Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 150945

Area Forecast Discussion
National Weather Service Billings MT
345 AM MDT Thu Mar 15 2018

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

Satellite imagery shows strong ridge axis now to our east over the
plains, with a deep low off the Pacific coast. Area of diffluence
exists from western WY through western MT. Shortwave lifting into
northwest WY will spread some precipitation to especially the west
half of our cwa between now and around 15z. Mountains will see
some snow, but lower elevations will see a mix of snow, rain and
even freezing rain as surface temps are below freezing in places.
Early morning travelers should keep this in mind. Also cannot
rule out some light precipitation briefly across our east this
morning as the tail of the shortwave passes. After this morning it
will be a dry day with temps ranging from the mid 30s in eastern
sheltered valleys to lower 50s along our western foothills.
Billings has not risen above 44F despite the upper level ridge
the past 3 days, but should today as the shortwave will finally
mix the strong low level inversion in place.

Things get more interesting tonight as jet approaching the CA
coast drives through the central Rockies, setting up a period of
moist/deep easterly flow with strong ascent associated with
deformation extending up the high plains and into southeast MT. As
for snowfall, of course surface temps will make things tricky but
models do show significant dynamic cooling with 850mb temps colder
than -5C on Friday. Using the garcia method with mixing ratios of
up to 3 g/kg on the 300K surface suggests up to 8-9 inches of snow
over a 18-21 hour period. Some of this will be lost to rain and
surface melting, but nonetheless the atmospheric moisture is
significant, and heavy snow should occur along convergent axis
which is expected to set up east of Billings. The higher passes
like Lame Deer Divide on 212 and the Hysham Hills on I-94 will
likely see very poor travel conditions on Friday.

Now the kicker: freezing rain. A warm layer centered around 800mb
on top of a cold surface, with easterly winds, seems to be an
ideal set up for freezing rain when precipitation begins in
southeast MT...sometime during the evening. GFS/NAM and HREF
members are all highly suggestive of freezing rain, and there very
well could be enough precipitation for ice accumulation before it
changes to all snow later in the night. In addition, a bit of
elevated instability exists on the north side of the surface low
in northeast WY. A few embedded lightning strikes are possible in
far southeast MT this evening. A very interesting system to say
the least. Precip will taper off from south to north Friday
afternoon and evening as a shortwave lifts slowly through the cwa.

With the increased risk of freezing rain in addition to the
snowfall, have opted to upgrade the Winter Storm Watch to a
Warning for an area from Hysham to Lame Deer eastward through
Miles City and Ekalaka. Baker has a risk of ZR- but w/o the heavy have issued an advisory for Fallon County. Big Horn and
Sheridan Counties will see weaker forcing but still some snow,
and have issue advisories for these areas as well. Places from
Billings westward (including the foothills) will miss out on this
event per the downslope component. Billings should see some wet
snow Friday morning but do not think it will stick to roads, and
any accumulation will melt in the afternoon. High temps on Friday
will range from the upper 40s along the foothills to near 30 in
our east.


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

Active beginning to the long term forecast from Saturday through
Monday before conditions quiet down by the middle of next week.
Largest forecast uncertainty resides around a large, and slowly
moving, upper level low over the western United States. Several
waves will rotate around this large area of low pressure this
weekend and into Monday generating rain and snow chances but the
finer details of of exactly where, when, and how much, are still
highly uncertain (as is typical in this type of stubborn weather
pattern). In any case, kept rain and snow chances elevated
through the weekend along with snow accumulations generally around
1 to 3 inches outside the mountains. Look for future updates to
these totals. Though these amounts will likely change through the

The upper level low pressure begins to fill and weaken
as it slides east Monday afternoon with one last day of isolated
to scattered rain/snow showers possible on Monday and Monday night
before a ridge of high pressure takes control of the weather
pattern Wednesday and Thursday (along with drier and warmer
conditions). Dobbs



Areas of rain and snow showers are impacting the mountains and
terminals west of KBIL bringing the possibility for IFR
conditions in the heaviest showers, and widespread MVFR conditions
near KLVM. These conditions will improve after 12z as the
disturbance lifts north. Expect VFR conditions at all terminals
through the day before another disturbance moves in after 00z
Friday bringing deteriorating conditions in eastern terminals
like KBHK and KMLS. Expect mountain obscurations to improve this
morning before returning later tonight. Dobbs



    Tdy Fri     Sat     Sun     Mon     Tue     Wed
BIL 048 028/040 023/040 024/038 023/041 022/044 024/047
    2/S 37/O    22/W    54/W    32/W    11/B    01/B
LVM 050 029/048 024/044 026/040 024/043 023/048 026/051
    3/O 23/O    13/W    54/W    32/W    21/B    11/B
HDN 048 025/039 018/041 020/038 018/040 017/043 017/046
    2/S 79/O    31/B    43/W    32/W    21/B    10/B
MLS 038 024/033 018/036 021/034 019/034 015/034 015/038
    2/S 89/S    51/B    34/J    33/J    21/B    10/B
4BQ 047 026/035 018/042 023/037 021/037 017/040 017/045
    2/S ++/S    31/B    23/W    32/W    21/B    10/B
BHK 035 024/031 017/038 022/034 020/032 015/033 014/038
    2/S 66/S    41/B    23/J    53/J    21/B    10/B
SHR 050 029/041 020/045 024/039 021/040 020/045 020/050
    1/B 67/O    22/W    33/W    32/W    11/B    10/B


MT...Winter Storm Warning in effect from 6 PM this evening to
      midnight MDT Friday night FOR ZONES 30>32-36-37-58.
     Winter Weather Advisory in effect from 6 PM this evening to
      midnight MDT Friday night FOR ZONE 33.
     Winter Weather Advisory in effect from 9 PM this evening to 7
      PM MDT Friday FOR ZONES 38-57.
WY...Winter Weather Advisory in effect from 9 PM this evening to 7
      PM MDT Friday FOR ZONES 98-99.


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