Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 191726
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1125 AM MDT Sat Jul 19 2014

Updated Aviation

.UPDATE...

Today...Strong winds aloft will continue through the day and keep
breezy surface winds in place across the Rockies most of the
central and northern zones. Smoke will continue to be a problem
but the air mass will remain stable and convection is not
expected. Just a few minor changes; updated to freshen SKY and
POPs. Zelzer

&&

.AVIATION...
UPDATED 1800Z.
Areas of smoke will continue to reduce visibility to MVFR at times
as westerly flow aloft persists. As surface winds continue to
increase this afternoon, conditions should improve, however
mountains will remain obscured through the period. Wind gusts along
the Rocky Mountain Front and adjacent plains, including KCTB could
gust up to 40kts this afternoon. Elsewhere across the plains, wind
gusts up to 35kts are expected. Winds should increase in the
southwest valleys this afternoon as well with wind gusts up to 20kts
possible at KHLN and KBZN. An isolated thunderstorm is possible this
afternoon in the higher terrain along the Rocky Mountain Front and
International Boundary, otherwise dry and VFR conditions will
prevail through the forecast period. MLV

&&

.PREV DISCUSSION...
/ISSUED 540 AM MDT Sat Jul 19 2014/
Saturday through Monday...A zonal upper level pattern will remain
over the area through the weekend as a broad upper level trough
over Canada slowly pushes the large continental ridge centered
over New Mexico eastward. This transition zone will continue to
keep the jet stream over the area and should allow for windy
conditions in the afternoon hours as high temperatures cause
enough thermal mixing to bring breezy conditions to the surface.
These breezy conditions will be most evident across the higher
Glacier National Park where gusty winds will combine with terrain
driven acceleration to cause wind speeds to exceed warning
criteria. Because of these concerns a High Wind Warning is in
effect for the Northern Rocky Mountain Front. By Monday a
shortwave will move into the area and could bring a limited chance
of showers as winds shift to out of the Southwest. This will also
bring a chance to limit smoke transport out of Washington and
Idaho and into the area...unfortunately large wildfires in Oregon
will be upstream of the region with the wind shift...and we could
end up just trading one smoke source for another. Conditions look
relatively dry throughout the period...with a slight chance of
showers and thunderstorms Sunday and Monday afternoons along the
Rocky Mountain Front. Temperatures will remain warm with highs
near seasonal averages. There is some concern for fire weather
conditions with these warm temperatures and winds...however fuels
appear to be too green to warrant any products at this time. Suk

Monday night through Saturday...The medium range period begins with
a closed upper low approaching British Columbia. Southwest flow
aloft resulting from this feature will bring moisture and
instability to the area with scattered thunderstorms developing over
the mountains of southwest Montana and then spreading north and east
over the plains Monday night. The upper low remains quasi-stationary
Tuesday offshore British Columbia. Diffluent southwest flow aloft
will contribute to thunderstorms again developing during the
afternoon and evening. By Wednesday, both the GFS and ECMWF models
begin to push the low inland. The airmass over the area will remain
unstable with afternoon convective activity again a possibility. The
models move the closed upper low across southern Canada on Thursday
with the ECMWF faster in pushing said feature east. With the low
centered further north than previously thought, the main
precipitation shield will remain in Canada with only isolated
thunderstorms over North Central Montana. By Friday, the GFS places
the low over southern Saskatchewan while the ECMWF has it over
central Manitoba. Westerly flow aloft will be over the area with
little to no precipitation the result. Upper ridging builds over the
area in the wake of the low`s passage Saturday with dry but cooler
conditions. Temperatures will be near seasonal averages to start the
period but will drop below seasonal averages by week`s end.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  86  60  85  58 /  10  10  10  20
CTB  82  55  79  52 /  10  10  10  20
HLN  88  60  88  59 /  10  10  10  20
BZN  87  52  87  54 /   0  10  10  10
WEY  79  41  79  43 /  10  10  10  20
DLN  85  51  86  55 /  10  10  10  20
HVR  92  60  87  56 /  10  10  20  10
LWT  89  57  87  56 /  10  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING until Midnight MDT Sunday Night Northern Rocky
Mountain Front.

&&

$$

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