Syracuse, N.Y. – Tuesday morning, it didn’t look like Central New York was at risk of flooding from an early season nor’easter, which was forecast to stay mostly to the southeast corner of the state.
But by late evening, roads in Central New York were closed, basements and businesses were taking on water, and some residents were forced to evacuate.
What happened?
Three things explain the unexpected flooding, weather officials say:
*The big storm shifted slightly to the north and northwest of forecasts, meaning more rain came to a wider area of Central New York and the Finger Lakes than expected.
* The ground was still soaked from a wet October and the second-rainiest summer on record.
* The late October timing of the storm meant trees hadn’t been pulling water out of the soil like they do in summer.
While the final rainfall totals were slightly more than forecast, meteorologists at the National Weather Service said they hadn’t anticipated how much water would run off into streets and creeks.
“It really didn’t rain that much more than we expected: It’s just that we had a lot more runoff than we expected,” said Dave Nicosia, the top meteorologist in the weather service’s Binghamton office, which forecasts for Central New York. “We just didn’t know the runoff would be so severe because of 2 inches of rain. That’s what took us by surprise.”
Tuesday morning, the weather service was projecting about 1.5 inches of rain for Syracuse. The final total for Tuesday was 2.33 inches, a record for Oct. 26 and the fifth-rainiest October day since records began in 1902.
Still, Nicosia said, 2 inches of rain wouldn’t typically cause the flooding seen Tuesday. He said the ground is still holding water from the excessively wet summer, and that’s hard to gauge when doing forecasts.
“The groundwater is very high and that continues to be an issue from the wet summer we had,” Nicosia said.
October had been wet, too, even before Tuesday’s deluge. Through Monday, Syracuse had seen 4.52 inches of rain since Oct. 1, well above the normal of 3.13 inches for that period.
All of that summer and fall rain meant the soil was full of water. Normally, half of the volume of soil will consist of empty spaces, or pores, said Don Leopold, a botanist at SUNY College of Environmental Science and Forestry.
“Now, every bit of pore space is filled, and there’s nowhere for the water to go,” Leopold said.
Trees play an important role in controlling runoff, Leopold said. Water taken up by roots is evaporated through the leaves, and leaves will catch and hold onto some of the rain during a storm.
In late October, however, many trees have lost their leaves and gone dormant.
“They’re not getting rid of the water as they would during the growing season,” Leopold said.
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