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Climate Prediction Center


March - May 2012


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Latest Seasonal Assessment - The drought outlook for February 16 – May 31, 2012 is based on short-, medium-, and long-range forecasts, climate anomalies associated with a weakening La Niña, initial conditions, and climatology. Since the release of the previous drought outlook on February 2, 2012, significant precipitation has fallen across the Pacific Northwest, portions of the Rockies, the southern Plains, the lower Mississippi Valley, and the central Gulf Coast region. The Climate Prediction Center (CPC) predicts a tilt in the odds for above-normal temperatures for most areas east of the Continental Divide in March, and enhanced odds for below-normal temperatures across the West Coast states and the southern two-thirds of Alaska. This general pattern is also anticipated for the March-May 2012 season, though with increased odds for above-normal temperatures across the Southwest. For precipitation, there is a tilt in the odds for wetter-than-normal conditions across the Pacific Northwest and the southern Alaska Panhandle in March, and for a fairly large area encompassing the Great Lakes, the Ohio Valley, and eastern portions of the upper and middle Mississippi Valley. In general, these same regions are expected to receive above-median precipitation during the March-May 2012 period, though with reduced coverage. Unfortunately, most of the anticipated precipitation is forecast to fall just east and southeast of where it is needed most in the upper Midwest. Most indicators support a westward expansion of dryness across the Dakotas. The CPC precipitation forecast for March also calls for elevated odds of below-median precipitation across most of California, the Southwest, and the Gulf Coast and southern Atlantic Coast regions. For the March-May 2012 forecast period, the same general areas are expected to receive below-median precipitation, though with the addition of south-central and southeastern Alaska. However, for Texas and the Gulf Coast region, the upcoming 5-7 days is likely to feature heavy to very heavy precipitation (2”-5”), which should provide at least temporary, short-term drought relief, but may have little impact on longer-term hydrologic deficits. In Hawaii, improvement is forecast for Oahu, with some improvement considered most likely for the leeward slopes of Maui, Molokai , Lanai, and the Big Island.

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 March 2012 and the long lead forecast for March through May 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 (MAM) 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 but are expected to diminish throughout this outlook period. Drier conditions have recently spread northward along the Atlantic Coast into the Delmarva Peninsula where D1 was recently introduced in the U.S. Drought Monitor. In the next two weeks, near- to above-normal precipitation is expected from eastern Texas eastward and northeastward across the Gulf Coast states and the Carolinas. This may provide some temporary short-term drought relief in the lower Delta and northern drought edge in the Southeast. Precipitation tools after this (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 parts of 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 Gulf Coast states from Louisiana eastward, and the southern and middle Atlantic Coast states is moderate.

Although a wet late summer and early fall rainy season greatly eased drought conditions across the Florida peninsula, the return of La Niña continues to favor drought development and persistence in central and south Florida. The probabilities of below median rainfall for MAM are greater than 50 percent across most of peninsular Florida, and this is Florida’s normal dry season (winter to early spring). 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 (13.14 feet) was still 1.44 feet below normal on February 13 ( South Florida Water Management District ), slightly lower than two weeks ago (13.26 feet, 1.39 feet below normal). La Niña composites and the CPC March and March–May outlooks also indicate a moderately 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, near- to above-normal precipitation received since the last USDO (issued Feb. 2) brought further drought relief to much of eastern and southern Texas, and eastern Oklahoma. Unfortunately, dry weather was observed in eastern New Mexico, western Texas, the Oklahoma Panhandle, southeastern Colorado, and Kansas. Odds are elevated across the region for above-normal temperatures (1- and 3-month outlooks). For precipitation, the monthly and seasonal forecasts generally favor below-median precipitation across the central and southern High Plains and Gulf Coast region, with Equal Chances (EC) for below-, near-, and above-median precipitation elsewhere. In the next 5-7 days, heavy precipitation is expected across a good portion of eastern Texas, which will benefit the region at least in the short-term. Once the predicted storm system moves through the area, it will be possible to evaluate its impact on the long-term drought situation.
Forecast confidence for the central and southern Great Plains is moderate.

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 February 13, water year to date (since Oct. 1) percent of normal precipitation (PNP) was running close to average across the mountains of Arizona and New Mexico. Basin average snow water content (SWC) ranged from 75-125 percent of normal throughout most of New Mexico, and generally 50-75 percent of normal across the Mogollon Rim of central Arizona. Temperatures have averaged above normal during January and the first half of February for Arizona, and up until a week ago, the same was true of New Mexico (below-normal temperatures have prevailed over eastern New Mexico during the past 7-days). Farther west, conditions have been drier in southern sections of California and Nevada. 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 MAM 2012 temperatures are favorable. 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, heavy rain and snow finally fell across the Northwest, after an unusually dry mid-November 2011 to mid-January 2012 period, which is very uncharacteristic of cold season La Niñas. Precipitation amounts returned to normal across much of Washington, northern California, and interior Oregon, with surplus precipitation for coastal Oregon. Heavy snow, freezing rain, and strong winds accompanied this series of storms. Though it is common for the coastal ranges and Cascades to receive heavy snowfall during the winter, even the lowlands of western Washington received significant snowfall (6.8” measured at Sea-Tac International Airport; up to 18” over southwestern Washington). Winds along the Oregon coast also peaked in excess of 100 mph. Dry weather returned to the Northwest, though lately more precipitation has fallen across the region. As of February 14th, Snow Water Content (SWC) values are currently 90-110 percent of average in the Washington Cascades, 50-90 percent of average in the Oregon Cascades, and only 25-50 percent of average farther south in the Sierras. 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. Although there is a moderate signal for wetness among the various longer-lead precipitation tools in the Northwest, the outlook for northern California is less optimistic. Therefore, improvement is limited to areas farther north (e.g. Washington and Oregon), with only some improvement in northern California. Todays 12z GFS model 384-hour total precipitation forecast map depicts the heavier precipitation amounts over western portions of Washington and Oregon, with significantly less precipitation across 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 the Pacific Northwest is moderate; for California and the Great Basin it is moderate to high.

Drought coverage and intensity has remained nearly steady across the western Corn Belt and upper Mississippi Valley since the previous outlook issued February 2nd. The CPC March 2012 outlook predicts only a slight tilt in the odds toward above-median precipitation in this region, with the MAM 2012 seasonal outlook anticipating Equal Chances (EC). 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, the most likely category is thought to be persistence, with dryness developing westward across the Dakotas.
Forecast confidence for the western Corn Belt and upper Midwest is moderate.

Drought redeveloped during the summer months across the western portions of 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 4.5 of 7 wet season months already finished and the drought worsening, some improvement may be a bit optimistic for most leeward locations, with improvement a better bet for Oahu.
Forecast confidence for Hawaii is moderate.

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Page Author: Climate Prediction Center Internet Team
Page last modified: March 1, 2012
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