I can hear it now, the sound of tree and corn leaves rustling and churning and the howling through the porch railing on the house. The first of many fall wind storms will be blowing across the region Thursday into early Friday. It happens every year around this time.
Cold fronts get stronger as we enter fall. The low sun angle and long nights allow air masses to get increasingly cold in poleward locations. The cold air masses grow in horizontal and vertical depth with accompanying higher surface air pressure within them. The high pressure systems often get up to 1025 or 1030 mb during early autumn and sometimes in the 1040 mb ranbe by late autumn. On the leading edge of the cold air of course is the cold front. It is common to have low pressure areas form along the cold front. The low pressure systems usually intensify this time of the year as they encounter the warmer air holding on in the U.S. and even over the warm waters of the Great Lakes.
The greater the difference is between the low pressure system and the high pressure system coming in behind it, the stronger the winds will be. We call this the pressure gradient. You can think of pressure gradient as basically potential energy. Much like electrical potential energy that builds up before a lightning strike between the cloud and the ground, this wind potential energy will eventually get released. It is turned into kinetic energy as air is squeezed from the high pressure area toward the low pressure area. If the we had no friction and the earth was not spinning, the air would travel in a straight path from the high pressure to the low pressure. However those two factors cause a moving air particle to turn a bit to the right as it is traveling in the Northern Hemisphere. It is just the opposite in the southern Hemisphere.
On a broader perspective, one could argue that wind such as you’ll be feeling the next few days is the result of uneven heating of the earth. The non-uniform heating results primarily from the tilt of the earth’s axis. It also has contribution from the different heat properties of land versus water, different soils, different vegetation, and even different colors of landscapes. The wind is a mechanical means by which the atmosphere tries to even out such thermal differences. By the way, the strongest wind speeds with this current event will likely occur over Lake Superior and around Door County and Lake Michigan where gusts to 55 mph are possible.
So while the blustery winds can be annoying and even somewhat dangerous in terms of bringing down tree limbs and pushing vehicles around, they do have a good side. That seems to be the case with so many weather events.
This post was written by Tony Schumacher on September 28, 2011