Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 170001
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
555 PM MDT Mon Oct 16 2017

...UPDATED AVIATION SECTION...

.SYNOPSIS...

A westerly flow aloft across the Northern Rockies and Montana will
maintain dry, mild and breezy conditions across the region through
mid-week. Strong winds are possible across much of north-central
Montana late tonight through Tuesday evening as a weather
disturbance moves across western Canada, with windy conditions
continuing through mid-week.

&&

.DISCUSSION...

Tonight through Wednesday...Fast westerly flow aloft continues
across the region today around a flattening upper level ridge
centered over the SW US. Surface pressure gradient across the
Rockies will continue to support locally strong winds along areas
immediately adjacent to the Northern Rocky Mtn front today with
afternoon mixing bringing an increase in winds, though not as
strong, to much of north-central MT again this afternoon. Upper
trough moves into BC tonight with band of strong flow aloft sagging
south to areas along the AB border by Tuesday morning. This will
support increasing winds tonight for much of north central MT with
gusts in excess of 50-60 kts developing along the Rocky Mtn Front
and Glacier County by Tuesday morning as a critical level (favorable
wind profile with low level maximum near ridgetops) increases along
the northern Rocky Mtn Front through Tuesday morning. Band of
strongest winds aloft sags further S and E into N-central MT Tuesday
while a surface trough in AB deepens ahead of the upper trough
moving across BC. Upper level trough emerges in AB Tuesday night
with surface low and cold front moving quickly east off the Rockies
with a trailing portion of the front sweeping SE across N-central MT
Tuesday night. Strong winds initially along the Rocky Mtn front
Tuesday morning will likely spread east into adjacent western
portions of n-central MT Tuesday afternoon with potential increasing
for a period of strong or even high winds to extend further east
across much of the remainder of n-central MT Tuesday late afternoon
into the evening. Strongest wind gusts along the Rocky Mtn Front are
likely to occur Tuesday afternoon and may exceed 80 mph locally in
areas favorable for enhanced winds. Further east, wind gusts of 60-
70 mph are most likely to occur late Tuesday afternoon and evening.
Winds aloft diminish slightly late Tuesday night and Wednesday,
maintaining windy conditions across the forecast area, however the
surface pressure gradient relaxes across the region as the surface
trough moves east into central Canada. CC/Hoenisch

Wednesday night through Monday...The overall windy and warm pattern
will persist well into the overnight hours Wednesday night as strong
upper-level winds continue aloft. However, things begin to change on
Thursday with the development of a west coast longwave trough. This
will allow for a progressive southwesterly flow to transition aloft
across the area. The effect will be much warmer temperatures during
the day on Thursday due to downsloping/chinook winds, which has been
reflected well by model trends the past few days. Another note will
be the overnight lows Thursday and Friday morning, as temperatures
wont drop too far given persistent nocturnal gusty winds and
downsloping. It is possible that some locations could reach near-
record warmest overnight low temperatures for those dates with many
only seeing lows in the upper 40`s to lower 50`s across the Plains.
During the day on Friday, a quick moving cold front will swing
through the CWA leaving behind slightly cooler temperatures, as well
as increasing light rain showers. As cooler air filters in behind
the passing cold front Friday afternoon, some higher elevations in
south central and southwestern MT may end up with some accumulating
snow through late Friday night. By Saturday, any early morning
lingering rain or mountain snow showers will quickly exit to the
east leaving behind moderating temperatures and intervals of sun and
clouds. The long range pattern does suggest the development of a
reinforcing strong ridge across SW US. As heights progressively
increase/steepen in this response, model guidance appears to support
a developing strong zonal jet right across the northwestern US. This
may introduce the next potential strong wind event at some point
Saturday and into Sunday followed by a trend in near to above normal
temperatures into early next week. KLG

&&

.AVIATION...
Updated 2355Z.

VFR conditions will continue through at least Tuesday afternoon. An
increasing westerly flow aloft will move areas of high clouds over
the area, but the main concern will be strong westerly winds, as
mountain wave turbulence and low level wind shear will be common.
Winds will remain strong close to the Rocky Mountain Front (gusts to
50 kt) overnight. However, winds over the plains will decrease to
between 10 and 20 kt this evening with some lingering gusts to
between 25 and 30 kt. Light winds are expected in the southwest
valleys. Overall, winds will become quite strong over the plains on
Tuesday, with gusts of mostly 40 to 50 kt expected, but gusts will
exceed 60 kt along the Rocky Mountain Front. Gusts in the southwest
valleys will likely increase to between 25 and 35 kt.
Coulston

&&

.FIRE WEATHER...

Given windy, warm, and very dry conditions only worsening tomorrow
(Tuesday) with even stronger winds across the plains, we have
decided to issue Red Flag Warnings. Expect critical fire weather
conditions to develop by late morning after poor to moderate RH
recoveries overnight tonight. Rapid fire spread will be possible
given the magnitude of the winds and RH values dropping well into
the teens, even given marginally dry fine fuels. CC

&&


.PRELIMINARY POINT TEMPS/POPS...
GTF  48  74  42  65 /   0   0   0   0
CTB  49  70  36  59 /   0   0  10   0
HLN  40  71  41  67 /   0   0   0  10
BZN  38  70  40  68 /   0   0   0   0
WEY  23  57  30  53 /   0   0   0   0
DLN  34  67  39  64 /   0   0   0   0
HVR  50  74  40  62 /   0   0   0   0
LWT  47  72  40  64 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 AM to 7 PM MDT Tuesday Central and
Eastern Lewis and Clark National Forest Areas...Chouteau and
Fergus Counties...Eastern Glacier/Toole/Central/Eastern
Pondera/Liberty...Hill and Blaine Counties...Lewis and Clark
National Forest Rocky Mountain District-Rocky Mountain Front.

High Wind Watch from Tuesday afternoon through Tuesday evening
Cascade...Central and Southern Lewis and Clark...Chouteau...
Eastern Pondera...Eastern Teton...Hill...Judith Basin...
Liberty...Toole.

High Wind Watch from Tuesday afternoon through late Tuesday
night Blaine...Fergus.

High Wind Warning from midnight tonight to midnight MDT Tuesday
night Eastern Glacier...Northern Rocky Mountain Front...Southern
Rocky Mountain Front.

&&

$$

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