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afdbyz

Area forecast discussion...updated
National Weather Service Billings Montana
851 PM MST Tue Feb 21 2017

Update...
thunder appears to be over for the night. Still have steep lapse
rates based on mesoanalysis, and these were contributing to
showers ahead of a strong shortwave moving through the area, seen
on water vapor and the new WRF. Spread 20 pops across the area
ahead of the shortwave through the night. Gusty winds continued
over western areas, but have come down over the rest of the
region. The exception was kshr where there was a gust to 56 mph
per the ASOS site. This seemed to be due to mixing down of high
winds due to showers in the vicinity and a large
temperature/dewpoint spread, as opposed to mountain wave activity
which was not supported by the models. Winds should continue
decreasing through the night over most areas with the loss of
insolation, so will cancel the wind highlights. Adjusted cloud
cover based on satellite and consshort which looked reasonable.
Temperatures were in good shape. Cold front over north Montana did not have
much frontogenesis with it and new models did not show much over
the area on Wednesday. The chance pops looked okay, but upslope
flow could bring better chances to some of the favored areas. Next
shift can take a closer look at the situation. Arthur

&&

Short term...valid for Wed and Thu...

Busy and challenging forecast for the short term. Strong 120kt
jet was crossing northern Wyoming with 700mb winds upwards of
55kts crossing far southern Montana. Strong downslope flow has
induced deep mixing and temperatures have responded in kind with
readings rising into the 60s this afternoon. Mixed winds have been
mainly in the 40-50mph range for most locations. Winds have been
very close to advisory criteria in Livingston but have stayed a
bit below warning criteria for Big Timber and areas of southern
Montana into Sheridan County Wyoming. Shortwave was moving through
the area as of this writing, and may induce a bit of subsidence
that could peak the winds over southern locations yet this
afternoon and early this evening. Winds looks to hang on a bit
longer over the west as the gradient orientates itself well for
the Big Timber to Harlowton corridor and 700mb winds hover around
50kts through the evening.

Attention then turns to cold frontal boundary pushing into the
area tonight and the potential for snow when combining this with
the approaching western trough. There have been differences on the
extent and timing of the 850mb frontal boundary dropping south
from northeast Montana. The NAM and European model (ecmwf) were more aggressive in
sending the boundary into south central Montana by late Wednesday
morning into early afternoon. The GFS holds off until late
Wednesday afternoon, or even early evening. Since the GFS was a
bit of an outlier, went with a ec/NAM combo. Am thus expecting
some precipitation to develop along the boundary over south
central Montana into southeast Montana by late Wednesday morning
into early afternoon. Would be a rain and snow mixture as the
airmass doesn't get adequately cold until Wednesday evening. At
any rate, this boundary brings an end to the very mild weather of
the last few days.

The western upper trough will swing into the northern rockies
Wednesday night and Thursday, with a low cutting off over southern
Wyoming early Thursday. The models have struggled greatly on
resolving this pattern, but have just lately pushed the system a
little farther north and deepened the low. This would provide
strong potential for accumulating snow over southern locations and
into northern Wyoming through Thursday. Have raised pops for
areas south of Billings with likely snow over southern Big Horn
County and Sheridan County Wyoming late Wednesday night through
the day Thursday. Added accumulating snow with a few inches
possible by the time the snow tapers off Thursday night. Will have
to watch these areas closely for potential highlights. Twh

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

Not many changes in the long term. Models continue to show a
general northwest flow pattern setting up Friday and continuing
through the weekend. While the general pattern in the models is
similar the timing and placement of the precip is still very
uncertain. This lower confidence has lead to only minor tweaks
based on a blend of the solutions. With moisture lingering in the
area have continued the chance pops. Temperatures will continue
to be slightly below normal through the period. With the cooler
temperatures still expecting any precip that falls to be snowfall.

Early next week a trough will move into the northern rockies
giving a chance for some better organized precip.

Reimer
&&

Aviation...

Winds will decrease tonight. Expect VFR conditions to prevail,
though some MVFR conditions could begin around kmls after sunrise
Wednesday as some rain and snow moves into the area.
Beartooth/Absaroka Mountains will be obscured tonight and
Wednesday. Crazy Mountains will be obscured on Wednesday.
Rms/Arthur

&&

Preliminary point temp/pops...

Wed Thu Fri Sat sun Mon Tue
-----------------------------------------------------------
bil 036/048 026/036 021/033 017/032 016/036 019/033 014/033
24/west 54/j 32/S 12/S 11/b 12/S 22/S
lvm 031/044 018/030 013/027 008/027 011/032 016/032 014/033
23/west 44/j 33/S 32/S 21/b 22/S 22/S
hdn 033/047 024/036 020/033 014/031 013/035 017/035 014/033
24/west 44/j 33/S 12/S 11/b 11/b 22/S
mls 034/044 026/037 021/034 019/032 017/034 019/034 017/033
35/west 33/j 22/S 12/S 11/b 11/east 22/S
4bq 034/047 025/037 020/035 017/032 015/035 017/038 017/036
24/west 45/j 42/S 12/S 11/b 01/b 22/S
bhk 034/041 024/034 017/030 017/028 013/030 015/032 014/030
25/west 33/j 21/east 12/S 11/b 01/east 22/S
shr 031/046 023/034 017/028 010/027 008/032 012/034 014/031
23/west 67/j 64/S 32/S 11/b 01/b 22/S

&&

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

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