I've never heard it described as wind shear before, but it was probably that which blew over our fence last year.
Top of 26°C here today.
A quote from our National Weather Service:
"Vertical Wind Shear:
The change in the wind's direction and speed with height. This is a critical factor in determining whether severe thunderstorms will develop.
Wind Shear:
The rate at which wind velocity changes from point to point in a given direction (as, vertically). The shear can be speed shear (where speed changes between the two points, but not direction), direction shear (where direction changes between the two points, but not speed) or a combination of the two.
Wind Shear Profile:
The change in wind speed and/or direction usually in the vertical. The characteristics of the wind shear profile are of critical importance in determining the potential for and type of severe weather."
Two strong fronts meeting in the atmosphere can wreak havoc with piloting and ground level activities. Depending upon whether the high pressure front meeting a low pressure front is above or below the oncoming front often determines severity and angles of the ensuing mayhem.
One other point to consider is that the travel speed of the fast moving front will usually climb over the slower moving front, but not always.
This is part of the reason the weather folks have so much fun trying to Analise radar to determine weather conditions.
Once you have a swiftly moving high pressure front overtaking a stable low pressure system and it climbs to higher elevation, we often get extreme downward winds at "hurricane force" which also confuses radar.
They can tell direction from radar and often they color winds coming toward a station red and those moving away from a station in green. Any close together red/green blobs have to be watched very carefully.
Any change in location of the green vs red could indicate rotation. That minor rotation (changing position of the green/red boundary) is often the beginning of a tornado.
BTW, there were only five killed in Indiana last Friday. That twenty one number was a combined total over Kentucky, Illinois, Tennessee and Missouri, where the outbreak was most severe. There were seventeen tonadoes that made landfall here in Indiana. Many more that hit elsewhere.
It was a rough night.
Here's a neat illustration pic of downward wind shear and the possible beginning of a tornado from a high pressure front over running a powerful low pressure system from above.
Standing anywhere near this exchange of atmospheric pressures can be deadly.
