Damaging Wind in Montana, September 7, 2018

Area Forecast Discussion
National Weather Service Billings MT
234 PM MDT Fri Sep 7 2018

.SHORT TERM...valid for Sat and Sun...

Upper level ridge with above normal heights exists over the region
today. A weak shortwave moving thru central MT is helping to
spark some convection mainly over our western mountains. Shear is
weak and this activity will not amount to much, but as ribbon of
modest ascent tracks east we may see a few storms in our eastern
cwa over the next few hours. Otherwise we should see convection
diminish after sunset.

A stronger Pacific shortwave will spread into the northern Rockies
tonight, bringing a chance of showers to our west late tonight and
early Saturday, tracking east thereafter. There is a small
opportunity for stronger storms along the Dakotas border in the
late afternoon as this wave passes, and interacts with surface
trof and axis of greater instability, but shear will be quite low.
Further west, trailing mid level frontogenesis during peak
heating will allow for isolated-scattered thunderstorms in the
afternoon and evening. A cold frontal passage will allow some
showers to persist overnight into early Sunday across our east.
Sunday and Sunday night will then be dry with a more stable
Pacific air mass in place.

Above normal temps will continue Saturday with highs still well
into the 80s. Sunday will be a handful of degrees cooler but still
a little above normal. Models have trended weaker with the
Saturday night fropa so Sunday's highs will be back to the upper
70s to lower 80s.

JKL

.LONG TERM...valid for Mon...Tue...Wed...Thu...Fri...

GFS and ECMWF were in decent agreement with the pattern until late
in the period. This made sense given that the GEFS and ECMWF
ensembles both showed uncertainty with the pattern late in the
period. Continuous development of tropical systems in the E.
Pacific may be contributing to the uncertainty.

Area will be under an upper ridge on Monday, then a flat SW flow
will overtake the area on Tuesday. Monday will have temperatures
well into the 80s with RH's in the teens. Winds will be light.
There will be a dry cold frontal passage Mon. night. Will keep
watching this period for fire weather concerns. Tuesday will be
cooler with low-level easterly flow behind the front. Highs will
be in the 70s. Some energy and moisture in the flow will bring a
slight chance of thunderstorms to the NW corner of the area Tue.
night. SW flow, with increased energy in the flow, will be over
the region on Wednesday. Forecast area stays mainly dry with
moisture confined N of the area, and temperatures will be similar
to Tuesday's readings. Area remains under SW flow Thursday, but
the GFS has a Pacific trough approaching the area that moves
through the region on Friday. ECMWF has shortwave ridging on
Friday. Thursday looked dry on both models. ECMWF brought
precipitation to much of the area Thu. night, then models were
generally dry on Friday. As mentioned above, there was a lot of
uncertainty late in the period. Kept forecast dry for now with
highs in the 70s. Will keep watching this period for better model
consensus. Arthur

&&

.AVIATION...

VFR will occur over the area this evening through Saturday
morning. Isolated thunderstorms are possible over and near the
high terrain this evening, as well as over areas E and S of KBIL.
Some storms may produce wind gusts of 40-45 kt. A few showers will
move into areas W and NW of KBIL overnight. Isolated showers will
spread E through KBIL into Rosebud County through 18Z Saturday.
Isolated to scattered thunderstorms will occur over the area Sat.
afternoon. MVFR conditions are possible in the thunderstorms.
Expect areas of mountain obscuration on Saturday. Arthur

&&

.PRELIMINARY POINT TEMP/POPS...

    Sat     Sun     Mon     Tue     Wed     Thu     Fri
-----------------------------------------------------------
BIL 060/084 053/080 052/085 052/075 048/076 048/076 048/076
    12/T    30/B    00/U    00/U    11/B    11/B    11/B
LVM 053/084 046/080 044/084 045/073 041/074 041/074 040/077
    23/T    30/B    00/U    00/U    11/B    11/B    10/B
HDN 056/085 050/081 048/088 049/076 045/078 046/078 047/079
    12/T    31/B    00/U    00/U    01/B    10/B    11/B
MLS 060/087 055/081 052/088 054/076 052/079 050/077 050/078
    21/B    22/T    00/U    00/U    00/B    11/B    11/B
4BQ 058/088 053/081 052/089 052/078 051/082 049/081 050/081
    22/T    22/T    00/U    00/U    00/B    11/U    11/U
BHK 057/087 052/081 050/087 052/076 048/079 047/077 047/076
    22/T    22/T    00/U    00/U    10/B    11/U    11/B
SHR 053/086 049/080 048/087 048/078 046/081 046/080 045/081
    22/T    30/U    00/U    00/U    00/U    10/U    01/U

&&

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

&&

weather.gov/billings