388
FXUS65 KTFX 260545
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1145 PM MDT Sat May 25 2024

UPDATED AVIATION SECTION

.SYNOPSIS...

Shower and isolated thunderstorm activity slowly diminishes from
west to east tonight. Breezy to windy conditions are expected on
Sunday with shower chances mostly confined to the Hi-Line. Much
Drier and warmer weather is expected for Memorial Day and most of
Tuesday before shower and thunderstorm chances return later Tuesday
into Wednesday.

&&

.UPDATE...

Scattered showers and thunderstorms are diminishing in a west to
east fashion, but more shortwave energy will move in later this
evening into tonight and bring more clouds and showers, mostly
over and near Gallatin/Madison mountain ranges. These areas look
to undergo partial clearing towards dawn, which may encourage some
patchy fog development in some valleys. Otherwise, expect winds
to increase along the Rocky Mountain Front tonight and then spread
eastward into the plains and valleys on Sunday. probabilistic
guidance supports wind gusts mostly in the 25 to 40 mph range,
except along the Rocky Mountain Front where winds may gust above
50 mph at times. - RCG

&&

.AVIATION...
26/06Z TAF Period

VFR conditions are expected through at least 27/06Z across North
Central (KCTB, KHVR), Central (KLWT, KGTF, KHLN), and Southwest
(KBZN, KEKS, KWYS) Montana, unless otherwise noted.

Earlier shower and thunderstorm activity has moved east out of the
area, allowing skies to partially clear. However, another weak
disturbance in the westerly flow aloft is forecast to bring
scattered showers to Southwest Montana again through 11Z or so,
possibly causing brief periods of MVFR conditions. Partial clearing
there after 11Z could cause areas of fog to form, but there is still
uncertainty as to just how dense it will become due to the
uncertainty as to the degree of clearing, so will hold off on
significant reduction to visibility for now at the terminals.

Otherwise, another disturbance is forecast to move east along the
Canadian border through the day on Sunday, which will increase
westerly winds across the area. As the winds increase on the Rocky
Mountain Front, there will be a period of low level wind shear there
through 12Z or so. After 15Z, wind gusts will mostly be in the 20 to
30 kt range, likely exceeding 35 kt on the Rocky Mountain Front.
However, this disturbance will also bring a chance for afternoon
showers and thunderstorms to the Hi-Line area (including KHVR).
Winds, clouds and showers should decrease after 02Z. -Coulston

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

&&

.PREV DISCUSSION...
/ISSUED 240 PM MDT Sat May 25 2024/

Tonight through Monday... Scattered showers and thunderstorms will
persist through the rest of the afternoon across most of central
and southwestern Montana. Overall, the threat for severe weather
is minimal, however, a gust or two up to 50 mph and some pea-sized
hail is possible. Showers will quickly taper off after sunset for
north-central and central Montana. Some lingering showers will
remain for southwestern Montana through around 3 AM before
tapering off.

For tonight, model soundings are still split on fog developing
around Bozeman. There is just enough confidence and potential for
fog developing after the last of the showers move through early
tomorrow morning that a 20% chance for patchy fog was added to the
Gallatin Valley and portions of far southwestern Montana.
Widespread dense fog is not expected but it would not be
surprising for a couple isolated places to reach a quarter of a
mile in visibility at times.

Otherwise, as the shortwave continues east there will be another
chance for isolated showers and thunderstorms along the hi-line
Sunday afternoon. Memorial Day will be warmer and drier across the
region with generally light winds and partly cloudy skies except
along the northern Rocky Mountain front.  -thor

Tuesday through Saturday... An upper level ridge will be over the
area on Tuesday morning, which will quickly break down by Tuesday
afternoon, as an upper level trof approaches from the west.
Tuesday will likely be the warmest day over the next week, but I
did lower NBM guidance a few degrees for Tuesday afternoon, as it
might be too warm. Otherwise, the main concern Tuesday is for the
potential for severe storms Tuesday afternoon/evening. With the
flow aloft becoming southwest, it will be unstable by late
afternoon. However, it is not that unstable, thus the potential
for widespread severe storms looks low at this time. On
Wednesday, the main cold front moves though. Temperatures will
start to cool a bit, as well as the potential for heavy rainfall
over Central MT. Right now there is about a 30 percent chance for
locations between Great Falls and Lewistown to receive 0.50 inches
of rainfall. This would be convective rainfall, thus portions of
Central MT are in a marginal risk for excessive rainfall during
this period. It does remain unsettled for Thus/Fri with scattered
showers continuing and afternoon temperatures just a few degrees
below normal. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  63  40  73 /  40  10   0   0
CTB  40  60  39  70 /  10  10   0   0
HLN  42  64  43  76 /  20  10   0   0
BZN  36  62  36  71 /  70  10   0   0
WYS  33  55  30  64 /  80  20   0   0
DLN  35  63  36  71 /  50   0   0   0
HVR  44  65  43  73 /  40  30  10   0
LWT  38  58  37  67 /  80  10   0   0

&&

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

$$

http://www.weather.gov/greatfalls