Ticker for February 6, 2001

                
MESONET TICKER ... MESONET TICKER ... MESONET TICKER ... MESONET TICKER ...
February 6, 2001   February 6, 2001   February 6, 2001   February 6, 2001

Great Mesonet In-Situ Cooling Case

Sometimes, the best meteorological events occur during the most placid
weather.  And we had an exciting in-situ cooling event in eastern
Oklahoma this morning.

Take a look at the Mesonet weather map from 1:15 this morning:


Light southerly or southeasterly winds across most of the state, a
ho-hum cold front pushing into northwestern Oklahoma ... not much to
write home about, right?

But take a look at conditions at Stigler, Wister and Broken Bow in
eastern Oklahoma.  While the rest of the region observed temps in the
mid-40s or even mid-50s, the temps at these sites were 39, 30 and 31 F,
respectively.  Wister's temperature of 30 was twenty-five degrees
colder than nearby Talihina.  Twenty-five degrees!

How can two stations that share a county report such different temps
in the absence of a front or some dramatic event?  The answer lies
in the wind field.  The three stations listed all have calm winds.
When locations are protected and/or decouple from the ambient wind
flow, they can cool rapidly via radiative processes.  This "in-situ
cooling" is exactly what happened here.

In-situ cooling is different from "cold air drainage" processes,
which take hours to set up and mature.  In-situ cooling can occur
rapidly after the location is protected from mixing, which is
evident in the Mesonet meteograms below.

Comparing Wister to Talihina:



Wister's winds dropped quickly to near zero shortly after sunset,
and the air temperature dropped rapidly to near the dew point.  At
Talihina, winds stayed above 5 mph all night, which was enough to
keep mixing processes up and temperatures around 50 F.

Stigler demonstrated in-situ cooling processes intermittently
throughout the evening:


Overnight winds at Stigler vacillated between near calm and strong
enough to support mixing.  The temperature trace vacillates with the
winds.

Another fun and exciting capture by Mesonet data!