-- Discussion containing changed information from previous version are highlighted. --
408
FXUS65 KTFX 211731
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1130 AM MDT Fri Jun 21 2024

Aviation Section Updated

.SYNOPSIS...
Thunderstorms develop and move through the area, today. Some
thunderstorms are forecast to become severe, producing gusty and
erratic strong winds, large hail, frequent lightning and periods of
heavy rain. A warming trend is forecast for the next few days. By
Sunday, low elevation highs range in the 90s.

&&

.UPDATE...
Big change with this morning`s update is to add gusty winds and
large hail in areas that are in the Storm Prediction Center`s
Slight risk today, which is for a 15% chance of wind and hail, and
some areas do have a 10% risk of seeing hail sizes of 2 inches or
greater, along with a low tornado risk (keep in mind all
percentages are within 25 miles of a given point in the slight
risk area - so any location in particular still has a very low
chance of seeing the severe weather as these phenomenon are
usually highly localized). We have already seen some convection
fire up near Havre that was capable of producing some small hail,
indicating that the atmosphere is already primed for a busy
thunderstorm day, helping to build confidence in the potential for
impactful severe weather this afternoon and evening. Ludwig

&&

.AVIATION...
-- Changed Discussion --
21/18Z TAF Period

Main concern this afternoon/evening will be the potential for severe
storms over North Central MT. The main threat from any severe storm
will be large hail/strong winds. There is also small probability of
an isolated tornado in the Havre/Lewistown areas. Storms are
developing currently at 18z, with the storms to become most
widespread/active around 00z Sat. Overall, most storms will diminish
between 03z and 06z Sat. There is a small potential for fog on
Saturday in morning in any areas that have heavy rain on Friday
evening. For now, kept fog out of the TAF, as the probability is too
low at this time. Mountains/passes over Central MT could be obscured
for a few hours by passing storms through 06z. Brusda

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.
-- End Changed Discussion --

&&

.PREV DISCUSSION...
/ISSUED 525 AM MDT Fri Jun 21 2024/

Note: The forecast area for the National Weather Service Great
Falls Weather Forecast Office includes north central, central and
southwest Montana.

Today...A low amplitude upper level trof enters our region, today.
An unstable atmosphere, with deep layer 35KT to 40KT wind shear
favorable for the development of severe thunderstorms, is
forecast. There is high confidence that some of these
thunderstorms will become severe, producing gusty and erratic high
winds, large hail, frequent lightning and periods of heavy rain.
Although it looks like these storms will move through the area at
a decent pace, some localized flash flooding is possible.

Saturday through Sunday...A weak upper level ridge builds into the
area, favoring warming and drying. By Sunday, low elevation high
temperatures push into the 90s, with minimum Relative Humidity
values falling into the teens. Sunday, the next upper level trof
approaches from the west; however, a building bubble of high
pressure over Arizona/New Mexico, adds mass to the trof, allowing
most of it`s energy to be directed northward into Canada. A few
thunderstorms and rain showers develop on Sunday.

Monday through Wednesday...In response to the building upper level
closed area of higher heights over Arizona/New Mexico, an upper
level ridge dominates The Treasure State. Low elevation high
temperatures continue in the 80s and 90s, through mid-week, while
conditions remain dry for our region.

Thursday and Friday...As the end of the week approaches, the next
upper level trof enters the region, temperatures cool a bit, and
widespread rainfall is forecast.
- Fogleman

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  76  50  82  55 /  60  20   0   0
CTB  72  44  81  51 /  70  30   0   0
HLN  83  53  88  58 /  30  10   0   0
BZN  81  48  85  52 /  20  10   0   0
WYS  76  41  79  45 /  10  10   0   0
DLN  80  47  85  51 /   0   0   0   0
HVR  76  49  82  56 /  60  60  10   0
LWT  72  47  77  54 /  70  50  10   0

&&

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

&&

$$

http://www.weather.gov/greatfalls