074
FXUS65 KTFX 201135
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
535 AM MDT Sun Apr 20 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Unsettled weather will continue through at least Tuesday with a
   widespread chance for mountain snow and lower elevation rain.

 - Isolated thunderstorms are possible today and tomorrow
   afternoon.

 - Near normal temperatures will continue through the middle of
   the week with a chance for another warm up towards the end of
   the week.

&&

.DISCUSSION...
/Issued 352 AM MDT Sun Apr 20 2025/

 - Meteorological Overview:

An upper level trough will continue to move across the western
CONUS bringing unsettled weather to the region through at least
Tuesday. Weak instability this afternoon will give way for a
chance of isolated thunderstorms with better chances expected on
Monday as the trough moves over the region.

The middle of the week brings more quasi-zonal flow with the
potential for a weak shortwave passing through on Thursday. Upper
level ridging starts to form Thursday into Friday but is quickly
pushed out to the east by the weekend as another trough comes
onshore with the potential for more unsettled weather to last
through next weekend.


 - Forecast Confidence & Scenarios:

Snowfall through Tuesday:

Overall, compared to previous forecasts there were no significant
chances in the expected snowfall amounts. Most places along the
Continental Divide, island ranges of central Montana and the
mountains of southwest Montana will see 1 to 3 inches of new snow.
Confidence for amounts above 3 inches drops off pretty quickly
with the probability of 4 inches or more sitting at less than 60%
and the probability for 6 inches or more at less than 30%. When
evaluating the potential for headlines, the heaviest snow is
expected to be confined to the highest elevations and far above
pass level. Thus there is no need for an advisory at this time but
those in the backcountry should be prepared for difficult
conditions over the next couple of days.


Rain through Tuesday:

Lower elevations across much of the region have a chance at seeing
rain starting today through Tuesday afternoon. The heaviest
amounts are expected Sunday evening through Monday afternoon with
the highest storm total amounts expected in southwest Montana.
Most locations are likely to see at least some precipitation,
however the Rocky Mountain Front and portions of north-central
Montana are expected to remain largely dry through this event with
precipitation amounts above a tenth of an inch more likely south
and east of a line from Havre to WSS to Helena. This same region
also has around a 50% chance of a quarter inch or more of
precipitation through Tuesday afternoon. Isolated higher amounts
are also possible under heavier showers and thunderstorms.


Thunderstorm Potential Today and Tomorrow:

Afternoon thunderstorms are possible today and tomorrow. For
today, there are two main areas of concern. The first is across
southwest Montana, particularly Madison and Gallatin counties, and
the second is along portions of north-central Montana including
Hill, Blaine, and Fergus counties. The timing of when these
thunderstorms are expected to kick off varies depending on which
hi-res model is to be believed. But there is a general consensus
that between 4 and 6 PM things will start to kick off across the
region and the chance for thunderstorms lingers as late as
midnight before diminishing. Should any thunderstorms develop, the
main concerns will be strong winds and small hail (less than half
an inch).

It is worth mentioning the limiting factors that could end up
preventing thunderstorm development. For starters, instability
parameters are not ideal with even MUCAPE generally staying below
300 J/kg. Combine that with the fact that highs are only expected
to reach into the 60s with dewpoints in the mid to upper 30s and
there is a potential for cloud cover to linger through most of the
morning which would limit diurnal heating. So overall the next
couple days very much fall into a category of thunderstorms may
very well not happen but, if they do, there is a concern for
impacts enough to warrant messaging.

Overall, Monday looks to have a better chance at isolated
thunderstorm development with better forcing from the upper level
trough. Similar to today the main concerns with any thunderstorm
that develops will be strong winds and small hail.  -thor


&&

.AVIATION...
20/12Z TAF Period

MVFR clouds and light rain showers over and near the higher
terrain along the Continental Divide and Southwest Montana gradually
thins out through early afternoon. KBZN and KEKS will continue to
trend towards VFR through 20/15Z, but KCTB may see the MVFR or near
MVFR clouds persist until around 20/18Z.

Diurnal instability combined with the forcing of a Pacific trough
will bring additional scattered showers and isolated thunderstorms
this afternoon and evening before transitioning to general areas of
light rain and mostly mountain snow heading into the overnight
hours. Mostly VFR conditions are expected following the partial
clearing early this afternoon, but expect MVFR/IFR conditions and
mountain obscuration to progressively become more widespread between
21/00 and 21/06Z, especially for KEKS and KBZN. - RCG


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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  60  38  54  33 /  40  50  70  20
CTB  54  33  51  29 /  40  20  60  40
HLN  60  38  53  31 /  50  60  80  10
BZN  57  32  47  23 /  40  80  90  10
WYS  49  25  46  15 /  60  70  90  20
DLN  57  32  49  24 /  30  60  60   0
HVR  60  34  55  31 /  50  50  70  50
LWT  56  35  50  29 /  60  70  90  30

&&

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

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