648
FXUS65 KTFX 140527
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1127 PM MDT Fri Jun 13 2025

Aviation Section Updated.

.KEY MESSAGES...

- Daily chances of showers and thunderstorms continue into the
  weekend, with a few strong to marginally severe thunderstorms
  possible.

- Next week is trending a little drier, with a few opportunities
  for low end chances for precipitation.

&&

.UPDATE...
/Issued 808 PM MDT Fri Jun 13 2025/
Updated forecast is out. The threat for severe weather is over for
our CWA for tonight. Overall, for the next few days, upper level
disturbances will move from southwest to northeast through the
CWA. This will result in daily chances for scattered
showers/thunderstorms. An isolated severe storm is possible most
days. However, at this time, the thunderstorm activity does not
look to be as widespread as it has been over the past few days.
Generally seasonable June temperatures can be expected across the
CWA through next Friday as well. Brusda

&&

.DISCUSSION...
/Issued 808 PM MDT Fri Jun 13 2025/

 - Meteorological Overview:

Discrete to multi cluster storms have developed across the region
off of a surface front. East of the I-15 corridor, 1,000-2,000
J/kg of MU CAPE has built in and 500-1,000 J/ML CAPE. This
environment has allowed for a few robust thunderstorms to develop
early this afternoon. Isolated to scattered showers and
thunderstorms will continue to initiate this afternoon as the
upper-level shortwave moves through. Strong to severe storms will
be likely through the early evening hours, with the best corridor
for severe weather residing east of the I-15 corridor. Later this
afternoon/early evening, discrete and multi clusters will merge
into a broken line as it heads towards Hill, Blaine, and Fergus
Counties. The main line of storms exit to the east in the evening
but there will be a few lingering isolated showers for the night.

As storms and precipitation clear out overnight, we will have to
watch for fog develop in the North-Central MT plains Saturday
morning. Weak subsidence settling in behind and low level
moisture from precipitation will allow for a slight chance for
fog development. -Wilson

The unstable southwesterly flow aloft responsible for the convective
activity will remain in place through at least Monday of next week
before becoming more westerly and at least temporarily drying things
out later next week. So there is an expectation of daily rounds of
showers and thunderstorms of a varying degree through at least
Monday. - RCG

 - Forecast Confidence & Scenarios:

Effective bulk shear ranging between 30-45kts east of the I-15
corridor will allow for good longevity with storms, and 0-6km
helicity up to 100-150m2/s2 will allow for rotating updrafts with
the strongest storms. Meaning, the environment will allow for
some super-cellular storms to develop. Main hazards will be
damaging winds, large hail, and heavy downpours. Although DCAPE up
to 1,000 J/kg is not super high for the region, it`ll be
sufficient enough for a strong wind potential with severe storms.
Mid level lapse rates of 7-8 C/km will allow for large hail to
develop (30% chance for 1" and a 15% chance for 2" hail). When the
main shortwave moves through later this afternoon, vertical
profile soundings show enough directional shear for an isolated
tornado, especially in Judith Basin and Fergus Counties where the
terrain can enhance vorticity/rotation in a storm. The Storm
Prediction Center has issued a Severe Thunderstorm Watch for areas
mainly east of the I-15 corridor through 9pm MDT. West of the
I-15 corridor will also have an isolated threat for strong to
severe storms at they move off the higher terrain.

The threat for convective storms continue through the weekend.
Saturday, storms will fire off along the frontal passage. Best
corridor for showers and thunderstorms look to set up north of the I-
90 corridor and east of the Helena to Great Falls line. Good deep
layer shear (0-6km) of 40-50kts and good moisture from 0.7-0.8"
PWATS will allow for a few storms to become strong to marginally
severe, with the usual hazards of gusty winds, hail, and brief
heavy downpours.

Sunday, a shortwave trough moves through which will develop another
risk for showers and thunderstorms. Depending on where this
shortwave trough develops, stronger forcing aloft bringing in
shear and moisture suggests there can be another threat for strong
to severe storms. More troughing Monday can allow for another
round for convection but will depend on how the weekend plays out.
-Wilson

&&

.AVIATION...
14/06Z TAF Period

An unstable southwesterly flow aloft will send waves of widely
scattered showers and thunderstorms through the Northern Rockies
over the next 24 hours and beyond. This activity will be most
prevalent over Central and North-central Montana between 14/06 and
14/18Z and then again after 15/00Z. Patchy fog development will
be a concern once again tonight into Saturday morning, especially
along the Milk River Valley (KHVR area) southward into northern
Fergus County where there is around a 30 to 50% chance for
visibility reductions less than a half mile. There will also be
some fog patches east of the KBZN area, but probabilities drop
off to less than 10% for impacts to the terminal. - RCG

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  52  78  53  78 /  20  30  30  40
CTB  45  76  45  76 /  30  20  10  20
HLN  54  83  55  83 /  10  30  30  40
BZN  48  83  49  83 /   0  20  30  30
WYS  39  76  37  80 /   0   0   0  20
DLN  46  80  45  79 /   0  10  10  20
HVR  52  81  53  83 /  20  30  30  40
LWT  49  75  51  75 /  30  50  70  60

&&

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

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