Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 172025

Area Forecast Discussion
National Weather Service Billings MT
225 PM MDT Thu Jun 17 2021


Tonight through Saturday night...

A small scale ridge sliding into the area from zonal flow will
keep the forecast area dry through Friday night. An upper trough
from British Columbia moves into northern Montana Saturday. This
will bring a cold front into far northern zones late Saturday
afternoon. Pre-frontal warming should be enough to get highs to
around 90 degrees for most locations despite falling mid level
heights. The cold front will move through the forecast area late
Saturday afternoon through Saturday night. A return flow of
southeast winds into southeast Montana will allow for some cape to
build up there and could be enough, with falling mid level
heights and shortwave influx, to trigger a thunderstorm. Showers
and a few thunderstorms will develop over northwest zones late
Saturday afternoon, and as upslope increases, spread south and
east through the night. This will set up a cool and potentially
wet day for Sunday (see extended discussion below). TWH

Sunday through Thursday...

A cold trough will be over the area Sunday through Monday.
Ensemble ECMWF showed 700 mb temps falling to below zero degrees C over
the area, and NAEFS had temps around zero. NBM showed snow levels
dropping to 8000-8500 ft by 12Z Monday. Most cluster ensemble
members showed /0.25/ inches of QPF on Sun. over the western
mountains which would be beneficial to the ongoing fires. However,
one cluster ensemble had very little precipitation. The QPF will
shift S Sun. night. Monday`s clusters showed a wide dispersion of
QPF values, lending uncertainty to the forecast. Temps will only
be in the 70s both days. Expect gusty winds Sun. per the ECMWF
ensemble charts. Fortunately, RH`s will be in the 40s and 50s. Had
likely PoPs for western two-thirds of area on Sun. with only a
slight chance of thunder. PoPs decrease N to S Sun. night through
Monday. Will have some light snow amounts in the mountains.

Temps will climb back into the 80s and 90s for Tuesday through
Thursday, as a ridge crosses the area, followed by a trough by the
end of the period. There will be a slight chance of
afternoon/evening thunderstorms over and near the mountains on
Wednesday due to a cold front. The approaching trough will bring
a chance of showers and thunderstorms from KBIL to KSHR W Thu.
afternoon. Chances for any strong storms were low during the
period based on the CWASP index. Fosberg index was low as well,
showing limited fire weather concerns. Arthur



VFR will prevail over the area through the period. A dry cold
front will push S through the area Friday morning, bringing some
gusty N winds to KMLS and KSHR before 18Z. Wildfire smoke could
reduce slant range visibility at times. Arthur



    Fri     Sat     Sun     Mon     Tue     Wed     Thu
BIL 055/086 057/092 058/070 048/074 049/084 056/091 060/089
    00/U    00/N    37/T    42/W    00/U    11/U    12/T
LVM 046/086 051/088 051/070 043/075 044/084 051/088 053/085
    00/U    01/N    36/T    41/U    00/U    12/T    23/T
HDN 052/087 055/094 056/072 046/073 046/086 053/093 057/091
    00/U    00/N    36/T    42/W    00/U    01/U    11/U
MLS 053/085 054/091 058/072 045/071 048/083 055/091 060/090
    00/U    00/N    34/W    31/U    00/U    00/U    11/U
4BQ 054/085 058/092 059/072 047/069 047/083 054/090 061/089
    00/U    01/N    34/T    42/W    00/U    00/U    11/U
BHK 051/082 052/089 056/071 042/069 044/080 051/088 056/088
    00/U    01/N    34/W    31/U    00/U    00/U    11/U
SHR 050/085 053/091 053/070 044/069 044/082 051/090 055/087
    00/U    00/N    36/T    53/W    10/U    01/U    22/T




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