Drought Summary for the Western United States Up-dated January 31, 2012
NOAA Drought Summary for the Western United States Up-dated January 31, 2012
Western U.S.: After last week's much-needed precipitation, dry weather returned from central California into the Four Corners Region. From southern California into southern Nevada and northwestern Arizona, Moderate Drought (D1) was introduced to reflect very low water-year-to-date precipitation (locally below 25 percent of normal) as well as declining snow water percentiles. The new D1 area also corresponds with the latest 3- and 6-month Standardized Precipitation Indices (SPI), which depict D1 conditions or worse in these same locales. Additionally, Abnormal Dryness (D0) was expanded to include much of southern California, where seasonal rainfall has totaled less than 50 percent of normal. Despite beneficial snowfall in the Sierra last week, snow water equivalent remained in the 20th percentile or lower, indicating this region may fall rapidly back into Severe Drought (D2) if additional snow does not fall soon.
In northern portions of the region, another round of moderate to heavy mountain snow (2-10 inches liquid equivalent) maintained favorable spring runoff prospects from the Klamath Mountains northward into the Cascades. However, the core Moderate Drought (D1) area received little if any precipitation, with no change made to this area. Additional snow (0.5-2.5 inches liquid equivalent) boosted snow water equivalents (SWE) in central and northern Idaho above the 40th percentile, although the D0 (Abnormal Dryness) area of southeastern Idaho – where SWE remained in the 20th percentile or lower – was mostly dry. In Montana, D0 was expanded into the southwestern quarter of the state to reflect SWE that ranged from the 10th to the 30th percentile. Northwestern Montana – in particular Flathead County – was a candidate for D0 introduction due to SWE locally in the 20th percentile or lower, but much-needed precipitation (1-4 inches liquid equivalent) provided a reprieve. There were no changes made to the drought designation in the central Rockies following last week's introduction of Moderate Drought; this region will be reassessed pending the final result of an approaching storm system.
Looking Ahead: A disturbance will race across the southeastern quarter of the nation, producing light to moderate rain over the central and southern Atlantic Coast States. However, rain is expected to rapidly diminish as it approaches the drought areas of southern Georgia and Florida. Meanwhile, an upper-air disturbance will trigger light to moderate snow across the central and northern Rockies. As this feature reaches the Plains, a storm will rapidly develop and intensify, generating increasingly heavy rain and snow from the central Plains into the Corn Belt, while a trailing cold front triggers showers and thunderstorms from central Texas into the Delta and interior Southeast. Little if any precipitation is expected in Florida and from California into the southern Rockies. Likewise, drought areas of the Upper Midwest will also remain dry. The CPC 6-10 day forecast for February 7-11 calls for drier-than-normal conditions from the Pacific Coast States eastward into the mid-Mississippi River Valley and Southeast, with wetter-than-normal conditions confined to southern Texas and the eastern Great Lakes. Warmer-than-normal weather from the central and northern Plains to the Pacific Coast will contrast with below-normal temperatures in the Gulf and southern Atlantic Coast States.
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| Dryness Categories |
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D0 ... Abnormally Dry ... used for areas showing dryness but not yet in drought, or for areas recovering from drought. |
