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.
Forecaster: D. Miskus
Next Outlook issued: February 16, 2012 at 8:30 AM EDT |
