Fall dryness may reduce spring flood risk
GRAND FORKS -- It has been an abnormally dry fall in the Red River Valley, but not one for the record books, according to the National Weather Service office in Grand Forks.
The lack of snow and rain and the region's days of unseasonably warm weather will likely come to an end this week, though, the service
"Normal temperatures are going to seem brutal because we've been so mild," said Mark Ewens, senior hydro-meteorologist technician with the weather service. "I think we all were getting used to it."
The recent dry streak "certainly doesn't hurt" the outlook for spring flooding next year, he said, but it also does not remove all risk of a fourth consecutive year of major flooding.
"We've been so wet for so long that while this dry spell is certainly welcome, it's drying out the topsoil but there's still so much water," he said.
And, he said, the two biggest factors are still up in the air: How quickly snow melts during the spring thaw and how much additional rain or snow falls as flooding begins.
"What this dry fall does is when the snow does melt, it allows more absorption into the topsoil," he said. "It's not going to immediately run off like it has in recent years."
Grand Forks recorded 3.47 inches of precipitation from Sept. 1 to Nov. 28, about 1.36 inches less than normal for fall. But that dry spell was just enough to rank fall 2011 as the city's 45th driest on record, ranking somewhere in the middle of all falls since the start of meteorological records in 1890.
Most of the season's precipitation came in September, when a Sept. 1 shower dumped 1.69 inches of rain and a Sept. 22 storm brought another 0.69 inches of rain.
Just 0.90 inches of precipitation have fallen on Grand Forks since Oct. 1, well below the normal amount.
The southern valley has been much drier.
As of Nov. 28, Fargo-Moorhead had just 1.41 inches of precipitation for the season -- about 4.25 inches less than normal.
But even that is only enough to tie with 1967 for the third-driest fall in the area, according to meteorological records dating back to 1881. The area's driest fall came in 1976, when just 0.97 inches of rain fell.
Both Fargo and Grand Forks had a record warm Thanksgiving, with temperatures climbing above 55 degrees. A new record of 55 degrees was set Monday at Grand Forks International Airport.
La Niña impact
Ewens said it was not a surprise the Valley has seen such a dry, mild fall -- those conditions were expected as early as summer when the La Niña phenomenon in the Pacific Ocean flared up again for a second consecutive year.
Many residents wondered if the region's ongoing wet cycle since 1993 has finally come to an end, he said, but that remains "the $10,000
The Valley has experienced similar dry spells during the current wet cycle, he said, including in fall 2003, spring 2005 and summer 2006. Eastern North Dakota was drier in 2007 than it is now, when an arid fall prompted drought conditions ahead of the winter.
"The year-to-year variability can be so extreme, and that's normal," he said. "Extreme variability in weather is what's normal."
He said a typical second-year La Niña, a relatively rare meteorological occurrence, means the Red River Valley gets a break from a stormy, cold fall.
"For lack of a better term, the atmosphere has kind of been worked over," he said. "The energy that's required to create a lot of storminess early in the winter isn't necessarily there. It takes time for the atmosphere to readjust."
Return to normal
But that break probably will not last much longer.
Ewens said weather conditions tend to be colder than normal and snowier than normal during a La Niña year, especially in the late winter and early spring as lower latitudes begin to heat up and provide more energy to the
"So far, this La Niña has kind of been following the playbook," he said.
The Red River Valley will transition to more seasonable weather this week, he said. Grand Forks has a slight chance of snow today and is expected to reach a high of 33.
High temperatures will dip below 20 degrees Thursday, and there is another chance of snow Sunday.
The 14-day outlook calls for normal temperatures and above normal precipitation, bringing Grand Forks to lows near 0 and daytime highs near the freezing point.
Johnson is a reporter for the Grand Forks Herald, which is owned by Forum Communications Co.