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Area forecast discussion 
National Weather Service Billings Montana
336 am MST Sat Dec 20 2014

Short term...valid for today and sun...

Active weather pattern for The Gap flow areas and the
beartooth/Absaroka Mountains for this weekend. A disturbance
currently moving across the forecast area will continue to bring a
slight chance for a rain/snow shower through the remainder of this
morning with the best chances across our far eastern counties.
Soundings continue to show a pocket of warm air just above the
surface so can't rule out some isolated areas of light freezing
drizzle this morning. Showers will move into the Dakotas this
afternoon leaving our lower elevations precip-free. Lee-side
troughing sets up this afternoon as a surface low develops across
southern Canada with surface high pressure over eastern Idaho
into northern Colorado. Pressure gradients will become very tight
across the Livingston area and the eastern foothills of the
beartooth/absaroka foothills tonight into Sunday night. Model
guidance and local research show high confidence in advisory winds
late tonight into Monday a result...will issue a Wind
Advisory for these areas for this timeframe.

The low across southern Canada will move southeast into the
western Dakotas by Sunday evening. As it will swing a
Pacific front across the forecast area. Pressure gradients will
tighten across the entire area. This combined with 700mb winds
around 55kts and 850mb winds of 40-50kts from the northwest will
result in strong mixing and windy conditions during the day
Sunday. We may need wind highlights for some of our lower
elevations but will hold off for now and see what new model data
has in store.

A series of disturbances along with a constant stream of Pacific
moisture will move onshore across the Pacific northwest and over
the Southwest Mountains of Montana and western Wyoming. This
continuous feed of moisture will begin late this afternoon and
continue into Monday morning. Time heights for the Cooke City area
show the best instability to be during the day Sunday and this is
when the heaviest snow accumulations are expected...but
accumulating snow will begin this evening and continue into early
Monday morning. As a result...have upgraded the Winter Storm Watch
to a warning for the beartooth/Absaroka Mountains for this evening
through Monday morning.

Temperatures will continue to be mild with most areas in the lower
40s today and middle to upper 40s Sunday due to strong mixing.

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

A lot of bouncing around with the models in the middle extended
including Christmas...particularly with the GFS. The European model (ecmwf) has
been more stable in general and is preferred model this morning
thus blended the European model (ecmwf) with the consall to get some of the GFS
flavor in the forecast but giving more weight to the European
solution. Overall this solution keep the Monday through early
Wednesday forecast pretty similar to previous forecast...but
increases probability of precipitation and brings in colder Canadian airmass faster on
Christmas evening.

The differences in the solutions are due to the stronger
California Ridge that the GFS develops Tuesday into Wednesday.
This pushes the jet further north and allows for less
amplification of western trough for Wednesday into Friday. In
general most of the model solutions are very similar with the jet
character but the displacement to the north in the GFS holds a
warmer and somewhat drier forecast for Wednesday into
Christmas...bringing Canadian front and snow in Christmas
afternoon into Christmas night. The weaker European model (ecmwf) California Ridge
allows for a quicker and deeper digging trough bringing
precipitation and colder Canadian air into the area Wednesday

Forecast highlites...Pacific moisture will continue to stream
over the area Monday into Monday night with a 160kt northwesterly
jet over the state. Downslope winds will cut precipitation chances
below whats expected in the mountains but still looking at chance
type probability of precipitation for most locations. Precipitation type looks to be
primarily snow based on BUFKIT soundings...but could see some rain
mixed in during the afternoon. Tuesday looks drier as jet backs to
a westerly direction for a more direct downslope flow and also the
focus of the Pacific moisture will be shifted a bit north of the
area. With downslope gradient will see Lee side troffing and an
increase in wind speeds along the foothills including Livingston
and Nye.

Christmas eve/Christmas...with both models generating
precipitation during this period have increased precipitation
chances and shaded timing toward the European model (ecmwf). This would keep snow
in the forecast for Christmas evening and Christmas day and went with
likely probability of precipitation in areas favored for upslope enhancement with the
Canadian cold during this period. If the GFS pans out
precipitation would be mainly Thursday into Friday and Wednesday
would be drier and warmer. Still too early with too much
uncertainty to get a handle on possible snow accumulations but
the chance for a white Christmas is definitely there for most of
the area. Temperature spreads between the models range from around
40 degrees to 20 degrees for highs on Christmas and going forecast
is right in the middle of this range with highs around 30.

For Friday and Saturday...are should remain under a general trough
for Friday keeping temperatures below average. Could see some
lingering snow showers around particularly in the mountains.
Models develop more zonal flow for Saturday which should help
temperatures warm a bit and bring more snow to area mountains with
breezy conditions in the lower elevations. Latest model iterations
have brought back the potential for an Arctic intrusion sometime
Sunday into Tuesday in the far extended...but given the high
uncertainty in the Middle Range its hard to get too excited about
this potential at this time...but still something to be aware of
for after Christmas Holiday travel. Chambers



Snow will increase over mountain areas today with occasional
obscurations this morning becoming predominant by this afternoon.
A disturbance crossing eastern Montana this morning will bring
scattered showers and local MVFR ceilings east of a Miles City to
Broadus line. This system will shift east of the area this
afternoon leaving prevailing VFR conditions. Outside of these
locations expect VFR conditions today. West to southwest winds
will increase over the western foothills this afternoon with gusts
of 30 to 40kts at times...including the klvm taf site. Chambers


Preliminary point temp/pops...

Today sun Monday Tuesday Wednesday Thursday Friday
bil 043 032/049 034/040 024/036 026/037 025/031 015/028
0/b 23/west 33/o 21/b 24/o 66/S 22/S
lvm 043 034/046 033/037 017/033 023/036 022/032 011/025
1/north 33/west 44/o 22/S 35/S 66/S 32/S
hdn 041 020/049 030/039 022/035 023/036 024/031 013/028
1/b 14/west 33/o 21/b 23/S 66/S 22/S
mls 041 022/044 027/036 024/036 023/034 022/028 013/024
2/j 14/west 22/o 21/b 12/S 33/S 22/S
4bq 042 021/044 029/036 023/036 023/037 022/032 014/026
2/j 04/west 33/o 31/b 12/o 23/S 22/S
bhk 040 024/043 024/031 022/032 019/031 018/026 009/020
3/j 16/west 34/S 22/S 22/S 23/S 22/S
shr 042 023/045 032/036 019/034 022/036 022/032 014/027
1/b 13/west 54/o 31/b 13/S 66/S 32/S


Byz watches/warnings/advisories...
Montana...Wind Advisory in effect from midnight tonight to noon MST
Monday for zones 65-66.
Winter Storm Warning in effect from 6 PM this evening to noon
MST Monday for zone 67.



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