Tornadoes and Flash Flood in Montana, July 12, 2024

Area Forecast Discussion
National Weather Service Glasgow MT
227 PM MDT Fri Jul 12 2024

.DISCUSSION...

KEY MESSAGES:
1) Hot conditions will continue into the weekend with the heat
advisory extended in the far south into Saturday.

2) Thunderstorms are expected this afternoon and evening. A few
storms could become severe with damaging winds across the
northeast. This will again occur Saturday afternoon and evening
in roughly the same areas but large hail will also be a threat
for Saturday.

+++ Update to key message number 2. SPC has upgraded most areas
north of the Missouri River to a Slight risk for severe weather
(level 2 of 5) spatial coverage. As highlighted above, the main
threats would be large hail and severe wind gusts, though an
isolated tornado would not be out of the question given the
isolated supercell storm mode. This will have to be monitored
carefully as the CAMS converge on timing and spatial location of
convective initiation. +++

WEATHER PATTERN OVERVIEW:
Upper ridge will remain in place over the western half of the
CONUS for the next several days. The heat advisory has reduced to
the southern two-thirds of the CWA for today as a weakened cold
front moves through. This will extend but further reduce to the
bottom third of counties for Saturday.

Keeping an eye to smoke models has allowed for some haze to sneak
into the area over the next couple days. Air quality has only
ticked down towards moderate but will need to be monitored through
the next several days.

FORECAST CONFIDENCE & DEVIATIONS:

First 24 hours of PoPs were updated to include a 50/50 blend of
the SREF NPoP along with the NBM PPI01 in order to capture the
afternoon thunderstorms better with the marginal threat for severe
weather in the area.

First 48 hours ended up getting a bump with the shrink stretch
tool over the CWA for afternoon highs and overnight lows, as
RTMA/URMA map passes are missing ASOS highs by roughly 2 to 4
degrees and this is clearly biasing baseline NBM downward compared
to the reality of these 100 degree+ extremes.

GAH/Enriquez

&&

.AVIATION...
LAST UPDATE: 0830Z

FLIGHT CAT RANGE: VFR

DISCUSSION: Used tempos to handle this from roughly 21 to 03Z.
Isolated HAZE is expected across the area through the cycle but
should not drop conditions below VFR.

DENSITY ALTITUDE: Afternoon highs will break 100 degrees in some
places through Saturday. This will make for less dense air and
lead to increased power needs and longer runway takeoffs.

WIND: NW'ly winds 10 to 15 kts. Outflow boundaries from any
thunderstorms that occur will create gusty and erratic winds. Then
becoming light and north to northeast Saturday morning.

GAH/Enriquez

&&

.GGW WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 9 PM MDT this evening for Central and
Southern Valley-Dawson-Eastern Roosevelt-Garfield-McCone-
Petroleum-Prairie-Richland-Western Roosevelt-Wibaux.

Heat Advisory from 10 PM this evening to 9 PM MDT Saturday for
Garfield-Petroleum-Prairie.

&&

weather.gov/glasgow