Saturday, July 07, 2007

HGB Area


Maximum 1-hr Ozone (ppb)

Maximum 8-hr Ozone (ppb)


55 C553


Statistical Model



Human Forecast



Acutal (Observed)

109 C45




Finally the weather changed - still cloudy, but wind shifted from SE to SW and rain chance is around 30%.
Wind is also getting weaker. This type of weather is not very common. It usually does not cause high ozone at
HGB. The max ozone may occur NE Houston, likely in Kingwood/Aldine area.

Yesterday's persistent rain brought low ozone across the region. The statistical model does not take rain
chances into account (due to rain is a rare event in previous three summers). The stat model will update each
year and next year's model may use the forecasted rain chances (PoP). Anytime there is a shower in the
region, the actual max ozone is likely to be lower than statistical forecast.

Yesterday's high is at C559 (Katy Park), likely due to brief morning partly cloud skies there.

7/7/2007 10:12:06 AM

HGB's overall ozone was low during the day except for a small area in Seabrook and La Porte. The average
peak of all the sites is 48 ppb. Only two sites, C45 (Seabrook) and C556 (La Porte) reported unusal high
ozone of 109 and 104 ppb respectively.

Forecasted ozone is 40 ppb lower than actual, primarily due to the small-scale convergence/stagnation not
present in the weather forecast. The convergence occurred from 13 CST to 15 CST at southeast Houston
(from Seabrook slowly moving west). In previous hours, emissions at ship channel moved east to southeast.
Starting from 13 CST, wind at Galveston Bay shifted from West/Northwest to East/Northeast, then southeast.
The wind reversal brought back the emissions originally blown away from the city. Even though it was still
partly cloudy, ozone production was running high. With relatively cool weather and low mixing height, plus
weak wind, ozone were trapped in a small volume, causing unusually high concentration in Seabrook and
its near surroundings.

Unfortunately, this small scale phenomenon is still the blind spot in weather forecasting.

7/8/2007 9:01:06 AM