|Forecast discussion, Fri., Aug. 25,
Today is a promising day for ozone. The winds are light and
there's a bit of a land breeze. Emissions should stay almost in
place this morning with very light southwesterlies developing this
morning, turning more southeasterly in the afternoon and stronger
behind the bay and gulf breeze. Background levels are near 40 ppb.
General pattern is similar to the first week of the experiment, so
expect early afternoon exceedences over the ship channel area and
over and north of downtown later in the afternoon.
The only fly in the ointment is the unstable airmass. There's
plenty of tropical moisture around, and convection is present
farther over the Gulf and to the southwest. It's not as widespread
and the models persist with their drying trend, so expect showers to
develop a little bit later and not hit as many spots. Earliest
expected onset of thunderstorms is 11 AM. Sea breeze showers will
move slowly inland; some shower development is also possible ahead
of the sea breeze, particularly over the Piney Woods. Otherwise,
midmorning low clouds will develop and remain scattered to broken
until late afternoon.
TNRCC expects 200 or more ppb ozone levels - it could happen if
the showers hold off.
Max temperature mid 90s, higher to the northeast.
Quick Look at Tomorrow
General drying trend is continued by all models. Precipitable
water drops below 1.5 inches, making it possible that we will be
shower-free again. Atmospheric and air chemistry models predict that
tomorrow will mark the onset of dirty continental air, so on the
whole tomorrow is likely to be a very high ozone level day.
Saturday marks the beginning of a weather regime widely scattered
showers, light winds, possible /likely flow reversals, and polluted
air from the Eastern US. It appears that the regime will last at
least through Tuesday, when disruption becomes more likely from the
tropical remnants of Debby (or the redeveloped hurricane Debby).
Unless the occasional showers happen to nail the metropolitan area,
this should be several consecutive days of ozone exceedances.
Forecaster John Nielsen-Gammon