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000
FXUS65 KTFX 210545
AFDTFX

Area Forecast Discussion National Weather Service Great Falls MT
1145 PM MDT Sat Apr 20 2024

Aviation Section Updated

.SYNOPSIS...
Very windy conditions develop on Sunday in association with a
passing frontal system with strong winds expected from the Rocky
Mountain Front east along the Alberta border. Warmer air will slowly
move into Central MT over the next few days. Overall, Wednesday is
looking to the be warmest day over the next week.

&&

.UPDATE...
Conditions remain relatively benign across the Treasure State as
upper-level ridging persists over the Northern Rockies through the
remainder of the evening and into the early morning hours. The
current forecast continues to describe the situation well, resulting
in no amendments to the forecast at this time. - Pierce

&&

.AVIATION...
1145 PM MDT Sat Apr 20 2024 (21/06Z TAF Period)

Quiet weather is expected overnight, with just some increasing high
clouds. By Sunday morning surface winds will be increasing, with
strong surface winds expected over the western half of North Central
MT by late Sunday morning. The strong winds will diminish a bit on
Sunday evening. There is a small chance for a light shower over the
Rocky Mountain Front and also in the mountains around Ennis/Big Sky.
Otherwise, dry conditions are expected elsewhere. The mountains
around the Rocky Mountain front and Big Sky could be obscured at
times on Sunday. Brusda

Refer to weather.gov/zlc for more detailed regional aviation weather
and hazard information.

&&

.PREV DISCUSSION...
/ISSUED 300 PM MDT Sat Apr 20 2024/

Key Message: Gusty West Winds Develop Across Central/N-central MT
Sunday With Strongest Winds and Potentially Difficult Cross-winds
Extending From The Rocky Mountain Front East Along The MT/Alberta
Border

Satellite imagery this afternoon shows an upper-level high centered
across AB with strongly meridional flow (southerly) to its west and
(northerly) east. A much flatter zonal flow exists to the south
along 40N with a low amplitude ridge progressing east into the
Northern Rockies downstream of a stronger wave in the base of a
negatively tilted trough approaching the BC/WA coast.

The main forecast concern is strong winds on Sunday as the
previously mentioned offshore wave races ENE across southern BC/AB
with compressed and increased westerly flow to its south. Strongest
winds look to develop following the passage of a mainly dry Pacific
cold front, aided by surface pressure rises and enhanced mixing as
mid-level cold advection coincides with daytime surface heating.
700MB winds in excess of 50kts generally line up with areas west of
I-15 within the current High Wind Warning, where probabilities for
gusts in excess of 55mph are also 90% or higher.
Similar probabilities exist for gusts in excess of 70 mph along the
immediate east slope areas, where mountain wave enhancement is most
likely to occur just prior to the front`s arrival Sunday morning.
Further east across Toole and Liberty counties, probabilities for
gusts in excess of 55 mph decrease, but deeper afternoon mixing
supports higher probabilities (60-80%) for sustained winds near 40
mph across these areas, particularly near the Sweetgrass Hills.

30-40 mph wind gusts will be common across the remainder of
north-central and southwest MT by Sunday afternoon with windy
conditions lingering through Sunday night an Monday across north-
central MT as the upper level wave and associated surface low
pressure track east across the Canadian Prairies. A few showers
are possible as the front continues through eastern portions of SW
MT Sunday evening with some showers likely to wrap around the low
and across far eastern portions of north-central MT Monday. There
is a substantial surface pressure gradient and mid-level NW flow
across Hill and Blaine counties on Monday to support continued
wind gusts in excess of 45 mph Monday afternoon, but clouds could
also limit deeper mixing in these areas.

Temperatures climb back to near seasonal averages Sunday and remain
close to seasonal averages Monday under a mainly dry west to
northwest flow aloft. Upper level ridging builds across the area
around the middle of next week with temperatures likely to peak
around 10 degrees above seasonal averages on Wednesday. Longer range
model ensembles continue to broadly support the next round of upper
level troughing moving into the western US by the end of next week
into the weekend. While there is a fair amount of uncertainty
with details within this larger scale trough, a trend back to
cooler temperatures and increasing chances for precipitation can
be expected going into next weekend. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  31  58  32  57 /   0   0   0   0
CTB  26  51  32  55 /   0   0   0   0
HLN  33  60  32  58 /   0   0   0   0
BZN  24  65  25  56 /   0  20  10   0
WYS  19  56  22  51 /   0  20  20   0
DLN  29  63  27  58 /   0  10   0   0
HVR  27  60  34  58 /   0   0   0  10
LWT  25  60  29  51 /   0  10  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 7 AM Sunday to midnight MDT Sunday night
for East Glacier Park Region-Eastern Glacier, Western Toole, and
Central Pondera-Eastern Toole and Liberty-Northern High Plains-
Southern High Plains.

&&

$$

http://www.weather.gov/greatfalls