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Area forecast discussion 
National Weather Service Billings Montana
849 PM MST Sat Dec 27 2014

Update...
forecast in good shape tonight and only made some minor changes
for coordination with neighboring offices. Gusty gap flow winds
are continuing at Livingston and near Nye this evening with
occasional gusts to 50 miles per hour. This will the strongest period of
winds with pressure falls ahead of advancing short wave. Winds are
expected to remain below advisor criteria as 700 mb winds only
forecasted around 35 kts. These winds will begin decreasing by
early morning. Snow still on track for tomorrow along with cold
Arctic air mass moving into the forecast area. Area radars
showing snow developing over northwest Montana with upper short
wave moving into the state. Snow is expected to develop over our
northwest zones around midnight and move south overnight. Heaviest
snowfall is still expected around midday Sunday for south central
Montana as dendritic layer lowers to near the surface. This will
bring good snow growth potential as the dendritic growth zone will
run through the strongest Omega. Will make no changes to current
highlights. Richmond

&&

Short term...valid for sun and Monday...

Winds have increased at Livingston with some gusts to 50 miles per hour.
Visibility has dropped below 10 miles...so they has been some
blowing and drifting snow there. Winds will stay strong this
evening before backing off overnight as a cold front approaches
from the north.

An upper trough currently just off the British Columbia coast
this afternoon will drop into the Great Basin tonight. This will
drop an Arctic cold front toward southern Montana. Both the GFS
and European model (ecmwf) send energy across our northwest zones overnight ahead
of the frontal boundary and provide decent ascent. The GFS was
more aggressive in this regard...but it appears snow will begin
north of Billings late tonight. Snow will kick in for the rest of
the area Sunday as the Arctic boundary slides in.

The strongest period of upper forcing looks to be early Sunday as
jet energy dives into northern Utah...but the strongest low level
forcing through upslope flow will be Sunday afternoon and evening.
The GFS continues to be quicker with the stronger upslope flow and
dendrite growth zone invasion. Considering all things...looks like
the period of heaviest snow for most locations of south central
Montana and northern Wyoming will be Sunday afternoon into Sunday
evening. This is the period of strongest upslope and when the
models were advertising the deepest dendrite growth zones in line
with low level ascent. Widespread snow amounts of 3 to 5 inches
looks on track for this event as the snow will continue into
Monday morning. Favored upslope locations...from Red Lodge to
McLeod could see heavier snow amounts as typically occurs for
these events. Due to lower quantitative precipitation forecast amounts with this event compared to
the most recent event...will not go with a warning at this time for
the foothills. Issued advisories for south central Montana and
north central Wyoming...and eastern parts of southeast Montana for
Sunday through Monday morning. Will have to watch Red Lodge
closely...as may need to upgrade to a warning if the snow piles up
quickly.

As the Arctic comes in Sunday...temperatures will plummet with
falling readings through the day. Highs will be Sunday morning.
North to northwest winds will cause some blowing and drifting of
fluffy snow. Judith Gap will be especially prone to blowing and
drifting snow as the Arctic invades. Expect near whiteout
conditions there for part of the day Sunday.

Snow will continue Sunday night...but accumulations will be
lessened by the Arctic airmass deepening and taking the efficient
dendrite growth zone out of play. The snow will taper off quicker
over the northeast...with lingering light snow over western and
central zones. Most of the snowfall should end Monday afternoon.
High temperatures on Monday will be very chilly with cold
advection through the day and 850mb temperatures of -20c over the
northern rockies. Lows Monday night will be tricky as models were
lingering low level moisture through the night. 850mb
temperatures would supports lows in the teens below zero...but
this may not be reached if clouds hang around. Twh

Long term...valid for Tuesday...Wed...Thu...Fri...Sat...

Only very minor tweaks for the short term forecast period this
afternoon.

The period begins on Tuesday...with minor ridging
developing over the region. This will keep skies clear over the
area. As a result of the ridging...less Lee troffing and
associated downslope flow...so temperatures will be quite cold as Arctic
airmass remains over the region. Lee troffing does develop Tuesday
night...with associated downslope flow developing...which should
limit cool off overnight Tuesday night. The Lee troffing remains
in place through about Thursday..allowing temperatures to climb
back toward freezing for highs by Thursday.

Another Arctic system is prognosticated into the area Friday and through
the weekend. Models continue to be very consistent in producing
snowfall for 3 straight days for most of the area. We are watching
this system very closely for any changes...but this system could
result in double digit snow accumulations if all factors remain
the same as currently prognosticated. Please stay tuned for updates on
this system...especially if you are planning on travelling over
the weekend following New Years Day. Aag
&&

Aviation...

Updated tafs to include the onset of snow and lowering
visibilities at all terminals tomorrow. By late tomorrow
afternoon...conditions will deteriorate significantly with
widespread accumulating snow...potential IFR conditions...and
bitterly cold temperatures. Singer

&&

Preliminary point temp/pops...

Sun Monday Tuesday Wednesday Thursday Friday Sat
-----------------------------------------------------------
bil 015/024 902/000 914/902 908/026 013/031 017/026 008/022
5+/S +6/S 31/I 00/north 11/north 23/j 33/j
lvm 014/024 902/005 924/004 916/025 008/035 018/031 014/028
6+/S +6/S 31/b 00/north 11/b 23/j 33/j
hdn 010/026 902/002 916/001 913/022 008/030 013/026 006/024
3+/S +3/S 21/b 00/u 11/b 23/j 32/j
mls 014/022 907/001 915/002 906/023 012/028 015/023 005/016
29/S 72/S 10/b 00/u 11/b 23/j 22/j
4bq 011/026 000/005 914/003 911/022 010/030 016/027 008/020
19/S 93/S 11/b 00/u 11/b 23/j 32/j
bhk 009/019 910/001 915/001 906/021 011/027 014/022 003/015
17/S 51/east 10/b 00/u 11/b 23/j 21/east
shr 008/025 901/005 918/000 913/025 008/034 015/031 011/025
18/S +6/S 21/b 00/u 11/b 24/j 32/j

&&

Byz watches/warnings/advisories...
Montana...Winter Weather Advisory in effect from midnight tonight to
noon MST Monday for zones 28-29-42-63.
Winter Weather Advisory in effect from 6 am Sunday to noon
MST Monday for zones 30-31-34>36-38>41-56>58-64>66.
Wyoming...Winter Weather Advisory in effect from 6 am Sunday to noon
MST Monday for zones 98-99.

&&

$$
Weather.Gov/Billings

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