Wet pattern a problem for DNC events?

History says Charlotte's weather during the Democratic National Convention will be warm and rather benign.

But this summer’s patterns could throw a meteorological monkey wrench into outdoor events planned for the DNC – notably, the outdoor festival on Labor Day and President Barack Obama’s scheduled nomination acceptance speech the night of Sept. 6 at Bank of America Stadium.

The Charlotte region has been locked in an unsettled weather pattern much of this summer, with lengthy stretches of dry weather few and far between.

In addition, hurricane specialists have upped the forecast for this season, adding the threat that the remnants of a dying hurricane or tropical storm could put a damper on outdoor events.

Climatology favors convention-organizers’ plans to stage an outdoor festival on uptown streets Sept. 3, and to stage the week’s highlight event, the president’s speech, in an outdoor venue. Trace amounts or less of rain have fallen from Sept. 3-6 in six of the last 10 years in Charlotte, and less than a quarter-inch fell during the same four-day span in two other years.

Only last year, when 1.62 inches fell on a stormy Sept. 5, and 2006, when it rained each of the four days, have been the exception. Temperatures also have been moderate, with highs reaching 90 degrees or more on only seven of 40 days between Sept. 3 and 6 in the last decade.

But the pattern should concern those who want to party outdoors in during the DNC this year.

“There has been a persistent trough over the eastern United States – low pressure between a strong high in the West and another high pressure system in the Atlantic,” said James Oh, of the National Weather Service’s office in Greer, S.C.

That trough has produced several stretches of weather like last week, when a weak cold front pushed south into the Carolinas and stalled, triggering days of thunderstorm activity. While this week’s weather is forecast to be mostly dry, another wet cycle is forecast for next week.

“Our reliable forecasts go out only about seven to 10 days, so it’s not possible to foresee what will happen when the convention is in Charlotte,” Oh said.

He said the Climate Prediction Center’s 30-day outlook isn’t much help. It calls for generally average temperature and rainfall conditions in the western Carolinas, although precipitation might be a bit higher than usual, Oh said.

The tropics are another issue. Last week, the National Hurricane Center increased the number of named storms it is expecting this season in the Atlantic and Caribbean basin. Early September is near the peak of the tropical season.

The original prediction of nine to 15 named storms is now 12 to 17.

Sept. 3-6 weather history

National Weather Service records show these averages over the past 10 years in Charlotte for the four days of the Democratic National Convention:

Sept. 3: 87.5, average high; 62.8, average low; trace of rain twice; dry the other eight years.

Sept. 4: 85 and 64; rained three times, including 0.96 inches in 2006.

Sept 5: 87.3 and 64.4; rained three times, including 1.62 inches last year.

Sept. 6: 85.0 and 63.8; rained three times, but the most was 0.17 inches, last year.