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afdbyz

Area forecast discussion...updated
National Weather Service Billings Montana
757 PM MST Fri Dec 9 2016

Update...

Further adjustments to highlites with this update. Added the
Bighorn Mountains and northern/eastern Carbon County to the going
winter weather advisories. Radar has shown a pretty strong snow
band from Cooney Reservoir east through Fromberg and Bridger over
the past hour or so. Models fill this area in with snow overnight
so expect poor travel on us212 all the way from Red Lodge into
Laurel tonight. For the bighorns the westerly flow pattern isn't
a great snow producer, but this atmospheric river pattern should
have enough moisture to overcome the inherent downslope off the
mountains to the west. In addition expect gusty winds to create
some significant blowing and drifting issues overnight into
tomorrow morning. So issued advisory for 4 to 6 inches of snow
combined with blowing and drifting snow problems along us14 over
the bighorns.

Updated precipitation chances to categorical values generally west
of a Hysham to Sheridan line. 00z NAM and hrrr have been
increasing precipitation amounts over this area and radar supports
this trend. Have a bit of a concern about the area right along the
northern beartooth foothills where radar has been showing a good
downslope shadow so far. Its possible that this feature will
persist tonight and that snow band currently setting up from
Fishtail to Cooney Reservoir and Bridger will be the main
precipitation producer leaving Red Lodge and Nye with just a
dusting. Still seeing some decent dynamics aloft to support some
snow though along with some slop over from the upslope into the
Cooke City area so kept high pops but lowered snow amounts right
along this area, and further lowering may be needed if this
downslope signature persists.

Latest NAM and hrrr showing axis of best snow from Livingston to
Billings overnight into tomorrow afternoon. Already snowing
moderately at times in Livingston. Radar has shown snow in the
vicinity of Billings the past hour or so and expect snow to get
going in central areas in the next hour or so. Heaviest
accumulations for western areas is from now through sunrise,
central zones from midnight through late morning.

Temperatures over western zones are near their lows already and
should see a gradual rise overnight. Areas at 6000 feet are
currently in the single digits there but climb to 7500 feet and
temps are in the mid 20s. May see a few degrees of cooling in
central zones thanks mainly to evaporative cooling as snow
develops, then a rise by sunrise into the teens in many areas.
Eastern zones will stay mainly in the single digits above and
below zero with a few teens below around Fallon County. Chambers

&&

Short term...valid for Sat and sun...

The first wave of energy is still lingering across Musselshell,
Treasure, and Rosebud counties. The next impulse of energy is
working into western Montana. As this wave moves into the area,
expect snow to spread across the area overnight. Lower elevations
will see an additional 1 to 2 inches of accumulation through
tomorrow afternoon. The foothills will see 3 to 4 with the high
mountains getting up to 6 to 10. This will result in roads
continuing to be snowpacked, especially the less traveled roads.

Given the accumulations and the snow cover on roads, will continue
the winter weathe advisory through tomorrow afternoon.

Through the day tomorrow, warmer west winds will begin to shift
east towards Billings. As it does, expect the snow to decrease and
temperatures to increase into the 20s. Sunday should be drier and
warmer. Much of the area will see temperatures in the 20s to near
30. Reimer

Long term...valid for Mon...Tue...Wed...Thu...Fri...

Not a lot of changes were made to the extended forecast.
Uncertainty is still very high in the global models after Tuesday
morning. While the details of the forecast (especially snowfall)
are very cloudy right now, it does appear the trend of cold
temperatures will continue through next week.

Extended begins with another Arctic cold front pushing south
through the forecast area early Monday. A good feed of Pacific
moisture in the westerly flow aloft will setup a good overrunning
situation (moisture forced to rise over The Wedge of Arctic air) and
give the region another good shot of snowfall around 1-2 inches
(2-4 in the mountains) beginning Monday morning. Snowfall will
taper off overnight Monday into Tuesday morning. After a mostly
quiet Tuesday (expect for some mountain snowfall), big differences
in the models begin to appear.

The source of these differences arise from the handling of a cut-
off upper level low off the western US, and its interaction with a
large upper level low over northern Canada. The GFS and Canadian
keep the Pacific low weaker, and allow a drier northwest flow to
preside over the region through at least Thursday night. The ec
solution has a stronger cut-off low in the Pacific, and a weaker
upper level low in Canada, this setup results in wetter westerly
flow over the region, and allows much better chances for snow late
Wednesday night into Thursday. While the details are sketchy at
this point, it certainly lent at least a mention of snow in the
forecast for Thursday based on these differences.

Looking to the end of next week and into next weekend, the global
models indicated another disturbance crossing the region, and another
shot of snow. Timing differences are quite large with this system however.
Ec gets the snow going again on Friday while the GFS and Canadian
are much slower. Either way, the extended period continues to look
unsettled and cold. This is supported well by the model
ensembles. Dobbs

&&

Aviation...



Snow will continue to overspread the region this evening and
overnight into Saturday bringing generally MVFR to IFR conditions
with LIFR possible under the heaviest Snow. Mountain obscurations
will be prevalent through the taf period and MVFR/IFR conditions
wont improve to VFR until after 12z, and from west to east. Kmls
and kshr should stay VFR through this system, though isolated MVFR
in a quick snow shower is certainly possible Saturday morning. Dobbs/stp

&&

Preliminary point temp/pops...

Sat sun Mon Tue Wed Thu Fri
-----------------------------------------------------------
bil 004/022 012/030 006/010 901/011 902/014 901/013 902/006
+8/S 31/b 25/j 41/b 10/u 12/j 33/j
lvm 006/033 017/031 014/020 003/014 902/014 002/015 901/003
+8/S 42/S 35/j 42/j 11/u 12/j 33/j
hdn 003/023 009/030 007/012 903/013 907/014 905/014 904/007
88/S 41/b 24/j 21/b 10/u 01/b 33/j
mls 902/013 001/022 002/004 905/011 904/012 904/012 905/006
45/S 31/b 34/j 21/b 10/u 01/b 33/j
4bq 901/020 006/027 005/010 904/012 903/013 902/014 902/007
33/S 41/b 13/j 21/b 10/u 01/b 33/j
bhk 909/008 902/017 902/001 907/007 904/006 906/006 906/001
24/S 41/b 24/j 11/b 11/b 01/b 23/j
shr 008/028 014/030 011/015 903/009 905/012 902/014 904/005
33/S 52/S 24/j 32/j 10/u 01/b 33/j

&&

Byz watches/warnings/advisories...
Montana...Winter Weather Advisory in effect until noon MST Saturday for
zones 28-29-34-35-39>42-56-63>66.
Winter Storm Warning in effect until 6 PM MST Saturday for
zone 67.
Wyoming...Winter Weather Advisory in effect until 6 PM MST Saturday for
zone 98.

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