Canadian Derecho & Potential of Some Storms HereJuly 19th, 2013 at 3:32 pm by Chad Evans under Chad's WLFI Weather Blog
CANADIAN DERECHO & OUR APPROACHING COLD FRONT WITH LIKELY BROKEN LINE OF STORMS TONIGHT…………..
Widespread, damaging straight line winds are lined up over 520 miles from Flint, Michigan to near Toronto to Montreal. Widespread wind damage has been reported across Ontario with winds up to 85 mph. The two embedded bows with the highest wind threat are north of Peterborough, Ontario or 73 miles northeast of Mississauga/Toronto area & another moving into Montreal, Quebec. Winds are sustained at 41 mph at St. Leonard, Quebec right now as line arrives.
Good thing is that the upper jet dynamics supporting this derecho will stay northeast of our area. So, we will not see such an impressive, solid line of storms. Rather, it looks broken. However, a few embedded microbursts with some hail are possible with it tonight with heavy downpours.
Sinking air ahead of the front is suppressing any spotty storm development here & keeping it confined to Ohio & southern Indiana to Kentucky. The sinking air is causing enhanced heating, however. Our northern tier of counties have temperatures at 95 degrees, with everyone else at 90-94. Also, Benton Harbor, Michigan hit at least 96 degrees (after a record warm low of 81!) & Chicago’s Midway Airport hit at least 96, O’Hare Airport at least 95. Kankakee Airport has hit 95 degrees, so far.
JET WINDS & THEIR ROLE IN STORM ORGANIZATION………..
Strong mid & upper winds vent storms, accelerating updrafts. Also, they make storms tilt, keeping updraft & downdraft separate, preventing the downdraft from choking it off. Thus, such wind promote organized lines of storms.
Less dynamical supports equals more pulsey, broken storms. However, with at least some side-swiping of stronger winds aloft, at least a broken line is likely to form.
Usually when the winds are same direction at each level, storms are more linear. Lack of wind aloft, but strong instability promotes random, pulsey storms. Strong low-level speed & directional shear at each level ‘ supports discrete supercells. Such extreme shear way upstairs will promote splitting supercells. Meanwhile, if cold pool forms with multi-cells, brief lines can form even without environment of decent dynamics. There are other factor involved in storm initiation & form, too. So many variables go into storm formation, mode & tendency, indeed!