Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 091613
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
913 AM MST Mon Jan 9 2017

.UPDATE...
Minor adjustments to the forecast this morning to keep
temperatures a bit cooler over northeast portions of southeast
Montana and adjust chances for precipitation this afternoon.
Warming along the foothills continues with lower elevations
showing signs of scouring out. Clouds may hinder this process a
bit in eastern areas so pulled temps back a bit. borsum

&&

.SHORT TERM...valid for Tdy and Tue...

Snow associated with a warm front, was moving ENE through the
eastern part of the forecast area. There was also snow over the
Beartooth/Absaroka mountains per radar imagery. Temperatures early
this morning were in the 40s at Nye and Roscoe, with 30s and 40s
observed over the high elevations SW. This warm air will push N
through the area today. Models had a decent handle on current
situation and have used a blend throughout the forecast. Kept high
chance PoPs ahead of the warm front this morning with low PoPs to
the S. Went with categorical over the SW mountains where 4-5
inches of snow is expected. Regarding chances for mixed
precipitaton, soundings supported a rain/snow mix over the far W,
with freezing rain and snow over the NE ahead of the front.
Checked road surface temperatures over KLVM and they were around
20 degrees. Opted to mention a freezing rain/snow mix over the W
through 15Z. Thereafter expect road surfaces to warm enough to be
able to go with plain rain in this area. Further NE will keep a
freezing rain/snow mix through the morning. Added areas of blowing
snow early to Fallon and Carter Counties due to gusty SE winds.
When the warm air reaches KLVM, it will switch winds around to the
WSW as a surface low moves through this area. Again, expect
possible wind gusts to 50 mph and will continue the DSS table for
these winds. Highs today will range from the upper 20s NE to the
40s W.

The flow aloft remains progressive through Tue. night with
occasional jets providing divergence over the area. Shortwaves
moving through the area will weaken late tonight and a cold front
will push S through the region. Frontogenesis will bring likely
precipitation to the N and NE zones this evening in the form of
snow. Had slight chance to chance PoPs over the rest of the area
with the exception of likelies in the SW mountains. Had much of
the area dry late tonight except for the mountains due to the lack
of energy. Only had 3 inches for the SW mountains. It will remain
windy in KLVM and have mentioned blowing snow there.

A strong shortwave rotates SE into the region from Canada late
Tue. through Tue. night. This wave will push a cold front S
through the area with strong frontogenesis. Increased PoPs across
the area from Tue. afternoon onward and had likelies Tue.
evening. A Winter Weather Advisory for snow may be needed late
Tue. onward. At this time, the potential for some accumulating
snow looked best over the west and mountains. Gusty winds will
create areas of blowing snow over portions of the region Tue. and
Tue. night. Highs on Tue. will run from the single digits E to the
lower 30s W. Arthur

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


Models were coming in better agreement for the Wednesday/Thursday
system, but still some differences exist. The general idea is for
an arctic boundary to deepen over the forecast area with pacific
moisture over running this cold air for snowfall. The GFS
continues to be the most ambitious in high QPF values up and also
in lingering snowfall into Thursday morning. That being said, the
GFS has decreased some of its snow amounts and thus has trended a
little closer to the ECMWF. The time of strongest dendrite growth
should be through the day Wednesday, with the atmosphere becoming
much colder Wednesday night and thus limiting the flake size.
Focus by both the models point to the western locations and
foothills for the heaviest snow and this consistent with snow
amounts progged by WPC. Have maintained high PoPs for Wednesday
and even raised them a bit more. Looks to be a possible advisory
type of snow event for western and central zones.

The GFS has warmed temperatures Thursday and ended up closer to
the ECMWF with the bulk of frigid 850mb air sliding east into the
Dakotas. Have raised highs a bit for this, but did not go too warm
as Wednesday night looks quite cold now with fresh arctic air and
fresh snow cover to add to the deep snowpack most locations are
seeing. The coldest day may turn out to be Wednesday as the models
turn low level gradients downslope by early Thursday afternoon.
Rising mid level heights with a mean ridge forming over the
Pacific northwest will lead to downslope warming Friday through
the weekend. Models want to warm 850mb temperatures to 3-4c by
Sunday. This may be a bit over done with deep snow cover and
arctic air still trapped in a lot of western valleys, so will
temper the warm up a bit.

The bigger potential issue could be increasing winds over the
west Friday and Saturday with a lee trough forming and cold high
pressure in place over the Great Basin. This could lead to more
blowing snow issues over western locations. The amount of blowing
snow will depend on snowfall received Tuesday/Wednesday and on the
degree of warming Friday and Saturday. Should temperatures rise
above freezing, the blowing snow threat would be greatly reduced.
Will have to monitor this potential closely the next couple of
days. TWH
&&

.AVIATION...


Isolated areas of light snow, and some freezing rain, will lessen
by early afternoon. Southwest winds will gust to 25-30kts at
KLVM at times. Additional rain/snow showers will move across the
region later this afternoon, possibly generating brief periods of
MVFR/IFR. The mountains will be obscured through the day with
heavy snow. TWH/Dobbs

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Tue     Wed     Thu     Fri     Sat     Sun
-------------------------------------------------------
BIL 038 014/022 902/006 910/005 910/020 008/028 016/032
    3/W 34/S    67/S    51/B    11/U    10/U    01/N
LVM 043 019/032 006/015 902/014 903/024 011/029 018/033
    6/W 44/S    57/S    51/B    11/N    11/N    11/N
HDN 035 010/020 904/007 914/003 916/017 902/024 005/030
    3/W 33/S    67/S    51/B    10/U    00/U    01/B
MLS 026 901/010 913/005 916/901 919/013 902/024 008/029
    4/J 73/S    53/S    31/I    10/U    00/U    00/U
4BQ 038 007/024 905/007 911/006 917/019 000/026 008/030
    2/W 32/S    46/S    42/J    10/U    00/U    00/U
BHK 026 001/009 912/004 918/903 920/013 902/021 008/028
    5/J 62/S    62/S    31/I    11/U    00/U    00/U
SHR 042 014/028 901/012 908/008 910/022 003/028 007/032
    2/W 22/S    45/S    62/J    10/U    00/U    00/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning in effect until 6 AM MST Thursday FOR
      ZONE 67.
WY...None.

&&

$$
weather.gov/billings



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