Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 230453
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
953 PM MST Wed Feb 22 2017

.UPDATE...

Latest regional analysis shows a deepening low taking shape over
southern Idaho and is very well defined on satellite imagery.
Meanwhile, a SFC high over southern Canada continues to build south
into northern MT at this time.

Latest model guidance takes the above-mentioned low generally ENE
into WY while at the same time, transferring energy to an even
strong lee-side low that is already in the process of developing
over western CO. Ultimately, while the ID/WY low will likely
continue to strengthen overnight, it should weaken as the CO
becomes the primary low. The ID/WY low makes the forecast over the
next 24hrs a bit tricky for SW MT from Dillon to Bozeman as large
scale lift, potentially aided by low/mid level frontogenesis, may
lead to a period of steadier/somewhat more widespread snow in
that area. That said, at this time, it is expected that the track
of the low and a general weakening trend expected by tomorrow
should tend to keep the heavier/steadier snow to our south/east.
For these reasons, I did not make significant changes to SW MT.
However, I did up the wind as a tightening pressure gradient
should lead to stronger E/NE winds in that area than currently
forecast. The track/intensity of this low will need to be
monitored in later forecast for any potential adjustments in
snowfall amounts across SW MT.

For central MT, low level moisture moving south out of Canada
combined with a developing easterly upslope flow should keep
areas of generally light snow going/redeveloping overnight into
Thursday. Given snow is expected to continue and/or redevelop, I
decided to extend the current Winter Wx Advisory for Fergus,
Judith Basin, and Meagher through Thursday morning. In this area,
snowfall amounts may be enhanced somewhat for easterly upslope
areas (ie. the Snowies, Highwoods, Little Belts). For now, am not
going to expand the Advisory in area, but later shifts will
closely monitor this potential. Martin

&&

.AVIATION...
UPDATED 0015Z.

A broad area of low pressure will continue to move east from the
northern Great Basin across southern Idaho to the Idaho/Wyoming
border over the next 24 hours. As a result, deep moisture will be
advected north, bringing mountain obscuration with widespread low
VFR/high MVFR conditions in low ceilings and snow showers by 06Z.
Some showers may cause brief IFR conditions, mainly between 06Z and
18Z. Winds will also be northerly between 5 and 15 kt during this
time.  Coulston

&&

.PREV DISCUSSION...
/ISSUED 515 PM MST Wed Feb 22 2017/

Tonight through Friday...An active pattern to continue through
much of the short term...however...impacts will be low to
moderate. Weak disturbance continues to linger scattered snow
showers across central portions late this afternoon. Impacts are
generally low...and warm roads have kept conditions mainly wet to
isolated slick spots. Decided to cancel many of the
advisories...except for Meagher...Judith Basin...and Fergus where
brief moderate snow is still possible through the evening. As this
initial round of snow diminishes two weak disturbances may bring
our next chances for snow. The first will be a large low to our
south in Wyoming. The inverted trough from this low will extend
into southern Montana tonight into Thursday...making areas of
light to moderate snow possible. There is still some uncertainty
on location and intensity of this feature...as much of the snow
should remain in Wyoming initially. It will have to be watched for
additional advisories...but for now held off. The best chances
for any impactful snow will be along I-90 from Butte to Bozeman
and south. Meanwhile across the north...a weak upper low sneaks
into the region from Canada...perhaps bringing scattered snow
showers through Thursday. Much like the feature to the
south...confidence is low to moderate on exact timing and location
for impactful snow. Again will hold off on additional advisories.
The weak disturbances move out of the area Friday...with weak
ridging trying to move in. Trapped moisture in this weak ridge
could still provide for a few snow showers on Friday...especially
across the south. Some areas could see 1 to 2 inches in the
north...with 2 to 6 in the south by Friday. Temperatures still
look to be on a cooling trend during the short term. The concern
is how cold it actually will be with limited new snow. Teens and
20s for lows are possible by Friday morning...with 20s to low 30s
for highs. Winds do not look to be a factor during the short term.
Anglin

Friday Night through Wednesday...A surface cold front moves into N-
central MT Friday night. The front could produce areas of light snow
beneath a weak overrunning southwest flow aloft, with flurries
continuing but gradually tapering through much of the day Saturday.
Generally fair, drier, and cold weather follows for Sunday and
Monday. Isolated, mainly mountain snow showers will continue,
associated with weak disturbances in the northwest flow aloft.
Temperatures will fall to around 10 to 15 degrees below average
through Monday night, with overnight lows in the single digits. A
stronger Pacific trough is forecast to develop Monday night
somewhere over the interior U.S. west. This could increase snow
chances for southwest MT on Tuesday, with possible travel hazards
heading into ID. Model solutions bring the cold snap to an end on
Wednesday with broad ridging over the PacNW. A strong Clipper system
developing in the NW flow downstream of the ridge could produce a
period of strong downslope winds Wednesday or Thursday. Confidence
in these late period model solutions remains low. PN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  21  27  15  29 /  40  50  20  20
CTB  16  26  10  26 /  40  30  20  10
HLN  22  29  13  26 /  30  50  20  20
BZN  20  30  12  25 /  50  50  40  30
WEY  11  23   5  20 /  30  40  30  40
DLN  17  26  12  22 /  50  50  30  30
HVR  24  29  18  30 /  80  60  20  20
LWT  21  27  15  27 /  80  40  30  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 AM MST Thursday Fergus...Judith
Basin...Meagher.

&&

$$

weather.gov/greatfalls



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