Flash Flood Warning 2, NWS Great Falls, MT

169 
WGUS75 KTFX 121457
FFSTFX

Flash Flood Statement
National Weather Service Great Falls MT
857 AM MDT Thu Sep 12 2024

MTC007-049-121615-
/O.CON.KTFX.FF.W.0002.000000T0000Z-240912T1615Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Broadwater MT-Lewis and Clark MT-
857 AM MDT Thu Sep 12 2024

...FLASH FLOOD WARNING FOR THE HORSE GULCH BURN SCAR REMAINS IN 
EFFECT UNTIL 1015 AM MDT THIS MORNING FOR BROADWATER AND LEWIS AND 
CLARK COUNTIES...

At 857 AM MDT, Doppler radar indicated that between 0.1 and 0.4 
inches of rain have fallen over the Horse Gulch burn scar. 
Additional scattered showers and thunderstorms with rainfall rates 
between 0.1 to 0.25 inches an hour can be expected for the remainder 
of the morning. Flash flooding is ongoing or expected to begin 
shortly.

Excessive rainfall over the burn scar may result in debris flow 
moving through the Horse Gulch burn scar area and vicinity. The 
debris flow can consist of rock, mud, vegetation and other loose 
materials.

HAZARD...Flash flooding caused by thunderstorms in and around the
         Horse Gulch Burn Scar.

SOURCE...Radar.

IMPACT...Flooding of areas in and around the Horse Gulch Burn
         Scar.

Some locations that will experience flash flooding include...
  Horse Gulch Burn Scar area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Heavy rainfall may cause flash flooding of creeks...streams...and 
ditches in the Horse Gulch Burn Scar. Severe debris flows can also 
be anticipated across roads. Roads and driveways may be washed away 
in places. If you encounter flood waters...climb to safety.

&&

LAT...LON 4666 11174 4668 11175 4671 11173 4673 11167
      4671 11161 4669 11159 4665 11161 4666 11172

FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL RATE...0.1-0.25 INCHES IN 1 HOUR

$$

RG

352 
WGUS75 KTFX 121613
FFSTFX

Flash Flood Statement
National Weather Service Great Falls MT
1013 AM MDT Thu Sep 12 2024

MTC007-049-121623-
/O.EXP.KTFX.FF.W.0002.000000T0000Z-240912T1615Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Broadwater MT-Lewis and Clark MT-
1013 AM MDT Thu Sep 12 2024

...FLASH FLOOD WARNING FOR THE HORSE GULCH BURN SCAR WILL EXPIRE AT 
1015 AM MDT THIS MORNING FOR BROADWATER AND LEWIS AND CLARK 
COUNTIES...

The heavy rain has ended. Flooding is no longer expected to pose an 
immediate threat, however, please continue to heed remaining road 
closures.

Additionally, a Flash Flood Watch remains in effect until 1200 AM 
MDT Friday for the Horse Gulch burn scar area.

&&

LAT...LON 4666 11174 4668 11175 4671 11173 4673 11167
      4671 11161 4669 11159 4665 11161 4666 11172

$$

RG

Area Forecast Discussion
National Weather Service Great Falls MT
545 AM MDT Thu Sep 12 2024

Aviation Section Updated

.SYNOPSIS...
Expect the precipitation to become a more widespread steady rain,
with the rain continuing into Friday morning. Some areas could
receive over one inch of rainfall. Some high mountain snow is
expected for portions of southwest Montana. Cooler temperatures
will continue through tomorrow before warming up a little this
weekend.

&&

.DISCUSSION...

Key Points:

 -Widespread rainfall today with the heaviest amounts expected
  between noon and midnight

 -Snowfall in the Gallatin and Madison county mountains could pose
  a hazard to those in the backcountry

 -Drier conditions expected this weekend

 -Another round of cooler and wetter conditions possible next
  week

Today... Scattered showers are underway across the region which
are expected to fill in and become more widespread heading into
the afternoon hours. Some periods of thunder are possible along
the eastern half of Blaine and Fergus county, however, it is
becoming less likely that these storms will pose a significant
severe threat. The most likely impact with any stronger
thunderstorms will be severe wind gusts. Otherwise, the worst of
it will be to the east of our area where there is greater support
for supercell development.

For most of the region, stratiform precipitation will be the
dominant mode for the remainder of this event. Model guidance has
shifted the focus for the highest precipitation amounts to the
mountains of central Montana including the Big Belts, Little
Belts, Highwoods, and Bear's Paw. In particular, the HREF shows a
20-30% chance of over 2 inches for portions of the Big Belts.
This will bring some flooding concerns, especially around the
Horse Gulch burn scar which has already experienced some flooding
over the past day. The flash flood watch for the burn scar remains
on track with no major updates needed at this time, however, other
locations in the region will need to be watched carefully for a
localized flooding potential.

When looking at the snow totals and probabilities, the northern
Rockies have all but dried up on snow probabilities for the eastern
side and while some snow may be possible at the highest elevations,
impacts are not expected at pass level and below. Where snow
probabilities and amounts have increased are along the Gallatin
and Madison county mountains. The probability of locations above
8000 feet receiving at least 4 inches jumped up to the 70 to 90%
range. As a result, a winter weather advisory has been issued for
that region through noon tomorrow. Confidence and model support
was not high enough to justify issuing a warning although isolated
snow amounts above 8 inches at the highest elevations cannot be
ruled out. The main impact will be to those in the backcountry as
wet snow and cold temperatures will pose a threat for hypothermia
as well as create slippery conditions that will make hiking
dangerous.

Saturday and Sunday... This weekend will be the lull in between two
troughs. By Saturday morning, quasi-zonal flow will set up over
Montana allowing temperatures to moderate a little bit back
towards normal and keep the region on the drier side of things. By
Sunday, the next upper level trough starts to make its way
onshore along the west coast. Ahead of the trough, moisture
advected into the region along with a weak embedded shortwave
could lead to some isolated to scattered afternoon thunderstorms.
That being said, the severe weather potential for Sunday afternoon
remains low with the most likely concern being strong wind gusts.

Monday through Wednesday... Confidence remains high that the upper
level trough will set up over the western CONUS during the first
half of the work week. This pattern is expected to bring another
round of cooler and wetter conditions to central and southwestern
Montana. At this time, specific details remain uncertain as even
slight changes in the track of the low have the potential to shift
where the heaviest rain is expected. But early signs point to
another round of wetting rain that will, at least for now, keep
fire weather concerns at bay.  -thor

&&

.AVIATION...
12/12Z TAF Period

A few isolated thunderstorms will affect the northern portions of
CWA through about 00z, but they are too isolated to include at most
terminal sites at this time. Otherwise scattered showers are
possible elsewhere through about 15z. After 15z, generally expect a
widespread rain to develop over much of the CWA, with the a steady
rain continuing into Friday morning. Ceilings/visibility will lower
into the MVFR/IFR range across much of the CWA. Mountains/passes
will be obscured throughout the period. Brusda

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

&&

.HYDROLOGY...
A flash flood watch remains in effect for the Horse Gulch burn scar
area. Any convective shower that produces over 0.40 inches of
precipitation in this region in less than a half hour could produce
another debris flow. Otherwise, periods of rain are expected across
the CWA today into Friday morning, with total rainfall amounts of 1
to 3 inches expected. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  47  67  45 /  90 100  70   0
CTB  54  46  64  44 /  90 100  70  10
HLN  54  49  68  46 / 100  90  60   0
BZN  53  44  67  40 / 100  90  50   0
WYS  44  31  57  28 /  90  80  30   0
DLN  49  40  64  40 / 100  80  10   0
HVR  65  49  67  46 /  90  90  90  10
LWT  61  43  64  41 /  90  90  60  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MDT Friday for Gallatin and
Madison County Mountains and Centennial Mountains.

Flash Flood Watch from 9 AM MDT this morning through this
evening for Big Belt, Bridger and Castle Mountains.

&&

http://www.weather.gov/greatfalls

Preliminary Local Storm Report
National Weather Service Great Falls MT
643 AM MDT Thu Sep 12 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0639 AM     Rain             7 SSE Ulm               47.33N 111.48W
09/12/2024  M1.33 Inch       Cascade            MT   Trained Spotter

&&

Moldan

Special Weather Statement
National Weather Service Great Falls MT
657 AM MDT Thu Sep 12 2024

MTZ317-319>323-121345-
Helena Valley MT-Little Belt and Highwood Mountains MT-
Elkhorn and Boulder Mountains MT-
Big Belt, Bridger and Castle Mountains MT-Meagher County Valleys MT-
Canyon Ferry Area MT-
657 AM MDT Thu Sep 12 2024

...THUNDERSTORMS WITH BRIEF HEAVY RAINFALL WILL IMPACT SOUTHEASTERN
LEWIS AND CLARK... NORTHERN BROADWATER AND WEST CENTRAL MEAGHER
COUNTIES THROUGH 745 AM MDT...

At 651 AM MDT, Doppler radar was tracking a cluster of thunderstorms
along a line extending from 16 miles northwest of Toston to near
Townsend. Movement was northeast at 20 mph.

HAZARD...Brief heavy rainfall between 0.20 and 0.50 inches and
         lightning.

SOURCE...Radar indicated.

IMPACT...Localized flooding impacts near the Horse Gulch burn scar.

Locations impacted include...
Townsend, Silos, Fort Logan, Winston, York, and Goose Bay.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Heavy rainfall is occurring with these storms and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4691 11179 4665 11096 4623 11141 4635 11176
TIME...MOT...LOC 1251Z 212DEG 22KT 4636 11164 4631 11146

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...<30 MPH

RCG