Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 131950

Area Forecast Discussion
National Weather Service Billings MT
150 PM MDT Fri Oct 13 2017

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

Water vapor imagery shows a shortwave moving from central ID into
south central MT, where showers are becoming more numerous, and
a strong northerly jet along the Pac coast as trof deepens to our
west. Increasing diurnal instability along with approaching
shortwave will bring a good chance of showers across our western
cwa thru the remainder of the afternoon and into the evening. This
will be in the form of mountain snow and lower elevation rain.
Trickier part of forecast involves snow potential tonight into
early Saturday.

First of all, today`s model trends (with the exception of the GFS)
have trended weaker with forcing and lower with QPF in our cwa
tonight into early tomorrow. Have trended the forecast slightly in
this direction. Main focus of forcing/baroclinicity will be from
southeast ID across central WY. Although we will have a period of
upper level ascent from the wave passing to our south, we will see
low-mid level descent behind the initial weak shortwave, so
precip will be dependent on orographics and instability. That
being said, focus of any snow accumulation will be over the NW
aspects including the Paradise Valley, Beartooth Foothills and
eventually the north slopes of the Bighorns, though moisture may
be limited. The GFS is actually wettest of all models, and veers
mid level winds more northerly, suggestive of Red Lodge snowfall
late tonight. The high res solutions are staying dry. That being
said, there seems to be enough moisture wrapping into the trof
such that with the instability we will see some snow showers. A
complex picture indeed.

Overall will keep forecast on the benign side, allowing for the
potential for up to 1-2 inch accums in the Paradise Valley and at
McLeod, Red Lodge and perhaps Story. Mountains will see a few
inches between now and early Saturday. As for Billings, we have
not seen a measurable snow yet this fall, and it may or may not
happen tonight. Looks like a dusting around the metro area, tops.
Precip will taper off fairly quickly on Saturday.

Attention then turns to wind as we transition to a downslope
regime by Saturday afternoon. WNW mid level flow increases to
35-45 kts by Saturday night, which along with strong downslope
gradients and stability should yield some healthy SW-W surface
along the foothills and up to Wheatland County. Given the flow
aloft and surface pressure max extending up to NW MT, this is not
an ideal set up for pure gap winds. Will introduce some messaging
for expected 50+ mph winds at Livingston, Nye, Big Timber and
Harlowton...with peak winds expected Saturday night. Not sure if
we will see advisory gusts at Livingston, but confidence is high
we will see cross wind impacts on I-90 and Hwy 191.

Temps will stay cool Saturday with highs in the mid 40s to lower
50s. Warming trend really kicks in Sunday with temps back to the
lower 60s in places.


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

A dry and mild week ahead with the exception of Friday in the
extended period. GEFS and deterministic models both showed
uncertainty in how the next trough will play out for late in the
period, otherwise the models were in decent agreement.

Upper ridging will give way to fast zonal flow, which will turn SW
by Friday. Went with a dry forecast through Wednesday night, then
had low PoPs over the western mountains Thursday and Thursday
night as some Pacific moisture streams into the area. For Friday,
the next upper Pacific trough was much more amplified on the GFS
than on the ECMWF. The trough remains W of the area. Despite the
model differences with the trough, moisture was confined to
mainly the western zones. A cold front brings a cooler day with
highs in the 50s.

The ridging early on, followed by fast zonal flow, will make for
periods of wind in the gap flow areas, with some wind spreading
onto the plains through midweek. No obvious wind advisory days as
of yet. Arthur



Mountain obscurations will increase late this afternoon over the
Crazys, Beartooths and Absarokas. In addition, rain and snow
showers will create MVFR conditions in KLVM. Scattered rain and
snow showers will spread E across most of the area tonight,
bringing occasional MVFR conditions and widespread obscurations to
the western mountains. Obscurations will increase over the NE
Bighorns. Precipitation will decrease over Sheridan County
Saturday morning. VFR returns to the entire area Sat. afternoon. Arthur



    Sat     Sun     Mon     Tue     Wed     Thu     Fri
BIL 033/050 036/061 042/069 043/070 044/066 044/067 043/058
    52/J    00/N    00/N    00/U    00/B    00/B    11/B
LVM 026/047 034/059 040/066 039/069 039/065 041/064 037/054
    62/J    00/N    00/N    00/N    00/N    11/N    12/W
HDN 033/051 031/062 035/071 038/071 040/068 041/070 041/061
    43/W    00/U    00/U    00/U    00/B    00/B    01/B
MLS 034/048 032/059 037/068 040/071 041/064 040/068 042/061
    22/W    00/U    00/U    00/U    00/B    00/B    01/B
4BQ 034/045 029/059 035/069 039/072 039/065 039/070 040/063
    23/W    00/U    00/U    00/U    00/U    00/U    00/B
BHK 032/044 029/057 036/067 039/071 040/063 040/068 040/062
    12/W    00/N    00/U    00/U    00/U    00/U    00/B
SHR 031/046 026/060 033/068 036/072 038/066 037/068 039/061
    35/W    00/U    00/U    00/U    00/U    00/B    01/B




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