Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 202046

Area Forecast Discussion
National Weather Service Great Falls MT
246 PM MDT Thu Oct 20 2016

This Afternoon through Saturday Evening...Latest analysis shows weak
high pressure ridging slowly drifting from central into eastern MT,
with moisture from an approaching shortwave trof spilling into the
ridge flow pattern.  Early areas of overcast clouds along the Hiline
and much of central MT have eroded somewhat as water vapor satellite
imagery shows the westerly flow splitting the moisture into two
branches: one along the US/Can border and the other over far
southwest MT, with subsidence/drying under the ridge axis.  This
split should become less dominant as the ridge moves further east
and our region comes under more uniform west-southwest flow aloft.
So we should see widespread cloud cover this evening, but still
little if any precipitation expected.  Models continue to indicate
an area of isolated showers developing over parts of Hill/Blaine/
Chouteau/Fergus counties this evening, but any rainfall will be very
light (a trace to few hundredths of an inch). The current breezy to
gusty winds will continue into the evening, then gradually decrease
following the shortwave`s passage.

The shortwave should be mostly east of us by early Fri morning, with
weak ridging, less cloud cover and slightly warmer temperatures in
the forecast for tomorrow. But as seen all week in our progressive
weather pattern, conditions rarely last longer than 24 hrs before
the next trof or ridge arrives. Such is the case for Sat as the next
Pacific shortwave brings another increase in clouds and slightly
higher chances (25-40 percent) for light valley/mtn snow (above 6000-
7000 ft) rain showers generally along/north of line from Helena and
White Sulphur Springs to Harlem/Malta. Models also suggesting the
moisture flow may be sufficient to produce 0.1 to 0.3 inches of
precip in swath from Lincoln to Great Falls to the Bears Paw Mtns
and Fort Belknap, with lighter amounts on the northern/southern
edges of the swath.  Tomorrow should be the warmest day over the
next 5 days or more, with the forecast sunny skies pushing temps
into the upper 50s and low 60s. Much of the region will cool back
into the mid 50s under the clouds with Saturday`s weather system,
though some of the southwest valleys may stay a few degrees warmer
as they`ll remain dry and have less cloud cover.

Saturday night through Thursday...Overall the models have changed a
bit from the 00z runs last night...with fairly quiet/little weather
expected from Saturday night through Thursday. The models have
mostly dry conditions over the region from Saturday night through
Tuesday morning...then the EC brings an upper level disturbance
through Southwest MT producing a few showers Tue/Tue night. For
Wednesday and Thursday...the models continue the mostly dry trend
over our region...but since this is a fairly big change from
previous runs...I have left small chances for pops in forecast for
most areas. Temperatures will be around normal through the
period...with highs generally ranging from the lower 50s to lower


Updated 1800Z.

VFR conditions expected. Widespread moisture accompanying an
approaching upper-level trough will generate widespread mid-level
cloud decks across central/southwest MT. Clouds will be generally
BKN-OVC from KGTF north to US/Can border and from KBZN south to the
MT/ID stateline, with SCT-BKN in-between those areas (KHLN/KLWT).
Other than -SHRA/-SHSN along the Rocky Mtn Front, little precip is
expected as the shortwave moves through; only mention of showers is
near KHVR for late aftn/early eve.  Surface winds will continue to
increase into the aftn hours as the pressure gradient tightens with
the shortwave`s arrival.  Widespread west-southwest gusts of 25-30
kts expected over the central plains and southwest valleys, with 55-
60 kts above ridgetops. Winds will steadily decrease later this


GTF  45  60  42  57 /  20  10  30  40
CTB  38  55  37  54 /  10  10  20  20
HLN  39  62  39  57 /  10  10  20  30
BZN  39  61  37  59 /  10  10  10  10
WEY  29  50  30  53 /   0   0   0  10
DLN  37  60  35  58 /  10  10  10  20
HVR  43  58  39  56 /  20   0  20  30
LWT  44  60  40  55 /  20  10  10  40



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