Southeast Weather Outlook Tends to Favor Small Grain Crops
Thursday, September 29th, 2011
The weather forecast for this fall and winter should be good news for Southeastern wheat producers, since the La Nina conditions that are expected usually are favorable for winter grain crops such as wheat, oats and rye.
"La Nina brings warmer than normal winter temperatures, so we'll get fewer chill hours this winter," says David Zierden, the state climatologist of Florida and an associate in research at Florida State University's Center for Ocean-Atmospheric Prediction Studies.
"Historically, wheat yields tend to be better in times of La Nina," said Zierden at the recent Central and South Alabama Wheat Expo held in Montgomery, Ala.
The Southeast Climate Consortium, of which FSU is a member, has issued a La Nina watch, meaning it is more likely than not that La Nina will redevelop in the Pacific Ocean in the next one to three months, he says.
La Nina, explains Zierden, refers to a state of the tropical Pacific Ocean in which surface temperatures along the equator from South America to the central Pacific turn colder than normal.
La Nina can be thought of as the opposite of El Nino, in which the same area of the Pacific is much warmer than normal.
"La Nina typically brings fall and winter weather patterns to parts of the Southeast that are warmer and drier than normal," he says.
"Historically, the peninsula of Florida averages rainfall 40 percent to 60 percent below normal in the months of November through March during La Nina events.
"Temperatures over the entire area average 3 to 4 degrees warmer than normal. The onset of warm and dry conditions normally begins in September, and the pattern intensifies as the season progresses."
This past year was a good one, he says, for wheat yields and grain quality.
"We started off last winter very cold," says Zierden. "Florida and south Georgia ranked as the coldest December on record since 1895, and it was among the coldest on record for the remainder of the Southeast. Along with colder temperatures, we accumulated chill hours at a much higher rate than normal."
Later in the season, in March and April, the Southern U.S. was warmer than normal, he says.
"So we were accumulating growing-degree days at a critical time when the crop needed it. But from last October through July, rainfall in south Georgia and south Alabama were running at 50 to 75 percent of normal. However, the wheat crop had enough moisture in the soil to work with," says Zierden.
Crops in parts of the Southeast were already suffering from extremely dry and hot conditions earlier this summer.
The three-month period of April through June was the driest on record since 1895 for the western Florida Panhandle and southern Georgia, while June ranked as one of the warmest on record.
Last year, says Zierden, the Pacific Ocean slipped into one of the strongest La Ninas on record and this was a key trigger for the development of drought in Florida and the Southeast as well as unprecedented drought in Texas and Oklahoma.
LAST FOR TWO OR MORE YEARS
"Historically, there is a tendency for strong La Nina events to last for two or more years. More recently, ocean temperatures along with wind and cloudiness patterns over the Pacific are indicating that the redevelopment of the cold water is likely after a summer of neutral conditions," he says.
The expected dry pattern could prolong or even worsen the widespread drought affecting the region, adds Zierden. Potential deficits in rainfall during the winter in these areas can be critical, as winter is the primary recharge season for surface and groundwater.
"Warmer temperatures may slow the necessary chill accumulation in flowering fruits such as blueberries, peaches and strawberries but may enhance development of other crops," he says.
"The forecasted warm and dry conditions are unfavorable for the production of winter forage for cattle when irrigation is not available.
While mild freezes can be expected every year in north and central Florida, La Nina reduces the risk of severe freezes in the citrus and vegetable belts."
The warmer temperatures, says Zierden, will result in less chill accumulation over the course of the winter season.
"Warmer temperatures will also mean greater evaporation rates. Due to the jet stream configuration, severe or damaging freezes are less likely during La Nina than in neutral years. We understand that many crops are at risk from an early season freeze due to delayed planting from the drought.
"However, the risk of early or late season freezes does not seem to be affected by the Pacific Ocean."
The shift towards drier than normal conditions becomes much more pronounced in Florida and coastal Georgia, Alabama, and the Carolinas as fall progresses into winter, resulting in much higher confidence in a forecast of dry conditions in these areas, he says.
"Keep in mind that winter rainfall is vital to the recharge of surface and groundwater in Georgia, Alabama and the Carolinas.
While the worsening of drought may slow during the winter months when water demand is much lower, it may intensify quickly come spring.
Summer evapotranspiration rates are greater even with normal rainfall, so heading into the spring with deficits already accumulating from winter is a sure recipe for rapid drought intensification.
"In Florida, where drought concerns are lower right now with recent rainfall, there is a strong possibility for drought to re-intensify this winter and spring. Wildfires will also be a concern, where studies show that La Nina normally leads to an active wildfire season in Florida and south Georgia."
Beginning in November, says Zierden, the Southeast can expect rainfall patterns of from 10 to 30 percent less than normal. "We'll see similar rainfall patterns through the winter that we saw last year."
Southeast Farm Press