611
FXUS65 KTFX 130543
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1143 PM MDT Thu Jun 12 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Fog, potentially dense, is expected to develop over the plains
   of Central and North Central Montana tonight and into the
   morning hours on Friday.

 - Another round of shower and thunderstorms is expected on
   Friday, with a few thunderstorms becoming severe and producing
   large hail and damaging winds.

 - Additional opportunities for showers and thunderstorms exist
   through this weekend and the first half of the upcoming work
   week.

&&

.UPDATE...
/Issued 805 PM MDT Thu Jun 12 2025/

No significant updates were necessary this evening. Scattered
showers and a few thunderstorms will linger through the evening,
becoming few and far between after midnight. The only mentionable
change was to slightly increase fog mention across the area into
Friday morning. This threat will be conditional on diminishing
cloud cover. -AM

&&

.DISCUSSION...
/Issued 144 PM MDT Thu Jun 12 2025/

 - Meteorological Overview:

Stratiform precipitation associated with a shortwave embedded within
southwest flow aloft will gradually exit the plains of Central and
North Central Montana through the late afternoon/early evening hours
tonight. Further to the south and west where clearing has occurred
through the late morning/early afternoon, which has allowed the
atmosphere has destabilize, scattered showers and thunderstorms will
persist into the evening hours tonight before gradually waning as
transient ridging moves overheard. As the transient ridge moves over
the Northern Rocking tonight most areas will see predominately dry
conditions; however, an isolated shower or storm can`t be ruled out
between I-90 and the MT Hwy 200 corridor where a weak mid-level warm
front will reside. Partly clearing skies beneath the transient ridge
combined with recent precipitation and light surface winds will also
support another night/morning for fog development, especially over
the plains of Central and North Central Montana and in prone valleys
in Southwest Montana. - Moldan

Heading into Friday a shortwave pivoting through the Pacific NW
troughing ejects toward the Northern Rockies in the late morning
through afternoon hours. Surface moisture from previous
precipitation across the plains and adjacent areas as well as
advection in from the east near the surface should be sufficient for
ample instability, even with cooler surface temperatures in place.
Increased southwesterly flow aloft overtop easterly surface winds
will help increase shear above 40 kts, helping to support a greater
threat for organized severe weather. Strong wind gusts in excess of
58 mph and large hail are the primary concerns with the stronger
thunderstorms Friday.

The setup is largely the same for Saturday, though the best
instability does look to be confined to eastern areas. Gusty winds
and hail will continue to be the primary concern with the strongest
thunderstorms that form.

Heading into Sunday and into Monday the southwesterly flow aloft
remains. Confidence in timing any shortwaves that would aid in
shower and thunderstorm development decreases quite a bit. That
said, lingering surface moisture and respectable shear profiles
suggest at least a low-end threat for stronger thunderstorms will
remain heading into early next week.

Cluster guidance for the middle of next week favors the
southwesterly flow aloft persisting. Where confidence lowers
significantly is whether this is a more cyclonic or anti-cyclonic
southwesterly flow. Regardless, at least low-end chances for
afternoon and evening showers and thunderstorms look to persist
heading into the middle of next week. -AM

 - Forecast Confidence & Scenarios:

Fog Development through Friday Morning :

HREF guidance strongly supports the development of fog over the
plains of Central and North Central Montana between midnight tonight
and 9 AM MDT Friday. This guidance even supports a 40-80% chance for
visibilities to fall below 1/4 mile northwest of a Great Falls to
Havre line and east of the US Hwy 89 corridor from Great Falls to
Babb. Forecasted light winds and recent precipitation combined with
transient ridging moving overheard would support these higher
probabilities for locally dense fog; however, some uncertainty
remains with how much clearing occurs beneath the aforementioned
ridge. BUFKIT guidance at both Cut Bank and Great Falls supports
some clearing around the midnight hour tonight, and should this
begin to materialize then the threat for dense fog developing across
the aforementioned areas will increase. - Moldan


Precipitation through early next week :

Greatest uncertainty in the forecast is related to just how  much
instability develops each day late weekend into early next week.
There remains significant discrepancies between magnitude of
instability that develops as well as where exactly it develops. As
mesoscale details become better resolved over the next couple days,
confidence in how Saturday and onward will play out will
subsequently increase. -AM

&&

.AVIATION...
13/06Z TAF Period

Spotty shower and isolated thunder activity will continue to
diminish heading into the overnight hours. IFR/LIFR stratus
developing along and east of a KHVR to KLWT line will continue to
lower and bring patchy dense fog in the vicinity of these
terminals. Partial clearing combined with lingering moisture
increases the chance for patchy dense fog development over the
remaining portions of the plains. The latest HREF probabilistic
guidance highlights areas between KCTB and KGTF with a 30 to 60%
chance for visibility falling to a half mile and similar
probabilities near KHVR and KLWT. Fog development in Southwest
Montana will be more isolated and mostly confined to the KWYS
area. The fog is expected to clear out by 13/16Z, but another
round of showers and thunderstorms develops Friday afternoon and
evening. Some of the stronger storms will be capable of damaging
winds, large hail, and brief heavy downpours. - RCG

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  69  50  75  52 /  70  30  70  60
CTB  64  48  72  46 / 100  40  50  50
HLN  76  52  77  52 /  60  40  70  50
BZN  80  49  79  48 /  30  20  40  30
WYS  72  39  74  37 /  30  30  10  10
DLN  75  46  76  43 /  20  30  40  30
HVR  65  49  75  52 /  90  30  80  50
LWT  65  48  71  50 /  70  40  80  60

&&

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

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