Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 112253

Area Forecast Discussion
National Weather Service Billings MT
353 PM MST Thu Jan 11 2018

.SHORT TERM...valid for Fri and Sat...

Arctic airmass over the region today kept many places in the
single digits above and below zero, while some of the foothill and
mountain locations were in the balmy teens and twenties above
zero. Winds have been a challenge today along the western
foothills, with a baroclinic zone hugging the slopes of the
mountains. Winds may turn southwest for a time late this evening
and overnight at Livingston with perhaps a bit of blowing and
drifting snow. Otherwise, snow will overspread the area this
evening and overnight as the next system moves into the region in
the form of a shortwave trough. Pacific moisture will overrun the
colder air near the surface, with a surface low diving south and
east into Wyoming continuing upslope flow, producing periods of
accumulating snowfall. Snow looks to end across portions of the
area during the day Friday, but continue through the afternoon and
into the evening for areas west of a Forsyth to Broadus line as a
baroclinic zone pushes south and west. When all is said and done,
the western mountains could pick up 10 to 15 inches of snowfall,
highest on south and west facing aspects, with significantly less
amounts on north and east facing aspects. For the lower
elevations, locations west of a Forsyth to Broadus line and areas
north of I-90 and I-94 could see amounts of 2 to 5 inches, with
locally higher amounts possible. Given winds aloft look to remain
out of the southwest, locations along the southwest foothills are
not expected to receive much snow. Have continued the Winter Storm
Warnings for the western mountains, and expanded the Winter
Weather Advisories across the rest of our Montana zones, with the
exception being the southwest foothill locations. Went with Winter
Weather Advisories for our far eastern areas tonight into Friday
instead of a Wind Chill Advisory because we are expecting a couple
inches of snow along with wind chill values down near 35 degrees
below zero. The rest of the Winter Weather Advisories go into
Friday evening.

A mainly dry day can be expected for Saturday with shortwave
ridging building over the area. A jet max moving overhead may
bring some snow showers to eastern areas during the evening and
night. High temperatures will range from the twenties across
western foothills, to near zero degrees across the east on
Friday, with thirties across the west and central zones on
Saturday, with twenties across the far east. Lows will continue
to be coldest east (lows below zero) and warmest west (teens to
near twenty above zero). STP

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

Next clipper dropping out of Canada in amplifying flow aloft will
bring our next chance of snow and next surge of colder air Sunday
afternoon and night. There is time for downslope warming ahead of
this 30s to lower 40s expected in our west, with gusty
winds along the foothills. Backdoor front arrives in the afternoon
and evening and temps should fall sharply with the wind shift to
NE-E. Models have differed with the strength of the energy and
magnitude of cooling, with the ECMWF being colder than the GFS,
but the 18z GFS has trended colder. Have kept temps sided with the
more consistent colder model, which is given further credence by
the large area of snow cover in the lee of the mountains and
strong high pressure dropping out of Canada. As for snowfall,
could see an inch or two in central/eastern zones with mostly weak
upper level forcing but a favorable dendritic layer along a low
level baroclinic zone. Snow could push all the way to the
foothills by late Sunday night, but this is more uncertain. Temps
will drop and highs on Monday should range from the single digits
in our east to maybe 30s in our west, depending on when downslope
winds kick back in.

The trend for the remainder of the extended period is for more
zonal flow as the west coast ridge breaks down. Tuesday looks like
a dry day. Could see some showers Wednesday with a Pacific
shortwave. Another shortwave and lower heights expected by
Thursday. Temperatures should moderate to the 30s to lower 40s in
this regime, and that should begin to melt some lower elevation
snow cover. Expect some gusty west winds as well, which could
cause blowing/drifting snow, especially Tuesday which is the
transition day from colder temps.



Snow will develop by this evening and continue into Friday across
most of the region. Poor flight conditions will become widespread.
Expect IFR or lower, and mountains will be completely obscured.
Snow will become lighter on Friday with MVFR-IFR persisting. KLVM
could see a period of gusty SW-W winds late tonight and early
Friday, but there is uncertainty with winds along the foothills,
with east winds across the lower elevations and west winds over
the high terrain. JKL



    Fri     Sat     Sun     Mon     Tue     Wed     Thu
BIL 000/007 004/038 026/038 011/025 013/037 027/041 026/041
    87/S    52/O    12/S    52/S    00/B    12/J    11/B
LVM 011/032 025/041 031/040 017/037 024/043 028/042 029/044
    95/S    32/R    11/N    21/B    00/N    22/J    12/W
HDN 905/004 903/037 019/034 006/022 005/034 021/042 026/044
    95/S    42/O    12/S    51/B    00/U    02/J    11/B
MLS 913/905 913/024 015/027 907/006 902/025 017/037 022/038
    +5/S    13/S    14/S    30/U    00/U    01/B    11/B
4BQ 905/005 906/034 021/033 901/017 002/031 020/041 024/044
    85/S    22/S    24/S    40/U    00/U    01/B    11/B
BHK 915/000 915/023 013/026 913/007 910/023 012/036 021/041
    85/S    13/S    25/S    20/U    00/U    01/B    11/B
SHR 007/015 006/039 024/039 014/028 010/039 024/042 026/046
    34/S    32/O    12/S    52/S    00/U    01/B    01/B


MT...Winter Weather Advisory in effect until 11 PM MST Friday FOR
      ZONES 28>31-34-35-38-40>42-57-58-63.
     Winter Weather Advisory in effect until 11 AM MST Friday FOR
      ZONES 32-33-36-37.
     Winter Storm Warning in effect until 11 PM MST Friday FOR
      ZONES 67-68.


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