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Posted at 01:10 PM ET, 02/22/2013

Historic U.S. drought will continue into spring and summer, experts say


Rain clouds move over the remnants of parched corn stalks on August 22, 2012 near Wiley, on the plains of eastern Colorado. (John Moore - GETTY IMAGES)

Nearly five months after expanding to cover the greatest area on record, the devastating drought of 2012 continues to spread woe across the central and western U.S. And, according to climate researchers, severely dry conditions will persist throughout the spring and summer.

Meteorologist Richard Heim, a drought expert at NOAA’s National Climatic Data Center said, in an interview, that while parts of the U.S. have received substantial precipitation in recent weeks, storms have largely missed the central and southern Plains, two of the areas hardest hit by exceptional drought.

Heim acknowledged the short-term improvement brought about by this week’s major snowstorm in the region, but said the storm’s 1.5-2 inches of liquid equivalent hardly eased drought conditions.


Marion Kujawa looks over a pond he uses to water the cattle on his farm on July 16, 2012 in Ashley, Illinois. Kujawa had been digging the pond deeper after it began to dry up during the drought. (Scott Olson - GETTY IMAGES)

Data certainly highlight the enormous gap between the precipitation that has fallen and the precipitation that would normally fall, revealing shortfalls on the order of 10 to 20 inches since April of last year.

Kansas City, for example, had been running a precipitation deficit of nearly 19.5 inches from April 1, 2012, through February 7 (according to statistics provided by the NWS forecast office serving the city). While the recent storm achieved a daily snowfall record of just over eight inches on Thursday, only about 1.5 inches of liquid equivalent precipitation have fallen in Kansas City since the 7th (shaving the deficit to a still staggering 18 inches).

What’s more, Heim contends the benefit of the heavy snow will be compromised somewhat by the time of year. Cold winter temperatures have frozen the topsoil over much of the Plains, which will limit the amount of snow that will sink into the ground. A soaking rain in the spring with its warmer soil temperatures would provide greater drought relief as the ground absorbs more of the moisture.

Updated statistics from the U.S. Drought Monitor show that nearly 56 percent of the contiguous U.S. is currently in drought. Heim says this value is the highest that’s ever been recorded for February (the index dates back to 2000). Though the latest percentage is well off its all-time peak of almost 65.5 percent from September 25 of last year, many of the regional drought statistics continue to impress. One such impressive figure: over 91 percent of the six-state (Kansas, Nebraska, Colorado, Wyoming and both Dakotas) High Plains region remains mired in moderate to exceptional drought. This percentage, too, is off its high-water mark of almost 99 percent from September 25.


The latest Drought Monitor analysis (as of February 19). Recent rains have alleviated drought conditions slightly over the Southeast, but the extreme to exceptional drought remains in place across the High Plains. (U.S. Drought Monitor)

While there will be an opportunity for more snow across the drought-plagued region early next week, most of the Central U.S. is expected to revert to an arid pattern as March begins. This should occur as the North Atlantic Oscillation (NAO) switches to its negative phase and the Pacific-North American (PNA) index trends more strongly positive. The former pattern (or “teleconnection”) should keep storminess suppressed over the Gulf Coast states and along the Eastern Seaboard, while the latter should keep surface high pressure parked over the Rockies and Plains, favoring dry conditions.


Note the long arc of forecast below-normal precipitation extending from the Southwest to the Tennessee Valley for the first week of March. Ridging and a southward displacement of the jet stream are the main culprits. (NWS Climate Prediction Center)

What about the outlook for the spring season, March through May? The National Weather Service’s Climate Prediction Center (CPC) forecasts persistence of the drought throughout most of the High Plains and Western U.S., citing primarily a consensus of dynamical model forecasts.


Areas from the Plains through the West will see drought conditions persist or intensify, according to the CPC. (NWS Climate Prediction Center)

Right now, neither a La Nina or an El Nino pattern - which can exacerbate or alleviate drought conditions - is in place. But what might happen if the eastern equatorial Pacific cools, signifying a renewed La Nina event?


Historic precipitation differences from average (anomalies) during La Nina summers. The La Nina summers (15 total since 1950) chosen for inclusion in this composite have tended to feature below average precipitation in the Plains and Midwest

“If we slip back into La Nina this spring, it’s [the drought] going to get worse,” says Heim. The development of El Nino, on the other hand, would present more of a mixed precipitation signal for the central Plains. These considerations leave Heim to conclude: “So we want El Nino, but we don’t want La Nina.”


Historic precipitation differences from average (anomalies) during El Nino summers. El Nino summers (12 total since 1950) chosen for inclusion in this composite have tended to favor above average precipitation in the Plains and Midwest (NOAA)

Even if El Nino develops by the end of spring or summer, many areas across the central and western U.S. will have to hope for the emergence of a pattern marked by excessive rain at times, perhaps via remnants of a tropical system in the case of the Plains and Midwest. Precipitation amounts needed to the end the drought are staggeringly high, ranging from 16 to 24 inches or more throughout these regions.


(NOAA National Climatic Data Center)

Tony Lupo, a meteorology professor at the University of Missouri, is not optimistic that the Midwest will see much improvement in the drought situation this summer.

“While the La Nina weather pattern has faded, it hasn’t been fully replaced by the much cooler and wetter weather pattern of El Nino,” Lupo said in a news release.

One of the long-lasting drought’s byproducts, depleted soil moisture content, alone will result in above-normal summer temperatures, adds Lupo. The positive feedback from dry ground could work to outmatch any cooling associated with a neutral or El Nino weather pattern should it develop.

Without the cooling provided by high soil moisture and correspondingly high evaporation, Lupo states that afternoon temperatures this summer “could be as much as 10 degrees Fahrenheit higher than average.”

This historic drought shows no signs of abating soon. It may be that the atmosphere will need to transition out of the current cold, or negative, Pacific Decadal Oscillation (PDO) cycle before real relief develops. After all, the severe droughts of the 1930s and 1950s occurred within the cold PDO phase as well. Considering that this period recently started in the 2000s, and that the warm/cold cycles each last for about 30 years, drought could remain a big issue even as its intensity waxes and wanes in the years to come.

* Meteorologist Rick Grow blogs about the weather for The Frederick News-Post . He has a degree in atmospheric sciences from UNC-Asheville and previously worked at MDA EarthSat as a forecaster.

By Rick Grow*  |  01:10 PM ET, 02/22/2013

Categories:  Droughts, Latest, U.S. Weather

 
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