Severe Thunderstorm Warning 49, NWS Glasgow, MT

Area Forecast Discussion
National Weather Service Glasgow MT
643 PM MDT Thu Jun 7 2018

.DISCUSSION...

Evening Update...

Showers and thunderstorms are developing over northeast Montana
this evening as a surface trough moves across the area. Some of
these storms could be producing large hail and damaging winds, and
as such, a Severe Thunderstorm Watch is in effect until 1 AM MDT.
Right now, the areas anticipated to potentially see some severe
weather will be from the Glasgow area and east, and especially
along a line of storms developing closer to the North Dakota
border. These storms will continue to develop and move generally
northeast through the rest of the evening. Flash flooding may also
occur under that line of storms as multiple storms may impact the
same areas. Will keep an eye on things as the situation develops.
Hickford

Previous Discussion...

-Short Term Discussion (Through Friday)

A surface trough continues to extend from northeast Phillips
County south-southeast through central Garfield County. The
environment across this boundary and points east remains capped at
this time, but that cap is expected to break early this
afternoon. As that occurs, an outflow boundary from earlier storms
to the west will meet this surface trough, and in conjunction
with the passing of an upper-level short wave trough, will trigger
thunderstorm development (expected in the 2 to 3 pm time frame).
Additional convection across southwest Phillips County will
continue to move off to the northeast early this afternoon and
may strengthen and become severe as it gets into central/northern
Phillips County. This overall complex of storms will progress
east across the CWA into the evening and early overnight hours.
The main threats with these storms will be hail to 2 inches in
diameter, damaging winds to 70 mph, and very heavy rain that may
lead to flooding.

As we head into the evening hours, additional thunderstorm
development may occur across the southeastern portion of the CWA
(McCone/Dawson/Prairie/Richland/Wibaux Counties). MLCAPE across
this area will be 2000 to 2500 J/KG with around 30 knots of
effective bulk shear. The focal point for thunderstorm development
would be a weak meso low emanating from the earlier complex of
thunderstorms in the Lewistown area. Surface dewpoints will be in
the lower 60s with backed winds at the surface. This will set the
stage for explosive thunderstorm development (or intensification
if the storms that form along the surface trough just continue
into this area) with storms quickly becoming severe. Multi-cell
clusters will dominate, but an embedded supercell is certainly
possible. These storms will have the potential to produce large
hail in excess of 2 inches, damaging winds to 70 mph, and perhaps
a tornado along either the southern edge of a multi-cell
cluster/squall line, or associated with a supercell.

The severe threat should come to an end by midnight as instability
wanes and the main complex of storms moves into North Dakota.
Southwest flow will return Friday with generally dry conditions
expected. However, some isolated thunderstorms will likely develop
during the afternoon hours across Phillips and Petroleum Counties.
These storms have an outside shot at becoming marginally severe,
but they will be pulsey in nature.

-Long Term Discussion

A large trough will be moving into the northwestern U.S. this
weekend. While we look to stay dry both days, strong winds are
expected. Winds will be gusty out of the southeast on Saturday
with sustained winds of at least 25 mph and gusts to around 40
mph. Winds will turn to the northwest Sunday as a surface low and
associated cold front sweet through the area. A Lake Wind
Advisory will be needed Saturday and Sunday. Pleasantly cooler
temperatures will be in control for Monday and Tuesday.

-Mottice

&&

.AVIATION...

FLIGHT CAT: VFR, becoming IFR/LIFR this afternoon and evening in
severe thunderstorms.

SYNOPSIS DISCUSSION: Scattered thunderstorms will move in from the
west and additional storms will develop this afternoon and
evening. Large hail, damaging winds, and frequent lightning will
be the main threats.

WINDS: Generally from the E and SE today at 10-15 kts, but strong
and erratic winds are expected with any thunderstorm. Later on
Friday, a west wind around 10 kts will settle into the region.

-Mottice

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

weather.gov/glasgow

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