531
FXUS65 KTFX 200222
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
822 PM MDT Sun May 19 2024

.SYNOPSIS...
Showers, thunderstorms, small hail and snow will all decrease over
the area tonight, as drier air moves in for a few hours. However,
expect showers and thunderstorms to redevelop over Southwest MT on
Monday, with the showers becoming more widespread on Tuesday. A
spring storm will affect much of the area Wed and Thu, with
periods of heavy rain and mountain snow expected. Generally, below
normal temperatures are expected for most areas this week.

&&

.UPDATE...

Two main changes with this update:

1. Increased precipitation chances in central Montana using the
convective allowing models to fit the band of showers currently
moving through. At this point in the evening, the main
thunderstorm threat is over. However, a couple weak thunderstorms
are still popping up across the area which may produce locally
heavier rain and gusty winds. But no major concerns are present at
this time.

2. The chance for fog was expanded along the hi-line overnight.
The best chances for fog will be along the Milk River Valley
north to the Canadian border east of Havre. In those locations
temperature and dewpoint will be within a couple degrees of each
other, skies will be mostly clear, and winds will be generally
light. Outside the main fog area, there is a broad chance for
patchy fog across north-central Montana with the probability
decreasing rapidly towards the south. Higher fog chances (up to
40%) were brought down along the Highway 87 corridor as far south
as Loma while lower fog chances (20-40%) were brought down to just
north of Great Falls. At this point, conditions are too marginal
for fog in Great Falls proper but should skies clear a bit more
after the band of showers move through then that will be
something to watch heading into tomorrow morning.

Otherwise, no major changes were made to the going forecast.

-thor


&&

.AVIATION...
20/00Z TAF Period

North-central and Central Montana (KCTB, KHVR, KGTF, KLWT, KHLN):
Scattered showers and thunderstorms will continue across north-
central and central Montana through the rest of the evening with a
chance for some lightning and small hail, particularly for KGTF and
KHVR. There will be a lull in the precipitation overnight into early
Monday morning before another round of showers moves through the
area starting after 20/19Z. Periods of MVFR will be possible with
heavier showers as well as periods of mountain obscuration around
KHLN.

Southwestern Montana (KEKS, KBZN, KWYS): A chance of showers will
persist through much of the TAF period with the potential for
mountain obscuration after 20/14Z. During the overnight hours, rain
is expected to transition to a rain/snow mix with periods of MVFR
conditions possible in heavier showers.

-thor

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

&&

.PREV DISCUSSION...
/ISSUED 544 PM MDT Sun May 19 2024/
Tonight through Tuesday...Expect a variety of weather conditions
over the CWA tonight, with rain, snow, thunderstorms and small
hail all diminishing this evening, as the main upper level trof
moves off to our east. No significant impacts are expected from
the weather this evening. Most snow or small hail accumulations
will only occur on grassy areas. Much of the area starts out dry
tomorrow morning, but a slow moving upper level disturbance moves
into Southwest MT by mid day, producing scattered
showers/thunderstorms by late morning and then continuing into
Tuesday. Again, this thunderstorm activity is expected to be on
the light side for most storms. Afternoon temperatures will warm
up a bit for Monday and Tuesday, with near normal afternoon
temperatures expected on Tuesday.

Wednesday into Friday...A spring storm is expected to affect much
of the CWA for the middle portion of the week. There is a 50
percent chance of 0.25 to 0.75 inches of liquid at lower
elevations and 1 to 1.50 inches in the mountains. There is less
than a 10 percent chance of getting over 2 inches of liquid in the
mountains at this time. The heavy rain could cause some impacts in
the Monarch and Neihart areas. Additionally, snow levels look to
be around 7000 feet. There is a 50 percent chance of over 8
inches of snow in the mountains of Northwest Beaverhead County and
the Tobacco Root Mountains, and about a 30 percent chance over
the Rocky Mountain Front and the Kings Hill area. Thus winter
statements are likely for portions of the CWA for this event. This
system is slow, and it will take almost 2 days to move through
the CWA. Below normal temperatures are expected during this time.
There is also a small concern that snow levels could lower to near
valley floors during the morning hours on Thurs/Fri, which could
impact some bigger lower elevation cities.

Saturday and Sunday...Some forecast models show the potential for
a 2nd spring storm to move through the CWA, while other models
have lighter precipitation. Never the less, below normal
temperatures and the chance for precipitation is looking likely
for most areas at this time next weekend. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  33  59  36  65 /  40  50  20  30
CTB  33  56  34  63 /  30  60  20  20
HLN  36  60  38  66 /  20  60  20  30
BZN  31  54  32  62 /  20  70  40  40
WYS  26  50  28  52 /  30  70  60  60
DLN  34  54  31  59 /  40  60  30  20
HVR  35  60  37  66 /  30  40  10  20
LWT  31  54  33  59 /  20  60  20  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Wednesday evening through Friday morning for
Little Belt and Highwood Mountains.

&&

$$

http://www.weather.gov/greatfalls