Wednesday, November 14, 2012

Sleet Last Night?

 That’s right.  A few areas of East Texas saw a mixture of hail, sleet, and graupel (snow pellets) late last night and early this morning.  So what happened?  Well a fast moving disturbance brought a lot of high clouds to the area last night and in a couple of areas these clouds developed into small thundershowers.  The image below shows the profile of the atmosphere early this morning.  Here we can see the cloud base was just over 10,000’ in elevation.  When air was lifted from this level it encountered elevated instability leading to the development of elevated showers and thundershowers.  Since most of the cloud’s temperature was below freezing, snow and snow pellets were forming instead of rain.  In the strongest updrafts the graupel, snow pellets, were held aloft allowing water vapor to freeze encasing them in ice until they grew too heavy for the updraft to hold allowing hail, some up to dime size, to reach the surface.

Outside the heavy core mainly snow and graupel feel from the cloud base where above freezing temperatures were encountered below 10,000’.  Here the ice crystals began to melt but not completely as the dry air began the process of evaporation.  As the precipitation evaporated it cooled rapidly allowing for the water droplet to refreeze into sleet.

In the lightest areas of precipitation most of the precipitation evaporated completely before reaching the ground.  The image above shows a radar shot of the shower across the Lake Fork area.  In addition to the precipitation the elevated instability allowed for the collision of ice crystals causing a large amount of static charge producing numerous cloud to ground lightning strike while over the Lake Fork area.

1 comment:

Anonymous said...

thanks for share..