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March - May 2012

 

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Latest Seasonal Assessment - The drought outlook for March 1 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 16, 2012, significant precipitation has fallen across the Pacific Northwest, portions of the Rockies, eastern Texas, the western and central Gulf Coast region, the Tennessee Valley, the mid-Atlantic region, and the Dakotas/Upper Midwest region. The Climate Prediction Center (CPC) predicts a tilt in the odds for above-normal temperatures for areas east of the Continental Divide in March, and enhanced odds for below-normal temperatures across the West Coast states and all of Alaska. This general pattern is also anticipated for the March-May 2012 season, though with less coverage of below-normal temperatures over the West and Alaska, and somewhat reduced coverage of above-normal temperatures across the CONUS. For precipitation, there is a tilt in the odds for wetter-than-normal conditions across the Pacific Northwest and northern Rockies, the Alaska Panhandle, and southwest Alaska in March, and for a fairly large area encompassing the Great Lakes, the Ohio and Tennessee Valleys, and eastern portions of the upper and middle Mississippi Valley. The March-May precipitation outlook calls for a tilt in the odds for wetter-than-normal conditions across western Washington, the Great Lakes, and the Ohio Valley. Prospects for drier-than-normal conditions for both March 2012 and March-May 2012 are elevated over the Southwest, the southern and central High Plains, the immediate Gulf Coast, and Florida. In Hawaii, with the wet season and the current La Niña beginning to wind down, some improvement in drought conditions is deemed the best bet, with limited relief anticipated.

 
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 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 Analog 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. During the next 5 days, heavy precipitation (1.5 - 3.5 inches) is predicted from the lower Mississippi Valley and central Gulf Coast region northeastward into the mid-Atlantic region. This rainfall should provide short-term relief for the northernmost portions of the drought area in the Southeast, including northern and central Georgia, and western portions of the Carolinas. From southern Georgia and southern Alabama southward across Florida however, little precipitation is expected. In Florida, extensive and persistent drought covers all but far southern parts of the state. With La Nina expected to wane, and the height of the dry season approaching, it does not appear that Florida will experience significant drought relief any time soon. The average water level at Lake Okeechobee has fallen to 12.99 feet (down from 13.14 feet two weeks ago), and is 1.54 feet below normal as of February 29th (South Florida Water Management District, www.sfwmd.gov). The same general precipitation pattern is anticipated across Florida and the rest of the Southeast U.S. for both the updated March precipitation outlook, and the March-May seasonal precipitation outlook. Therefore, the odds favor drought persistence across Florida and the Southern Atlantic Coastal Plain, with some improvement indicated for interior areas.
Forecast confidence for the Gulf Coast states from Louisiana eastward, and the southern and middle Atlantic Coast states is moderate. Forecast confidence for Florida is moderate to high.

Almost two weeks ago, very beneficial heavy precipitation fell across eastern portions of Texas, associated with a significant low pressure system that tracked across the western and central Gulf states. In the past week though, little if any precipitation has fallen across Texas, as well as Oklahoma. The concern now is that the unexpected beneficial precipitation received over the past 1-2 months, may be giving way to a drier pattern, aided by an increasingly dry climatology. The central and southern High Plains has been fairly dry during the past few weeks. In the next 5 days, up to 0.25-inch of rain is forecast across eastern portions of Texas, though extreme eastern Texas could receive up to 0.50-inch of rain. Little if any precipitation is predicted for the remainder of the south-central U.S. Odds are elevated across the region for above-normal temperatures (1- and 3-month outlooks). For precipitation, the updated CPC monthly outlook, as well as the seasonal outlook for March-May issued February 16th, favors below-median precipitation across the central and southern High Plains, and most of Texas, with Equal Chances (EC) expected for eastern sections of both Kansas and Oklahoma, and northeastern Texas.
Forecast confidence for the central and southern Great Plains is moderate.

From mid-November into December, shortwave troughs digging into the desert Southwest brought 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 29, Water-Year-To-Date (WYTD, since Oct. 1) percent of normal precipitation (PNP) was running close to average (70 to 120 percent of normal) across the mountains of Arizona and New Mexico. Over most of Utah and Colorado, PNPs ranged between 70 and 110 percent of normal. Moving westward toward the California Sierras, the PNP values dropped off sharply, reaching only 40-45 percent of normal in far western Nevada. Basin average snow water content (SWC) varied widely across Arizona (25-110 percent of normal) and New Mexico (50-125 percent of normal). Both Colorado and Utah SWC values generally ranged from 50-90 percent of normal, though western portions of the central Great Basin and the Sierras reported SWCs between 25 and 50 percent of normal. Most of the Southwest during the past 30 days has experienced above-normal temperatures, in some cases as high as 5 degrees F above-normal for the monthly average. For the March 2012 and the March-May 2012 periods, prognostic tools such as the National Multi-Model Ensemble (NMME), both versions of the Climate Forecast System coupled model (CFSv1 and CFSv2), and the official CPC Outlooks favor elevated odds of above-normal temperatures and below-median precipitation across the Southwest. Therefore, a combination of both persisting and developing drought can be expected.
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 28th, Water-Year-To-Date (WYTD) PNP has ranged from a relative minimum of 50-70 percent of normal across south-central Oregon, to a relative maximum of 90-110 percent of normal over the Washington Cascades and the northern Rockies. Snow Water Content (SWC) values are currently 90-150 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 California 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. Although there is a moderate signal for at least some improvement among the various longer-lead precipitation tools in the Northwest, the outlook for northern California is less optimistic. Some improvement is expected over northwestern California, with drought persistence across the rest of the state. Todays 12z GFS model 384-hour total precipitation forecast map depicts the heavier precipitation amounts over western portions of Washington and Oregon, with somewhat 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 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 in the last 1-2 months. In South Dakota, a recent snowstorm brought a wide range of snow accumulations (1.9 inches at Rapid City, 4 inches at Pierre, 6.4 inches at Aberdeen, and accumulations approaching a foot at Wessington Springs and Miller (24-hours ending this morning at 8am local time)). Some of this water will likely seep into any unfrozen ground (which is possible given the mild winter in this part of the country) while some will either runoff or sublimate as temperatures rebound. Drought development was therefore removed from much of the state because of this significant snowfall event, and also the high Snow Water Equivalent (SWE) values. In the next 5 days, light precipitation (up to 0.25-inch, liquid equivalent) is forecast for eastern portions of the Dakotas, with near-median amounts of precipitation expected for the 6-10 day and 8-14 day periods. The updated CPC precipitation outlook for March favors a slight tilt in the odds for above-median precipitation in the upper Mississippi Valley including eastern North Dakota. The MAM 2012 seasonal outlook calls for Equal Chances (EC) of below-, near-, and above-median precipitation.
Forecast confidence for the western Corn Belt and upper Midwest is moderate.

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. The prospects for late season Kona Lows and bouts of moisture appear to be lessening. Therefore, some improvement may be the best bet for the Islands.
Forecast confidence for Hawaii is moderate.


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