Sept 21st, the day before the start of Astronomical Fall, or the Equinox, a healthy (and severe) squall line approaches NE IL from Iowa. Taking on a bit of a "bow" shape, as severe winds push this squall line towards us. Reports of Semi's being pushed over and power lines down have been pretty common so far. The shear (how the winds change with speed or direction as you go up in height) is not conducive to tornadoes today but for winds and heavy rain, it sure is.
I love our atmosphere!
Later on, as the squall line approached, most of the severe weather remained north. However, a very evident "outflow boundary" was visible on radar. The thin green line ahead of the storms shows us the leading edge of the rain cooled air that has moved ahead of the storms. The cooler, less dense, air, spreads out ahead of the storms. When that boundary passes, one can expect higher winds (often severe), a wind shift, and a drop off in temps.
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