413
FXUS65 KTFX 272024
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
224 PM MDT Wed Aug 27 2025

.KEY MESSAGES...

 - Isolated thunderstorms producing heavy rainfall remain a threat
   across the burn scars in Southwest Montana through this evening,
   most notably in Madison and Beaverhead Counties.

 - Precipitation will gradually lift north into portions of North
   Central Montana through the end of the work week.

 - Temperatures trend cooler through the work week, but moderate
   over the weekend.

&&

.DISCUSSION...

 - Meteorological Overview:

High temperatures will continue to cool from south to north across
Southwest through North Central Montana as monsoonal moisture
lifts north from the Great Basin and across the Northern Rockies.
showers with embedded thunderstorms will slowly lift north from
Southwest Montana tonight and into Central and portions of North
Central Montana through the end of the work week, with areas along
and north of the US Hwy 2 having the lowest opportunities for
seeing wetting rainfall amounts. By this weekend a transient ridge
sliding east from the Pacific Northwest and over the Northern
Rockies will allow temperatures to moderate near to slightly above
normal. Despite the ridge moving overhead this weekend an isolated
shower or thunderstorm can`t be ruled out, most notably over the
mountains of Central Montana and along the Continental Divide. -
Moldan

 - Forecast Confidence & Scenarios:

Heavy Rainfall through Friday :

Precipitable Water (PWATs) values will continue to run in excess of
the 99th Percentile along and south of the I-90 corridor in
Southwest Montana through this evening, with these anomalously high
PWATs then shifting north across Central and into portions of North
Central Montana through the day on Thursday. Anomalously high PWATs
will continue to reside over portions of North Central Montana
through the day on Friday, but as compared to the previous two days
values will be lower and largely range from the 90th to 97.5th
Percentile. While these anomalous values are concerning, especially
with ECMWF EFIs of 0.8+ with respect to rainfall along and south of
a Dillon to Ennis line through this evening, extensive cloud cover
thus far has significantly limited instability across the region and
kept rainfall to generally less than 0.1"/hr. The lack of
instability has thus led to 24 hour rainfall accumulations (spread
out vs occurring in one short burst) of 0.2"-0.5" across most lower
elevations and generally 0.5"-1" of rain in the mountains south of
the I-90 corridor in Southwest Montana. With BUFKIT soundings
supporting continued mid- to upper level cloudiness across Southwest
Montana through this evening confidence in Flash Flooding occurring
is decreasing; however, an isolated thunderstorm moving over any one
of the burn scars still can`t be ruled out given some breaks in the
cloud cover occurring over Northeast Idaho this afternoon. Given this
threat for an isolated thunderstorm, while low in nature, the Flash
Flood Watch for burn scars across Madison and Northwest Beaverhead
Counties remains in effect solely because of the anomalous moisture
readily available. Should the threat for even an isolated
thunderstorm or two continue to decrease then the Flash Flood Watch
can be canceled early. For the remainder of the work (Thursday
through Friday) week NBM probabilities for rainfall amounts
exceeding 1" generally range from a 10-20% chance north of the I-90
corridor in Southwest Montana to along and south of the Montana Hwy
200 corridor. As has been the case so far extensive cloud cover will
limit instability through the end of the work week across Central
and into portions of North Central Montana, which should help to
limit opportunities for short and intense rainfall rates despite the
anomalously high PWATs. - Moldan

&&

.AVIATION...
27/18Z TAF Period

VFR conditions will prevail across all terminals except for the KWYS
and KEKS terminals during this TAF Period. However there is a 20 -
50% chance for a thunderstorm at the KBZN terminal at the end of this
TAF period which would reduce visibility to MVFR levels. At the KHLN
terminal there is a 25 - 45% chance for showers during the duration
of this TAF Period. At the KEKS and KWYS terminals during the
majority of this TAF Period there is a 20 - 40% chance for
thunderstorms. At the KBZN terminal there is a 20% chance for a
thunderstorm between 28/00Z and 28/11Z. Any thunderstorm will
produce frequent lightning, a heavy downpour, and gusty, erratic
winds. During the majority of this TAF Period across Southwestern
Montana there will be mountain obscuration. By the end of this TAF
Period across Central Montana there will be mountain obscuration.
-IG

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  59  70  55  73 /  20  50  50  40
CTB  56  74  53  67 /  10  20  20  30
HLN  57  70  55  77 /  60  90  40  40
BZN  53  69  50  76 /  70  90  70  30
WYS  45  64  38  70 /  90  90  60  30
DLN  51  69  47  75 /  90  70  20  20
HVR  57  82  57  73 /   0  20  30  30
LWT  56  70  53  66 /  20  50  60  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 9 PM MDT this evening for Beaverhead and
Western Madison below 6000ft-Gallatin and Madison County
Mountains and Centennial Mountains-Madison River Valley-Missouri
Headwaters.

Flash Flood Watch until midnight MDT tonight for Northwest
Beaverhead County.

&&

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