Area Forecast Discussion
Issued by NWS Billings, MT

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780
FXUS65 KBYZ 220238
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
738 PM MST Tue Nov 21 2017

.UPDATE...
Mid and high clouds have spread across our entire cwa as Pacific
moisture streams over a western CONUS ridge. There is ascent in
advance of shortwave moving through southern British Columbia, and
we are starting to see some echoes develop a bit west of Roundup
and Billings. Latest high res models show a bit more QPF tonight,
and cannot argue with this as surface dew points are largely in
the 30s across our western cwa, without strong downsloping yet. So
have added some small pops for isolated light rain showers or
sprinkles tonight into early Wednesday, with best chances along
and east of surface trof.

Main story is of course the wind along our western foothills. Lee
side pressures are falling and the IDA-LWT gradient is up to
8.6mb. As the gradient tightens and we warm advect/stabilize, wind
gusts will increase at the gap areas tonight. In fact just
recently a 50 mph gust was observed at Livingston. Will make no
changes to the wind advisories in effect at Livingston and Nye.

Have adjusted forecast low temps down a bit, especially across
our eastern valleys as temps have fallen a bit faster than
anticipated this evening. We will see warming temps through the
night, and current temps are about as low as they will get.

JKL

&&

.SHORT TERM...valid for Wed and Thu...

The disturbance that brought the rain and snow to portions of our
forecast area last night has moved well east of the area this
afternoon leaving partly to mostly sunny skies in its wake. We did
not make any significant changes to the short term forecast with
this issuance. No strong storm systems are expected with the only
impact for the holiday travel Wednesday and Thursday being strong
gusty winds for the Livingston area and adjacent
Beartooth/Absaroka Foothills.

High pressure ridging builds back again tonight into Thursday
resulting in dry conditions and much above normal temperatures by
Thursday. Pressure gradients begin to tighten this evening along
east slopes of the Rockies as low pressure will be situated over
southern Canada with high pressure across southwest Wyoming. This
pattern will continue through Thursday night resulting in very
strong winds across the Livingston area and Beartooth Foothills.
The strongest winds look to be tonight but especially Thursday
afternoon and evening with a slight lull during the day Wednesday,
although they will still be gusty.

Some moisture will stream in off the Pacific tonight bringing a
chance for snow showers to the mountains, foothills and adjacent
plains but otherwise a dry forecast is expected through Thursday.
By Thursday night, another Pacific front moves across the forecast
area bringing an end to the Livingston area winds but will also
bring the likelihood for rain showers through the night as
temperatures look to be warm enough to support rain instead of
snow. Near record to record highs are expected Thursday with many
areas in the middle 60s. Temperatures will cool down behind the
front for Friday but still be about 10 degrees above normal with
readings in the lower 50s. Hooley

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

Most of the extended period will be dry with mild and windy
conditions. Ensemble spread increased beginning on Monday, adding
uncertainty to the forecast late in the period.

A shortwave departs the area Friday morning and upper ridging
amplifies over the area through Saturday. There will be a chance
of showers mainly over the SE zones Fri. morning, then the
forecast becomes dry. It will be windy on Fri. due to strong winds
aloft. Highs will average in the lower 50s both days. The flow
turns SW on Sunday and the GFS/ECMWF differ on the timing of the
next Pacific shortwave moving into/through the area Monday through
Monday night. So went with blended PoPs and had low chances for
rain and snow showers over the area Mon. through Mon. night. Gap
flow is possible Sat. night into Sunday ahead of the wave. Sunday
looked like the warmest day in the extended with highs near 60.
Upper ridging was forecast to build back into the area on Tuesday
with dry weather. Arthur

&&

.AVIATION...

Gusty winds 40 to 50 kts through tomorrow at LVM. A few vicinity
snow showers possible at LVM and BIL through the early morning
hours. The only possible impact would be ceilings flirting with
the MVFR threshold. LLWS expected at KMLS late tonight into the
morning hours Wednesday with winds around 50 kts at 1700 ft. Walsh

&&

.PRELIMINARY POINT TEMP/POPS...

    Wed     Thu     Fri     Sat     Sun     Mon     Tue
-----------------------------------------------------------
BIL 036/061 042/066 041/053 031/052 037/060 036/050 031/043
    22/W    00/N    61/N    00/B    10/B    13/W    21/N
LVM 044/059 047/068 038/047 029/051 038/057 035/044 028/040
    22/W    10/N    61/N    01/N    11/N    23/W    31/N
HDN 031/062 038/069 039/055 028/053 034/061 034/052 029/045
    12/W    00/B    41/N    00/B    10/B    13/W    21/B
MLS 022/060 041/067 041/053 028/051 032/058 033/050 028/041
    11/N    00/B    31/N    10/U    10/B    12/W    32/J
4BQ 028/063 040/071 041/053 029/053 034/061 035/054 030/042
    11/N    00/B    32/W    00/U    10/B    11/B    22/J
BHK 016/059 037/067 040/051 025/049 028/057 032/049 026/039
    01/N    00/N    32/W    11/U    00/B    12/W    22/J
SHR 029/063 036/067 038/051 026/053 032/061 033/053 027/043
    01/B    00/B    22/W    00/U    00/B    02/W    32/J

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Wind Advisory in effect until 11 PM MST Thursday FOR ZONES
      65-66.
WY...None.

&&

$$
weather.gov/billings



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