Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 161021
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
421 AM MDT Sun Jul 16 2017

...Strong Gusty Winds to Bring Heightened Fire Concerns to much of
Central Montana Today...

.SYNOPSIS...

A cold front will gradually settle south into Southwest Montana by
tonight. Along the front, it will be breezy across central Montana
this afternoon and early evening. Meanwhile, scattered thunderstorms
are expected further south across Southwest Montana. The front
eventually pushes through with a lower chance of thunderstorms by
next week. Temperatures stay warm into next week.

&&

.DISCUSSION...

Today through Monday Night...Latest SFC analysis shows a Pacific
cold front arcing from SW AB through western MT/western ID as of
4am. Ahead of it, thunderstorms will primarily be focused over SW MT
(along and south of a Helena to Lewistown line). Like yesterday, the
better shear will be somewhat removed from the better instability.
That said, shear across SW MT should be more than sufficient for
organized thunderstorms with gusty winds and hail possible. The
threat of a few severe storms would likely be higher if better
instability can be realized. At this time, though, a lack of better
shear/instability should keep the threat isolated. A few
thunderstorms may linger in this area on Monday, but instability
looks even weaker then.

Across central Montana, increasingly dry low/mid levels should allow
deep mixing to occur, bringing down the increasing winds aloft. All
this spells a breezy late-morning through early evening period with
gusts of 25-35 mph common. This should also lead to downsloping and
limit the thunderstorm potential. Winds aloft relax on Monday with a
subsequent decrease in SFC winds. See the fire section below for how
this will impact those with fire interests. MARTIN

Tuesday through Sunday...A disturbance moving through the westerly
flow aloft may bring a few thunderstorms to the mountain areas of
Southwest Montana Tuesday afternoon/evening. Otherwise, the upper
level high pressure ridge will rebuild north into the forecast area
into Thursday, keeping the area dry and warming temperatures back up
to between 5 and 10 degrees above normal. Medium range models are
showing some disagreement for the Thursday into Friday period
regarding the timing and placement of a shortwave trough moving
along or just north of the Canadian border. The GFS keeps it more so
along the border and moves it through Thursday into Thursday night,
which would bring a good chance of breezy westerly winds, especially
to the Rocky Mountain Front. The ECMWF and CMC models keep it a bit
farther north of the border and move it through on Friday. Recent
trends have leaned a bit closer to the GFS solutions, so have
focused the increased winds to the Thursday afternoon/evening time
frame. After the passage of the shortwave, the high pressure ridge
remains flattened over Montana through Sunday, resulting in a
relatively dry westerly flow aloft. Because of the differences in
timing of the shortwave, the forecast models differ somewhat on
temperature trends as well. The ECMWF keeps temperatures on the warm
side Thursday into Friday, then cools temperatures a bit for the
weekend. The GFS cools temperatures for Thursday and Friday, then
warms them up for the weekend. With this kind of discrepancy, will
stay with the model blend solution of a more broad-brushed period of
5-to-10-degree-above-normal temperatures (i.e. mostly upper 80s to
lower 90s for highs at lower elevations - still quite warm, but not
as hot as recent temperatures). Will look to fine tune this portion
of the forecast once models come into better agreement. Regardless,
this kind of an extended dry and warm period will only increase fire
weather concerns. Fortunately, at this point, there is very little
chance of additional thunderstorms.
Coulston

&&

.AVIATION... Updated 0440Z.

Thunderstorms activity has largely exited to the east of central and
SW MT with a few lingering showers and very localized MVFR
conditions possible through the next several hours before stronger
drying arrives from the west. Winds remain somewhat variable across
the region this evening with persistent westerly winds expected to
develop overnight as high pressure builds into western MT. Westerly
winds increase and become gusty after 15Z Sunday, particularly over
North central MT. Hoenisch

&&

.FIRE WEATHER...

Critical fire conditions continue to be expected today across much
of central Montana and a small part of SW MT. Hot temperatures
and increased lightning activity over the past couple of days will
be followed by increasing winds by this afternoon, especially
central Montana. The increasing winds should offset the lack of a
higher fire danger class and is the reason the ongoing Red Flag
Warning for fire zones 112, 113, 114, and 115 was expanded to
include fire zone 116 and part of 117. Of note, Meagher and Park
Counties are NOT included in the Red Flag Warning for zone 117 as
those two counties have a lower fire danger class and winds are
not expected to be quite as strong there. That said, elevated fire
concerns are certainly possible there, especially in any area that
saw more lightning activity over the past couple of days. Beyond
today, the wind will decrease through early next week, but breezy
conditions may return mid to late week along with warming
temperatures, potentially creating additional fire weather
concerns. MARTIN/Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  89  49  83  51 /   0   0   0  10
CTB  80  45  77  45 /  20   0   0   0
HLN  87  54  85  54 /  20  10   0  10
BZN  86  49  84  50 /  30  20  10  20
WEY  80  41  79  41 /  50  50  20  10
DLN  86  49  82  50 /  20  10  20  10
HVR  92  49  84  51 /  20   0   0   0
LWT  85  51  81  51 /  30  20  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 9 AM this morning to 9 PM MDT this evening
Central and Eastern Lewis and Clark National Forest Areas...
Lincoln Ranger District of the Helena National Forest.

Red Flag Warning from 9 AM this morning 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 until 9 PM MDT this evening Chouteau and Fergus
Counties...Hill and Blaine Counties.

&&

$$

weather.gov/greatfalls



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