Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 240449
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1045 PM MDT Sun Apr 23 2017

...UPDATED AVIATION SECTION...

.UPDATE...

921pm update...Showers and isolated thunderstorms continue to
fire along and ahead of a vigorous shortwave in a post-frontal
environment. Have extended slight chance/isolated t-storms east
and southeast until midnight based on observed and model trends.
Storms will be capable of producing small hail, gusty winds, and
abundant lightning. Cassell


655pm update...Increased PoPs and expanded thunderstorm
potential along and near the Interstate 15 corridor on the plains
as a vigorous shortwave approaches from the west over an
increasingly less stable post- frontal near-surface environment.
Expect showers and isolated thunderstorms to work their way east
to northeast through the evening, gradually diminishing in
intensity with loss of daytime heating. Cassell

&&



.AVIATION...
Updated 0445Z.

VFR conditions are mostly expected through the day on Monday, but
MVFR conditions with possibly brief IFR conditions are possible with
showers. A few showers and thunderstorms may hold together through
08Z as they move southeast toward KLWT. Otherwise, another weak
disturbance will bring a good chance for additional rain/snow
showers through 12Z to Southwest Montana (KHLN KBZN KEKS). Yet
another disturbance will move into the destabilizing atmosphere
after 15Z Monday, bringing another round of showers/thunderstorms,
especially over Southwest Montana. Deep moisture will then combine
with a stationary frontal boundary and its upslope flow to bring
widespread MVFR/IFR conditions in rain/mountain snow after 00Z.
Coulston

&&

.PREVIOUS DISCUSSION...
/ISSUED 535 PM MDT Sun Apr 23 2017/

Tonight through Tuesday...Complicated forecast today under a
progressive westerly flow aloft. A widespread area of light to
moderate rain developed over North-central Montana today as a
shortwave trough lifted over a cold front. This area of rain will
continue to slowly move away to the north and east through this
evening. Low level convergence associated with inverted surface
trough curving across southern Montana may help a few
thunderstorms form this afternoon, possibly producing small hail.
Mostly sunny skies and warmer temperatures along and south of
this boundary has caused weak instability to develop in this
environment. Short-term models indicate the showers over southwest
Montana will evolve into an overnight band of rain and mountain
snow, providing an inch or two of snow above 7000 feet over
southern Madison and Gallatin Counties. Precipitation coverage
declines Monday morning with only isolated, mainly mountain
showers. The next wave arrives Monday afternoon, once again
beginning with scattered thunderstorms possible over southwest
Montana. Precipitation spreads Monday night across much of the
forecast area, with moderate to at times heavy rain and snow
across southwest Montana. Rain mixes with snow across North-
central Montana early Tuesday morning, though with little to now
accumulation on the plains. Snow levels over southwest Montana
drop below 6000 feet, with 1 to 3 inches of snow possible through
Tuesday morning over Raynolds Pass and around West Yellowstone.
Precipitation gradually tapers later Tuesday. Overall confidence
for this progressive pattern remains low to moderate, so continue
to watch for updates. PN

Tuesday night through Sunday...Overall an unsettled weather pattern
will continue to reside over the region through much of the extended
period. With a deep upper level trof of low pressure over the area
until at least Friday, expect periods of rain/snow along with below
normal temperatures. The best chance for snow will be for elevations
above 5500 feet, but snow levels could lower to around 4000 feet
during the overnight/early morning hours. A few inches of snow are
possible in the mountains daily. Overall rainfall amounts for lower
elevations will generally average between 0.20 and 0.40 inches for
Wed thru Fri. In terms of pops, leaned towards the higher pop
solution of the National Blend, especially for Wed through Fri. By
next weekend, the upper level trof will start to move eastward a
bit, thus the chances for showers will be getting lower, and
temperatures will start to warm a touch, closer to seasonal normals.
Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  37  54  34  51 /  40  20  40  60
CTB  35  50  33  48 /  40  50  60  70
HLN  39  54  37  55 /  20  30  50  50
BZN  37  51  35  52 /  50  60  70  60
WEY  30  41  29  44 /  60  60  80  60
DLN  35  50  35  52 /  50  60  70  50
HVR  36  55  34  49 /  50  30  50  40
LWT  35  51  32  44 /  50  40  50  60

&&

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

$$

weather.gov/greatfalls



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