908
FXUS65 KTFX 171800
AFDTFX

Area Forecast Discussion
1159 AM MDT Fri May 17 2024

Updated Aviation Discussion

.SYNOPSIS...

A gusty day is in store for the region as a Pacific cold front
progresses eastward this morning and early afternoon. Cooler
temperatures will be the theme this weekend into next week, with
opportunities for precipitation most days.

&&

.UPDATE...

A band of showers continues to make its way across central
Montana this morning. These showers are expected to move out of
the area by the early afternoon providing a brief lull for north-
central and central Montana before things start to pick up by mid
to late afternoon as the front continues its push through the
region.

The latest hi-res models showed more robust coverage of the
precipitation potential for this afternoon along the hi-line so
precipitation chances were expanded a little to reflect that in
the update. The chance for widespread severe weather remains
minimal but an isolated severe thunderstorm cannot be ruled out
with the primary threat being wind.

Otherwise, no major changes were made to the going forecast. The
expected wind potential for today is still on track with a chance
for some isolated strong gusts associated with showers but the
widespread potential is still well below threshold.

-thor

&&

.AVIATION...
17/18Z TAF Period

A Pacific cold front will continue east through eastern portions of
central and southwest MT early this afternoon with a few showers
occurring near the front while additional showers develop this
afternoon across primarily central and north-central MT. Greatest
concentration of showers this afternoon and evening will be along
northern portions of the continental divide including Glacier NP and
eastward along the Hi-line, where a few thunderstorms are also
possible. Mainly VFR conditions are expected with some brief MVFR
and local mountain obscuration in/near any showers or thunderstorms.
Winds will be the most widespread impact to aviation through this
evening with 35-45kt gusts likely at most terminals. Isolated
stronger gusts are possible over the mountains and in the vicinity
of showers. Strong westerly flow aloft across the Rockies will
maintain the risk for mountain wave turbulence until winds aloft
begin to relax later tonight.


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

&&

.PREV DISCUSSION...
/ISSUED 546 AM MDT Fri May 17 2024/

A quick morning update has been published. Outflow from showers
off to the north have limited southwest winds from making many
inroads onto the plains so far this morning. Additionally, where
precip has fallen overnight and skies are at least briefly clear,
patchy fog has developed. Hence the update was made to reduce wind
over the next few hours across portions of the plains and to add
patchy fog mention in similar areas. No changes otherwise.

Through Tonight... Zonal flow aloft largely persists through today,
though a wave pivoting through a larger scale trough will, with the
help of a developing surface low across southern SK, propel a
Pacific cold front through the Northern Rockies this morning into
early afternoon. Temperatures this morning will be on the mild side,
but fail to rise too much before the Pacific front arrives, allowing
temperatures to stagnate or fall slightly through the afternoon.
Forecast soundings support wind gusts in the 40-55 mph range
today, with only isolated instances of stronger gusts approaching
60 mph away from the Rocky Mountain Front (Where the chances are
moderate today). Given a lack of high confidence for more than a
few isolated synoptically driven wind gusts 50 kts or greater, I
have opted to forego any High Wind Warnings at this time. A
complicating factor will be any showers that form where winds
aloft are on the stronger side. Given respectable inverted-V
soundings, decaying showers will be able to produce a bit more
momentum transfer to the surface compared to mixing alone.
Confidence in a timing or location of this is quite low, which
will necessitate monitoring of trends through the day today. Winds
will slowly diminish heading into tonight.

Aside from winds, zonal flow aloft will also bring snow to the high
terrain of the Rocky Mountain Front. Although impacts don`t look
to occur at or below pass level, those recreating should be aware
of forecast conditions.

This weekend... Large scale upper troughing will remain in place
across SW Canada and the far northern portions of the NW CONUS this
weekend, resulting in largely zonal flow aloft, with shortwaves
pivoting across the region at times. The end result is for
unsettled conditions remaining. Temperatures will be on the cooler
side, with opportunities for showers and perhaps a few
thunderstorms.

Sunday looks to be the day more favored for showers and
thunderstorms, as a robust shortwave pivots through the broad
troughing. Confidence in timing is not yet high, but the chance for
a tenth of an inch of precipitation Sunday into Sunday night is
largely greater than 50% across the region.

Next Week... Ensembles favor a continuation of unsettled conditions
heading into next week as large scale troughing remains in place
across much of the Pacific NW and Northern Rockies. Although
confidence is high that unsettled conditions will remain, specifics
with respect to timing and magnitude of any precipitation is murky
at best at this point. -AM

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  60  38  63  40 /  50  40   0  20
CTB  54  35  59  34 /  60  50  20  10
HLN  62  38  66  41 /  40  10   0  20
BZN  65  30  66  39 /  40  10   0  20
WYS  61  25  57  35 /  20  10   0  10
DLN  62  29  66  37 /  10   0   0  10
HVR  62  39  64  38 /  50  90  10  10
LWT  60  35  60  38 /  50  30   0  20

&&

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

$$

http://www.weather.gov/greatfalls