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Area forecast discussion 
National Weather Service Billings Montana
235 PM MST Tuesday Jan 27 2015

Short term...valid for Wednesday and Thursday...

Another mild day across the forecast area with an unusually warm
air mass in place across our region. Model proggs are in good
agreement with regards to a subtropical weather system
undercutting the ridge aloft. Look for increasing clouds later
today as this system will track through the Great Basin and
approach our SW zones this evening. The moisture is mainly middle
level and lift is moderate at best. Thus I expect to see areas of
virga or sprinkles over the plains...but some decent rain and snow
showers in the high country. Snow levels may drop to around 6kft
late tonight...but being of subtropical origin...I do not expect
to see accumulations pile up much lower than this. The system will
then track east/southeast thanks to the cyclonic flow over the
area...and this will take it by the big horns as well on Wednesday
with some scattered showers into the Sheridan area briefly at some
point as well. The cloud cover and height falls will result in
cooler temperatures tomorrow...but still generally on the mild
side for late January.

Things dry out Wednesday night and Thursday as the system exits to
the southeast. However...the air mass will have been modified a
bit and temperatures will be cooler for Thursday...though still
above seasonal norms. Bt

Long term...valid for Friday...Sat...sun...Mon...Tue...

The normalized Standard deviation for the European model (ecmwf) ensembles showed
a low confidence forecast through the extended period.
Similarly...the GFS spaghetti plots showed a fair amount of spread
through much of the period. Thus forecast confidence will not be
very high with this package.

Period starts off on Friday with a flat northwest flow over the forecast
area...while the large trough along 131w on water vapor imagery
this afternoon...moves into the SW U.S.. models keep the moisture
from this system S of the area. A shortwave in the northwest flow will
move through the area Friday night through Sat driving a backdoor
cold front into the region. Friday looked dry on both the European model (ecmwf) and
GFS. The models then differed on frontal and precipitation timing
into the area for Friday night and Sat. Went with a model blend for
probability of precipitation which resulted in the best precipitation chances on Sat. Flow
will remain basically northwest over the region through Tuesday with ridging
upstream of the area through Monday. The frontal boundary will get
reinforced through sun and Pacific flow will overrun the boundary
bringing additional precipitation to the area. Will again need to
go with a model blend for probability of precipitation. Waves of low pressure will move
along the frontal boundary through Monday...then the boundary was
forecast to move out on the GFS on Tuesday. The European model (ecmwf) brought the
boundary back into the area on Tuesday. So chances for precipitation
will continue through Tuesday. Previous forecast carried this idea
well.

There were large temperature differences between the models for
portions of the extended due to the differences in the ways
the models handled the frontal boundaries. Will go with super
blend for the temperatures. Arthur
&&

Aviation...

Scattered rain and snow showers will move NE into the area
tonight through Wednesday morning producing MVFR conditions from klvm southeast
to kshr. Mountain obscurations will increase tonight through Wednesday
morning as well...with the most widespread obscurations over the
beartooths...absarokas and NE big horns. Precipitation will
decrease Wednesday afternoon confined to mountains and nearby areas.
Surface winds will shift to the northwest Wednesday afternoon as a cold front
moves through the area. Arthur

&&

Preliminary point temp/pops...

Wednesday Thursday Friday Sat sun Monday Tuesday
-----------------------------------------------------------
bil 042/054 029/046 029/049 028/038 019/032 019/035 021/035
11/east 00/b 00/u 13/west 23/j 33/j 22/west
lvm 041/051 027/047 029/048 024/040 018/037 023/041 024/040
33/west 00/b 01/u 13/west 23/j 44/west 32/west
hdn 036/051 024/044 025/048 023/035 014/031 014/033 015/034
01/east 00/b 00/u 13/j 22/j 33/j 22/j
mls 037/048 026/043 026/044 024/032 014/027 010/027 012/028
00/north 00/b 00/b 13/j 22/j 22/j 22/j
4bq 035/051 025/046 027/047 025/037 016/032 014/034 017/035
00/east 00/b 00/b 13/west 22/j 22/j 22/west
bhk 034/045 025/039 025/043 023/029 010/024 007/023 011/028
00/north 10/b 00/b 13/j 22/j 22/j 22/j
shr 032/049 021/043 022/045 020/036 013/033 014/036 017/034
33/west 00/b 00/b 13/j 32/j 33/west 22/j

&&

Byz watches/warnings/advisories...
Montana...none.
Wyoming...none.

&&

$$
Weather.Gov/Billings

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