338
FXUS65 KTFX 190235
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
835 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.

&&

.UPDATE...

Adjustments were made to the precipitation chances to reflect
current conditions and the latest model guidance. Rain will
continue to slowly migrate to the east as the low moves further
into North Dakota. For the most part, showers will taper off for
locations in Hill, Blaine, and Fergus counties by midnight.
Thursday is still on track to be dry which will allow locations
currently under the Flood Advisory to experience some relief.

Wind speeds have diminished considerably over the past couple
hours leading to an early cancellation of the high wind warning.
Some gusty winds are still possible around the Lewistown Divide
and into the higher elevations of Fergus county, however, no
significant impacts are expected from here on out.

Looking to the overnight hours, there are increasing chances for
fog development along the valleys of southwestern Montana.
Widespread impacts are not expected at this time, however, there
is around a 40-60% chance for localized dense fog developing in
and around West Yellowstone tonight.  -thor


&&

.AVIATION...
19/00Z TAF Period

Widespread IFR or lower conditions are expected for areas east of a
line from Shelby to Great Falls through tonight, as widespread
rainfall continues in this area. Elsewhere, showers are decreasing
and ceilings are slowly increasing. Most areas will see skies begin
to clear after 12z Thu. There is the potential for some fog on Thu
morning, but wind speeds/cloud cover limit that potential at the
terminals right now. Mountains/passes will be obscured over Central
MT through 12z Thu. Brusda

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

&&

.HYDROLOGY...
Heavy rainfall continues to affect portions of Central MT as of 7 PM
Wednesday evening. Rainfall reports of 4 to 6 inches are common from
Belt to Lewistown today. An additional 1 to 2 inches of rainfall is
possible in this area. A very good rainfall also extends further
northward up into the Bears Paw Mountains. Thus this entire area is
now under a flood advisory until Noon on Thursday, as minor flood
impacts are possible. There is the potential that flood warnings
might need to be issued for portions of the Lewistown area should
more significant flooding impacts develop because of the additional
expected rainfall this evening.

The area flood watch has been cancelled, as a flood advisory is now
in effect.

The flash flood watch for the burn scar of Horse Gulch has been
cancelled.

Brusda

&&

.PREV DISCUSSION...
/ISSUED 700 PM MDT Wed Sep 18 2024/
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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  47  73  48  70 /  30   0   0   0
CTB  46  71  45  64 /  10   0   0  30
HLN  48  74  48  73 /  10   0   0   0
BZN  41  71  42  73 /  30   0   0  10
WYS  32  60  31  64 /  40  10   0  10
DLN  39  68  41  69 /  10   0   0   0
HVR  48  71  47  67 / 100   0   0  10
LWT  46  66  45  67 / 100   0   0  10

&&

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

$$

http://www.weather.gov/greatfalls