661
FXUS65 KTFX 192011
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
211 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.

&&

.DISCUSSION...
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

&&

.AVIATION...
19/18Z TAF Period

For all but the KBZN and KLWT terminals VFR conditions will prevail
during this TAF period. At the KBZN and KLWT terminals rain is
reducing ceilings to MVFR levels and will continue to do so for the
first few hours of this TAF period. At the KCTB, KGTF, and KHLN
terminals this afternoon and early evening there will be isolated
thunderstorms. At the KBZN, KEKS, KLWT, KHVR, and KWYS terminals
this afternoon and evening there is a slight chance (%20) for a
thunderstorm or two but there wasn`t enough probabilistic support to
include it in those TAFs. For all terminals light rain showers will
continue through this afternoon into the early evening with minimal
impacts to aviation operations. For the KBZN, KEKS, and KHLN there
is a 40% chance of rain/snow Monday morning which could reduce
visibility and ceilings to MVFR levels and so a PROB30 group was
included for those terminals. Tonight there is a 50% chance of
rain/snow reducing visibility and ceilings to MVFR levels at the
KWYS terminal and so a PROB30 group was included for it. For the
KLWT and KGTF terminals there is a 20% chance of rain on Monday
morning but there wasn`t enough probabilistic support to include a
PROB30 group for it. This afternoon and Monday morning there will be
mountain obscuration across Southwestern Montana. This afternoon and
early evening there will be instances of mountain wave turbulence. -
IG

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

&&

.HYDROLOGY...
A flood watch has been issued for the Kings Hill, Monarch and
Neihart areas from Wednesday night into Friday. There is a 50
percent chance of 1 inch of liquid from this event in this area.
There is a 10 percent chance of 2 inches of liquid. Some of the
precipitation will fall as snow, especially for elevations above
7000 feet, which will help, but for areas lower than 7000 feet,
impacts could develop fairly quickly given how saturated the soil
is and how full the creeks/streams are currently in this region.

At this time, other areas of North Central and Southwest MT should
be able to handle the expected rainfall, but there is the
potential that additional flood statements might be needed. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  33  59  36  65 /  20  50  20  30
CTB  33  57  34  63 /  30  60  10  20
HLN  36  61  38  66 /  20  60  20  30
BZN  31  56  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  61  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