Area Forecast Discussion
Issued by NWS Billings, MT

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691
FXUS65 KBYZ 061012
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
312 AM MST Tue Dec 6 2016

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

A band of snow formed over the I-90 corridor late this evening
ahead of a small upper PV anomaly. Radar has already indicated
weakening of this band as it slides southward into northern
Wyoming although light snow is still ongoing from Fort Smith to
Sheridan.

Today, another upper impulse slides southeastward out of Idaho and
southwest of our area. Expect isolated off and on snow showers
between Bozeman and Laurel from this afternoon through the
evening hours, however we are not anticipating significant
accumulations with these showers.

Currently, in Billings the temperatures is 12 degrees however
temps are in the single digits over the eastern Plains. Winds at
Roundup and Hysham have begun to switch more easterly and temperatures
should begin to fall more rapidly through the morning hours as the
arctic air mass moves up the river valleys. Temperature forecast
is pretty much unchanged for the short term. Model guidance
continues to point to below zero temperatures for the next two
nights for the entire area. Areas that received snow cover such as
Red Lodge and Sheridan could see temps fall below -10 F on
Thursday morning as cloud cover wanes.

Current observations from Fallon and Carter county show wind
chills near -20 F tonight with gusty winds being generated by a strong
low over the Dakotas. Longer duration wind chills will likely be a
concern over the eastern Plains for Tuesday night through
Wednesday as winds above 15 mph combined with below zero
temperatures will bring wind chills below -20 F. The decision on
wind chill advisories will likely be made later this morning by
the day crew. Walsh


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

Very challenging forecast for the extended period with a lot of
energy over northern Canada producing generally zonal flow for the
area. This complicated by the arctic boundary that will be laying
over the northern Rockies and trying to slosh eastward out of the
area. Overall trend that was identified yesterday, for a slower
retreat of the arctic, still looks on track today. Both GFS and
ECMWF keep the baroclinic zones somewhere over our western zones,
being thinned by zonal flow aloft. The GFS was more aggressive in
edging the boundary east Thursday, but even its guidance keeps
highs in the single digits for central and eastern zones Thursday,
with some slight modification over the west. Have trimmed back
highs once again for Thursday to match MAV and MET guidance.
Current forecast was warmer than ECMWF guidance, which seems too
warm given the 850mb temperature forecast from all the models.

The ECMWF keeps a lot of energy over the Pacific Northwest and
this keeps lower surface pressures over the Great Basin and thus
does not move the arctic airmass east much at all this weekend.
The GFS does show signs of pushing the arctic east briefly Friday
and Saturday but not sure this is correct given the amount of
energy the model moves into Washington and Oregon on Saturday.
Will need to watch highs for Friday and Saturday, as may be too
warm. Both models have a ton of cold air over southern Canada late
in the weekend that they spill in early next week. This air looks
colder than the current batch. That is also complicated by a
couple of over running events. One Friday night and Saturday,
(most of this may be over western and northern Montana), and the
other Monday into Tuesday of next week. This second one could be a
significant winter event as models were taping into deep Pacific
moisture to throw over the top of arctic air. Stay tuned. TWH
&&

.AVIATION...

A band of light to moderate snow will move across southern Big
Horn county and Sheridan county early this morning, impacting
KSHR. This snow will produce IFR to occasional LIFR conditions.
The snow will taper off by 14Z. MVFR conditions can be expected at
KBHK this morning in lower clouds. Also, strong northwest winds of
20-30kts at KBHK, will produce some blowing snow. The rest of the
area will have mainly VFR weather, with localized MVFR conditions
in isolated snow showers. Mountains will be frequently obscured.
TWH
&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Wed     Thu     Fri     Sat     Sun     Mon
-------------------------------------------------------
BIL 011 904/006 906/007 006/028 017/026 014/030 016/028
    1/E 11/B    10/U    12/J    33/J    21/B    12/J
LVM 011 908/007 908/011 011/036 021/031 018/031 020/032
    2/J 21/B    11/B    33/W    43/J    32/J    22/J
HDN 012 904/005 906/009 005/023 014/026 011/031 014/027
    1/E 11/B    10/U    12/J    24/J    21/B    12/J
MLS 011 903/005 907/006 902/015 005/018 002/020 006/021
    1/E 11/E    00/U    02/J    24/J    21/B    22/J
4BQ 010 905/005 912/010 901/023 011/024 004/028 010/029
    1/B 11/B    00/U    01/B    24/J    21/B    12/J
BHK 007 905/004 909/004 906/012 002/015 000/017 005/021
    1/N 11/E    00/B    01/E    23/J    21/E    12/J
SHR 009 908/006 909/011 005/033 014/029 011/030 012/031
    2/J 21/B    00/U    11/B    33/J    21/B    12/J

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

$$
weather.gov/billings



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