Hail and Damaging Winds in Montana, August 24 to 25, 2024

Area Forecast Discussion
National Weather Service Glasgow MT
212 PM MDT Sat Aug 24 2024

.DISCUSSION...

KEY MESSAGES:

 - Isolated, discrete supercells may for across northern Valley,
   Daniels, and Sheridan Counties this afternoon, moving NNE'ward
   into Saskatchewan. Large hail in excess of 2 inches is the
   biggest threat, with gusty winds as a secondary threat.

 - A cold front moving in central Montana tonight, will bring
   areas of showers and thunderstorms across the northern half of
   the CWA. A LLJ enhancement brings a continuation of frequent
   lightning and gusty winds closer to the MT/ND Border Saturday.

 - Rainfall returns Monday and Tuesday, with the areas south of
   I-94 having the higher chance of rainfall in excess of 0.5".

WEATHER PATTERN OVERVIEW:

An upper level trough off the US West Coast continues to bring
upper-level divergence, aiding in a broad area of vertical motion.
15Z surface observations hand analysis showed a gradient of 60F+
dewpoints intruding into portions of the CWA (and even areas in
excess of 70F dewpoints generally east of Glasgow). East of
Glasgow, the dewpoints drop into the 40s. This, in combination
with surface temperatures increasing again into the upper 90s,
will erode any CINH, and prime the atmosphere for yet another hail
threat.

12Z HREF members are targeting northern Valley, Daniels, and
Sheridan Counties for convective initiation along any convergence
boundary in the area (of which, one was observed moving SE'ward
into the US side of the International Border earlier this
morning). Given bulk shear in excess of 40 kt (as seen from the
15Z RAP13 forecast sounding) along the International border,
MUCAPE in excess of 2000 J/kg and 700-500 hPa lapse rates in
excess of 7deg/km, storm mode for the International Border region
will be discrete supercells, with some CAMs/12Z RRFS showing
possible splitting supercells. For the aforementioned region of
interest, large hail in excess of 2 inches can be expected, along
with gusty winds.

Additionally tonight, a disturbance moves NE'ward across central
Montana into NE Montana, bringing thunderstorms with frequent
lighting and gusty winds with a cold front passage. As the front
clears E of Glasgow, low-level jet enhancement of instability may
aid in areas of small hail and keeping the threat of gusty winds
all the way into NW North Dakota.

From Monday, the trough over the West Coast moves into the
Interior West, detaching from the jet stream, and moving through
the Montana through Tuesday afternoon. This will bring a broad
area of greater than a 0.25" of rainfall (for the 48 hr period
ending at 00Z Wednesday). WPC as such has included our SE'ern
zones in a Marginal Risk for Excessive Rainfall. This will be
something worth monitoring to see if convective storms locally
enhance this forecast rainfall amount.

FORECAST CONFIDENCE & DEVIATIONS:

Decided to revert back to NBM mean wind through Monday given that
winds observed today have been under the NBM90 guidance. Blended
in both ConsShort and NAMNest PoP guidance through 12Z Sunday,
given the Marginal Risk of Severe Weather highlighted across the
northern zones.
There is high confidence (50%-80% chance) that areas south of the
Missouri River will receive a wetting rain (at least 0.1" of
rainfall) for the 48 hr period ending on 00Z Wednesday. For the
same period, the chance of 0.5" of rainfall drops to a 40%-60%
chance for areas south of MT Hwy 200, and as high as a 20%-30%
chance in our far southern zones.

-Enriquez

&&

.AVIATION...

LAST UPDATED: 2000Z

FLIGHT CONDITIONS: VFR (IFR in the vicinity of a thunderstorm)

DISCUSSION: An isolated thunderstorm along the International
Border will bring reduced visibility and large hail threats.
A cold front moving through the region after 03Z will bring brief
MVFR conditions in showers and thunderstorms. Sunday morning and
afternoon look mostly dry with increasing showers moving in from
the south from Sunday night.

WINDS: Light and variable winds today switch to more NW'ly by
sunrise Sunday morning. Winds then will be sustained at 10-15 kts
gusting as high as 25 kts.

-Enriquez

&&

.GGW WATCHES/WARNINGS/ADVISORIES...
None.
&&

weather.gov/glasgow

Preliminary Local Storm Report
National Weather Service Glasgow MT
111 PM MDT Sat Aug 24 2024

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

0707 PM     Hail             6 NNW Larslan           48.66N 106.24W
08/23/2024  M2.50 Inch       Valley             MT   Public

            Accompanied by estimated 60 mph wind. Damage
            to pick-ups (dimples in hoods and cracked
            windshields). Flattened 2 foot high grass.

&&

TFJ

Special Weather Statement
National Weather Service Glasgow MT
423 PM MDT Sat Aug 24 2024

MTZ017-018-020-242315-
Daniels MT-Western Roosevelt MT-Central and Southern Valley MT-
423 PM MDT Sat Aug 24 2024

...A strong thunderstorm will impact portions of central Daniels,
northwestern Roosevelt and northeastern Valley Counties through 515
PM MDT
...

At 422 PM MDT, Doppler radar was tracking a strong thunderstorm 12
miles northeast of Lustre, or 22 miles southwest of Scobey, moving
northeast at 10 mph.

HAZARD...Winds in excess of 40 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Scobey, Flaxville, Madoc, Peerless, and Four Buttes.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4886 10504 4840 10563 4849 10586 4900 10594
      4900 10578
TIME...MOT...LOC 2222Z 209DEG 9KT 4852 10570

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH

GAH