Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 201334
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
735 AM MDT Wed Aug 20 2014

.DISCUSSION...

735 AM update...Showers/thunderstorms have become a bit more
widespread west of the Continental Divide this morning, so have
raised POPs to categorical along there throughout the day. No other
updates needed at this time. Coulston

550 AM Update...Have issued a dense fog advisory for the West
Yellowstone area until 10 AM this morning.

Today through Friday...A slow moving upper level low pressure
system will affect the region over the next several days. As a
result...expect temperatures to cool down quite a bit...and the
chances for precipitation to increase. Scattered thunderstorms
will move through the region this morning...then the precip should
get more widespread and stratiform this evening...with the
heaviest precip falling over North Central MT. Expect a break in
the precip for a few hours on Thursday...only for another round of
steady precipitation to redevelop Thursday night and continue
through the day on Friday. The airmass will be cool enough by late
Thursday night for some light accumulating snow to fall above 8000
feet in Glacier Park. Any snow accumulations should be less than
1 inch. Widespread precipitation amounts of 0.50 to 1.00 inches
still look good from today through Friday over much of Central and
North Central MT. Afternoon high temperatures are going to be
greatly dependent on cloud cover/precip...but overall by Friday
many areas will be seeing afternoon temperatures close to 20
degrees or more below normal.

Friday Night through Wednesday...Medium range models are in good
agreement that wetter and much cooler conditions will prevail
through the weekend. Objective guidance temperatures continue to
trend cooler keeping high temperatures in the 50s and 60s Saturday
and Sunday. Overnight lows will be cold enough to support minor snow
accumulations over the highest elevations of Glacier Park, but it
does not appear that any significant impacts should be expected.
Models are in better agreement for the Monday through Wednesday
period with upper level troughing remaining over the Northern
Rockies through Tuesday. Unsettled conditions will keep isolated to
scattered showers and thunderstorms in the forecast but temperatures
are expected to warm back toward the 70s. By Wednesday the trough
will finally progress eastward allowing shortwave ridging to build
over Montana and temperatures to trend back toward seasonal
averages. mpj

&&

.AVIATION...
UPDATED 1145Z.
An upper level trough continues to develop over the Northern Rockies
and an associated surface cold front will push south out of Canada.
Scattered showers and thunderstorms will continue across much of the
forecast area today before changing over to a widespread rain
overnight. VFR conditions should prevail through about 00Z Thursday
when low clouds and light rain will cause areas MVFR conditions. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  76  55  66  51 /  50  80  70  60
CTB  70  51  58  47 /  80  80  70  60
HLN  80  54  72  51 /  40  70  70  60
BZN  79  50  73  49 /  40  50  70  60
WEY  65  43  63  42 /  50  50  50  40
DLN  75  47  73  45 /  50  50  50  50
HVR  78  57  66  53 /  30  80  70  60
LWT  76  54  65  50 /  30  60  70  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Dense Fog Advisory until 10 AM for the West Yellowstone area.

&&

$$

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