Grab the boots and umbrella.
Even as the 1998 freshwater flows into the Chesapeake remained on track to set a record, meteorologists are predicting a wet winter for the upper portions of the Bay watershed.
The National Weather Service is forecasting a slightly wetter than normal winter and early spring for upper portions of the watershed, including most of the Susquehanna River basin, which normally supplies half of all the fresh water reaching the Bay.
It’s all a byproduct of La Nina, a relative of El Nino, which was blamed for bringing so much water — and warm temperatures — last winter and spring.
“While this forecast may not sound severe, it represents a major change from the very mild winter experienced last year in association with the strong El Nino,” said Anthony Barnston, a National Atmospheric and Oceanic Administration research meteorologist with the weather service’s Climate Prediction Center.
“What we’re looking at with La Nina is a tilt of the odds toward a colder winter in the Northeast with more snow and perhaps bigger storms than usual,” he said.
Like its climatological relative El Nino, La Nina is centered in the Pacific Ocean but affects weather patterns around the globe.
In La Nina years, Pacific ocean temperatures are colder and the air overhead drier because there is less evaporation. This tends to result in weaker wintertime jet streams over the central and eastern Pacific and stronger monsoons over Australia, Southeast Asia, South and Central America and Africa.
An El Nino event, such as the one that brought severe weather to many areas into this summer, is characterized by unusually warm water in the eastern Pacific.
According to the weather service forecast, the Bay watershed straddles a middle ground for receiving the effects of La Nina. It predicts that northern areas — including most of the Susquehanna watershed — will be wetter, and possibly colder, than normal. But southern Virginia may have a normal winter, but a warmer and drier than normal spring. Areas in between are expected to be near normal.
“The further north you go, the greater the chance of a harsher than normal winter and the further south you go, the greater the chance of milder than normal weather with less precipitation,” Barnston said.
If the Susquehanna basin gets a wetter than normal winter and spring, it could continue a trend toward increased flows into the Bay — something that makes cleanup efforts more difficult. Flows into the Bay during three of the last five years — 1993, 1994 and 1996 — were much higher than normal.
And this year is on track to surpass 1996 for the greatest freshwater flow into the Bay, according to the U.S. Geological Survey.
From January through August, flows from the Chesapeake’s tributaries averaged 90 billion gallons per day, about 8 percent higher than the 83 billion gallon a day average for the same period of 1996, according to the USGS.
The flows for August were actually below normal, according to USGS, at 13.5 billion gallons a day compared with the 20-billion-gallon-a-day average for the month. It was the second month in a row that flows into the Bay were below average, but those months were more than offset by the higher than average flows this spring.
The main cause for the low flow in August was dry conditions in the Susquehanna basin. Normally, the Susquehanna supplies half the freshwater to the Bay, but in August it accounted for only 35 percent of the flow. The Potomac River, the Bay’s second largest tributary, remained above average for the month.
High flows into the Bay contribute to water quality problems by flushing large amounts of sediment and nutrients off the land and into rivers and streams. The nutrients cause algae blooms which, along with sediment, cloud water and prevent sunlight from reaching important beds of underwater grasses. And when the algae die, they sink to the bottom and are decomposed in a process that depletes the water of oxygen.
The USGS has monitored flows into the Bay since 1951. Real-time streamflow data and other information on water resources can be found through the USGS Chesapeake Bay web page at http://chesapeake.usgs.gov/chesbay/