storm approaching 10 13 15.JPG

A record level of moisture could be in the air over Upstate New York this weekend, and other factors could help create thunderstorms with torrential rain.

(Glenn Coin | gcoin@syracuse.com)

Buffalo, N.Y. -- In the next couple of days, Upstate New York could set a weather record you've probably never heard of - but it's one that could cause flash flooding.

Forecasters are predicting that by Friday or Saturday, the amount of water suspended in the air above the state could be higher than has ever been recorded at this time of year.

"We could see a record for the date for most amount of moisture in the atmosphere," said National Weather Service meteorologist David Thomas.

It's called "precipitable water value," or PWAT, and it measures how much water is floating in a given column of air. The average PWAT this time of year in Upstate New York is about 1 inch. That means that if all the water in a column of atmosphere could be wrung out, an inch of rain would fall.

The mid-August record as measured by weather balloons released from the Buffalo weather service is 2.3 inches. This week, forecasts say, that value could be as high as 2.5 inches.

That would be "literally off the charts," the weather service said.

That much water falling out of the atmosphere could produce torrential rains and flash flooding, meteorologists warn. That's particularly worrisome in urban areas where there's less exposed soil to soak up the rain. Even when the ground is dry, as it is now

during a severe drought,

much of the heavy rain can run off quickly.

It would take about 1 to 3 inches of rain per hour to cause flash flooding this week in Upstate New York, according to the weather service. Storms this weekend could drop 2 inches or more per hour.

There's little fear about rivers and creeks overflowing their banks and causing more general flooding because the drought has kept them very low this summer.

Record levels of water level in the air above Upstate New York don't guarantee heavy rain and flash floods, though, Thomas said.

"It's not a direct relationship," he said, "but it's something that kind of opens your eyes when you see this much moisture, especially if other factors come together."

Those other factors are what meteorologists call instability and lift, which are needed to bring that water to the ground in the form of thunderstorms. Those factors, in turn, are partially dependent upon heat, and Upstate is forecast to have a couple of 90-degree days.

"It's increasing likely there could be some much heavier storms this weekend," Thomas said.

Thunderstorms develop quickly and it's impossible to know precisely where across a wide swath of land they will form. Parts of Upstate New York, especially Western and Central New York, could see several inches of rain Friday night and Saturday, but some areas might get next to nothing.

Even if these storms drop rain in New York's severe drought area, they probably won't be enough to end the drought, Thomas said. Some areas of Western New York have a rainfall deficit this spring and summer of 8 inches.

"It takes more than one or two events to end a drought," Thomas said. "It will take a couple months of above-normal precipitation."

We're already feeling all that water in the air, too: The relative humidity is 72 percent in Syracuse. The higher the humidity, the harder your body has to work to sweat to cool off.

This moisture is being drawn up from the Gulf Coast, where storms have dropped 8 to 12 inches of rain in Florida.

Contact Glenn Coin: Email | Twitter | Google + | (315) 470-3251