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Climate Prediction Center


May - July 2013


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Latest Seasonal Assessment - The Drought Outlook for May 2 - July 31, 2013 is based primarily on short-, medium-, and long-range forecasts, initial conditions, and climatology. Several inches of rain fell in the past two weeks across portions of the Carolinas, Georgia, and parts of Florida eliminating some of the remaining areas of drought. Improvement is indicated for the continuing drought area in north-central Florida due to short-term rainfall and the approaching onset of the rainy season. Improvement is forecast across the upper Mississippi Valley and the lower Plains, due to frontal activity and/or the seasonal upswing in nocturnal thunderstorm activity. Limited drought improvement is anticipated over much of the High Plains. Drought is forecast to either develop or persist across the western contiguous U.S. as this region enters its dry season. Some improvement is expected for the drought area across northern Alaska, while areas of persistence and development of drought are anticipated for the Hawaiian Islands.

Discussion for the Seasonal Drought Outlook

Tools used in the U.S. Drought Outlook (USDO) included the updated CPC temperature and precipitation outlooks for May 2013, the CPC seasonal temperature and precipitation outlooks from May through July 2013, various short- and medium-range forecasts and models such as the 5-day and experimental 7-day WPC precipitation totals (released May 1), 6-10 day and 8-14 day forecasts (released May 1), the NAEFS precipitation outlooks, the soil moisture tools based on the Constructed Analog on Soil (CAS) moisture, dynamical models (CFSv2, NMME, and IMME), the 384-hour total precipitation forecasts from several runs of the GFS, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions.

In the past 2 weeks, rainfall amounts of 2-4 inches across parts of the Carolinas and Georgia continued to alleviate drought conditions in these areas. Levels on Lake Lanier have recovered nicely, and are now 1.3 feet above full conservation pool (defined as the water below the normal maximum level of a reservoir). Additional improvement is likely, according to CPCs 6-10 day, 8-14 day, and updated 30-day precipitation outlooks. During this same period, Florida received widespread 0.5 - 2 inch rains (locally heavier). According to the U.S. Army Corps of Engineers, the level of Lake Okeechobee (as of April 30) is at 13.4 feet which is slightly below average for this time of year. Additional improvement is anticipated across Florida due to short-term rainfall and the traditional onset of Florida's rainy season only 3-4 weeks away.
Forecast confidence for the Southeast is moderate to high.

During the past two weeks, most of the western half of Texas received little if any rainfall. Moderate rainfall (0.5 1.5 inches) was reported over northeastern Texas, and heavy rain (2-4 inches, locally as much as 4-6 inches) fell near the coast of southeastern Texas. According to NCEPs NLDAS Ensemble Mean of various soil moisture models (April 26), soil moisture values for the past week (root-zone) are at or below the 5th percentile across much of far southern Texas and western portions of the panhandle, extending northward to include southeastern Colorado and western Kansas. Stream flows are generally running below to much-below normal across the southern half of the Great Plains, with the exception of near-normal stream flows in central and eastern Oklahoma, and above to much-above normal near the Texas coast. The Weather Prediction Center (WPC) precipitation forecast for the ensuing 7-day period calls for little if any rainfall across most of Texas, with up to an inch expected over north-central parts of the state. Moderate to heavy precipitation (0.5 2.5 inches) is predicted for Oklahoma and Kansas, with the heaviest amounts in northeastern Kansas. In general, the best chances for continuing drought relief are over the lower Plains, though southern stream short-wave energy may bring some relief in the extended-range (6-10 day and 8-14 day) period to the southern High Plains region.
Forecast confidence for the southern halves of the Plains and Mississippi Valley is moderate.

Across the northern halves of the Great Plains and Mississippi Valley, temperatures for the past 30 days have averaged about 6-10 degrees below normal. However, in recent days, high temperatures have reached into the 70s and low 80s in many areas, resulting in the rapid melting of almost all of the deep and extensive snow cover that was over the region. According to the National Operational Hydrologic Remote Sensing Center on May 1, significant snow cover lingers only over portions of northeastern Minnesota and the western third of Upper Michigan. Snow-water equivalent values range from 2 to 6 inches across this area. Frozen soil had significantly delayed the onset of the planting season, and even as recently as two weeks ago, there was much uncertainty as to how effectively melting snow would be able to percolate into the soil. Very dry antecedent soil moisture conditions have permitted excellent infiltration of melted snow-water into the top soil layers. This has resulted in less-than-anticipated flooding, and has permitted some spring planting. The May-July season is typically a relatively wet time of year for this area, due in part to passing frontal systems and nocturnal thunderstorm clusters (MCSs). Improvement is deemed the best bet for the eastern portions of both the Dakotas and Nebraska, and the upper Mississippi Valley, with Some Improvement thought to be most likely for much of the remainder of this region.
Forecast confidence for the northern halves of the Great Plains and Mississippi Valley is moderate.

Drought persistence is expected for western Colorado, most of New Mexico, Utah, Nevada, and Arizona due to below average snow-water equivalent values (generally at or below 75 percent of normal), below average stream flows forecast for spring and summer, and climatology. Eastern Colorado continues to experience a prolonged cold and snowy spring. The storm system currently moving through the region is forecast to bring 6 inches or more of new snow to Denver and the surrounding foothills of the Front Range. In the extended-range period (days 6-14), southern stream short-wave energy is expected to bring additional opportunities for more precipitation.
Forecast confidence for Colorado, New Mexico, Utah, Nevada, and Arizona is moderate to high.

Snow-water equivalent values are well-below average across California, and southern and eastern Oregon. By late spring, climatological prospects for precipitation in the region decrease rapidly. Persistence of drought is the most likely forecast.
Forecast confidence for California and Oregon is high.

Snow-water equivalent values are running close to average across the northern Rockies (as of May 1). Precipitation anomalies for the past two weeks, as well as regional stream flows for the same period, show a slight tilt toward drier-than-normal conditions. The precipitation outlook for all time periods favors the continuation of relatively dry conditions. However, this region typically receives about 50-55 percent of its annual precipitation during the May-July season, which suggests that moderate (as opposed to high) confidence is warranted.
Forecast confidence for the northern Rockies is moderate.

No changes appear necessary to the Alaska depiction.
Forecast confidence in Alaska is moderate.

The Hawaiian depiction continues to show drought persistence over the leeward portions of the Islands from Oahu southeastward to the Big Island, and drought development is still expected across the windward areas from Molokai to the Big Island. As May through July is typically part of the dry season for Hawaii, no alterations to the current depiction appear warranted.
Forecast confidence in Hawaii is moderate to high.

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Page Author: Climate Prediction Center Internet Team
Page last modified: May 2, 2013
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