Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211749

1145 AM MDT Thu Aug 21 2014


A weather disturbance aloft will be moving through the forecast
area today and expect showers and a few thunderstorms ahead of it.
Have left the high chances of precipitation in the forecast but
have changed wording from rain showers likely to occasional rain
showers as do not expect precipitation to last any more than a
couple of hours at any one location. Have removed the mention of
thunderstorms over the northwest forecast zones as do not see
enough instability for thunderstorms. Behind the weather
disturbance should see a little sunshine over western portions of
southwest Montana this afternoon so have changed the sky forecast
to reflect that. Generally left most high temperatures for today
alone as some guidance was indicating warmer than currently
forecast highs while other guidance was indicating cooler than
currently forecast highs. Did raise highs for today at Great Falls
and Havre slightly as had fairly high confidence in warmer
temperatures. First glance at the this mornings NAM model run
shows wet forecast for Friday through Saturday is on track. Blank


A broad upper level trough of low pressure will remain over the
Pacific Northwest and Northern Rocky Mountains at least through
Friday morning. A disturbance in the resulting westerly flow aloft
will exit the area by 02Z, bringing at least scattered showers to
most of the area during the peak daytime heating. A few
thunderstorms are also possible, but mainly along and south of a
KHLN-KLWT line. A few showers will linger across the area through
06Z. For this afternoon and evening, conditions will mostly be VFR
with some mountain obscuration, but occasional MVFR/IFR conditions
are possible with heavier showers. Rain with MVFR/IFR conditions and
mountain obscuration will then become more widespread from the west
after 06Z, as another disturbance begins moving into the area.


/ISSUED 540 AM MDT Thu Aug 21 2014/
Today through Saturday...An upper level low pressure system is
slowly moving through the region...while a Canadian cold front has
pushed southward through the CWA. The end result is scattered
showers and isolated thunderstorms will continue to move through
the region today. The precipitation has not been as widespread as
previously thought over North Central MT so far. However...because
humidities are so high...passing areas of precipitation are
possible in most areas today. Thus pops remain high for
today...even though overall QPF amounts will generally not be
significant today...and a widespread all day rain is not expected
either. The scattered precip continues tonight...again with high
pops mainly for the event. On the upper level trof
comes close to Central MT...and a surface low develops over the
Central Rockies...better upslope conditions are expected to
develop over Central/North Central MT. Thus Friday night through
Saturday...a band of widespread precipitation is expected to move
through the region. The heaviest precip is expected over the
Rocky Mountain Front and the Central Mountain ranges...with 1.50
to 2.50 inches possible in the lower elevations
1.00 to 1.50 inches will be possible. Precip amounts will
generally be less than 1.00 inches in Southwest MT. In terms of
snow...the latest forecast models indicate snow levels should
generally be above 7500 feet in the Glacier Park region. For
now...I will leave the snow level down to the currently forecasted
snow level near 6500 feet in case latter model runs bring down
some colder air. In either case...snow accumulations of 1 to 2
inches will be possible at mountain peaks over Glacier Park Friday
into Saturday. In terms of temperatures...well below normal
temperatures are expected through Saturday. There is the
potential that temperatures could be a few degrees cooler than
forecasted highs should clouds/precip continue for several hours
during the afternoon hours. Brusda

Saturday Night through Thursday...A slow moving upper level trough
will remain over the region through the weekend until at least
Tuesday. Models are in decent agreement on details through Monday
morning keeping a good likelihood of precipitation over the region
Saturday evening then a chance of showers into Monday. Solutions
once again diverge as a jet streak moves over the ridge in the Gulf
of Alaska and moves south along the British Columbia coast. The
ECMWF depicts a stronger and faster jet thereby digging further
south along the west coast and elongating the trough southwestward
while the GFS reinforces the trough over the Northern Rockies. GFS
solution drives the trough eastward and places Montana into a
generally dry northwest to westerly flow aloft. Meanwhile, the ECMWF
develops a closed low over the west coast then drifts this feature
eastward through the Great Basin and Wyoming with wrap around
moisture being advected into Southwest Montana. At this time the GFS
is more in keeping with previous forecasts so have continued to
trend the forecast towards a warmer and dryer solution. mpj


GTF  66  51  64  52 /  70  60  90 100
CTB  61  49  58  49 /  70  60  90  90
HLN  68  53  65  52 /  60  60  90 100
BZN  69  51  67  49 /  50  60  80  80
WEY  60  45  61  40 /  40  40  50  40
DLN  69  48  65  45 /  40  50  80  70
HVR  69  55  66  55 /  70  50  80  80
LWT  62  50  60  51 /  70  60  80  90



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