Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 231144
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
540 AM MDT Wed Aug 23 2017

...UPDATED AVIATION SECTION...

.SYNOPSIS...
A high pressure ridge will keep most of the region dry and hot
again today with mostly sunny skies. However, a weak disturbance
will bring isolated thunderstorms to southwest Montana. A strong
Pacific cold front will then bring scattered showers and
thunderstorms to much of the region Thursday into Thursday
evening. West winds behind the front will become quite gusty, and
they will usher in cooler air for Thursday into Friday.

&&

.DISCUSSION...

Today through Friday...An upper level ridge of high pressure will
keep most of the forecast area hot and dry again today. A weak
disturbance will also cause gusty west mid level winds to mix down
to the surface along the Rocky Mountain Front and into central
Montana this afternoon and evening. This change in winds will likely
shift the smoke from just along the Continental Divide/into
southwest Montana to more so over the plains of north central
Montana. This same disturbance will also bring a few thunderstorms
to far southwest Montana this afternoon and evening. A strong cold
front will then move through the forecast area Thursday afternoon
into Thursday evening, bringing scattered showers and thunderstorms.
However, increasing westerly downslope winds behind the front will
hinder shower/thunderstorm development along the Rocky Mountain
Front and adjacent plains. The moist and unstable southwest flow
aloft accompanying the front is still forecast to bring high
precipitable water values into the favored thunderstorm area, so
heavy rain may come from some storms. Moderate instability and wind
shear may also cause gusty winds and small hail from storms.
Overall, the increasing west winds will spread over the area behind
the front Thursday into Thursday evening, especially along the Rocky
Mountain Front, where gusts could reach 40 mph at times. However,
cooler and less dry air will also move into the area, causing
temperatures to cool to near/slightly below normal by Friday.
Coulston

Friday night through Wednesday...Overall a warming and dry
pattern will be found through the long term, with elevated fire
weather danger to continue. Friday night through Saturday we will
find ourselves in the wake of Thursday/Friday`s disturbance. This
will bring weakly unstable zonal flow with a weak jet max
overhead. The result will bring some lingering chances for
showers and thunderstorms across southern and eastern portions
during this time period. A large area of high pressure will then
build across much of the western US starting Sunday and
continuing through at least the rest of the long term period. The
result will be warming temperatures and mainly dry conditions.
Afternoon RH values will continue to be low. This combined with
normal afternoon breezes may continue at least elevated fire
weather danger through the long term. A slight shift in location
of this high pressure on Tuesday and Wednesday may bring just
enough moisture and instability for isolated thunderstorms across
western and southern portions. With pwats expected to be low,
this looks to be mainly a dry thunderstorm threat, perhaps
further enhancing fire weather danger. Temperatures will start
near normal on Saturday, then start a warming trend with the
mentioned high pressure. Highs in the 90s are possible by next
week...especially Monday through Wednesday.
Anglin

&&

.AVIATION...
Updated 1140Z.

VFR conditions will continue across the forecast area through at
least 12Z Thursday. High pressure will keep skies clear but hazy
today. A more southwest flow aloft will cause mainly high clouds to
increase across southwest Montana later this afternoon into this
evening, then out onto the plains overnight. Areas of smoke will
cause slightly reduced visibility (though still mainly VFR) along
the Continental Divide and into southwest Montana today, but breezy
westerly winds will spread this smoke out over the plains this
afternoon into this evening. Cannot totally rule out some areas
having brief periods of high MVFR visibility (4 to 5 SM).
Coulston

&&

.FIRE WEATHER...

The Fire Weather Watch for this afternoon and early this evening
for fire weather zones 112, 114, and 117 has been upgraded to a
Red Flag Warning. Confidence has increased that mid level west
winds will mix down to the surface along the Rocky Mountain Front
and into portions of central Montana, causing gusts of 25 to 35
mph at times. However, the Watch for fire zone 118 has been
cancelled. The mid level winds are likely going to be quite a bit
lighter there and over areas south to the Idaho border, likely
only yielding gusts to 15 mph at times. All of north central and
southwest Montana looks to have very low afternoon humidity once
again, likely bottoming out mostly in the 10 to 15 percent range.
Coulston

Thunderstorms are possible on Thursday, but look too isolated
right now for any highlights. After some slightly cooler
temperatures on Friday, it then turns mostly dry and warm again
over the weekend and early next week.
Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  93  57  85  51 /   0   0  30  20
CTB  90  55  81  46 /   0  10  20  10
HLN  91  58  84  54 /   0  10  40  30
BZN  89  51  82  50 /   0  10  40  40
WEY  77  40  72  38 /  10  10  40  40
DLN  85  51  79  47 /   0  10  40  30
HVR  94  56  90  54 /   0   0  10  30
LWT  90  55  87  53 /   0   0  20  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 9 PM MDT this evening
Eastern Glacier/Toole/Central/Eastern Pondera/Liberty...Lewis
and Clark National Forest Rocky Mountain District-Rocky Mountain
Front.

Red Flag Warning from noon today to 9 PM MDT this evening
Central and Eastern Lewis and Clark National Forest Areas.

&&

$$

weather.gov/greatfalls



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