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> September 4th, 2017 Severe Weather, Widespread damaging winds possible
post Sep 4 2017, 10:59 AM
Post #1

Rank: F5 Superstorm

Group: Member
Posts: 1,079
Joined: 9-February 14
From: Northdale, London, ON
Member No.: 29,229

Watches are up

10:51 AM EDT Monday 04 September 2017
Severe thunderstorm watch in effect for:

Rodney - Shedden - Western Elgin County
St. Thomas - Aylmer - Eastern Elgin County

Chatham-Kent - Rondeau Park
Windsor - Leamington - Essex County

Sarnia - Petrolia - Western Lambton County
Watford - Pinery Park - Eastern Lambton County

London - Parkhill - Eastern Middlesex County
Strathroy - Komoka - Western Middlesex County

Conditions are favourable for the development of dangerous thunderstorms that may be capable of producing damaging wind gusts.

An approaching cold front is expected to trigger thunderstorms after 2 pm and into the early evening hours. The potential exists for several of these thunderstorms to produce severe weather with winds in excess of 100 km/h being the primary threat.

Very strong wind gusts can damage buildings, down trees and blow large vehicles off the road. Intense lightning is likely with any thunderstorm that develops. Remember, severe thunderstorms can produce tornadoes. Lightning kills and injures Canadians every year. Remember, when thunder roars, go indoors!

Severe thunderstorm watches are issued when atmospheric conditions are favourable for the development of thunderstorms that could produce one or more of the following: large hail, damaging winds, torrential rainfall.

The Office of the Fire Marshal and Emergency Management recommends that you take cover immediately if threatening weather approaches.

Please continue to monitor alerts and forecasts issued by Environment Canada. To report severe weather, send an email to ec.cpio-tempetes-ospc-storms.ec@canada.ca or tweet reports using #ONStorm.

For more information:

The National Weather Service has a 15% wind risk outlined up to the Canadian border.

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...Lower Great Lakes/Ohio Valley/Mid Mississippi Valley/Central
An upper-level trough will dig quickly southeastward into the Upper
Mississippi Valley today. A broad belt of west to west-southwesterly
cyclonic flow will be in place ahead of the trough across much of
the Great Lakes and Ohio Valley. At the surface, a cold front will
advance southeastward today across the central Great Lakes, upper to
mid Mississippi Valley and central Plains. A few thunderstorms
should be ongoing along the front this morning. Ahead of the front,
surface dewpoints are forecast to increase into the mid to upper 60s
F by this afternoon. This combined with warming surface
temperatures should result in the development of moderate
instability. Moderate instability is expected to first develop in
the mid Mississippi Valley by late this morning and then spread
east-northeastward into the Ohio Valley and southern Great Lakes
this afternoon. This will aid convective initiation of surface-based
thunderstorms along and just ahead of the front during the 20Z to
22Z timeframe beginning in southern Lower Michigan and far northern
Indiana. Thunderstorm coverage should expand quickly
west-southwestward along the front during the late afternoon. The
development of a linear MCS will be possible by early evening from
the Great Lakes west-southwestward into the mid Mississippi Valley.

At mid-levels, a 70 to 80 kt jet max associated with the upper-level
trough will translate eastward across the upper Mississippi Valley.
This jet max is forecast to increase in strength as it approaches
the Slight and Enhanced risk areas. 0-6 km shear is forecast to
reach the 40 to 50 kt range along the front as convection organizes
late this afternoon. As a result, the combination of instability and
deep-layer shear will be favorable for severe thunderstorm
development. Although supercells will be possible early in the
event, the models suggest that linear development will be favored
due to low-level convergence and forced ascent along the front. This
will likely make wind damage the greatest severe weather hazard as a
line of storms moves southeastward across the region. An enhanced
risk for wind damage will be most likely from far eastern Illinois
northeastward across north-central Indiana into northwest Ohio, near
the southwestern section of a 40 to 50 kt low-level jet. Isolated
large hail may also develop with the more discrete rotating storms
that develop during the late afternoon, when instability is forecast
to be maximized. A marginal threat for hail and strong wind gusts
will be possible across southwestern Missouri and southeast Kansas
late this afternoon into this early evening.
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post Sep 4 2017, 11:07 AM
Post #2

Rank: F5 Superstorm

Group: Member
Posts: 1,079
Joined: 9-February 14
From: Northdale, London, ON
Member No.: 29,229

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post Sep 4 2017, 11:14 AM
Post #3

Rank: Tornado

Group: Member
Posts: 245
Joined: 15-December 14
From: Northern Dufferin County
Member No.: 30,103

Yes , quite the squall line developing over northern Lake Huron right now . Should make for an interesting afternoon and probably the last severe thunderstorm of the year for this area .
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