Wednesday, May 15, 2013

bright band

Radar measures reflectivity. Reflectivitiy is proportional to the diamater of the partical to the sixth power dbz~(D)^6.

Snow and rain reflect different amounts of radiation. This causes problems to decide how much it is actually raining or snowing.

Melting snow can be very deceiving. When snow starts to melt it gets a watery shell around the flakes. To a radar beam it looks like a 10 cm rain drop.

Often this phenomenon is evident on radar in what is called a "bright band" where the radar shows a high echo but there are actually less rain that is thought to be there.

Hot day in the Midwest

Two weeks ago the Midwest had lots of snow. Yesterday, May 14 2013, the Midwest had broke record temperatures. It was HOT! Click the link to view a Mesowest profile of the day. Notice the winds coming from the southwest. Also, take a look at the humidity. It was very dry in the hottests areas.

Milwaukee Heat Burst

At 20:00 (8:00 PM) there was a sharp rise in temperature. This temperature rise is related to an increase in wind speed. The increased wind speed was caused by a heat burst. In a heat burst, virga evaporates, cooling the air making, and becomes more dense. The air suddenly sinks and compression causes adiabatic warming. At the surface, people experience sudden gusts of warm air.

Mesowest profile of temperature and wind in Milwaukee on May 14, 2013:

National Weather Service description of the Heat Burst: 

Virga and heat burst video (go to 8:00 PM)

More about heat bursts: