Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 220244
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
844 PM MDT Sat Oct 21 2017

.SHORT TERM...for northeast Montana...tonight through Sun...

900PM UPDATE:
Changes for the evening were minimal. Main concern with winds
becoming light so fast... a few isolated valley and drainage prone
areas such as Jordan and coulees around Dawson County have already
reached and broken minimums. For this reason shrink-stretched
these locations a little lower to compensate for the low
dewpoints already establish for tonight. GAH


500PM UPDATE:
Took a very hard look at the High Wind Warning for tomorrow. Upon
investigation, found multiple 12Z models are placing a 700mb jet
spike over Garfield county. CMCreg, GFS, NMM, NAMNest, DNG etc...
in addition each model is placing lapse rates between 7-9 C/km
along the frontal passage as it moves under this spike. These
models are also placing very light QPF in place next to the
boundary with the passage. We`ve seen this before twice already in
the last week, a relatively warm afternoon leads to a late cold
front which generates showers into a high dewpoint depression
environment. The showers evaporate, cool, and drag the wind spike
down the surface which exceeds well beyond what the model surface
wind output gives. Because of this, expanded the High wind warning
over Petroleum, Garfield, Prairie, McCone, Dawson, Wibaux, and
Richland county. 18Z run of the models has moved the spike only
slightly southeast by about 20 to 30 miles. So, the spike itself
is high confidence, but areal placement is only moderate
confidence. GAH


PREVIOUS SHORT TERM DISCUSSION:
By 00Z this evening, the base of the trough will be fully into
North Dakota to be followed by a weak ridge over the Montana
prairie tonight. Winds will be diminishing as clearing skies allow
for airmass to decouple and the ridging weakens the winds aloft.
Expect most lows to fall into the 30s due to the much cooler air
in place.

Very strong Pacific jet punches across the Rockies on Sunday,
forming an Alberta clipper in the morning. Stacked westerly flow
will bring the winds down across the prairie fairly quickly in the
morning. With 50 to 60 kts at 850 and 700mb will upgrade High
Wind Watch to a warning for southwest Phillips county. Near term
models indicate that ridge tops across the remainder of Phillips
county will likely see gusts to 55 or 60 mph, so will expand
warning into all of Phillips County. With the winds increasing
early in the day, the lake wind advisory was extended from today,
although winds will be temporarily diminishing tonight. With
westerly wind, highs will warm up 5-10F higher than Saturday.

Templer


.LONG TERM...Sun night through Sat...
AFTERNOON UPDATE:
The clipper system expands into a deep trough as it heads towards
the Great Lakes. This will maintain strong northwest winds locally
through Monday. This new infusion of CAA will knock highs down
to normal again. The next major change will come from a trough in
Western Canada digging through the Northern High Plains on
Wednesday. This will bring much cooler temperatures, a quick shot
of precipitation, some mixed, Wednesday night and Thursday, along
with strong winds again. Used FB through Thursday to update with
the latest guidance.

Templer


PREVIOUS LONG TERM DISCUSSION:
Clipper system dives toward the Great Lakes early in the week,
with upper trof digging over the northern Plains. Cold air
advection and pressure rises behind the clipper will keep strong
winds over the region Sunday night into Monday, with lake wind
advisory extended through Monday afternoon.
Tuesday into Wednesday, a warming and drying trend returns to the
area thanks to high pressure building over the northern Rockies.

Wednesday night through Thursday night, a strong cold front pushes
through the region. Models differing on how quickly this system
moves and develops, but some precipitation Wednesday night and
colder temperatures on Thursday. Ebert


&&

.AVIATION...

LLWS: With an inversion and winds aloft being strong Low level
wind shear will be a concern from 12-17Z.

CROSSWIND: Expect strong crosswinds for N-S runways from 17-02Z.

FLIGHT CAT: VFR.

SYNOPSIS: The upper level trough exits east to be replaced
by a weak ridge with diminishing winds overnight. Then Sunday an
Alberta Clipper races through the area to bring very strong west
winds of 30-40G50kt that will mix down to the ground during the
afternoon. Models indicate scattered light afternoon showers
which could bring even stronger winds to the ground in isolated
pockets.

WIND: West to southwest at less than 10 kts overnight, veering to
the west and increasing after sunup to 30-40G50kts by the late
afternoon, decreasing after dark to less than 20 kts.

Templer/GAH


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 10 AM to 8 PM MDT Sunday for Central and
Southeast Phillips...Central and Southern Valley...Dawson...
Garfield...McCone...Northern Phillips...Petroleum...Prairie...
Richland...Southwest Phillips...Wibaux.

Lake Wind Advisory until 10 AM MDT Sunday For Fort Peck Lake for
Central and Southeast Phillips...Central and Southern Valley...
Garfield...McCone...Petroleum.

Lake Wind Advisory from 8 PM Sunday to 6 PM MDT Monday For Fort
Peck Lake for Central and Southeast Phillips...Central and
Southern Valley...Garfield...McCone...Petroleum.


&&

$$

weather.gov/glasgow


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