Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 151530
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
930 AM MDT Fri Sep 15 2017

.UPDATE...
Updates this morning for text and digital forecasts were to add
some fog to the higher elevations and bump up the winds and wind
gusts today through around 1500 MDT. &&

.SHORT TERM...valid for Tdy and Sat...
Light to moderate rain, with occasionally heavy periods, was
falling across the forecast area early this morning per radar
imagery and surface observations. The strong system driving this
rain was evident on satellite imagery with cold clouds tops over
the region and a shortwave moving into SW WY from UT. This system
has lots of dynamic and thermodynamic support. The main upper
trough was over the Pacific NW this morning with the right-rear
quadrant of a 120 kt 300 mb jet providing ample upper divergence
over the area. This support will continue through the day as the
jet pulls off to the ENE over Southern Canada. The shortwave will
move up from the SW through SE MT aiding lift and rainfall totals
in this area. Isentropic lift will move N into the area, then
shift E out of the area around 18Z. Finally, deep NE upslope flow
will provide additional lift today. Precipitable waters on the
order of /0.75/ inches over the central portion of the area to
greater than an inch over the SE will provide ample moisture this
morning, before values start to decrease during the day. Snow
levels are progged to fall to around 7000 ft AGL today over the
Beartooths/Absarokas and will be somewhat higher over the NE
Bighorns. Continued high PoPs through the day. There will be a mix
of rain and snow over the mountains. Temperatures will not move
much, remaining in the 40s to lower 50s, which is well below
normal. In addition, 850 mb winds around 30 kt will mix down
creating breezy NE winds today.

The main upper trough then slides E across the area tonight
through Saturday, accompanied by strong q-vector convergence. The
left-front quadrant of another jet rounding the trough will bring
more upper divergence to the region tonight. Rain will continue
across the area tonight with some snow mixing with the rain in the
foothills. Snow will continue in the mountains with snow levels
not changing over the Beartooths/Absarokas, but dropping a bit in
the NE Bighorns. The heaviest mountain snow is expected today into
early Saturday. Had likely PoPs Sat. morning across the area,
dropping to chance in the afternoon as the bulk of the lift moves
out of the area. It will be slightly warmer on Sat. with highs in
the 50s. Total QPF amounts through Sat. will be 1 to 2 inches,
with higher amounts from Forsyth E. With snow levels remaining
high through the event, do not anticipate changing the ongoing
mountain warnings, nor issuing anything for the foothills. A
slight chance of precipitation will linger Sat. evening, then it
will be dry overnight. Low temperatures Sat. night will be in the
30s as skies clear out. Arthur

.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...
Flat ridging will bring a period of dry weather with a warming
trend Sunday and Monday. Expect temps to be a little below normal
Sunday, then a little above normal Monday in a pre-frontal regime.
Some locations in our east should reach 80F on Monday, before
temps crash again.

A fairly deep Pacific low will move over the northern/Canadian
Rockies Monday night. This along with a cold front will bring a
good chance of showers to the area into Tuesday. Models begin to
diverge here as the low splits, with a northern circulation
forming in Alberta and a strong jet driving toward the great basin
and central Rockies. The splitting nature of such a high-
amplitude trof results in low confidence in any specifics in the
latter portion of the extended period. There is some consensus for
a bit of drying and gusty west winds Tuesday into Wednesday, then
perhaps a better chance of pcpn as a shortwave rotates around the
trof and lifts thru WY by Thursday. Expect below normal temps
Tuesday thru Thursday as we remain under the influence of the cold
upper trof. Also, mountain precipitation will be in the form of
rain/snow showers as 700mb temps remain below zero. Anyone with
outdoor plans in the high country next week should be prepared for
the cold.

JKL

&&

.AVIATION...
Widespread rain and high elevation snow will keep flying
conditions poor across the region over the next 24 hours. Expect
MVFR-LIFR at lower elevations along with persistent mountain
obscurations. NE-E winds will gust 15-25 kts at times. JKL &&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Sat     Sun     Mon     Tue     Wed     Thu
-------------------------------------------------------
BIL 047 039/054 039/070 047/077 046/062 044/063 043/063
    +/R 86/R    20/B    01/B    45/W    22/W    34/W
LVM 045 034/049 032/065 038/071 037/057 038/058 035/059
    +/R 87/O    10/B    01/N    55/T    33/W    44/W
HDN 051 040/058 036/073 040/080 042/064 040/067 039/064
    +/R 86/R    20/B    01/B    44/W    32/W    44/W
MLS 051 041/054 036/070 043/080 047/066 042/067 042/066
    +/R 76/R    20/B    00/U    24/W    22/W    44/W
4BQ 050 040/054 035/070 041/080 047/067 041/066 041/066
    +/R 75/R    20/B    00/U    13/W    32/W    45/W
BHK 049 039/051 034/067 041/078 048/069 042/066 042/065
    +/R 76/R    30/B    10/U    12/W    32/W    55/W
SHR 047 038/053 031/069 038/079 042/063 037/061 038/062
    +/R 86/R    20/B    00/U    24/T    43/W    55/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning in effect until 6 PM MDT Saturday FOR
      ZONES 67-68.
WY...Winter Storm Warning in effect until 6 PM MDT Saturday FOR
      ZONE 98.

&&

$$
weather.gov/billings



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