Area Forecast Discussion
Issued by NWS Billings, MT

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736
FXUS65 KBYZ 210943
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
343 AM MDT Thu Sep 21 2017

.SHORT TERM...valid for Tdy and Fri...

Water vapor imagery shows elongated trof extending from Alberta/
Saskatchewan to northern CA. Moist southwest flow is streaming
ahead of this trof into our cwa. Precipitation has expanded
through the night in response to divergence in RRQ of 130kt H3 jet
in northeast MT, and mid level frontogenesis. Snow level over the
Beartooth Absarokas appears to be around 7500 feet. Web camera
shows a bit of accumulation at Cooke City, but nearby Fisher Creek
Snotel at 9100 feet has picked up about 4 inches since last
evening. Things are just getting started.

As aforementioned jet streak departs would expected precipitation
to diminish some early today but remain over our SW upslope
areas. By late this afternoon and evening the ascent really cranks
up in the form of isentropic ascent and strong mid level
frontogenesis as 700mb winds back to easterly. This will set up a
period of fairly heavy precipitation across the west half of our
cwa tonight into early Friday. This will be in the form of
snowfall over our western high terrain, and will make no changes
to the Winter Storm Warning already in effect for the Beartooth
Absarokas. Will need to consider a highlight for the Crazy
Mountains beginning this evening, primarily on east aspects. Will
let the day shift take a look at this. The Bighorns look to remain
in drier air longer, with ascent/moisture to their west, and
higher snow levels on the warm side of the baroclinicity.

Lower elevations will see rain of course, with the only potential
issue being the eastern edge of the forcing. Areas from Billings
westward should see anywhere from 0.75 to 1.50 inches of
precipitation thru Friday night, greatest on east aspects, and
much lesser amounts to the east of this area.

A forecast concern remains whether or not the western foothills
including Red Lodge see some wet snow accumulation. Models remain
a bit spread, with the GFS being warmer than the EC/NAM, so there
is uncertainty. There is some cooler air in Canada that will
advect into this system tonight, so am hedging toward the EC,
which shows snow levels down to near 5000 feet by late tonight.
Right now, feel a 2-4 inch snowfall is a fair bet at Nye and Red
lodge, as well as the higher terrain of northern Sweet Grass
County, east of the Crazies near Melville. For Billings, this
should just be a chilly rain, but could see some snowflakes in the
air over the higher nearby ridges by early Friday morning. The
Billings airport has not measured a snowfall in September since
2000.

Forcing will relax some in our west by Friday night, but
isentropic upglide will pick up in our east as upper trof axis
remains to our west, so slightly higher pops warranted for places
like Sheridan, Broadus and Baker.

Temperatures will remain below normal the next two days. Highs
today should reach the mid 60s near the Dakotas border, but will
struggle to get much over 50F in our west. Friday will be cooler
yet, with highs mainly in the upper 30s and 40s, except mid 50s in
our far east.

JKL

.LONG TERM...valid for Sat...Sun...Mon...Tue...Wed...

Much below normal temperatures and continued unsettled weather
can be expected for the weekend before a slight improvement
arrives early next week. Models keep a large upper low over the
Great Basin area and trough over the northern Rockies Saturday and
Sunday. This will result in very cool temperatures along with a
good chance for showers. The upper low will be over Utah during
the weekend before moving northeast across Wyoming Monday into
Tuesday. This track will bring the highest chances for rain
across our eastern areas, mainly along and east of a Miles City to
Sheridan County line for the weekend into Monday.

Temperatures will continue to be cold for snow to continue over
the mountains. Some snow may also mix in with the rain Saturday
morning across the lower elevations for areas from Billings
westward. Temperatures will only be in the 40s Saturday, with
lower 50s Sunday through Tuesday. Lower 60s will be possible by
Wednesday as high pressure ridging begins to build across the
forecast area. Hooley

&&

.AVIATION...

Areas of rain can be expected through mid morning across all but
far southeast Montana. Rain will decrease to scattered showers
this afternoon along and east of a Roundup-Billings-Sheridan line.
West of this line, rain will increase in coverage once again this
afternoon into this evening. VFR to MVFR conditions will prevail
for the TAF sites into this afternoon. However, MVFR to IFR
conditions are expected by mid to late afternoon into this evening
from KBIL to KVLM. Snow will be likely for mountain locations.
Expect mountain and foothill obscurations throughout the day.
Hooley

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Fri     Sat     Sun     Mon     Tue     Wed
-------------------------------------------------------
BIL 053 039/043 036/048 036/052 037/055 039/059 043/064
    6/R 98/R    54/W    33/W    22/W    11/B    11/U
LVM 050 035/040 030/046 028/052 030/054 034/056 037/061
    8/R +9/O    53/W    22/W    22/W    11/B    22/W
HDN 056 040/046 038/051 036/054 036/056 037/060 041/065
    5/R 76/R    54/W    34/W    22/W    11/B    11/U
MLS 062 043/054 039/052 037/053 038/055 038/059 040/066
    3/R 33/R    44/W    44/W    22/W    11/B    11/B
4BQ 062 042/057 039/047 037/050 037/051 036/055 037/062
    2/R 12/R    56/W    54/W    22/W    21/B    11/B
BHK 064 042/055 038/051 038/052 037/054 036/055 037/063
    1/B 12/R    44/W    64/W    22/W    11/B    11/B
SHR 058 039/049 036/045 032/047 032/050 032/055 035/060
    4/R 44/R    56/W    54/W    33/W    21/B    11/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning in effect until 6 AM MDT Saturday FOR
      ZONE 67.
WY...None.

&&

$$
weather.gov/billings



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