John Grymes | 4/16/2005 2:05:07 AM
As the New Year begins, so returns the threat of too much rain for the Bayou State. With the distinction as the nation's "wettest" state, Louisiana must always be on guard for the potential for flooding, according to LSU AgCenter climatologist Jay Grymes.
"Now is a good time for businesses, agricultural interests and every resident to re-evaluate the potential for flooding of property and consider potential strategies for mitigation and protection," Grymes says.
Why now? Grymes points out that although many of the state's major rainstorms have been linked to tropical weather, history indicates that river-basin floods are tied to winter and spring storm systems rather than tropical storms and hurricanes.
So the question becomes: What is the climate outlook for the upcoming months in Louisiana?
Early 2005 seasonal projections for Louisiana, issued by the National Weather Service's Climate Prediction Center (NWS/CPC), www.cpc.ncep.noaa.gov, indicate that near-normal to wetter-than-normal weather is anticipated through the first quarter of 2005. Temperature forecasts lean to near-normal or cooler-than-normal seasonal temperatures for the same period.
"These NWS/CPC projections, however, offer no indication of ‘how wet’ or ‘how cool,’" Grymes notes.
Their projections are driven principally by the development of a weak El Niño, the warmer-than-normal sea-surface temperatures over portions of the central Pacific Ocean.
Grymes explains the El Niño works like this: changes in the location and/or presence of warmer-than-normal surface waters in the ocean basin affect the motion of the atmosphere above the basin. A change in the flow of the atmosphere over the Pacific results in "downstream" changes to the motion and position of jet streams over the United States. Jet stream behavior is the driving force behind winter and spring storm systems.
Winters and springs for much of the Gulf Coast have been cooler and wetter than normal during El Niño. The 1997-98 El Niño, for example, resulted in an average January-April rainfall in Louisiana of more than 27 inches, compared to a norm of less than 20 inches. Although all of Louisiana is affected by El Niño, precipitation is most pronounced across the southern parishes, where winter-spring rain is sometimes double that of non-El Niño years.
Roughly one in five winters coincides with the presence of El Niño, but it is important to note that not all El Niño events are identical in their development and intensity, Grymes cautions. The presence of El Niño offers guidance, but it does not guarantee wet and/or cool weather. In fact, Grymes notes that although uncommon, a few El Niño winters and springs have been drier than normal for our state.
This season's El Niño is rated as "weak" by most groups that track the progress of these ocean-atmosphere features. In fact, Grymes says a few climate scientists argue that this may not truly be an El Niño at all.
"Still, even with all the 'what-ifs' involved, there is good reason to anticipate near-normal to wetter-than-normal weather through the first three to five months of 2005," Grymes says, adding, "From the state as a whole, there is about a seven in 10 chance that rainfall will range between near-normal or above-normal over the next months, with that likelihood running a bit higher for the southern third of the state."
For information on related topics, visit the AgCenter Web site at www.lsuagcenter.com/. For local information and educational programs, contact an extension agent in your parish LSU AgCenter office.