Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 190313
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
813 PM MST Wed Jan 18 2017

.UPDATE...

Main updates this evening were to increase winds along the Rocky
Mountain Front and in the Ennis valley area to better reflect
current conditions. Otherwise, temperatures and winds appear to be
on track. The breezy downslope winds and passing cloudiness will
keep the plains mild. Precipitation should mostly remain in the
mountains as well. Although temperatures warmed above freezing in
the Helena Valley, winds there have remained fairly light,
leading me and the MT Dept of Environmental Quality to believe
that air quality will be slow to improve. The MT DEQ have
therefore extended the Air Quality Alert for the Helena Valley
until at least 9 am Thursday morning.
Coulston

&&

.AVIATION...
Updated 2322Z.

Predominantly VFR expected next 24-hours as cloud cover increases
in advance of a weather disturbance approaching from the Pac NW
and northern CA. Periods of snow showers and mountain obscuration
are expected along the Continental Divide and higher terrain of
Southwest Montana. All of the TAF sites should remain dry
throughout the period, but occasional MVFR CIGS cannot be ruled-
out at KBZN/KEKS, especially after 06Z/Thu. Jaszka

&&

.PREV DISCUSSION...
/ISSUED 422 PM MST Wed Jan 18 2017/

Tonight through Friday...Temperatures today climbed over 60F for
portions of southeast Fergus county. Helena and most other
southwest valleys finally broke their temperature inversions as
expected. Observations suggest West Yellowstone and the Treasure
Valley remain the only areas still locked into the cold air.
Breezy conditions continue across north-central MT tonight with
temperatures remaining above freezing for most areas. However,
scattered black ice remains likely on road surfaces overnight as
meltwater in contact with the cold ground will cool quickly.
Expect teens for the southwest valleys tonight, with teens to near
30 for high temperatures tomorrow.

Winds are tapering as the pressure gradient gradually weakens and
the upper level flow turns more southwesterly. Periods of light
snow continue over the northern Rockies. A longwave trough splits
while crossing the central west coast tonight. The southern
shortwave tracks south of Montana, but just close enough to
produce light snow Thursday afternoon through Friday Morning south
of a line from Lewistown to Helena. Snowfall amounts of an inch or
higher will most likely be confined to the higher terrain south of
Interstate 90. Scattered rain or snow showers will be possible
Thursday afternoon over eastern portions of North-central MT.
Temperatures trend slightly cooler on Friday. PN

Friday night through Wednesday...Have not made any significant
changes to the medium range forecast tonight and models continue
to be in relatively decent agreement through the period. Overall
trend for Montana weather favors seasonable temperatures with
breezy conditions across north central Montana. Models continue to
suggest that southwest Montana should also see a return to more
seasonable temperatures but I suspect that colder air may remain
trapped in this region so confidence in temperatures across the
southern half of the forecast area is low.

Period starts off with a broad upper level trough over western North
America. This trough will move through the Desert Southwest into the
southern Great Plains over the weekend. Shortwave ridging develops
over the Great Basin in the wake of this system but another broad
upper trough moves inland along the West Coast early next week. Once
again, the core of energy associated with this trough will remain
well south of Montana. Models move this system into the central and
northern Great Plains and end up developing a winter storm across
Nebraska and the Dakotas by Tuesday/Wednesday. Montana, however, is
expected to remain far removed from the active weather pattern and I
anticipate that models are not doing a very good job resolving the
location or timing for any shortwave energy that may pass through
the region. Have therefore continued a broad-brushed forecast that
favors scattered showers over the western mountains and southwest
Montana with only isolated to scattered showers over the plains. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  34  41  29  37 /   0  10  10  10
CTB  35  41  25  36 /   0  10  10  10
HLN  19  30  15  27 /  10  20  30  20
BZN  17  25  14  32 /   0  30  50  40
WEY   1  17   8  22 /  40  50  50  40
DLN  17  25  15  30 /  10  30  30  30
HVR  31  38  28  36 /   0  10  10  10
LWT  33  39  28  35 /  10  30  40  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls



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