903
FXUS65 KTFX 202019
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
219 PM MDT Thu Jun 20 2024

.SYNOPSIS...

Showers and a few stronger thunderstorms will be around again
today, with Friday bringing a better chance for strong to severe
thunderstorms across Central and North-central Montana. A warming
and drying trend commences for this weekend, with Sunday looking
to be the warmest day of the forecast period. Breezy winds develop
across the plains late Sunday into Monday as a mainly dry Pacific
front moves across the region.

&&

.DISCUSSION...

The rest of today... Strong ridging across the eastern CONUS will
keep broad troughing in place across the western CONUS through the
next 36 hours or so. An embedded wave within the west to
southwesterly flow aloft across the Northern Rockies will combine
with sufficient instability to result in showers and a few
stronger thunderstorms across primarily Central and North-central
Montana this afternoon and evening. A corridor of slightly higher
instability (On the order of 750-1,000 m2/s2 or so with locally
higher amounts up to 1,500 m2/s2) looks to set up along and
adjacent to the 87 corridor between Great Falls to Grass Range.
Marginal yet sufficient shear will be in place in this area to
allow for a few stronger storms to develop, with a marginal risk
for severe thunderstorms (Greatest risk is for hail). Storm motion
appears to be rather slow so far this afternoon, yielding concern
for localized flooding where thunderstorms are most persistent.
Showers and thunderstorms move off to the northeast and or
diminish tonight. There is less concern for patchy fog tonight,
given mid and high level clouds that will be in place across the
Northern Rockies.

Friday... Broad troughing will still be in place, but begin to shift
eastward with an embedded shortwave crossing the Northern Rockies
late morning through the evening. Meanwhile at the surface, high
pressure well off to the east (Across the northern Great Lakes) will
result in an easterly component to wind across the plains. Higher
dew point temperatures (Upper 40s to mid 50s) will be advected in as
a result. All of these ingredients will combine with relatively
steep mid level lapse rates and vertical wind shear to result in
several thunderstorms tomorrow, primarily across Central and North-
central Montana. Straight hodographs suggest hail and wind will be
the main concern with the strongest thunderstorms. The timeframe of
greatest concern will be around/just after noon until just after
sunset.

An additional concern will be for heavy rain with thunderstorms.
Storm motions look to be quick enough (On the order of 20 mph or so)
to mitigate most concerns for flooding or flash flooding, but the
risk will exist regardless.

Saturday into next week... Upper level ridging further east across
the eastern CONUS will begin to gradually break down Friday night
into Saturday, allowing for the upper level troughing that has been
over the Northern Rockies to shift eastward, away from the region.
This will allow an upper level ridge to build in from the west this
weekend, propelling temperatures above average by Sunday as the
ridge axis starts slipping east of the region. A compact upper level
low off the coast of BC will open up into a wave and shift
eastward beginning Sunday afternoon. The best upper level support
for precipitation with this system looks to remain north of the
border Sunday into Monday, resulting in the only impact being
breezy westerly winds across the plains.

Ridging is favored into Tuesday, but confidence beyond Tuesday
decreases. Ensembles favor an eventual breakdown of the ridge, but
are struggling to time it at this range. -AM

&&

.AVIATION...
20/18Z TAF Period

VFR conditions prevail this TAF period. Scattered showers and
thunderstorms will be around this afternoon and early evening, but
the probability for these to impact terminals is too low to warrant
a mention in TAFs (Aside from KLWT) at this time. Concerns for any
patchy fog tonight in areas that see precipitation this afternoon
will be mitigated by mid and upper level cloudiness tonight across
the region. Additional showers and thunderstorms will develop late
tomorrow morning into the afternoon, mainly across Central and North-
central Montana. -AM

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  49  76  49  82 /  20  70  20   0
CTB  44  72  44  80 /  20  70  20   0
HLN  52  83  53  87 /  20  40  10   0
BZN  46  81  48  84 /   0  30  10   0
WYS  39  76  41  79 /   0  20  10   0
DLN  44  80  47  85 /   0  10   0   0
HVR  51  77  50  82 /  30  80  40  10
LWT  46  72  47  77 /  20  80  40  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

http://www.weather.gov/greatfalls