826
FXUS65 KGGW 271924
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
124 PM MDT Thu Jun 27 2024

.DISCUSSION...
KEY MESSAGES:

1) A Severe Thunderstorm Watch is in effect until 8 PM MDT this
evening.

2) Breezy west to northwest winds are expected on Friday behind
the cold front, with Lake Wind criteria expected.

3) Cooler temperatures are also expected Friday and Saturday with
chances for showers and thunderstorms on Friday.

WEATHER PATTERN OVERVIEW:

Surface low pressure will shift east across eastern Montana
during the afternoon and evening along with a surface cold front.
SE winds ahead of the cold front will bring dew points into the
60s over most of NE Montana today and will reach near 70 around
Sidney. The mean surface based CAPE over eastern portions of the
CWA looks to reach 2000 J/KG or better this afternoon and evening
while forecast soundings show 40-50 kts of 0-6 km shear present.
This will all set the stage for active severe weather across NE
Montana and in fact a Severe Thunderstorm Watch is now in effect
until 8 pm MDT for all of NE Montana.

HREF shows storm coverage increasing along the MT/ND border
during the late afternoon and evening hours. Initial supercells
may congeal into line segments during the evening as storms shift
into the Dakotas. All hazards are favored including up to 2.5 inch
diameter hail, wind gusts to 80 mph, an isolated tornado, and
locally heavy rainfall. The SPC has eastern portions of the CWA
under an enhanced risk for severe storms. Fast progression of the
storms to the east should limit the flooding threat, but
conditions will continue to be monitored.

The upper trough will push into eastern Montana on Friday with
additional lingering general thunderstorms along with gusty west
winds (sustained 20 to 25, gust 30 to 40), and cooler
temperatures. These conditions may be sufficient for the Lake Wind
Advisory. Given active existing weather, will let the next shift
finalize that decision.

Upper ridging will guide warm and dry weather on Saturday before
more ensembles hint at more active weather early next week.

FORECAST CONFIDENCE & DEVIATIONS:

NBM has handled the forecast well with little deviation except to
include severe wording in the weather grids for today.

Confidence is high that there will be thunderstorms through this
evening. Confidence is low on rainfall amounts as there will be
widely varying precipitation depending on exactly where storms
track; ranging from a trace to upwards of an inch. Forecast
soundings show precipitable water values exceeding an inch as WPC
has the NE corner of the state under a slight risk for excessive
rainfall and the remainder of NE MT in a marginal risk. Widespread
hydrology concerns are not expected as the storms will move
fairly steadily eastward, but locally heavy rainfall may result in
some of the storms.


&&

.AVIATION...
VFR conditions are expected to start but MVFR/IFR will be
increasingly common through this evening with scattered to
numerous showers and thunderstorms.

Some storms will become severe with erratic wind guts that could
exceed 50 knots, hail and heavy rain that could bring periods of
MVFR/IFR conditions. Skies will clear after 03z at KGGW and after
06z at the other TAF sites tonight.

Winds will range west to northwest through tonight at 5 to 15 kts,
except gusty and shifting winds likely near storms. On Friday,
look for increasing west winds of 15 to 25 kts, gusting to 35 kts.


&&

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

$$

weather.gov/glasgow