Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 161637

Area Forecast Discussion...Updated
National Weather Service Billings MT
937 AM MST Tue Jan 16 2018

Some rather shallow arctic air resides across much of the central
and eastern zones this morning. For example, its 11 degrees at
Logan Airport in Billings, and a few hundred feet lower its still
1 below at our office. In Big Horn County, Little Big Horn raws
was 14 degrees below while Wolf Mountain is 28 degrees above. So a
difficult forecast today trying to determine how much of the
colder air scours out. Confidence is reasonably high the western
zones and foothills will see a decent warm up, but eastern river
valleys may be hard-pressed to dig out of the bitter cold until
maybe mid afternoon at best. Made some minor tweaks to forecast
highs and sky. Fog around Big Timber and Reedpoint should
dissipate by 1030 AM. BT


.SHORT TERM...valid for Tdy and Wed...

Weak upslope flow has kept a shallow layer of low clouds and fog
in place for areas west of a Roundup to Billings line through the
night. Starting to see pressures fall over central and eastern
portions of the state in the past few hours which should increase
westerly wind component over the next several hours. As this
process develops should see low clouds and any fog dissipate by
mid morning, though some may stubbornly hold along the Yellowstone
and Musselshell river valleys a bit longer.

Dry and mostly sunny conditions expected today into tomorrow as
ridge of high pressure builds in from the west aloft. Arctic
surface high slowly shifts east of the area over the next 24
hours. As this occurs will see downslope westerly winds increase
along the front range and spread eastward across the plains. This
will help scour out the arctic air thats been in place for the
past couple of days. River valleys will be the last locations to
warm up and with the significant snowpack it could take into
tomorrow before these areas fully emerge from the cold. Another
factor that may limit the warming trend is the clear skies at
night that will allow for significant radiational cooling for cold
overnight temperatures and strong surface inversions that will
need to be overcome early in the day. Latest guidance suggests 20s
and 30s for highs today with mainly 30s tomorrow.

A Pacific trof pushes in from the west Wednesday evening bringing
increased cloud cover and a chance for mountain snow showers. The
approach of this system will also increase winds along the front
range which may reach 50 to 60 mph in the Livingston and Nye
areas. May need a wind advisory for these areas going forward.
Downslope winds should keep precipitation chances confined to the
mountains. Chambers

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

The models were in pretty good agreement Thursday through Sunday,
then pattern differences showed up for late in the period. The
GEFS plumes reflected the above, as they showed large temperature
spreads late in the period as well.

A strong Pacific jet oriented NE to SW over the western U.S. early
on Thursday will bring periods of jet divergence to the area as it
sinks SE through the region through Friday night. Models were
forecasting an atmospheric river of subtropical origin to move
through the area Thu. through Thu. night. This moisture will cause
high precipitable waters for this time of year, on the order of
a half an inch. On Thursday, upper ridging will shift E out of the
area. The ridge will be followed by an energetic Pacific SW flow
that will continue through Fri. evening.

Pacific moisture will bring a chance of rain to the far western
zones and a chance of snow to the mountains on Thursday. The
moisture will overspread the area Thu. night, bringing a rain/snow
mix in the evening and snow overnight, as a cold front crosses
the area. Accumulations around 2 inches are possible in the far W,
with several inches in the western mountains. Snow continues
Friday morning, with a rain/snow mix in the afternoon.
Accumulations looked light over the plains with several inches in
the mountains. The GEFS plumes have been consistently showing a
small chance of freezing rain for KBIL on Friday and now are
showing the same thing for KMLS.

Temperatures on Thursday were forecast to be in the 40s to low
50s. Readings will fall below freezing Thu. night and reach the
30s on Friday. Will continue the HWO to mention the accumulating
snow and mixed precipitation potential, both of which will create
hazardous travel. The precipitation chances decrease from N to S
Fri. night.

On Saturday, the northern branch of a split trough will be over
the area with not much moisture. Sunday will have weak upper
ridging with low precipitation chances. Highs will be in the 20s
and 30s. The flow remains progressive through Tuesday, but models
diverged on the pattern details. Went with a slight chance of snow
across the area. Possible arctic air may return to the eastern
zones on Tuesday.

Kept gap areas windy on Thursday when an Advisory might be needed.
These areas will also be windy Sun. through Sun. night. Arthur


Areas of fog and low clouds will continue from KBIL area to the
west this morning, including Big Timber and Livingston.
Confidence is low as to whether these conditions will affect the
airport directly. Otherwise, no significant aviation impacts are
expected, with prevailing VFR prevailing across the area through
tonight. AAG



    Tdy Wed     Thu     Fri     Sat     Sun     Mon
BIL 028 021/039 029/048 028/038 018/032 014/030 012/029
    0/U 00/U    01/N    65/O    21/B    11/N    22/S
LVM 037 025/044 035/051 029/039 013/034 014/034 018/036
    0/N 00/N    02/R    86/S    31/N    22/S    33/S
HDN 022 010/038 022/045 023/039 016/033 013/029 009/029
    0/U 00/U    01/B    55/O    31/B    11/B    22/S
MLS 010 006/036 021/040 026/039 016/030 011/026 008/022
    0/U 00/U    01/B    43/S    21/B    11/B    12/S
4BQ 022 007/038 021/045 027/039 019/034 014/030 012/027
    0/U 00/U    00/B    24/O    31/B    11/B    12/S
BHK 014 005/037 020/044 026/041 018/034 010/027 008/023
    0/U 00/U    00/B    23/O    21/B    11/B    12/S
SHR 025 012/042 021/048 028/039 018/032 014/031 012/030
    0/U 00/U    00/B    25/O    42/S    11/B    12/S


MT...Wind Chill Advisory in effect until 11 AM MST this morning
      FOR ZONES 31>33-36-37.


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