Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 191717
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1120 AM MDT Fri Sep 19 2014

Aviation Section Updated.

.UPDATE...Fog in the valleys of far Southwest Montana is rapidly
clearing out and is not expected to re-develop. Have, therefore,
cancelled the Dense Fog Advisory and updated weather in all relevant
products. mpj

&&

.AVIATION...
UPDATED 1720Z.
Mid to high level clouds will continue to thin this afternoon as a
weak upper level disturbance exits the region. Strong winds aloft
will weaken during the day. However brisk winds across the Northern
Rockies and plains will continue through the afternoon. VFR
conditions will prevail through the next 24 hours. PN/CZ

&&

.PREV DISCUSSION...
/ISSUED 530 AM MDT Fri Sep 19 2014/

Quick update this morning...West Yellowstone area is reporting dense
fog and satellite imagery indicates that surrounding valleys have
similarly dense fog. This generally is southeast of a line from
Monida Pass to Ennis to Bozeman. Have therefore decided to issue a
Dense Fog Advisory for those areas until 10 am MDT.
Coulston

Today through Sunday...Patchy fog has formed in some of the
valleys of southwest Montana, but this should dissipate by mid
morning. Otherwise, the upper level trough of low pressure
currently over Montana and southwest to the central California
coast will split today. The shortwave over over Montana will move
east out of the area. The base of the trough will form a cutoff
low that will linger over the central CA coast through Saturday,
but it will come back to affect Montana`s weather beginning Sunday
afternoon. Until then, the northwesterly flow aloft in the wake of
the shortwave will keep isolated to scattered showers over the
western mountains, with mainly scattered mid level cloudiness
elsewhere. Westerly surface winds will also remain breezy across
much of north central and southwest Montana, especially along the
Rocky Mountain Front, where gusts will continue to exceed 50 mph
at times in favored canyon and downslope areas. Winds and clouds
will decrease overnight and continue through the remainder of the
weekend for most of the area as an upper level high pressure ridge
rebuilds into the state from the west. However, an approaching
long wave low pressure trough off the Pacific coast will lift the
cutoff low (mentioned above) northeast across the Great Basin on
Sunday. This will bring increasing cloudiness to southwest
Montana, but the chance for showers/storms will likely hold off
until Sunday night.

Temperatures in the wake of the shortwave will cool a bit for
today and Saturday, but they will generally remain about 3 to 5
degrees above normal. As the ridge builds into the area by Sunday,
temperatures will mostly be 5 to 10 degrees above normal. Smoke
may also continue to be a nuisance in some areas, but the shift of
the winds aloft may help generally lessen the smoke.
Coulston

Sunday night through Friday...A high pressure ridge will be
moving east of the zones Sunday night and a weak shortwave will
track across Southern Idaho towards Central Montana. This will
bring moisture and instability across Southwest Montana by Monday
afternoon and this flow continues through Tuesday. A slight
chance of showers or thunderstorms is expected but overall the
air mass will remain quite dry. A ridge will be in place again
over the region by Wednesday and the air mass will warm and temps
will be well above seasonal normals through Thursday. A deep low
pressure trof moving over the West Coast will bring moist,
unsettled flow aloft over Central Montana by late Thursday
afternoon...and instability and a chance of thunderstorms will
again develop. Zelzer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  75  47  72  46 /  10   0   0   0
CTB  72  42  71  42 /  10   0   0   0
HLN  76  47  77  46 /  10   0   0   0
BZN  73  42  74  42 /  10   0   0   0
WEY  68  29  70  29 /  10   0   0   0
DLN  74  44  75  45 /  10   0   0   0
HVR  78  48  73  44 /  10   0   0   0
LWT  74  47  71  45 /  10   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

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