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Climate Prediction Center


February - April 2012


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Latest Seasonal Assessment - The updated drought outlook for February 2 - April 30, 2012 was based upon climate anomalies associated with La Niña, short to medium range forecasts, climatology, and initial conditions. Since the last FMA’12 USDO on Jan. 19, heavy precipitation finally paid a visit to the Northwest after near-record dryness during December and early January. SNOTEL Water-Year-to-date basin-averaged precipitation rose from 40-75 percent of normal on Jan. 16 to 60-110 in Washington, Oregon, and southern Idaho on Jan. 30. Farther south, values increased in California’s Sierra Nevada and northern parts of Nevada and Utah, rising from 25-65 percent of normal on Jan. 16 to 50-85 percent on Jan. 30. Basin average snow water content (SWC) also increased as well, approximately doubling from the Jan. 16 amount; however, the SWC totals were still below normal across much of the region. In contrast, little or no precipitation fell across southern California, southern Nevada, and most of Arizona and New Mexico during the past 2 weeks. Farther east, more precipitation in the south-central Plains and the Southeast brought additional drought relief to Oklahoma, Texas, and the northern edge of the drought area in the Southeast. Meanwhile, subnormal precipitation fell on southern Texas and from Florida northward to the mid-Atlantic.

The ongoing La Niña event favors drought persistence and development for the next 3 months across the southern tier of States, from southern California eastward into Florida and northward into the Carolinas. Much of this same area will also have enhanced odds for above-normal temperatures (from Arizona and Utah eastward to the Carolinas and mid-Atlantic). Although the Northwest finally received ample precipitation during the past two weeks (usually expected in the Northwest during a La Niña), moderate drought still lingered in eastern Washington, southern Oregon, most of California and Nevada, and central Utah from a very dry start to the winter season. Unfortunately, short and medium-term forecasts maintain an upper-air ridge (high pressure) over the Far West, diverting the storms to the north and keeping decent moisture away from the region. And with another normally wet month (Feb) looking less so, the odds for significant drought improvement were lowered. Therefore, this outlook is more pessimistic toward drought recovery in northern California and Nevada, with less improvement and more persistence in these areas as compared to the Jan. 19 FMA USDO. To the south, despite early winter snowfall in Arizona and New Mexico, the odds for subnormal precipitation and above-normal temperatures across the Southwest are elevated in the monthly and seasonal outlooks. Therefore, persistence or development is forecasted across most of California, the Great Basin, Southwest, and southern Plains. Some improvement is possible along the northern drought boundary in the central Great Plains and lower Delta with expected short-term moderate to heavy precipitation, favorable odds of above-normal February and FMA precipitation in the middle Mississippi, Ohio, and Tennessee Valleys, and persistent bouts of wet weather in this area since mid-October. Farther south and east, however, recent dryness and favorable odds of subnormal precipitation in the short and long-term maintains drought along the Gulf and southern Atlantic Coasts and expands it into the mid-Atlantic Coast. A dry (and cold) winter climatology, much below-normal precipitation (minimal snow) since the Fall, and equal odd chances (1- and 3-month outlooks) elevates the chances for persistence across the western Corn Belt and upper Midwest, with drought expansion possible in the central Dakotas. Lastly, an updated study found that recent La Niñas in Hawaii brought drier conditions than earlier events, meaning fewer events in wet tercile but not necessarily in the dry tercile. And since 4 out of 7 wet season months have already occurred and the drought has worsened, Improvement was not used. But since Hawaii can still get above-normal rainfall during the next 3 months which may be enough for a 1-category drought improvement by April 30, using Persistence was too strong in the other direction. Therefore, Some Improvement was the best forecast.

Discussion for the Seasonal Drought Outlook

Tools used in the U.S. Drought Outlook (USDO) included the official updated CPC temperature and precipitation outlooks for and the long lead forecast for February through April 2012, various medium- and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the most recent 384-hour 12Z GFS total precipitation amounts, the soil moisture tools based on the GFS model and the Constructed Analogue on Soil (CAS) moisture, the Climate Forecast System (CFS, versions 1 and 2) and the National Multi-Model Ensemble (NMME) seasonal precipitation forecasts, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions, composite standardized precipitation and temperature seasonal (FMA) anomalies for all La Niña episodes and for a smaller set of back to back La Niña years, and an updated recent study on precipitation in Hawaii during La Niña, El Niño, and Neutral condition events.

Since the La Niña event of 2010-2011, widespread moderate to extreme drought remains entrenched across parts of the Southeast. La Niña conditions returned during fall 2011 and are expected to persist throughout the outlook period. Drier conditions have recently spread northward along the Atlantic Coast into the Delmarva Peninsula where D1 was just introduced this week in the U.S. Drought Monitor. In the short-term (Days 1-5), above-normal precipitation is expected from eastern Texas to southern Mississippi and northeastward into the central Appalachians, and this may provide some temporary short-term drought relief in the lower Delta and northern drought edge in the Southeast. Precipitation tools after this (6-10 day, 8-14 day, 384-hour GFS, 1- and 3-months), however, favor below median precipitation across the Southeast and southern Atlantic Coasts which is consistent with a La Niña event. Persistence or development can be expected across these areas. But with favorable odds for above-normal precipitation at 1- and 3-months in the middle Mississippi, Ohio, and Tennessee Valleys and Great Lakes region lurking just to the north of this region, plus frequent bouts of wet weather since November in the lower Mississippi Valley and northern portions of the Southeast, the gradient between improvement, persistence, and development is very tight, making the forecast for the lower Mississippi Valley and central Gulf Coast States difficult.
Forecast confidence for the Delmarva Peninsula, Virginia, the Carolinas, and Georgia is moderate; low to moderate for central Gulf Coast and lower Mississippi valley (Alabama, Mississippi, and Louisiana).

Although a wet late summer and early fall rainy season greatly eased drought conditions across the Florida peninsula, the return of La Niña strongly favors drought development in central and south Florida. The probabilities of below median rainfall for FMA are greater than 60 percent in the southern half of the state, and this is Florida’s normal dry season (winter to early spring). Since the initial FMA outlook, moderate drought (D1) has expanded southward into central and extreme southern sections of Florida with abnormal dryness now covered all of the state. Severe to extreme drought continued across parts of the Florida Panhandle which missed the surplus summer and early fall rainfall. The average water level at Lake Okeechobee (13.26 feet) was still 1.39 feet below normal on Jan. 31. La Niña composites and the CPC February and February–April outlooks also indicate a high probability for below median precipitation across the Florida Panhandle where persistence is forecast.
Forecast confidence for Florida is high.

Across the central and southern Plains, additional surplus precipitation since the last USDO (Jan. 19) brought further drought relief to most of Texas and Oklahoma. Unfortunately, dry weather was observed in eastern New Mexico, southern and northwestern Texas, the Oklahoma Panhandle, southeastern Colorado, and Kansas. With odds for above-normal temperatures (1- and 3-month outlooks) and subnormal precipitation (e.g. La Niña composites and precipitation tools), persistence is favored across much of the southern Plains, with development in Texas areas currently without drought. Although the 6-10 and 8-14 day outlooks favor above-normal rainfall in extreme southern Texas, the long-term drought conditions and high probabilities for subnormal rainfall during a La Niña outweighed suggestions for Some Improvement, thus persistence was kept in this region. However, some improvement is forecast across eastern parts of Kansas and Oklahoma and the Arklatex region where the CPC seasonal outlook indicates equal chances for below, near, or above precipitation, the 1-5 day HPC forecast indicates moderate to heavy totals, and numerous bouts of wet weather have frequented these areas since late October, improving or erasing drought.
Forecast confidence for the southern High Plains is high, and moderate for areas to the east (e.g. southeast Kansas, eastern Oklahoma, and eastern Texas).

From mid-November into December, shortwave troughs digging into the desert Southwest have resulted in widespread moderate to heavy snow across the higher elevations of Arizona and New Mexico, and above-normal precipitation at lower elevation locations. As of January 16, water year to date (since Oct. 1) basin average snow water content (SWC) and precipitation were running above average across the mountains of Arizona and New Mexico. However, the values have slowly declined as little or no precipitation has fallen since late December, and temperatures have averaged above normal during January. Still, Jan. 30 basin averaged precipitation and SWC were close to normal in Arizona and above-normal in New Mexico. To the west, however, conditions have been drier in southern sections of California and Nevada, and D0 and D1 has expanded into this region. Precipitation tools on all time scales favor below median precipitation which is typical for a La Niña winter. In addition, the odds for above-normal FMA temperatures are favorable, especially in eastern sections of the Southwest. Therefore, drought persistence is forecast across the Southwest, with development in areas to the north (southeastern California, western Arizona, and southern sections of Nevada, Utah, and Colorado).
Forecast confidence for the Southwest is moderate to high.

In mid-January, a surprising lack of early winter precipitation (not expected during a La Niña) in the Northwest resulted in the introduction of severe drought (D2) to the Sierra Nevadas, moderate drought (D1) from central California northward into central Washington and eastward into northwestern Nevada, and an expansion of abnormal dryness (D0) across the Great Basin and into most of Idaho and northern Utah. Since then, however, heavy precipitation during the past 2 weeks has somewhat eased drought conditions in the Northwest and Sierra Nevada. As of January 16, snow water content values were less than 15 percent of average in the Sierras and 24 to 38 percent of average in the southern Cascades, but 2 weeks later had increased to 38 and 60 percent, respectively. It should be noted that reservoir levels have not suffered yet due to the surplus 2010-11 winter precipitation and cool and wet spring. Unfortunately, the wet weather missed the southern sections of California and Nevada, and conditions have deteriorated. In addition, drier weather has returned to the Far West, and the short to medium range forecasts (including the updated February outlook) indicate subnormal precipitation for the area. Although there is a moderate signal for wetness among the various longer-lead precipitation tools in the Northwest including northern California, the increasing odds for a drier February have led to a more pessimistic forecast for northern California. Therefore, improvement is limited to areas farther north (e.g. Washington and Oregon), with only some improvement in northern California. Persistence is favored across the rest of California and Nevada, with development in the non-drought areas of those two states and into Utah. The drought development is based on La Niña composites and the CPC monthly and seasonal precipitation outlooks that indicated a tilt in the odds towards below median precipitation.
Forecast confidence for California and the Great Basin is moderate in the north, moderate to high in the south.

Drought coverage and intensity has remained nearly steady across the western Corn Belt and upper Mississippi Valley since the previous outlook of January 5. The CPC February and February-April outlooks indicated equal chances for below, near, or above median precipitation, except for slight above-normal FMA precipitation odds in the western Great Lakes region. However, a dry climatology limits prospects for significant drought relief, and very dry (little or no snow) and mild conditions since the Fall will require excessive precipitation for any relief. In addition, since the ground and streams in this region freeze over during the winter months, it is likely that the benefits of improved moisture would not be realized until the spring thaw which normally occurs in March or April. Therefore, persistence is favored across much of the western Corn Belt and upper Midwest, with some possible expansion into North Dakota based upon current conditions (90-day precipitation between 25 and 50 percent of normal).
Forecast confidence for the western Corn Belt and upper Midwest is moderate.

Drought redeveloped during the summer months across the western portions of the Hawaii, but recent winter rainfall reduced drought coverage across Kauai and Oahu. Farther east, adequate rainfall did fall on the windward sides of Maui, Molokai, and the Big Island, but have yet to materialize on the leeward sides of these islands during this La Niña event. Traditionally, a La Niña event was thought to bring surplus rainfall to Hawaii. However, an updated study found that recent La Niña events (past 30 years) brought drier conditions than earlier La Niña events (1957-1986), meaning fewer events in the wet tercile but not necessarily in the dry tercile. And with 4 of 7 wet season months already finished and the drought worsening, improvement is not appropriate. But since Hawaii can still get above-normal rainfall during the next 3 months, persistence is not correct either. Instead, some drought improvement is forecasted for the leeward sides of the Hawaiian Islands, with improvement for the windward side of Oahu.
Forecast confidence for the Hawaii is moderate.

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Page Author: Climate Prediction Center Internet Team
Page last modified: March 19, 2012
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