Area Forecast Discussion
Issued by NWS Billings, MT

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
FXUS65 KBYZ 091059

Area Forecast Discussion
National Weather Service Billings MT
359 AM MST Fri Dec 9 2016

.SHORT TERM...valid for Tdy and Sat...

Active weather pattern will continue across the forecast area
today and into at least the first half of the weekend. A strong
jet stream will continue to move onshore across the Pacific
northwest and move eastward across the northern Rockies today
through Saturday. This flow will bring abundant Pacific moisture
across these areas as well, with nearly continuous snow for the
mountain locations across Idaho, as well as western Montana and

Warm air advection combined with Pacific moisture will move over
the arctic air that is in place. This will result in a 48 hour
period of overrunning bringing periods of light snow through
Saturday night. Snow accumulations look to be around an inch today
for areas from about Yellowstone County westward with the
possibility of slightly higher amounts around the foothills

Models then bring a stronger disturbance across the forecast area
tonight and again Saturday night along with higher QPF amounts.
The highest chances look to be along and south of a Livingston-
Billings line. Total accumulations today through Saturday night
look to be in the 2 to 3 inch range as it stands now. At this
time, we do not plan to issue any advisories as the snow looks to
be light with total accumulations spreading out over a 48 hour

Temperatures today will again be in the single digits across the
lower elevations with teens and 20s along the foothills locations.
On Saturday, models try to scour out the arctic air along and west
of a Billings to Sheridan line where temperatures may reach the
20s to lower 30s, with single digits and teens continuing east of
this line. Hooley

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

Active and cold weather pattern will persist thru next week as we
continue to see surges of Canadian air and overrunning Pacific

Sunday will be the warmest day of the extended with a period of
downslope winds behind departing Saturday night wave and ahead of
next approaching Canadian cold front. Should see highs into the
20s to lower 30s, still below normal but not nearly as cold as its
been. Have reduced pops across the lower elevations.

Cold front will arrive late Sunday night bring sharply colder
temps along with a good chance of snow Monday into Monday night as
shortwave drops out of Canada with strong cyclonic flow aloft,
associated with very cold low in northern Saskatchewan/Manitoba.
GFS/EC and the GEFS mean all suggest 850mb temps to around -20C,
so expect temps back down to the single digits during the day on
Monday and below zero Monday night. Pacific moisture, synoptic
ascent and a deep dendritic layer all warrant raising pops and
have done so especially for our upslope areas Monday into Monday
night. At first glance this looks like a typical arctic 1-3 inch
snowfall, with temps turning too cold for elevated snow ratios by
Monday night. Will sustain low pops into Tuesday along the
foothills given some model timing uncertainty.

Temps will remain cold thru midweek as Canadian surface ridge
settles in, but there is some confidence among the models to
suggest a dry period of weather Tuesday night through Wednesday.

00z GFS and ECMWF runs diverge with regard to snowfall potential
by Thursday, with the GFS now drier for our cwa while keeping
Pacific moisture and baroclinicity well to our south. The ECMWF is
less aggressive with the NW flow aloft and allows for Pacific trof
and another round of snowfall Thursday into Friday. This is a
change for the GFS so have sustained pops for these periods. It
appears that temperatures will take another dive as well, and in
fact, the coldest air yet of the season may be in store for us by
Friday. Even the GEFS mean shows mean 850mb temps to near -24C
with an airmass diving out of the Canadian arctic. We could see
our first taste of widespread highs below zero by the end of next




Moist Pacific flow will overrun cold air at the surface to produce
areas of light snow today and tonight. Reductions to MVFR/IFR are
expected, mainly from KLVM-KBIL, along with periods of mountain
obscurations. KSHR, KMLS and KBHK are most likely to remain VFR.



    Tdy Sat     Sun     Mon     Tue     Wed     Thu
BIL 008 005/021 014/031 005/010 901/010 000/014 901/011
    6/S 64/S    41/B    56/S    62/J    11/U    12/S
LVM 020 016/032 021/032 014/020 000/012 902/016 901/012
    6/S 66/S    62/J    46/S    62/J    11/U    12/S
HDN 011 006/019 008/033 006/012 902/012 904/013 903/012
    3/S 64/S    41/B    46/S    52/J    10/U    11/B
MLS 003 903/011 000/026 002/007 907/008 903/013 905/009
    2/S 46/S    21/E    45/S    21/B    11/B    11/B
4BQ 009 002/018 006/030 005/013 904/009 903/014 903/012
    1/E 33/S    31/B    24/S    31/B    10/U    01/B
BHK 001 908/009 903/021 902/003 907/005 904/008 907/007
    1/E 36/S    21/E    34/S    21/B    10/B    01/B
SHR 014 007/028 014/030 011/016 905/008 906/013 904/013
    1/B 24/S    31/B    26/S    52/J    10/U    02/S




$$ is the U.S. government's official web portal to all federal, state and local government web resources and services.