557
FXUS65 KTFX 181951
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
151 PM MDT Wed Sep 18 2024

.SYNOPSIS...

This afternoon through tonight there will be rain showers across
most of North-central, Central, and Southwestern Montana. The rain
showers will end in Southwestern Montana this evening and from west
to east across North-central and Central Montana by Thursday
morning. Thursday it will warm up and be dry during most of the day.
Unsettled weather returns to close out the work week continuing
through the weekend. Early next week widespread precipitation looks
to return to North-central, Central, and Southwestern Montana.

&&

.DISCUSSION...

Rest of Today... There is a surface low over Petroleum County that
will track east this afternoon before moving north out of Montana by
midnight tonight. This is bringing precipitation to much of North-
central, Central, and Southwestern Montana this afternoon. The
heaviest precipitation will be in Hill, Blaine, Choteau, Fergus, and
Judith Basin Counties. The precipitation will end by early Thursday
morning from west to east across North-central and Central Montana.
The precipitation will end in Southwestern Montana by 6 pm tonight.
There is a 40 - 80% chance for greater than a half inch of rain in
Hill, Blaine, Choteau, Judith Basin, and Fergus Counties through
midnight tonight. There is a 50% chance for an inch of rain or
greater through midnight tonight from Havre to Fort Benton to
southern Fergus County to northeastern Blaine County. For the other
areas that are east of the I-15 Corridor there is a 20 - 50% chance
for a tenth of an inch of rain or greater through midnight tonight.
For more hydrology information see the HYDROLOGY section below. Due
to the rain and clouds temperatures across North-central, Central,
and Southwestern Montana will struggle to get to 60 degrees this
afternoon. Due to a strong surface pressure gradient and an upper-
level jet it will be windy across the plains of North-central
Montana this afternoon through tonight. There is a 90% chance for
wind gusts of 55 mph or greater in Fergus and Judith Basin Counties
through midnight tonight. There is also a 70% chance for sustained
winds of 40 mph or greater in Fergus and Judith Basin Counties
through midnight tonight. As a result a High Wind Warning remains in
effect for Fergus County and Judith Basin County below 5000 feet
through midnight tonight.

Thursday through Saturday... On Thursday an upper-level ridge moves
over North-central, Central, and Southwestern Montana. As result due
to clearing skies, thursday morning there is a 50% chance for fog to
form in the West Yellowstone area. The upper-level ridge will warm
up temperatures to around seasonal averages and bring dry conditions
to the area for the day on Thursday. Between midnight and 6 AM
Thursday there is 30 - 60% chance for a quarter inch of rain in
Hill, Blaine, Choteau, Judith Basin, and Fergus Counties. On Friday
a weak upper-level trough moves above North-central, Central, and
Southwestern Montana. This will bring isolated showers to the area
with slightly cooler temperatures. On Friday there is a 5 to 30%
chance for a tenth of an inch of rain or greater across North-
central, Central, and Southwestern Montana. On Saturday the upper-
level trough remains over North-central, Central, and Southwestern
Montana. This will cool temperatures down to a few degrees below
seasonal averages. There will also be an isolated rain shower across
North-central, Central, and Southwestern Montana. On Saturday there
is a 5 - 10% chance for a tenth of an inch of rain or greater across
the area.

Sunday through next Wednesday... On Sunday an upper-level ridge
moves over North-central, Central, and Southwestern Montana. Then an
upper-level shortwave will move through the flow. This will bring a
5 - 10% chance for rain to North-central, Central, and
Southwestern Montana. On Monday clusters indicate that there will
be zonal flow over North-central, Central, and Southwestern
Montana. This will keep unsettled weather in place for the area.
On Tuesday and next Wednesday ensemble clusters and deterministic
models begin to diverge. One scenario is for zonal flow to remain
over North- central, Central, and Southwestern Montana. This keeps
the unsettled weather in place for the area. Another scenario is
for an upper- level ridge to move over North-central, Central, and
Southwestern Montana. This would warm up temperatures and bring
dry and calm conditions to the area. The third and final scenario
is for an upper-level trough to begin to move over North-central,
Central, and Southwestern Montana. This would bring cooler
temperatures and widespread precipitation to the area. -IG

&&

.AVIATION...
18/18Z TAF Period

Widespread rain will continue through the remainder of the day on
Wednesday as a notable weather system continues to affect North
Central and Southwestern Montana. Currently, a band of moderate to
heavy rain was along a line extending north of KGTF and then east to
KLWT, and this band is not expected to move much through 0z or so.
Expect IFR to LIFR conditions in and near this band, particularly at
KLWT. Outside of this band, expect gusty winds but generally better
cigs and vis, with occasional -RA brining cigs below 025 and vis
under 6sm. Rain will taper off overnight, though some pockets of fog
may develop at various airports, though confidence is not high
enough to mention in the TAFs quite yet. Ludwig

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

&&

.HYDROLOGY...

Moderate to heavy rain will continue to pivot through the Plains and
island mountain ranges of North Central Montana through the
remainder of the afternoon and evening. As this moderate to heavy
rain continues, watch for areas of minor flooding and rockslides,
especially in low lying areas and steep terrain. River flooding is
not expected to be a major concern, however, as rivers remain
seasonally low with adequate capacity to absorb the extra runoff.
Ludwig

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  47  73  48  70 /  40   0   0   0
CTB  46  71  45  64 /  10   0   0  30
HLN  47  74  48  73 /  10   0   0   0
BZN  40  71  42  73 /  30   0   0  10
WYS  29  60  31  64 /  40  10   0  10
DLN  39  68  41  69 /  10   0   0   0
HVR  47  72  47  67 /  90   0   0  10
LWT  45  68  45  67 /  90   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late tonight for Bears Paw Mountains and
Southern Blaine-Fergus County below 4500ft-Judith Basin County
and Judith Gap-Little Belt and Highwood Mountains-Snowy and
Judith Mountains.

High Wind Warning until midnight MDT tonight for Fergus County
below 4500ft-Judith Basin County and Judith Gap-Snowy and Judith
Mountains.

Flash Flood Watch until 6 PM MDT this evening for Big Belt,
Bridger and Castle Mountains.

&&

$$

http://www.weather.gov/greatfalls