Severe Weather Expected from the Great Lakes to the Virginias Late-Week

Tom Moore
Published: June 7,2016
As we move to the latter part of the week, the chance for strong to severe thunderstorms will develop, beginning Friday, from the Upper Midwest to the northern Great Lakes. On Saturday the threat for severe weather increases from the lower Great Lakes to the Virginias.

The severe weather will be triggered by a strong disturbance, riding along with the jet stream, from the Upper Midwest northern Great Lakes region on Friday to the lower Great Lakes and parts of the mid-Atlantic Saturday.
The main severe threats will be damaging winds and large hail. The probability of tornadoes appears to be low, but isolated tornadoes can occur in these situations.
Below is our latest forecast thinking on the timing and magnitude of the severe threats, followed by the severe weather setup.

Severe Weather Forecast

Friday

• Widely scattered strong to severe storms mainly from the eastern Dakotas through northern Minnesota to parts of Wisconsin.
• Threats: A few locations could see large hail and damaging winds.
• Cities: Fargo | Duluth | La Crosse

Friday's Thunderstorm Forecast

Saturday

• A more widespread threat for severe thunderstorms from southeast Michigan and northern Ohio through parts of western New York and Pennsylvania and down to the Virginias.
• Threats: Large hail, damaging winds and isolated tornadoes are possible.
• Cities: Detroit | Columbus | Cleveland | Buffalo | Pittsburgh

Saturday's Thunderstorm Forecast

Severe Setup
The jet stream pattern will be quite exaggerated by the end of the week. A large ridge (bulge in the jet stream) will build into western and central Canada. At the same time a trough (dip in the jet stream) will be located just off the East Coast of the U.S.
Mid to upper-level winds from the Great Lakes to the Mid-Atlantic will be racing from the northwest to the southeast (often referred to as a "northwest flow" pattern). This pattern is not uncommon in June when high pressure ridges become stronger, but significant troughs can still be in place farther east.
Occasionally, a strong disturbance (or a series of disturbances) can ride down the eastern side of the ridge toward the trough. The disturbance gains strength as it approaches the trough. At the surface, temperature and moisture contrasts along a frontal boundary become enhanced. This creates a more favorable environment for thunderstorm development.
Thunderstorms that develop can feed on the dynamics (energy in the atmosphere) created by the disturbance gaining strength. Depending on the situation, strong to severe thunderstorms can develop. These storms are capable of producing large hail and damaging winds.
By Friday, we expect that a disturbance riding down the east side of a high pressure ridge aloft will trigger thunderstorms, some severe, in the Upper Midwest and northern Great Lakes regions.
On Saturday, a stronger disturbance aloft and a frontal boundary at the surface will enhance the threat of severe weather from the lower Great Lakes to the Virginias.
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