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Area forecast discussion...updated 
National Weather Service Billings Montana
949 am MST Sat Jan 31 2015

Update...

The going forecast appears to be on track...so we only made a few
small changes with this update...namely to increase probability of precipitation up to 100
percent from Miles City to Baker this afternoon and to increase
Post-frontal wind speeds a bit in most areas based on the observed
surface pressure rises upstream as of 16 UTC. Radar trends support
snow spreading south and east this afternoon as model guidance has
been and still is simulating...with the greatest accumulations of
an inch or two in southeastern Montana where qg-forcing is strongest.

One item that we will be investigating further today is whether or
not the foothills like Red Lodge and Fishtail could get more snow
than currently forecast. Recent hrrr runs support enough quantitative precipitation forecast for a
couple inches there...likely in part because that model is fed by
the GFS on the large-scale and the GFS is more supportive of
upslope snow than its European model (ecmwf) global counterpart. We will watch the
observational trends and digest additional model guidance before
adjusting that part of the forecast based on those disparities.
Schultz

&&

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

Cold front moving into northern Montana this morning but not very
Arctic like with temperatures only down to 18 degrees at Calgary.
However its a big airmass change from we have been experiencing
and temperatures will become much colder today during the
afternoon hours. Ahead of the frontal arrival there is a patch of
stratus that is trying to progress into northern sections of
southeast Montana but cloud cover is causing it slow its movement.
Still expect this stratus to get close to a Baker to Miles City
line by sunrise and some patches of freezing fog are expected.

Front will progress through the area from north to south through
the late morning and early afternoon hours with its progress a bit
faster through southeast Montana. Models show light snow
developing mainly in the Post frontal area in southeast Montana as
shortwave energy tracks over the area later in the day. Hrrr shows
another area of snow developing in the Billings area and locations
30 miles south and west as upslope plays a factor in providing
lift. This window for snow already dissipates by midnight as
heights begin to build aloft and the cold air push begins to
translate east. Given the short window and not a strong alignment
for lift confident snow amounts will be light and generally around
an inch though a few locations could see closer to 2. Bigger
threat is the snow falling on warm roads and melting and freezing.
This still looks reasonable especially if a few hours of sunshine
occur before the front. Current infrared imagery indicates this is
likely especially for the western half of the area.

Temperatures will be falling from the middle to upper 30s this
morning through the 20s this afternoon. Lows will settle in the 5
to 15 degree range overnight. Cold by comparison to this past week
but not dramatic for January.

Sunday the airmass moderates as the deeper cold air moves away
from the region with a warm front moving into the western zones by
late afternoon and across the area Sunday night. Most of the day
will be dry but the warm front does increase moisture over the
western zones which will bring a chance for mountains snow. Borsum

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

Little in the way of changes to the extended forecast period...as
the overall story remains the same. Colder and unsettled weather
to start the work week...with a return to above seasonal average
temperatures to end the week.

Models continue to have timing differences for Arctic
intrusion...but general consensus points toward best precipitation
potential on Tuesday afternoon/evening. One trend that seems to
persist over the past few model runs is a lower quantitative precipitation forecast type
event...for both the GFS and the European model (ecmwf)...so heavy snow is
less likely.

Upper level ridging begins pushing into the region Wednesday
night into Thursday morning. The ridge dominates the pattern
through the remainder of the period...keeping generally dry
conditions in place. There do appear to be several shortwaves
slipping through the flow however...bringing periodic potential
for mountain showers through the period. A stronger wave pushes
into the region Saturday...with plenty of associated Pacific
moisture...which should bring showers across the region. Aag
&&

Aviation...

A cold front will March through the area this morning. This front
will produce north to northeast winds...with some gusts to 20kts
in the first few hours of passage. The front will also drag some
low stratus and fog into eastern sections impacting kmls and kbhk
with occasional IFR and LIFR conditions. Some light freezing
drizzle is possible east of kbil this morning as the front moves
in too. Light snow will develop by this afternoon over the area
with some conditions lowering to IFR...especially east of kbil and
along the east slopes. Mountains will be obscured. The snow will
taper off this evening. Twh

&&

Preliminary point temp/pops...

Today sun Monday Tuesday Wednesday Thursday Friday
-------------------------------------------------------
bil 037 014/032 029/045 028/028 012/028 021/043 033/053
6/S 71/east 23/west 55/j 42/j 21/b 11/north
lvm 039 016/038 032/047 034/040 020/035 026/046 034/055
2/o 51/north 33/west 46/j 42/j 21/b 11/north
hdn 036 010/030 024/043 024/028 006/026 015/041 026/051
6/S 61/b 23/west 55/j 41/b 21/b 11/b
mls 029 007/024 020/035 018/019 000/019 009/035 023/047
+/S 61/b 24/j 55/j 21/b 11/b 11/b
4bq 041 009/028 022/043 025/029 007/023 016/042 027/055
3/o 71/b 23/west 34/j 41/b 11/b 11/b
bhk 025 003/020 015/033 016/019 901/014 005/034 022/046
+/S 81/b 24/j 54/j 21/b 11/b 11/b
shr 039 011/029 021/044 025/036 009/030 015/042 026/053
1/north 31/b 22/west 25/j 52/j 21/b 11/b

&&

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

&&

$$
Weather.Gov/Billings

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