Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 281116

Area Forecast Discussion
National Weather Service Great Falls MT
515 AM MDT Fri Apr 28 2017

Updated Aviation

Today through Saturday Night...A complex weather scenario today as a
northeast-southwest oriented upper level system/front drops
southeast onto the north-central plains this morning into the
afternoon, situated roughly along a Havre-Great Falls line by around
6 pm this evening. Weak stability indices along and behind the
front suggest a marginal threat for thunder with showers that form
along this boundary on the plains, though stability parameters
appear a bit better over the mountains of central and southwest
Montana Friday afternoon, and will thus yield a bit better threat
for thunder. Subsequent to this first system, a deeper upper level
system/front makes its way across western Montana toward the Rocky
Mountain Front late in the afternoon and into the evening.
Instability values appear to be a bit more conducive to more
vigorous showers along with a slight chance of thunder, with MUCAPE
values approaching 500 J/kg by early evening along and just east of
the Continental Divide. Thus, I would not be surprised to see a
broken line of showers/storms extend from Glacier County south to
near Great Falls, as post-frontal systems with strong upper level
disturbances approaching near peak diurnal heating can tend to
slightly over-perform model projections. Shower activity diminishes
overnight tonight with drier air moving in, with another upper level
system approaching from the west Saturday. Models depict showers and
possibly a few thunderstorms developing along and ahead of this
system, mainly in the afternoon and early evening along a north-
south line east of Great Falls. This system will then move east into
the eastern half of the state by late Saturday evening, with
tranquil conditions for the most part Saturday night, though clouds
will again increase toward morning ahead of another system for
Sunday. Cassell

Sunday through Friday...Overall periods of active weather to
continue...with a brief glimpse of nice weather mid next week.
Sunday will see a clipper system skirt to our north bringing
unstable nw flow to our region...and provide chances for scattered
showers. Large closed low in the midwest absorbs this disturbance
and keeps us stuck in an unstable northwest flow pattern for Monday
and again Tuesday. Once again widespread showers will be found.
There is limited cold air with Sunday`s through Tuesday`s unsettled snow levels should remain above 5000 feet or slightly
lower...with Tuesday morning possibly seeing the lowest snow levels
around 4500 feet. Instability is also weak during this time
period...keeping thunderstorm activity to isolated coverage. A long
awaited ridge of high pressure then looks to move into the region
Wednesday bringing dry and warming condtions. Models vary on how
long this ridge lasts. Euro wants to continue through
Thursday...with the GFS bringing a cold front Thursday afternoon and
evening. Added in some thunderstorms for Thursday to account for the
unstable GFS solution. Another clipper system to our north could
then return unsettled weather for Friday with isolated to scattered
shower activity possible. The west to northwesterly flow component
of the mid level winds could bring some breezy conditions at times
during the long term...especially on Sunday...Monday...Wednesday and
Thursday. Temperatures will continue to hover around normal to
slightly below normal Sunday through Tuesday during the unsettled
pattern. High pressure and some downsloping winds will warm
temperatures Wednesday and Thursday. Some models indicate
temperatures in the 60s and 70s may even return. Anglin


Updated 1115z.

Overall, no significant changes from the 06Z TAF issuance. Still
looking at low VFR/high MVFR CIGS and mtn obscurations at most
terminals through Friday afternoon and/or early evening. Thereafter,
drier low/mid level air should allow clouds to decrease some, or at
least cause CIGS to rise, especially across central MT. Before then,
SHRASN will continue to impact much of the area. The heavier showers
may produce IFR or lower CIGS/VIS. At this time, there is only a
marginal chance of TSRA expected on Friday, so left out of all
terminals at this time until higher confidence. Like Thursday, there
could be enough instability for some small hail/graupel with the
SHRA in the afternoon. Martin/Cassell


GTF  48  33  56  37 /  30  30  20  10
CTB  47  32  53  38 /  30  30  20  10
HLN  50  34  58  39 /  30  30  20  10
BZN  44  29  55  34 /  60  50  20  10
WEY  37  20  44  25 /  40  20  20  10
DLN  45  30  53  34 /  30  30  20  10
HVR  52  33  59  37 /  30  20  20  20
LWT  44  31  53  34 /  50  40  30  20



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