Severe Thunderstorm Warning 91, NWS Glasgow, MT

Area Forecast Discussion
National Weather Service Glasgow MT
230 PM MDT Tue Jul 10 2018

.DISCUSSION...

The current GOES water vapor loop depicts a shortwave trough over
Washington State/British Columbia that is moving east along the
International border. This trough will cross the Divide and send
a cold front through NE MT late this afternoon and evening. This
cold front will find a very unstable environment.

With the Heat Index around 100, low-level moisture flowing in from
the southeast, upper-level moisture flowing in from the
southwest, moderate lapse rates, strong CAPE, an upper air profile
with effective shear, strong thunderstorms are expected, some
likely severe. SPC suggests the main threats will be very strong,
damaging winds and large hail. SPC's Convective Outlook covers the
northern half of NE MT with Enhanced risk for Severe
Thunderstorms tonight. Initial thunderstorms may develop off high
terrain to the southwest. More northerly storms will be associated
with the cold front. The separate storm areas will merge this
evening along the Northern Tier while moving into North Dakota.
KGGW conducted a special upper air run for 18Z. The sounding
indicate very strong instability with large CAPE and other
convective parameters. As a result, as proposed by SPC, the entire
CWA, initially, will be be covered with a Severe Thunderstorm
Watch for this afternoon and early evening.

Today, the current in-place threat is the Heat Index, which
prompted a Heat Advisory for most of NE MT today. This is due to
the combination of temperatures in the 90s and Dew Points in the
upper 50s to around 70. The advisory is expected to expire around
an hour before sunset.

Wednesday, will be a cooler day behind the departed cold front and
northwesterly flow aloft. Surface winds behind the front may
become strong enough to require a Lake Wind Advisory for Fort Peck
Lake.

Previous Discussion for Wednesday night and beyond:
Remainder of the week should be relatively quiet. Temperatures
will rebound back into the 90s by Friday. Another upper trof moves
across the region through the weekend with a slight potential for
thunderstorms with cold front passage Saturday night. Ebert

&&

.AVIATION...

Generally VFR conditions expected. This afternoon and evening,
restricted flight conditions may occur with any thunderstorms
that move through the terminal areas.

Strong to severe thunderstorms are expected to be moving across
northeast Montana during the late afternoon and evening
(approximately 21z to 6z), with the threat highest near the
Canadian border.

Wind: Very strong wind is expected near any of the severe
thunderstorms that develop. Otherwise, expect easterly wind,
veering around to the southeast at 10-20kt. After the cold front
passes, wind will become northwesterly.

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM MDT this evening for Central and
Southeast Phillips...Central and Southern Valley...Dawson...
Eastern Roosevelt...Garfield...McCone...Prairie...Richland...
Southwest Phillips...Western Roosevelt.

&&

weather.gov/glasgow

Special Weather Statement
National Weather Service Glasgow MT
405 PM MDT TUE JUL 10 2018

MTZ016-022-060-102245-
Garfield MT-Southwest Phillips MT-Central and Southeast Phillips MT-
405 PM MDT TUE JUL 10 2018

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN PHILLIPS AND
NORTHWESTERN GARFIELD COUNTIES UNTIL 445 PM MDT...

At 405 PM MDT, Doppler radar was tracking a line of strong
thunderstorms near Hays, or 11 miles northwest of Zortman, moving
northeast at 40 mph.

Wind gusts up to 50 mph will be possible with this storm.

Locations impacted include...
Zortman, Dodson, Fourchette, Phillips, Wagner, Landusky, Sun Prairie
and Fred Robinson Bridge.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

A Severe Thunderstorm Watch remains in effect until 900 PM MDT for
northeastern Montana.

LAT...LON 4792 10863 4799 10861 4798 10844 4845 10841
      4844 10840 4843 10835 4850 10834 4855 10808
      4763 10764 4761 10851 4762 10852 4761 10858
      4763 10870 4792 10875
TIME...MOT...LOC 2205Z 246DEG 35KT 4806 10864

Hickford

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