Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 111135

Area Forecast Discussion
National Weather Service Billings MT
435 AM MST Thu Jan 11 2018

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

Difficult and complicated forecast for next couple of days as
arctic air and associated baroclinic zone fluctuate across our
CWA under an unstable and fairly moist NW flow. We have issued
some new highlights, and continued the inherited wind chill
highlights out east as well.

Wind chills are 20 to 25 below zero in Custer and Powder River
counties this morning, and easily 30 to 35 below in Fallon and
Carter counties. This may need to be extended past the expiration
of 9 AM, at least for Fallon and Carter Counties. Next shift can
evaluate at that time, though it looks like winds should come down
some by then and temps moderate slightly.

As for Absaroka/Beartooth and Crazy mountains...short wave moving
through region later today and tonight brings a good slug of
moisture into high country. Snow will develop and increase this
afternoon. Lapse rates look rather steep during period of best
forcing tonight. We expect 10 to 15 inches of snow in the
mountains, much of it overnight with decreasing snowfall rates
Friday. West facing slopes will get hit the hardest. Winds of 25
to 45 mph look like a good bet up there as well, creating
visibility and drifting issues. We issued winter storm warnings
for mountains from noon today until 5 pm Friday.

For the short wave moves across the region late today
and tonight, it will push moisture over cold air and a weak
baroclinic boundary generally situated from the Snowies
southeastward. Moderate forcing and overrunning is expected to
produce some decent snowfall rates for a spell tonight. Proggs
keep downslope flow in the foothills and nearby areas, and highest
QPF across our northern tier. So expect highest amounts north of
Billings and I-94. However, confidence low in placement as
perturbations in NW flow will cause arctic air to meander from
current position. So some of this snowfall may end up a little
further west or east than our highlights suggest. We issued
winter weather advisories for northwest and central zones from 5
PM to noon Friday. Next few shifts may need to expand advisories
west or east depending on how this actually unfolds.

Other forecast issue concerns wind potential around Paradise
Valley and Livingston. Our tools and some guidance suggests
increasing winds later today through the evening with gusts over
50 mph around the gap flow locations. However, the overall surface
pressure pattern does not fit what we would typically see. There
is some indication of a tighter gradient setting up across the
Paradise Valley and Beartooth Foothills this afternoon and into
the evening on some of the high resolution models. These would
support a mini arctic retreat scenario in the valley and
Livingston vicinity. If this occurs, it will create some blowing
snow with visibilities under 2 miles at times, as well as drifting
snow problems, at least for a brief period. If this mini retreat
happens temps may warm up above freezing and blowing snow issues
alleviated. Confidence is low in how this turns out. We will
continue to carry areas of blowing snow out west and mention in
the Hazardous Weather Outlook. BT

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

The next best chance of snow will be Sunday into Sunday night.
The models were in generally good agreement until late in the
period. Of note was a large spread in the GEFS plumes for
temperatures in the Monday and Mon. night periods.

The forecast area will be on the front side of a high amplitude
rige anchored over the far western U.S. on Saturday. A shortwave
moves SE through E MT Sat. afternoon through Sat. evening,
bringing a slight chance of snow to the area. Temperatures will be
near normal on Sat. with highs in the 20s E to low 40s W. It will
be windy in the KLVM and Big Timber areas due to lee troughing.
The next wave pushes S through the Dakotas Sunday night, pushing
another arctic front into the area, along with a good shot of snow
Sunday afternoon and night. After near normal highs on Sunday,
temperatures will drop back down below zero in the eastern zones
Sun. night. The position of the front was in question on Monday,
creating a difficult temperature forecast. Model blends had 20s
and 30s central and W, with single digits and teens E.

The ridge axis moves E through the area on Tuesday and the next
Pacific wave approaches the area. Tuesday will feature a warmup
back into the 20s to 40s. Had a chance of snow in the SW mountains
Tue. night with the wave. Models differed on the wave timing for
Wednesday, but kept the area mainly dry and mild. Pattern timing
differences between the models showed up for Thursday. For now,
kept precipitation chances confined to the western mountains, with
continued mild conditions. Arthur


VFR to MVFR conditions will occur over the area today, due to
areas of low ceilings, and chances for snow this afternoon N and
W of KBIL. Expect areas of blowing snow around KLVM. Snow will
increase across the region tonight with areas of blowing snow
around KLVM. MVFR/IFR conditions will occur, with localized lower
conditions possible. Areas of mountain obscuration this afternoon
will become widespread tonight. Arthur


    Tdy Fri     Sat     Sun     Mon     Tue     Wed
BIL 006 002/010 005/038 024/037 012/025 011/039 025/043
    2/S 76/S    42/W    12/S    41/B    11/N    11/N
LVM 025 022/032 023/040 029/041 021/037 022/044 027/044
    4/S 95/S    32/W    21/N    21/B    01/N    12/S
HDN 007 904/008 903/036 018/034 006/022 005/034 021/042
    2/S 96/S    32/J    23/S    51/B    01/U    11/B
MLS 903 911/903 912/022 013/027 907/008 901/026 017/039
    2/S +4/S    13/J    24/S    30/U    00/U    12/O
4BQ 004 903/010 905/033 019/033 901/017 002/031 021/041
    1/B 84/S    12/J    23/S    40/U    00/U    01/B
BHK 903 912/000 914/021 011/026 910/009 907/024 014/037
    2/S 84/S    12/J    24/S    20/U    00/U    01/B
SHR 014 007/016 005/037 023/039 014/028 010/038 025/043
    1/B 33/S    32/W    22/O    51/B    00/U    01/B


MT...Winter Weather Advisory in effect from 5 PM this afternoon to
      noon MST Friday FOR ZONES 28>31-35-40-42-57-63.
     Wind Chill Advisory in effect until 9 AM MST this morning FOR
      ZONES 32-33-36-37.
     Winter Storm Warning in effect from noon today to 5 PM MST
      Friday FOR ZONES 67-68.


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