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539
FXUS65 KTFX 031823
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1223 PM MDT Mon Jun 3 2024

...AVIATION SECTION UPDATED...

.SYNOPSIS...

A cold front will move through the area today bringing a chance
for showers and isolated thunderstorms across the entire region.
Behind the front, strong westerly winds will develop towards the
evening and continue through Wednesday morning. Above normal
temperatures and drier conditions return for later in the week.

&&

.UPDATE...

For the morning update, increased probability of precipitation
for the rest of this morning through the afternoon hours as latest
surface observations and radar imagery continues to show light rain
shower activity across Central and portions of North Central
Montana. General thunderstorms and scattered rain showers are
still on track for this afternoon across Southwest and into Central
Montana. Webb

&&

.AVIATION...

-- Changed Discussion --
03/18Z TAF Period

Primary concern for this afternoon and early evening will be
convective showers and isolated thunderstorms associated with a
Pacific cold front. Although there will be little in the way of
lightning and mostly VFR conditions, stronger upper level winds and
cold air advection aloft increase the chances for showers
transferring wind gusts in excess of 35 kts to the surface. This
will be most likely to occur over locations south and east of a KHLN
to KHVR line where there is around a 40 to 70% chance for gusts over
30 kts. Strong westerly flow moves in behind the cold front with
winds initially increasing tonight along the Rocky Mountain
Front/central ranges and their adjacent eastern plains. Very windy
conditions are then expected over much of Central/North-central MT
on Tuesday. Expect mountain wave activity to increase along with
instances of low level wind shear. - RCG

Refer to weather.gov/zlc for more detailed regional aviation weather
and hazard information.
-- End Changed Discussion --

&&

.PREV DISCUSSION...
-- Changed Discussion --
/ISSUED 504 AM MDT Mon Jun 3 2024/

General Forecast Main Points:

- General thunderstorm risk across Montana today. Locally high
  wind gusts will be the main threat.

- Above normal temperatures will continue with the warmest
  temperatures expected later in the week towards the weekend.

- Generally dry conditions for the region starting Tuesday except
  for some scattered showers in southwestern Montana towards the
  end of the week.

High Wind Event Main Points:

- Winds will start picking up this afternoon along the Rocky
  Mountain Front and become widespread overnight.

- Wind gusts up to 75 mph along the Rocky Mountain Front.

- Wind gusts up to 65 mph across the remainder of north-central
  and central Montana.

- Widespread wind gusts of 40 to 55 mph possible across southwest
  Montana.

- High crosswind risk Monday evening through Wednesday morning.

Detailed Expected Impacts: The main concern will be travel
hazards related to the high winds especially for light and/or
high-profile vehicles and any vehicle towing a trailer. The risk
to I-15, US-2, US-87, and MT-200 will be of particularly high
concern through this event.

The secondary threat will be tree damage and flying debris from
loose or unsecured objects which may damage property and/or cause
isolated power outages. There is an ongoing concern that trees
that have been weakened by past storms, including the most recent
snow events in the last couple months, may be more susceptible to
falling under the stress of another round of high winds.

Short-Term Forecast: A Pacific cold front will move across the
region today bringing a widespread chance for showers with some
isolated thunderstorms possible. The greatest risk for
thunderstorms will be across southwestern Montana with gusty,
erratic winds being the main threat. Along the higher elevations
of the Rocky Mountain Front precipitation will start off as rain
and transition to snow later in the evening. Up to 2 inches of new
snow is possible at the highest elevations but currently no major
snow-related impacts are expected at pass level.

Behind the cold front westerly flow aloft will set up over north-
central and central Montana which will work to start increasing
wind speeds Monday night into early Tuesday morning. A second push
of wind will occur Tuesday afternoon into the evening which will
be when locations along the northern plains and hi-line are
expected to reach their highest wind gusts. When comparing this
setup to climatology, this event is still showing up as 3 to 4
standard deviations above normal in the ensembles. Thus,
confidence remains high in the expected severity of this event.

Warning/Watch Updates: With this forecast update, the remainder of
Fergus county was added to the high wind warning that starts this
evening. The rest of central Montana was added to the high wind
watch including the Little Belts, the Highwoods, and the rest of
Meagher county including White Sulphur Springs.

The tricky question for future updates will be what to do with the
areas currently under a high wind watch. Probabilities for wind
gusts exceeding 55 mph have continued to increase, but not to the
level or with the same level of confidence as locations further
north. Another consideration was the fact that in all the zones
under a watch there is reasonably high confidence that isolated
portions may reach high wind criteria but will it be widespread
enough to warrant putting the whole zone in a warning. Simply put,
there is enough confidence and threat potential that a watch is
warranted. But confidence at this point in time remains just
below what would ideally justify upgrading that area to a warning.
This scenario can reasonably go either way and it should be
anticipated by folks living in central Montana that their area
could be upgraded to a warning in the next update.

Otherwise, come Wednesday afternoon, winds will slowly start to
diminish with some lingering strong gusts up to 45 mph possible
along the Rocky Mountain Front, the hi-line east of Havre, and
higher elevations of north-central and central Montana through
late Wednesday night into early Thursday morning. As the trough
gets pushed out of the region by the emergence of an upper level
ridge, things will continue to calm down while warming up through
the rest of the week.

Thursday through Next Monday... By late this week, an upper level
ridge will build over the western CONUS bringing well above
normal temperatures across the state through the weekend. Exactly
how warm it will get remains uncertain at this time as there is
still some model disagreement on both the strength and the axis
of the ridge. There is also some disagreement on the mechanisms of
the ridge either breaking down or departing the region,
especially heading into next week. All of this means that, for
now, it will be quite warm and generally dry over the weekend but
beyond that uncertainty is too high for specifics.

-thor
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  68  43  68  49 /  50  10   0   0
CTB  63  41  62  45 /  30  20   0  10
HLN  68  43  69  52 /  80  20   0  10
BZN  68  36  68  48 /  90  70   0  10
WYS  54  35  61  41 / 100  90   0   0
DLN  65  38  68  48 /  60  20   0   0
HVR  73  45  72  48 /  90  50   0   0
LWT  68  38  66  46 /  80  60   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 6 PM this evening to noon MDT Wednesday
for Bears Paw Mountains and Southern Blaine-Cascade County below
5000ft-East Glacier Park Region-Eastern Glacier, Western Toole,
and Central Pondera-Fergus County below 4500ft-Judith Basin
County and Judith Gap-Northern High Plains-Snowy and Judith
Mountains-Southern High Plains-Southern Rocky Mountain Front-
Upper Blackfoot and MacDonald Pass.

High Wind Watch from Tuesday morning through Wednesday morning
for Big Belt, Bridger and Castle Mountains-Gates of the
Mountains-Helena Valley-Little Belt and Highwood Mountains-
Meagher County Valleys.

High Wind Warning from 9 AM Tuesday to noon MDT Wednesday for
Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Hill
County-Northern Blaine County-Western and Central Chouteau
County.

&&

$$

http://www.weather.gov/greatfalls