Windy evening...

A cold front moved through the area early Tuesday evening. It was not a strong front in terms of  temperatures, but the winds surely kicked up. What set this front apart from others that don't generate extremely gusty winds? The answer is in the wind shear of this atmospheric setup.

Wind shear is a term we use to describe the change in wind speed and direction with height. Most of the time there is wind shear in the atmosphere. Just watch the skies when there are different layers of clouds. In general the higher clouds move more from the west to east and the lower clouds move more with the lower level winds. Their direction is dependent on the position of lows and highs. For instance, if a low pressure area is approaching, the lower level clouds will move from the south or southwest to the north or northeast, while the upper level winds will often be from the west or southwest.

The surface wind speeds are usually at their strongest when the upper level winds are blowing from the same direction as the surface winds. When that happens the upper level winds "drag" the surface winds along as if they have established a connection. That's what happened this evening. Fortunately the winds died down quite a bit within an hour or two after the front passed.

Here are some of the highest gusts recorded for Tuesday evening:

Grand Meadow School (MN)        58 mph
Rochester - Kellogg (MN)                51 mph
Mt. Sterling (WI)                                   44 mph
La Crosse Municipal Airport       43 mph
Sparta (WI)                                                43 mph
Preston (MN)                                            41 mph
Decorah (IA)                                              37 mph

Dan Breeden
News 19 Chief Meteorologist