Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 302021

Area Forecast Discussion
National Weather Service Great Falls MT
221 PM MDT Fri Sep 30 2016


Tonight through Sunday Evening...Area remains under a
south/southwest flow aloft through the weekend as an upper level
trough off the west coast slowly moves inland over the next
several days. Airmass has destabilized with cumulus growing and a
few isolated thunderstorms developing over SW MT and central ID this
afternoon. Some of this activity will lift north later this
evening, primarily along and west of I15, but coverage will be
very limited. On Saturday, shortwave and jet energy ejecting out
of the west coast low will lift NE into the Northern Rockies with
a N-S cold front crossing the region Saturday afternoon and
evening. Combination of these forcing features and additional
moisture/instability will lead to a better coverage of showers and
thunderstorms Saturday afternoon and evening. Cooler and somewhat
drier air moves in behind the cold front Saturday night through
Sunday. Hoenisch

Sunday night through Friday...Medium range models have a decent
handle on the overall timing of the movement of the upper level low
pressure trough through this period. However, differences in the
projected positioning of the low pressure center are causing
somewhat of a spread in forecasted precipitation amounts; the ECMWF
is a bit of an outlier by keeping the low pressure center closer to
the forecast area than the GFS/CMC. With the GFS having a better
track record with these systems recently, will lean more towards it
overall, but will increase the chance for precipitation in TFX`s
eastern zones due to better agreement among the models on placing
precipitation there. The trough will swing southeast from the
Pacific Northwest coast Sunday evening to the central Rockies Monday
afternoon, which will bring a good chance of showers to the area,
especially over the eastern TFX zones due to a diffluent flow
bringing enhanced lift there. A lingering frontal boundary over
Southwest Montana may also cause a few thunderstorms develop during
the afternoon and evening hours. As the trough then swings northeast
into the northern Great Plains through Tuesday, moisture wrapping
around the upper low pressure center will move the better chance for
showers into Eastern Montana. A weak ridge of high pressure will
then move into the area in the wake of this trough through Thursday,
decreasing the chance for showers and generally limiting them to the
mountains. A weaker trough will move into the Pacific Northwest on
Friday, bringing a slight chance of showers to much of the area once
again. With an upper level trough and its associated clouds/showers
generally over the area for much of the period, high temperatures
will remain 5 to 10 degrees below normal (mostly 50s expected)
during this period, while lows remain a bit above normal (mostly mid
30s to mid 40s). Coulston


Updated 1800Z.

Narrow band of mid-level cloud-cover and isolated showers continues
to shift east across N-central and SW MT today with a few isolated
thunderstorms possible this afternoon as the airmass becomes somewhat
unstable. Coverage of precipitation will be very limited with VFR
conditions prevailing, though localized MVFR is is possible near
any isolated thunderstorms this afternoon. Hoenisch


GTF  54  74  43  64 /  10  50  60  20
CTB  49  65  37  60 /  10  30  40  10
HLN  52  72  40  63 /  20  60  40  30
BZN  49  76  41  63 /  10  30  30  30
WEY  42  61  33  59 /  10  30  30  40
DLN  49  67  36  62 /  20  50  30  30
HVR  52  82  44  65 /   0  10  70  10
LWT  53  79  42  62 /  10  20  50  20



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