925
FXUS65 KTFX 170251
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
851 PM MDT Thu May 16 2024

.SYNOPSIS...

Gusty west winds will increase and become more widespread through
Friday as a Pacific weather system moves into the region with its
associated cold front crossing the region by Friday afternoon.
Scattered showers and isolated thunderstorms are possible in some
areas through Friday evening, with cooler temperatures following
through the weekend while an active weather pattern brings
additional chances for precipitation late this weekend into next
week.

&&

.UPDATE...

No significant changes needed to ongoing forecast for the
overnight period. However, winds have already started to decrease
on the Rocky Mountain Front and adjacent plains after widespread
gusts in the 45 to 55 mph range. winds area a little slower to
decrease across the northeast TFX plains, including Hill, Blaine,
and Chouteau Counties, and there are a few lingering showers and
weak thunderstorms. This is occurring on the trailing edge of an
exiting disturbance, so winds and shower/storm activity should
continue to diminish through midnight. Otherwise, winds and at
least scattered showers will return tomorrow morning as a passing
cold front cools temperatures back closer to seasonal averages.
-Coulston

&&

.AVIATION...
17/00Z TAF Period

VFR conditions are mostly expected to continue across North
Central (KCTB, KHVR), Central (KLWT, KGTF, KHLN), and Southwest
(KBZN, KEKS, KWYS) Montana through at least 18/00Z, unless
otherwise mentioned.

The main concern for this period will be winds. A strong westerly
flow aloft will continue widespread mountain wave turbulence
across the area, as well as periods of low level wind shear
mainly during the decoupling (02Z-08Z) and mix-down (13Z-19Z)
periods. Gusts in excess of 35 kt will persist until winds
decouple this evening, then gusts in excess of 40 kt will become
widespread after mix-down tomorrow.

Otherwise, the few showers and weak thunderstorms that have
developed over the plains should diminish through 04Z with the
loss of daytime heating. However, a disturbance is forecast to
move east across the area between 10Z and 18Z, bringing scattered
showers to the area, possibly with brief periods of MVFR
ceilings. A stronger shortwave trough and associated Canadian
cold front will then move through the area after 18Z, bringing
another round of scattered showers to much of the area. Showers
with low VFR/MVFR conditions, possibly with a few thunderstorms,
will be more widespread along the Canadian border, as the
westerly winds also shift more northwesterly. -Coulston

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

&&

.PREV DISCUSSION...
/ISSUED 720 PM MDT Thu May 16 2024/

An upper level trough digging into BC today will progress east
across western Canada tonight through Friday. Meanwhile, A fairly
vigorous shortwave and strong upper level jet (for May) move
onshore in the Pacific NW tonight and across the Northern Rockies
Friday with an associated Pacific cold front at the surface.
Surface low pressure emerging ahead of these features in southern
AB will move off to the east into western SK by Friday morning
with the Pacific cold front trailing SW across central and
western MT. Breezy to windy conditions persist through this
evening across much of the area with 30-40 mph gusts over the
mountains and across western portions of north-central MT. These
areas will see winds persist through the overnight period while
areas further east across north-central MT and in the SW MT
valleys should see winds diminish some overnight. Showers and a
few thunderstorms are possible near the Canadian border (mainly
northern Hill/Blaine counties) through this evening with showers
increasing later tonight along northern portions of the
Continental divide near Glacier NP. Better support for organized
thunderstorms will exist north of the border through this
evening, but there may be some potential for wind gusts from
storms in far SE AB and SK to reach into portions of Hill and
Blaine counties.

Wind continues to be the primary concern for tomorrow across much
of the area with most areas likely (>60% probability) to see
gusts in excess of 40 mph with a reasonable chance (30-50%) for
localized gusts in excess of 50 mph, especially across areas
adjacent to the Rocky Mtn Front and mountains of central and
southwest MT. Strong winds (gusts in excess of 50kts) are not
expected to be widespread but a few isolated higher gusts are
possible, piratically with the passage of the cold front across
SW MT Friday afternoon. Westerly/downslope flow will be a
limiting factor for precipitation coverage/amounts on Friday,
however there will be ample mid to upper level support from the
incoming shortwave, upper jet energy and modest instability for
showers, particularly across southwest MT and increasing in the
afternoon and evening as moisture and another disturbance move
southeast from AB. Hoenisch

Saturday through Sunday...ensemble clusters strongly favor
longwave troughing over the Northern Rockies throughout the
weekend, with the leading mode of uncertainty being the overall
amplitude of the longwave trough, specifically on Sunday. A
deeper longwave trough on Sunday, which is overall favored in 3
of the 4 clusters, would result in cooler and "wetter" conditions
through the weekend across much of Southwest through North
Central Montana. Latest NBM probabilities for a 0.25" of
precipitation from 12z Sunday to 12z Monday generally range from
20-40% south of the US Hwy 2 corridor and north of the US Hwy 12
corridor. Additionally, the probability for snowfall of 2" or
more along the Continental Divide and across the mountains of
Central Montana over this timeframe is approximately 30%, with
48hr probabilities (including Saturday and Saturday night)
ranging from 30-50% for these same areas. High temperatures on
Saturday in wake of Friday`s Pacific front will fall into the
60s, with Sunday only seeing highs rise into the 50s.

Monday through next Thursday...an unsettled and "cooler" pattern
is favored through the upcoming work week, with the multi-model
ensemble cluster suggesting overall longwave troughing over the
Western CONUS and Western Canada and inconsequential periods of
transient shortwave ridging moving over the Northern Rockies.
Some uncertainty exists with the timing, position, and amplitude
of individual shortwaves troughs rotating through the longwave
trough, but the main message to put forward will be that their
exists multiple chances for precipitation (some of which may fall
as mountain snow) and below normal temperatures through the
upcoming work week. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  61  40  64 /  10  40  30  10
CTB  45  55  35  60 /  10  70  40  10
HLN  51  62  39  67 /   0  40  10   0
BZN  43  65  30  66 /   0  50  10   0
WYS  37  61  24  57 /  10  30  10   0
DLN  43  63  29  66 /   0  20   0   0
HVR  50  64  39  65 /  20  60  80  10
LWT  45  61  36  61 /  10  60  40  10

&&

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

$$

http://www.weather.gov/greatfalls