Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 161609

Area Forecast Discussion
National Weather Service Great Falls MT
909 AM MST Thu Nov 16 2017


The anticipated cold front with its associated band of light
precipitation is advancing across the Continental Divide, nearing
a line from Helena to Great Falls to Inverness. Freezing rain was
reported earlier in Missoula, with rain and snow observed over our
forecast area. Rain showers are entering the Helena valley, where
temperatures at the lowest portions of the valley remain near to
below freezing. However, with daylight, there are no reports of
icing in the valley. Overall the forecast remains on track, so
only minor updates were issued to better match observed trends.



A Pacific cold front will bring periods of snow to the mountains
at and above pass level through Friday. A period of snow is also
possible for valley locations along the Interstate 90 corridor
late tonight through Friday afternoon. Over the plains, breezy and
mostly dry conditions are expected through Friday.


Updated 1143Z.

MVFR/IFR conditions possible at KEKS/KBZN, especially later this
evening into Friday.

A Pacific cold front will bring periods of mtn snow/obscurations
through the current TAF cycle. At KEKS/KBZN, RA/SN is expected this
evening through Friday. However, confidence remains lower regarding
the timing/location of the worst impacts and the current TAFs for
both terminals do not reflect the worst case scenario (which would
be a period of IFR/LIFR conditions). Trends will continue to be
monitored in later forecasts and TAFs updated accordingly as
confidence increases. Elsewhere, VFR conditions with gusty winds are
expected. MARTIN


/ISSUED 443 AM MST Thu Nov 16 2017/

Today through Saturday...Latest surface analysis still shows a
stationary front draped SE across our forecast area early this
morning (roughly from Cut Bank to Lewistown to just north of
Billings). To the west, a Pacific cold front stretches from the ID
panhandle south into northern CA. Moisture overrunning the
stationary boundary may lead to a very light wintry mix from Havre
to Lewistown, but with little to no impact. This boundary should
eventually get pushed NE through the day as the Pacific front
approaches, helping to erode the colder air that has been locked in
place along the Hi-line for a couple of days. Along and ahead of the
Pacific front, moisture/lift will be focused along the Rocky Mtn
Front/Marias Pass area with moderate snow likely at times this
morning. As the front crosses the Divide, the better lift will
decrease in that area, leading to lower snowfall rates/lessening
impacts. For these reasons, the Winter Weather Advisory will not
be extended in that area as impacts should be confined through the
early afternoon hours. That said, a second surge of moisture will
reach that area late tonight and it is possible another Winter
Weather Advisory will be needed for that time period.

Across SW MT, the forecast is a bit more tricky. Snow continues
early this morning along the MT/ID/WY border, but by this afternoon
the depth of moisture decreases which should lead to reduced
snowfall rates in the mountains and high valleys. In addition,
rising thickness values may allow a rain/snow mix or changeover
to all rain for a short time. Moisture then quickly increases
tonight as the Pacific front settles into the area with better
convergence/synoptic lift. Hi-res models still depict the
potential of some banded/heavier snow tonight through Friday
afternoon, but differ on the exact location, and have backed off
on this potential somewhat. I still expect the greatest impacts
to be right along the MT/ID/WY border, with lower confidence on
impacts from Dillon to Bozeman. For now, we`ll keep the Winter
Weather Advisory as- is. For the I-90 corridor, snowfall amounts
will be highly dependent on where/if bands of heavier snow
develop. MARTIN

Saturday night through Thanksgiving Day...Mostly dry and
windy conditions start off the medium range period across Montana.
Northwest flow aloft will prevail Saturday night and Sunday with a
low pressure surface trough in Alberta and mountain-top level winds
in excess of 70 mph helping to fuel strong winds along the Rocky
Mountain Front. Model discrepancies are not as pronounced for the
Monday/Tuesday time frame as they have been and suggest that an
upper level trough will move over the region while a Canadian cold
front pushes southward through Montana. This suggests cooler
temperatures and an increasing chance for precipitation, especially
over the western mountains. However, is should still be noted that
models are not in very good agreement with regard to timing and
placement of precipitation during this period. Model solutions
continue to diverge through the Wednesday/Thursday time frame but
continue to suggest that warmer temperatures and breezy conditions
will be on-tap for the holiday. Unfortunately, however, neither
model is 100 percent dry so the possibility of rain/snow during this
travel period can not be ruled out. mpj


GTF  47  27  39  26 /  10  10  20  10
CTB  38  21  35  22 /  20  10  10  10
HLN  44  24  34  25 /  30  20  30  10
BZN  46  24  33  17 /  30  50  40  10
WEY  38  22  30  10 /  90  80  70  20
DLN  48  24  32  15 /  20  40  40  10
HVR  43  20  36  16 /  20  10  30  10
LWT  48  25  36  23 /  10  20  20  10


Winter Weather Advisory from 5 PM this afternoon to 5 PM MST
Friday Beaverhead...Gallatin...Madison.

Winter Weather Advisory until 3 PM MST this afternoon above 5000
feet for Northern Rocky Mountain Front.


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