27 November 2003

An interesting weather phenomenon occurred across parts of central Oklahoma on Thanksgiving 2003. Around 11am, a brief half hour-to an hour of strong winds buffeted the area with gusts frequently reaching 40-45 mph. Why did these winds occur? A very strong upper level disturbance began affecting the southern Plains overnight Wednesday through Thanksgiving day. Strong ascent associated with this system was sufficient in generating mid/high level clouds/precipitation (radar image below). However, according to the 6am balloon data for Norman (below), very dry air existed in the lower levels of the atmosphere from the surface to 11, 000 feet. Thus, precipitation that was generated above this layer evaporated before reaching the ground (virga). Eventually, the ascent became so strong that a lot of cloud and precipitation were generated and gradually moistened the lower levels sufficiently for a few rain showers (Dew point chart below). As the precipitation evaporated, the air temperature cooled, much like how water evaporation off the skin causes us to feel cool after jumping out of the pool or shower. The cool air, now more dense than the surrounding air, rushed to the surface, causing winds to gust into the 40-45 mph range. Notice the temperature drop around noon in the temperature chart below and the increase in dew point coincident with the peak winds and the brief rain shower. After the upper level impulse passed by, very strong subsidence caused the sky to clear and dew points to drop rapidly. The remainder of Thanksgiving 2003 was cool and breezy, but very sunny.

The following are some captured graphs that highlight the event

Radar image with surface observations/mesonet for around 11am CST:

6 am Norman, OK Balloon:

Outside temperature graph:

Dew Point:

High Wind:

Rainfall: