396
FXUS65 KTFX 170606
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1200 AM MDT Mon Jun 17 2024

Aviation Section Updated

.SYNOPSIS...
Cooler than normal temperatures prevail, while the next weather
producer enters the region. Mountain snow and widespread low
elevation rain are forecast, through the early part of the coming
week. Low elevation high temperatures reach back into the 70s by
Thursday.

&&

.UPDATE...

Only minor adjustments needed to this evening`s forecast period.
Cooler Canadian air has already pushed south over the plains of
North Central Montana, so have lowered hourly temperatures to
reflect this.

Mid-level moisture is increasing from the southwest ahead of the
approaching system, but no precipitation has been observed yet
west of the Continental Divide, so the timing of the precipitation
moving into the area mainly after midnight appears to be on track.
-Coulston

&&

.AVIATION...
17/06Z TAF Period

Showers will move in in overnight (already ongoing at KGTF) and into
the morning hours across all terminals. Ceilings will transition to
VFR to MVRF with initial showers, and then to IFR conditions (by
late morning at KGTF and during the evening for KBZN, KEKS, KWYS,
and KLWT). Widespread showers (possibly some light snow showers
mixing in at KWYS) will last through the TAF period. There`s a 10-
30% of a few embedded thunderstorms with showers that can drop
visibilities to MVR/IFR Monday this afternoon. Mountain obscuration
will be persistent through the TAF period, with snow falling above
6,000ft. -Wilson

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

&&

.PREV DISCUSSION...
/ISSUED 550 PM MDT Sun Jun 16 2024/
Today and Tomorrow...Cool low elevation temperatures are
forecast. Areas of light rain are forecast north of the Hi-Line
through this afternoon. This evening, the next weather producer
enters the region, beginning with precipitation falling across
southwest Montana. The forecast is for low elevation rainfall,
with accumulating snow forecast at elevations, generally, above
6000 feet.
- Fogleman

Tomorrow, continued...Precipitation will become more widespread
and heavier Monday morning with the upper level low moving
passing through the region. There may be a few embedded
thunderstorms with precipitation on Monday/Tuesday afternoon due
to a little amount of instability present. Precipitation lingers
into Tuesday along another wave passing through the region. Snow
probabilities in the mountains are between 30-50% for exceeding
8" of snow. Considering the bulk of the snow being above pass
level and probabilities for accumulations to reach winter warning
criteria (9 inches) remain on the lower side, I have opted to
transition the Winter Storm Watches for mountain zones into
Winter Weather Advisories. Another change I`ve made to the winter
highlights is to move up the timing to 6pm Sunday to 6pm Tuesday
to account for the earlier start and end times for precipitation.
Greatest QPF amounts look to set up across Central MT, where they
have around a 50% of exceeding 1". Most other lower elevations
across the CWA have at least a 50% of exceeding 0.25". In terms of
possible higher end QPF amounts, the 75th NBM percentile ranges
between 1.25-1.5" across Central MT and 0.35-0.75" across most
other lower elevations.

With the upper level low bringing down colder air, cold overnight
temperatures are forecasted for Monday and Tuesday morning.
Tuesday morning wind chills in the mountains can drop down to the
teens and 20s. Those in the backcountry should prepare for
cold/raw conditions.

Wednesday and looking beyond...The main upper level low will move
off to the east, and a zonal/southwest flow aloft pattern will
settle in behind for the remainder of the week. There looks to be
enough moisture around and small disturbances that passes through
to keep low chances of precipitation daily. With the southwest
flow aloft bringing in warmer air, temperatures will gradually
warm up through the weekend. By Saturday, lower elevations have a
60-80% of high temperatures reaching 80 degrees or higher.
-Wilson

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  42  49  40  57 /  40  90  80  80
CTB  37  53  37  55 /  20  80  60  70
HLN  44  54  42  63 /  60 100  80  80
BZN  41  56  37  59 /  30  90  90  70
WYS  38  52  30  52 /  20  70  70  60
DLN  39  52  34  56 /  30  90  70  50
HVR  42  57  42  61 /  10  90  70  60
LWT  38  52  35  55 /  30  90  90  80

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM MDT Tuesday for Big Belt,
Bridger and Castle Mountains-East Glacier Park Region-Elkhorn
and Boulder Mountains-Gallatin and Madison County Mountains and
Centennial Mountains-Little Belt and Highwood Mountains-
Northwest Beaverhead County-Southern Rocky Mountain Front.

&&

$$

http://www.weather.gov/greatfalls