Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 012224

Area Forecast Discussion
National Weather Service Billings MT
324 PM MST Thu Dec 1 2016

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

Quiet weather pattern continues through the short term with the
exception of winds for the Livingston and adjacent foothills
areas. General troughiness will continue tonight into Friday which
will keep a slight chance for a rain or snow shower across the
forecast area through Friday morning. In addition, snow cover
across the far east combined with some clearing skies and light
winds may allow for some patchy fog to develop late tonight into
Friday morning so this has been added to the forecast from the
eastern portions of Custer and Powder River Counties eastward into
the Dakotas.

The main weather impact through Saturday night will be winds.
High pressure ridging and heights build Friday afternoon into
Friday night. At the same time, a surface low over southern Canada
and a surface high pressure over northern Utah will result in
tight pressure gradients across the upper Yellowstone and
Stillwater Valleys Friday night into Saturday. A weak front will
swing across the area Saturday afternoon which may allow for a
slight decrease in pressure gradients and a slight lull in the
winds. However, another and yet stronger surface low develops over
southern Saskatchewan Saturday night and drops south into
northwest Montana Sunday morning. This will result in tightening
pressure gradients once again for the Livingston to Nye areas
bringing another period of strong winds. As a result, a wind
advisory has been issued for the Upper Yellowstone and Stillwater
River Valleys from Friday evening through Sunday.

High temperatures will remain at or slightly above normal Friday
and Saturday with readings in the middle 30s to lower 40s. Hooley

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

Made just a few adjustments to the going extended forecast which still
featured a period of cold and possibly snowy weather for next
week. Regarding model uncertainties, the GEFS/GFS had some
uncertainty for Sun. and Tue. as well as Wed./Thursday. The ECMWF
ensembles had uncertainty in the Sunday/Monday time frame. The
uncertainty was well reflected in the differences between the
deterministic GFS and ECMWF beginning with the pattern aloft on

Going back to the start of the period on Sunday, a strong pacific
jet will sink S through the Pacific NW/Intermountain W as it
brings divergence to the forecast area through Sun. night. A
Pacific wave will approach the area by late Sun. and move into
the region Sun. night. By 12Z Mon., the GFS had the wave E of the
area while the ECMWF had it to the W. Moisture will mainly affect
the western zones Sun. morning, especially the mountains. The
moisture then spreads E in the afternoon. Trimmed the morning PoPs
back westward and left the afternoon alone. Several inches of snow
are likely in the SW mountains. Both models move a cold front E
into the area on Sunday. The GFS pushes the front E of the area by
12Z Mon., with a surface low over ND, while the ECMWF keeps the
front in the area with a low over NE WY. So, PoPs Sun. night were
a bit uncertain as the ECMWF wraps more precipitation back around
the low into the area while the GFS is drier. Highs still looked
to be in the 40s on Sunday. The pressure gradient on Sunday will
support a Wind Advisory in the gap-flow areas.

On Monday, the GFS has the system/s upper low N of NE ND and the
ECMWF has a trough still to the W of the area. As a result, the
ECMWF keeps a significant amount of QPF over the area and the GFS
is basically dry. Left PoPs in the chance category. Meanwhile,
both models agree on an arctic surge into the area from Canada,
with 850 mb temperatures dropping to -16 degrees C by day/s end.
Expect early high temperatures in the 20s. The model timing
differences aloft continue through the end of the period with the
ECMWF bringing the upper system slowly across the area while the
GFS is more progressive with the flow. The QPF becomes scant on
both models for Mon. night and Tuesday and remains that way on
Wednesday. The coldest air of the season will move in for Tue. and
linger on Wed. with -20 degrees C at 850 mb. CIPS analogs
supported temperatures well below normal for these periods. Have
lowered temperatures both days and had single digit highs on Tue.
with single digits to teens on Wednesday. Slight warming is
possible for Thursday, but large model differences lended low
confidence to the forecast at the end of the period. Arthur



Occasional MVFR ceilings will affect KMLS into tonight. Patchy
fog will affect SE MT through Fri. morning. Otherwise there will
be isolated snow showers over the area with MVFR/IFR conditions
through Fri. morning. By 12Z Fri., expect LIFR ceilings and light
snow in KMLS. These ceilings will persist for most of the day. VFR
will return to the remainder of the area Fri. afternoon. Expect
areas of mountain obscuration through Fri morning. Arthur



    Fri     Sat     Sun     Mon     Tue     Wed     Thu
BIL 023/038 026/043 028/043 022/028 007/009 000/013 005/026
    22/J    22/W    23/W    54/J    32/J    22/J    11/B
LVM 022/036 033/040 031/042 021/022 001/010 903/016 009/026
    42/J    32/W    45/W    53/J    32/J    22/J    22/J
HDN 022/035 022/043 027/045 024/028 007/010 901/011 003/024
    22/J    22/W    22/W    44/J    32/J    22/J    21/B
MLS 019/035 022/041 025/041 021/026 004/008 904/010 000/016
    22/J    03/W    12/W    34/J    32/J    22/J    11/B
4BQ 017/031 017/040 023/041 021/025 004/011 904/009 903/021
    22/J    02/W    11/E    22/J    32/J    22/J    21/B
BHK 017/031 016/038 022/037 019/023 002/008 906/007 906/013
    22/J    02/W    11/B    23/J    42/J    22/J    21/B
SHR 019/037 015/041 020/042 020/024 004/011 903/012 003/026
    32/J    12/J    11/E    22/J    32/J    22/J    11/B


MT...Wind Advisory in effect from 6 PM Friday to 6 PM MST Sunday
      FOR ZONES 65-66.


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