Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 201551
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
951 AM MDT Wed Sep 20 2017

.UPDATE...

No changes to the going forecast this morning. Downslope winds
will provide dry conditions across the lower elevations and warmer
temperatures compared to the past few days. Upper dynamics
increase over western mountains this afternoon for a chance of
rain/snow showers with a few thunderstorms mixed in. No changes to
the going wind advisory with current gusts in the 40 to 50 mph
range from Big Timber to Livingston.

Challenge for this afternoon will be snow and qpf forecasting.
Some models hitting areas west of Rosebud county with 1 to 3
inches of precipitation through Friday night now with strong jet
dynamics enhancing upslope flow. Stay tuned if you have late week
outdoor plans. Chambers

&&

.SHORT TERM...valid for Tdy and Thu...

Interesting weather the next few days. Wind first, then a return
of rain and snow.

Really not seeing much wind along the foothills yet, but there is
a fairly tight gradient and mid levels are stabilizing under zonal
yet strengthening westerly flow aloft. The development of modest
Lee side troffing should allow gap flow to begin soon, probably
early this morning, and already seeing hints of that at some raws
sites. Stable winds will evolve into mixed SW winds in our west
this afternoon, w/ 50+ mph gusts possible. Showers moving west to
east thru central MT could increase the gusts at times. We may
reach advisory level gusts at Livingston and Nye.

Could see 40-55 mph mixed gusts at Big Timber and up toward
Harlowton as well during peak heating hours and with some showery
help. Travel on Hwy 191 will be impacted in addition to the usual
spots along I-90.

Water vapor imagery shows energetic trof along the Pac NW coast
moving to the southeast. As this energy pushes toward the northern
great basin and eventually forms a closed low over southern ID by
late Thursday, mid level baroclinicity will remain over our
southwest mountains w/ moist flow backing from westerly to
southerly. This is shaping up to be a prolonged period of
precipitation for our orographically favored Beartooth Absarokas.
Snow level will rise today, then fall back toward 7500 feet
tonight. Cold air will deepen further by Thursday night as
northerly winds increase. Overall, heavy snow expected above
7500-8000 feet, with models projecting over an inch of QPF, and
the GEFS mean at WEY over 1.5 inches. This should translate to
over a foot of snow at the high elevations and have issued a
winter storm watch to cover the period from tonight through Friday
night. Impacts will be to Beartooth Pass and anyone with outdoor
plans in the high country. Heaviest precip expected with greatest
forcing Thursday night.

Other than scattered showers and an isolated thunderstorm in our
west later today, precipitation chances will increase across our
west/central parts late tonight and Thursday, with a widespread
rain expected by Thursday night. Will need to watch carefully the
snow potential for our foothills (e.g Red Lodge) beginning
Thursday night. Both the GFS/EC show wet bulb zero heights
lowering to near 5500 feet, with the NAM a bit lower, so some wet
snow accumulation is a definite possibility.

Temperatures will warm a bit today with highs into the 60s across
most of our cwa, and 70F possible in the east. Cooler air arrives
tomorrow with highs in the 50s to mid 60s, warmest again in our
east.

JKL

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

Still looks like an active weather period into Sunday, then drier
weather will follow with warmer conditions. GEFS continued to show
model spread regarding the upper low/trough that moves into the
region. So have blended with the latest blended model guidance
which did not change the forecast too much.

Strong jet on the E side of the system will pull the system E
gradually. The jet buckles on Saturday for some divergence in the
E. Continued likely PoPs central and W Fri. morning with chance in
the afternoon. Temperatures will support a rain/snow mix W of KBIL
in the morning, and the foothills could see around 2 inches of
snow. A few inches are possible in the mountains as well. Highs
will range from the 40s W to the 50s E. Have chance PoPs Fri.
night and Sat. with likelies in the SE Sat. due to the jet.
Saturday will have similar temperatures to Friday. Precipitation
focus will be in SE MT and Sheridan County Sat. night as the
system shifts E. KBIL could see a rain/snow mix Sat. morning and
Sat. night.

Precipitation chances decrease on Sunday. Upper trough then
gradually moves out through Tuesday with drier weather. Models
differ for Wednesday with the GFS keeping a ridge over the area
and the ECMWF showing NW flow with a shortwave in the flow N of
the MT/Canadian border, but this is a long way out. Models also
had some differences in the their temperature profiles Mon.
through Wed., but blended guidance showed a warming trend. Arthur

&&

.AVIATION...

VFR will prevail today and tonight. Expect gusty WSW surface
winds in the KLVM and K6S0 area with gusts of 45 to 50 kt today.
Breezy conditions will affect the rest of the area as well,
especially this afternoon. Isolated to scattered showers possible
this afternoon and evening. An isolated thunderstorms is also
possible. Expect mountain obscurations to increase. Arthur/Reimer

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Thu     Fri     Sat     Sun     Mon     Tue
-------------------------------------------------------
BIL 066 046/056 039/046 036/047 036/051 037/055 040/058
    1/N 33/W    87/W    45/W    33/W    21/B    12/W
LVM 057 037/052 034/043 030/046 028/049 030/052 034/057
    5/T 65/W    86/W    33/W    22/W    21/U    22/W
HDN 069 045/058 040/051 038/050 038/053 037/057 038/061
    1/N 23/W    75/W    45/W    44/W    22/W    12/W
MLS 069 046/061 042/053 039/051 038/053 038/055 038/060
    0/N 12/W    45/W    33/W    44/W    41/B    11/B
4BQ 069 046/062 041/054 038/048 038/050 036/052 035/057
    0/U 22/W    34/W    45/W    54/W    31/B    12/W
BHK 068 046/065 042/056 038/052 038/052 036/054 036/058
    0/N 11/B    23/W    34/W    54/W    31/B    11/B
SHR 068 043/055 037/049 034/045 032/048 031/051 031/055
    0/N 24/W    65/W    55/W    54/W    32/W    12/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Wind Advisory in effect until 9 PM MDT this evening FOR ZONES
      65-66.
     Winter Storm Watch in effect from 6 PM MDT this evening
      through late Friday night FOR ZONE 67.
WY...None.

&&

$$
weather.gov/billings



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