-- Discussion containing changed information from previous version are highlighted. --
412
FXUS65 KTFX 260241
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
841 PM MDT Tue Jun 25 2024

.SYNOPSIS...

High pressure will maintain dry conditions through tonight before
an approaching Pacific weather weather system brings scattered
showers and thunderstorms on Wednesday and Thursday followed by
general unsettled weather on Friday. Temperatures warm above
average on Wednesday and then trend cooler during the second half
of the week.

&&

.Update...

-- Changed Discussion --
On-going forecast is performing well, so no adjustments were made
outside of re-running diurnal trends to better match observations
(although even these trends were doing quite well). Isolated
showers and thunderstorms across extreme Southwest Montana,
predominately along the Idaho and Wyoming borders, will gradually
wane through evening hours and give way to clearing skies through
the remainder of the night. Can`t rule out an elevated isolated
shower or storm beyond the midnight hour given embedded waves
within the moist, southwest flow aloft continuing to ripple
northeast overnight, but all available CAMs do not support this
happening so kept PoPs below 10%. - Moldan
-- End Changed Discussion --

&&

.AVIATION...
26/00Z TAF Period

VFR conditions are expected through 18z Wednesday across all
terminals; however, isolated showers and even a thunderstorm will
remain possible across far Southwest Montana near the Idaho/Wyoming
borders through approximately 03z this evening. Main impact from
these showers or storms at the KWYS terminal would be a reduction in
CIGS, but even these CIGS would remain VFR. Beyond 18z Wednesday,
showers and thunderstorms will begin to increase in coverage across
Southwest Montana, with CIGS beneath precipitation lowering to low-
VFR. In addition to reductions in CIGS Wednesday afternoon, any
shower or storm will be capable of producing gusty and erratic
winds. Little to no mountain obscuration is expected through
Wednesday morning. - Moldan

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

&&

.PREV DISCUSSION...
-- Changed Discussion --
/ISSUED 507 PM MDT Tue Jun 25 2024/

Upper level ridging remains in place through tonight, yielding
generally dry conditions and seasonable temperatures. The latest
satellite imagery does show some scattered clouds, most notably
over far Southwest MT and Hill and Blaine counties farther north.
Surface CAPE values have risen to around 100 to 200 J/kg and an
isolated shower or thunderstorm can`t be ruled out, particularly
for the higher terrain along the MT/ID/WY border. Any convective
activity will end this evening with the loss of diurnal heating.
Aside from some patchy fog development along the Milk River Valley
heading toward Wednesday morning, a relatively night is expected.

Diffluent southwesterly flow aloft develops ahead of an
approaching Pacific trough on Wednesday, resulting in increased
mid- and higher level cloudiness during the morning and scattered
shower and thunderstorm development by the afternoon. Hi-res
models have increased ML CAPE level up to around 400 - 800 J/kg
for Wednesday afternoon for locations south of a Helena to White
Sulphur Springs line. This combined with inverted V forecast
soundings and bulk shear around 30 top 40 kts creates an
environment for isolated severe wind gusts and perhaps some small
hail in addition to lightning. At least isolated convective
activity looks to persist into the overnight hours Wednesday
night, through the next viable chance for stronger thunderstorms
will come on Thursday over the eastern portions of the CWA. These
areas will be on the western fringe of higher end instability and
shear for at least a marginal threat of severe wind gusts, hail,
and heavy downpours. Showery precipitation continues Thursday
night into Friday, mostly for northern areas. There will also be
sufficient cold air for a dusting of light, high mountain snow.

Much cooler and windy conditions area expected on the back side
of the Pacific low later Thursday into Friday. Winds initially
increase along the Rocky Mountain Front Thursday night before
spreading eastward onto the plains by Friday. Probabilistic
guidance generally keeps wind gusts in the 30 to 50 mph range, but
locations along the Rocky Mountain Front on the immediate lee
side of the central ranges may see gusts over 55 mph. Shower
activity will need to be monitored for being a catalyst of
transferring higher wind guts to the surface. While no high wind
products are planned at this time, the situation will continue to
be monitored. Transient ridging aloft brings drier conditions for
the first half of the weekend before unsettled weather return
Sunday into early next week. - RCG
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  49  87  57  72 /   0  10  40  80
CTB  46  81  54  68 /   0  10  30  50
HLN  55  88  61  73 /   0  30  50  70
BZN  51  84  56  77 /   0  30  30  70
WYS  45  77  48  71 /  20  30  30  40
DLN  50  82  53  75 /   0  30  20  40
HVR  50  84  58  72 /   0   0  40  80
LWT  48  82  55  72 /   0   0  40  90

&&

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

$$

http://www.weather.gov/greatfalls