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Area forecast discussion...updated 
National Weather Service Billings Montana
940 am MST Friday Dec 26 2014

current forecast in good shape and did not make any changes. Weak
northerly flow over the state with a shortwave trough moving
slowly toward the area. This wave will bring in a few snow showers
this afternoon...with the main focus over western and central
zones. Patchy fog and flurries over the east will gradually burn
off by noon. Chilly start...along with increasing clouds...will
keep highs below seasonal averages. Twh


Short term...valid for today and Sat...

The weather will be relatively benign through Saturday and in fact
the only real issue may be gusty winds and patchy blowing snow for
some of the foothills locations like Livingston come Saturday.

Today...a stratus field /area of low clouds with bases around 2000
feet above ground level/ exists over north central Wyoming and southeastern Montana as of the
10 UTC hour. Model guidance is not simulating these clouds well so
the questions we have to answer are how long will they last during
the day and what other impacts to sensible weather will they have.
Recent satellite imagery and observations do show an eastward trek
to the back edge of the stratus...which passed through Billings at
about 08 UTC...followed by shallow/relatively brief fog once cloud
cover broke. Simple extrapolation of these trends supported clouds
lingering over all of southeastern Montana through at least middle morning
and insertion of patchy fog into the forecast on its west side for
the Sheridan...Lame Deer...Hysham and Forsyth areas. We also chose
to include scattered flurries with the stratus through 18 UTC with
that activity also observed in spots overnight...and with a bit of
support in high-resolution model guidance for it too. It seems the
cloud cover or lack thereof will not have much affect on highs for
today since the air mass is relatively cold and weakly mixed...and
we thus expect highs mainly in the 20s f everywhere.

By this afternoon...we have a small chance of snow showers in play
for much of the area as far east as Miles City and Lame Deer which
is predicated on modest qg-forcing tied to a weak shortwave trough
passage. Based on the 00 UTC guidance depiction of that forcing we
did spread the slight chance of snow showers further southwest and
thus into the Livingston and Billings corridor after 18 UTC. More-
over...we added some low probability of precipitation into southeastern Montana for the evening
hours too given similar trends.

On Saturday...pressure falls will increase over the northwest U.S.
And a Lee-side pressure trough will deepen...leading to some gusty
winds in the foothills areas. Forecast soundings at Livingston are
supportive of this scenario with a stable layer aloft...but 700-mb
winds are only 40 knots or less and that is not well-correlated to an
advisory-type wind event. Our in-house statistical guidance there-
fore only has about a 40 percent probability for 60 miles per hour wind gusts
at Livingston. We thus kept forecast wind gusts capped near 50 miles per hour
for now. Still...that could be enough for some patchy blowing snow
and that was also added to the forecast in the foothills. Highs in
most areas should warm a bit more on Saturday with downslope flow. Saturday night the chance of light snow will increase
over south central Montana...but the timing of the snow onset does have
some increasing uncertainty to it with some spread in 00 UTC model
solutions. Schultz

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

Sunday a weakening disturbance moving along the Idaho Montana
border travels across southwest Montana in the broader slightly
cyclonic flow aloft over the state. This brings slightly deeper
moisture into the region but dynamics are not very strong with
this system. However...its arrival phases with an Arctic airmass
traveling into Montana. Expect the Arctic frontal passage to be
between 06z to 15z for Judith Gap and 10z to 19z for Billings and
15z to 00z for Sheridan so impacts on Sunday are not quite certain
yet. Regardless of timing...when the Arctic arrives it will bring
a period of light snow with BUFKIT sounding indicating a good
dendritic growth region for a 9 hour period. Thinking is lighter
precipitation event with better snowfall ratios so another low
elevation 2 to 4 inch event expected with foothills seeing higher

Cold air behind this system is the coldest of December and below
zero temperatures are expected. Monday temperatures will not rise
above the single digits and then plummet Monday night as the
Arctic high pressure axis is over southern Montana and northern
Wyoming. Expect areas Billings and west to see lows in the 10 to
20 below zero range as greater snow depth helps power the cold

Northerly flow aloft drives the surface high pressure south of the
area on Tuesday and a weak downslope pattern evolves with still
relatively cold airmass over the area. This brings a period of dry
but cool weather through Thursday.

Thursday the models show another Arctic begins moving into
northern Alberta with this system reaching Montana and Wyoming on
Friday. This system is expected to have an alignment similar to
the Sunday system where cyclonic flow aloft provides only marginal
dynamics but deepens moisture to support light snow. Borsum



Low clouds with flurries areas east and south of Billings
including kshr and kmls producing MVFR conditions. Kbil and areas
west will see partly cloudy conditions with a band of furries
moving through the area middle afternoon. Borsum


Preliminary point temp/pops...

Today Sat sun Monday Tuesday Wednesday Thursday
bil 025 010/026 016/025 903/002 915/008 000/030 015/030
2/j 11/north 36/j 72/j 11/north 00/north 11/north
lvm 025 000/026 014/026 905/010 919/013 902/030 015/035
2/j 11/q 57/j 62/j 11/b 00/north 11/north
hdn 026 003/027 013/026 904/004 917/008 904/028 013/029
2/j 21/b 26/j 72/j 11/b 00/north 11/b
mls 027 011/028 016/025 901/005 907/011 003/027 014/028
2/j 21/b 25/j 41/east 10/u 00/b 11/b
4bq 024 007/028 013/026 901/006 912/008 902/027 014/029
1/M 20/b 15/j 62/j 11/b 00/u 11/b
bhk 022 010/027 012/022 905/003 908/009 002/025 013/026
1/M 21/b 14/j 31/east 10/u 00/b 11/b
shr 024 901/026 010/024 901/008 916/012 902/031 015/034
1/M 20/b 15/j 73/j 21/b 00/u 11/b


Byz watches/warnings/advisories...



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