221
FXUS65 KTFX 250453
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
953 PM MST Sun Nov 24 2024

Aviation Section Updated.

.KEY MESSAGES...

-Low temperatures and wind chills fall to the single digits above
and below zero across North-Central Montana for much of this
upcoming week, especially along the Hi-line.

-Temperatures warm closer near seasonal averages for southwest
Montana.

-Accumulations from scattered snow showers over the next couple of
 days will be negligible, though chances for accumulating snow
 increase heading into the holiday weekend.

&&

.UPDATE...
/Issued 751 PM MST Sun Nov 24 2024/

It will be cold across North-central Montana tonight into tomorrow
morning with isolated light snow. Locations along the Hi-line will
see below zero lows tonight into tomorrow morning. Tomorrow it
will warm up but locations across the plains of North-central
Montana will remain below seasonal averages. For the update low
temperatures across the plains of North-central Montana were
decreased to better reflect current trends and observations. As a
result hourly temperatures and dewpoints were decreased across the
plains of North-central Montana. Sky grids were adjusted to
better reflect current trends and satellite imagery. The rest of
the forecast is on track. -IG

&&

.DISCUSSION...
/Issued 751 PM MST Sun Nov 24 2024/

- Meteorological Overview:

Transient ridging moves into the Northern Rockies tonight into
Monday, but warm air advection aloft will maintain cloud cover and
chances for light snow for central and north-central areas. Looking
ahead, there is a general expectation for a northwesterly flow aloft
to persist for most if not all the upcoming week. Passing
disturbances initially offer little in the way for appreciable
snowfall until a more defined wave moves through Tuesday into
Wednesday and brings mostly mountain snow. More shortwaves dive
southeastward into the region during the Thanksgiving holiday for
lower elevation accumulating snow potential.

- Forecast Confidence & Scenarios:

Pops were increased to the 20 to 40% range over Central and North-
central MT tonight into Monday in response to the expected mid-
level warm air advection, but snowfall will be scattered and on the
lighter side with minimal impacts. Any patchy fog development tonight
and Monday morning should be limited by cloud cover.

The northwesterly flow aloft will support a parade of systems that
will reinforce the cold air for northern areas. Daily lows in the
single digits above and below zero can be expected, especially along
the Hi-line. The cold looks to be far more intermittent for central
and southwestern areas south of the highway 200 corridor. I did
lower temperatures for the normally cooler plains locations to match
closer the Canadian model guidance. The probability for one inch of
snow of more is only above 40% for mountain areas for the
Tuesday/Wednesday system. Then lower elevation snow potential
increases during the holiday weekend, when the chance for an inch or
more of snow increases to the 30 to 50% each day Thursday through
Saturday. - RCG

&&

.AVIATION...
25/06Z TAF Period

VFR conditions will prevail across all terminals except for the KCTB
and KHVR terminals during this TAF period. Between now and 25/10Z
there is a 30% chance for snow at the KCTB terminal which would
reduce visibility to MVFR levels. Additionally at the KCTB terminal
between now and 25/10Z there will be fog intermittently reducing
visibility to MVFR levels. At the KHVR terminal there will be MVFR-
level ceilings until 15/12Z when they will go to VFR-levels. At the
KLWT and KGTF terminals there is a 20% chance for snow between now
and 25/10Z. Between 25/12Z and 26/00Z there is a 20 - 30% chance for
snow at the KHVR terminal. At the KCTB terminal there is a 20%
chance for snow from 25/17Z to 26/00Z. There is a 20% chance for fog
to form at the KHVR terminal Monday morning. There will be winds
gusting up to 25kts during most of this TAF period at the KEKS
terminal. During this TAF period there will be periods of mountain
obscuration in Southwestern Montana. -IG

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  -2  28  14  40 /  20  10  10  20
CTB -12  17   7  32 /  30  20  10  10
HLN  10  38  20  40 /  10   0   0  30
BZN   9  37  18  38 /  10   0  10  30
WYS   3  28   9  31 /  20   0  20  70
DLN  13  36  17  35 /  10   0   0  20
HVR -11  11  -1  24 /  20  30  10  30
LWT   6  37  19  41 /  20   0  10  30

&&

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

$$
http://www.weather.gov/greatfalls