370
FXUS65 KBYZ 070058
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
658 PM MDT Mon May 6 2024

.DISCUSSION...

UPDATE...

The Severe Thunderstorm Watch for Carter and Fallon counties has
been cancelled.

Tonight through Tuesday night...

Dynamic upper low currently over northeastern WY is affecting our
weather in several ways, with a severe thunderstorm threat over
Carter and Fallon Counties as low-level east/southeasterly winds
bring relatively warm, moist air and associated instability to
those areas, steady rain over central areas, snow in the Bighorn
Mountains, and strong gusty winds over western and central areas.

Ensemble means generally show 500 mb low meander over the western
Dakotas into Tuesday night, with more weather impacts for our
area. They also show 700 mb winds strengthening over our area late
this afternoon-evening then staying strong through Tuesday night.
At the surface, low pressure probably in the lower 980s mb will
also meander in the western Dakotas.

As we go through the rest of this afternoon, the surface boundary
in Carter/Fallon Counties should move northeastward and the area
of appreciable instability will depart the area. Thus, the severe
thunderstorm threat should diminish late this afternoon or early
evening. The Severe Thunderstorm Watch for Carter and Fallon
Counties is in effect until 7 PM MDT tonight. Main hazards from
the thunderstorms will be strong, damaging wind gusts and large
hail.

The surface pressure gradient between the surface low to our east
and higher surface pressure to our west plus strong 700 mb winds
over our area should support more strong, gusty winds over much of
the area tonight into Tuesday evening. Look for wind gusts to
50-60 mph through Tuesday night, so have extended the High Wind
Warning and expanded it in area to include much of the lower
elevations except for Fallon County. If you will be traveling with
a high profile vehicle during this time please use caution.

The low pressure system should also bring more precipitation to
the region. A band of rain forced by frontogenesis is gradually
sliding eastward, east of Billings, into southeast MT. Look for
much of the additional rainfall tonight into Tuesday morning to
occur in southeast MT, where large-scale ascent and frontogenesis
work constructively to produce precipitation. NBM shows a 30-65%
chance of at least 0.75 inches additional rain tonight from
roughly Rosebud/Treasure Counties eastward to the Dakota border.
Greatest probability is near Miles City. Then for Tuesday
afternoon a disturbance rotating around the upper low should bring
another round of rain into Tuesday night to much of the area
including Billings. The combination of rain and wind will make for
unfavorable conditions for travelers and anyone outdoors.

Snow in the Bighorn Mountains will continue into this evening
before diminishing. Additional snow accumulation there will be up
to 7 inches or so. Use caution if you will be heading to the high
country. Snow should return to the Bighorn Mountains Tuesday
afternoon into Tuesday night.

Low temperatures will generally be in the 30s and 40s tonight
then 30s Tuesday night. High temperatures on Tuesday will be in
the 40s and 50s. RMS

Wednesday through Monday...

Cool and unsettled weather to start the extended period, then dry
weather with a warming trend expected. On Wednesday, models were
not in good agreement with the position of the upper low that is
affecting the area during the short-term. Upper low was progged to
be E or SE of the forecast area depending on the model. Either
way, cyclonic flow will be over the region and a back-door cold
front moves SW through the eastern part of the area. PWAT`s
are forecast to be around normal for this time of year with not
any notable instability. Highs will only be in the 40s and 50s.
With plenty of energy in the flow aloft, PoPs are high, near 100%
through the day. NBM probabilities of a half /0.50/ inch or more
of rainfall were 58% for KBIL and 39% for KSHR on Wednesday. And
the EFI had a high value of .8 for snow over areas NW and S of
KBIL (this includes Tue. night). So have a mix of rain and snow W
and S of KBIL mainly in the morning. Not expecting any low
elevation snow accumulation, but the mountains will have decent
accumulation with close to a foot in the highest elevations of the
Beartooths/Absarokas. In addition, winds will still be an issue
based on the ECMWF ensemble, and the EFI showing .8-.9 over the SW
half of the forecast area. Gusts into the 50s are not out of the
question for this area. For Thursday, upper ridge builds in from
the W and results in a high over low pressure situation. PoPs
remain moderately high, from 40-60% through Thursday. Low-
elevation rain with mountain snow will continue, with the
mountains picking up a few more inches of snow. Highs will be near
normal.

A high over low situation will continue through Saturday with
model differences. Other than some low PoPs over the NE Bighorns,
the area will be dry with highs climbing into the 70s. NW flow
will be over the area for Sunday and ridging or zonal flow will be
over the region on Monday. Next best precipitation chance is Mon.
afternoon with 20-40% chances of showers and thunderstorms. Arthur

&&

.AVIATION...

Strong wind gusts will continue tonight through Tuesday with NW
winds gusting from 45 to 55 kt, and lighter winds in the KBHK
area. From KBIL-KSHR W, expect MVFR to VFR conditions. E of this
line, there will be IFR/LIFR conditions due to rain and
thunderstorms. Severe thunderstorms, with wind gusts to 65 kt and
large hail, are possible over Fallon and Carter Counties through
this evening. Conditions will be from MVFR to LIFR over the entire
area Tue. afternoon. Expect localized to areas of mountain
obscuration through Tuesday. Arthur


&&

.PRELIMINARY POINT TEMP/POPS...

    Tue     Wed     Thu     Fri     Sat     Sun     Mon
-----------------------------------------------------------
BIL 043/051 039/050 043/060 042/069 045/075 047/077 049/076
    46/W    9+/W    97/T    11/U    01/U    11/U    13/T
LVM 037/049 036/046 038/057 037/065 040/071 043/073 045/074
    15/W    9+/W    84/W    10/U    01/U    12/W    13/W
HDN 041/050 037/053 042/062 040/069 041/075 044/078 046/077
    +8/W    ++/W    97/T    21/B    01/U    11/U    12/W
MLS 039/045 039/055 042/063 043/067 043/074 045/076 047/076
    99/W    99/W    64/W    11/U    01/U    11/U    12/W
4BQ 037/045 037/051 041/060 043/066 041/072 045/076 047/075
    +8/W    99/W    85/W    11/B    01/U    11/U    12/T
BHK 036/045 034/054 038/063 040/065 040/070 042/073 044/074
    89/T    88/W    43/W    11/U    01/U    01/U    11/U
SHR 039/053 034/046 038/057 037/064 037/070 041/073 043/073
    74/W    9+/W    97/T    21/B    01/U    12/T    13/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Warning in effect until midnight MDT Tuesday night
      FOR ZONES 29>32-57-173.
     High Wind Warning now in effect until midnight MDT Tuesday
      night FOR ZONES 34-42-138-170-235.
     High Wind Warning in effect until 6 PM MDT Tuesday FOR ZONES
      36-37-58.
     High Wind Warning remains in effect until 6 AM MDT Wednesday
      FOR ZONES 63-65-66-141-172-228.
WY...High Wind Warning now in effect until midnight MDT Tuesday
      night FOR ZONE 199.
     Winter Weather Advisory remains in effect until midnight MDT
      tonight FOR ZONE 198.

&&

$$
weather.gov/billings