occurrence. The Canadian and ECMWF
ensembles are settling on a different solution keeping the low
farther to the east bringing heavier precipitation to GGWs CWA
and locations in our east. This solution currently has a 60%
chance of occuring. Thursday will be a similar story only with
more model mixing than Wednesday. Roughly 50% of models have the
low farther to the east with the other 50% keeping it farther to
the west. In this case the farther the low is to the west the
more precipitation that will be seen across the region. For event
totals, there is general agreement in precipitation amounts from
Rosebud County and locations to the west and large disagreement in
rainfall totals for locations to the east. Currently ensembles
are showing a 40-50% chance of 1 in of precipitation for locations
west of Billings, a 60-80% chance for locations from Billings to
Miles City, and a 60-70% chance for locations in the east such as
Baker. High elevations will get significant snowfall Wednesday
before snowfall intensity lowers on Thursday. Locations in the
Bighorns and Beartooths have 70-80% chance of getting over 1 foot
of snow from this system. The combination of heavy snow and strong
winds will lead to dangerous in the backcountry.

Winds will also be a large factor Wednesday and Thursday. Wednesday
morning could see gusts into the 40s and 50s mph from Bighorn up
to Wheatland Counties. These locations have a 60-80% chance of
getting a wind gust over 50mph. Winds will continue to be strong
in these areas until the overnight hours when winds look to calm.
Thursday could see breezy conditions linger in the afternoon,
though it will be much calmer than Wednesday with gusts generally
in the 20s mph. Friday into Saturday there is the potential (50%)
for an upper wave to drop south near our eastern border that would
bring the return for gusty winds in the 30s mph, mainly for
locations from Rosebud county and east.

After this long duration storm system moves out of the area, there
is good ensemble agreement that some form of ridging will return
to the region bringing dry and warm conditions. Temperatures will
likely go from the 50sF Wednesday and Thursday to 70sF for the
weekend. Torgerson


&&

.AVIATION...

Isolated showers and possibly a few thunderstorms will persist in
the early morning hours today before becoming more widespread
after 12Z this morning. Best chance for showers and thunderstorms
today will be from KBIL and locations to the east. Strong winds
will be present across most of the region today with Widespread
gusts into the 30s and 40s kts with some locations in the west
such as K6SO, K1KM, and KLVM approaching 50 kts. Mountains will
likely be obscured from high elevation snow. Torgerson
&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Tue     Wed     Thu     Fri     Sat     Sun
-------------------------------------------------------
BIL 053 042/053 039/049 042/059 042/067 044/073 047/077
    8/R 23/O    69/O    97/T    22/R    01/U    12/T
LVM 052 036/048 036/046 038/055 036/064 038/070 043/074
    4/R 13/O    69/O    95/R    11/B    01/U    12/R
HDN 052 040/054 037/051 041/061 041/067 039/075 043/077
    9/R 44/R    89/R    98/R    32/R    01/U    12/T
MLS 056 037/047 037/054 041/063 043/066 043/072 045/076
    9/T 86/R    79/R    65/R    21/B    00/U    11/U
4BQ 055 038/051 036/050 039/061 043/064 042/070 043/074
    9/R 84/O    58/R    86/R    22/R    00/U    11/U
BHK 061 035/047 033/054 037/062 040/064 039/069 040/072
    8/T 97/R    58/R    54/R    11/B    00/U    11/U
SHR 050 039/056 035/047 036/056 038/063 037/069 040/073
    9/R 32/R    59/O    97/T    32/R    11/U    12/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Watch in effect from Tuesday morning through late
      Tuesday night FOR ZONES 29-34-42-57-138-170-173-235.
     High Wind Warning in effect from 10 AM this morning to
      midnight MDT tonight FOR ZONES 34-42-138-170-235.
     High Wind Watch in effect from this evening through Tuesday
      afternoon FOR ZONES 36-37-58.
     High Wind Warning in effect from 10 AM this morning to 6 AM
      MDT Wednesday FOR ZONES 63-65-66-141-172-228.
WY...High Wind Watch in effect from Tuesday morning through late
      Tuesday night FOR ZONE 199.
     High Wind Warning in effect from 10 AM this morning to
      midnight MDT tonight FOR ZONE 199.
     Winter Weather Advisory in effect until midnight MDT tonight
      FOR ZONE 198.

&&

$$
weather.gov/billings