U.S. Seasonal Drought Outlook for Nov. 1 to Jan. 31, 2013 (Text)
Latest Seasonal Assessment - During the previous two weeks, cool, wet weather overspread the northwestern U.S., while showers helped to improve drought conditions across parts of the Midwest. In the East, heavy rains associated with extratropical transitioning Hurricane Sandy erased drought across much of the mid-Atlantic and Northeast, but also caused flooding, wind damage and destructive storm surge. In contrast, abnormal dryness persisted across the central and southern Plains and much of the Southeast, promoting drought persistence and modest expansion outside of some spotty relief in central Texas. During the upcoming three months, enhanced chances of abnormal dryness across the West keep prospects of significant improvement low, though further drought expansion into the Northwest is less likely due to the initial wet conditions and falling probabilities of abnormal dryness in the more recent model data. Some improvement is expected for central and southern California due primarily to the wet season climatology. Some improvement is also expected across the northern tier of the U.S. due to a greater chance of enhanced wetness in November, with further drought reduction possible across parts of North Dakota and Minnesota before the winter freeze. Drought persistence is likely across the remainder of the Plains and the Southwest due to dry seasonal climatology and a dry November outlook. In the East, further improvements are likely across the mid-Atlantic and eastern Corn Belt as the remnants of Sandy stall over the region with additional storminess in the week 2 period, while increasing short term dryness in the interior Southeast make significant improvements less likely despite a tilt towards wetness in the long range outlooks.
Discussion for the Seasonal Drought Outlook
Tools used in the U.S. Drought Outlook (USDO) included the official CPC temperature and precipitation outlooks for November 2012, the long lead forecast for November 2012 through January 2013, various short- and medium-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the NAEFS precipitation outlooks, the soil moisture tools based on the Constructed Analog on Soil (CAS) moisture, the Climate Forecast System (CFS version 2), the 384-hour total precipitation forecasts from several runs of the GFS, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions. Some consideration was also given to the El Niño precipitation anomalies for November through January due to the possibility of a weak El Niño event, but not much.
Heavy rainfall, high elevation snowfall, and below normal temperatures persisted across the Pacific Northwest and northern Rockies during the previous two weeks. Although much of the precipitation fell outside of existing drought areas, there were reductions of drought and abnormal dryness in some locations. Additional precipitation is expected during the upcoming five day period, followed by a pattern change with drier conditions overspreading the region. The updated CPC November outlook indicates enhanced probabilities of below median precipitation for western Oregon, contrasting with enhanced odds of wetness for the front range of the northern Rockies. While the CPC seasonal outlook issued on 18 October maintained abnormal dryness for the Northwest based on a near consensus of model data, more recent runs of the CFS version 2 have suggested reduced probabilities of significant dry anomalies, with even a flip to wet anomalies during December. Based on the wetness extant at the start of the outlook period and the reduced probabilities of dry precipitation anomalies during the November-January period, it is unlikely that significant drought development will occur during the climatologically wet winter months. Therefore, the development area across the Northwest included in the initial outlook has been removed in this update. For existing drought areas, persistence is maintained in deference to the overall dry seasonal outlooks, except across the northern Rockies, where the November outlook tilts the odds towards above median precipitation. Forecast confidence for the Northwest is moderate.
Widespread rain and mountain snows fell across northern California, contrasting with drier, warm conditions in the remainder of the Southwest. Continued precipitation is expected for northern California during the upcoming five days, with dry conditions developing along the coast during the week 2 period. The November-January period is climatologically wet for much of California, and an average wet season has a high probability of ameliorating the current drought conditions, particularly across central and southern California. The CPC update November outlook, however, places enhanced probabilities of abnormal dryness throughout California and the desert Southwest, and while the CPC seasonal outlook maintains equal chances, recent guidance such as the CFS version 2 predict a moderate to robust dry precipitation anomaly for the three month period. Based on the dry trending guidance, coupled with diminishing chances of a substantive El Niño event, drought reduction during the rainy season becomes less likely. Therefore, some improvement is forecast for central California, with persistence across the remainder of the Southwest. Forecast confidence for the Southwest is moderate.
Dry weather dominated much of the Plains during the previous two weeks, with a winter storm in the Midwest generating strong winds and dust storms. The only exception was across the eastern Dakotas, where widespread precipitation eased drought conditions along the Red River Valley. The November-January period is climatologically dry along the Plains, which reduces the impact of precipitation anomalies. A similar pattern is expected over the next two weeks, with wet conditions across the Dakotas contrasting with drier weather for the remainder of the Plains. A drier signal for the upper Midwest is suggested by the CPC seasonal outlook, but November precipitation would allow soils and streams to recharge ahead of the winter freeze. Therefore, some improvement is expected across the northern Plains, with further improvements likely for central North Dakota through western Minnesota. In contrast, drought persistence is expected for the remainder of the Plains states, particularly across the southern High Plains, where November probabilities of abnormal dryness are the greatest. Forecast confidence for the Plains is moderate to high.
Scattered showers fell across central and eastern Texas, further eroding drought in areas that had received previous rainfall. Additional light to moderate rainfall is expected across far southern and eastern Texas, which is mostly outside of the existing drought areas. Beyond the five day period, abnormal dryness becomes more likely for western and northern Texas. Therefore, drought persistence is expected for most of Texas during the upcoming three month period. Some improvement is limited to far southern and northeastern Texas, where additional short term rainfall is most likely. Forecast confidence for Texas is moderate to high.
Above average rainfall fell across the northern and central Mississippi Valley, promoting drought reduction north of Arkansas. Additional light to moderate rainfall is forecast during the upcoming five day period, and above normal rainfall is more likely during the week 2 period as far south as the Ohio-Mississippi River confluence. With the growing season over, this additional rainfall will help to efficiently recharge soil moisture ahead of the winter season. The CPC seasonal outlook maintains enhanced chances of below median precipitation for Iowa and western Missouri. Therefore, some improvement is expected across Wisconsin, Illinois, and parts of Missouri, while drought persistence is more likely west of the Mississippi. Heavier rainfall amounts typically fall across Arkansas and Tennessee during the winter months, so given mostly weak climate signals during the entire period, some improvement is forecast. Forecast confidence for the Mississippi River Valley is moderate.
Areas of deep, long term drought continue to plague eastern Alabama, central Georgia, and southwestern South Carolina. Dry, warm weather during the previous two weeks exacerbated the drought conditions, causing some southward expansion. A storm system expected to bring short term rainfall to the western Gulf coast northwestward into Tennessee will largely miss the Southeastern core drought region, and abnormal dryness is expected to persist into the week 2 period. Continued short term drought expansion and intensification is therefore likely. Beyond the short range, monthly and seasonal guidance provide little signal across the existing drought regions. The CPC seasonal outlook tilts the odds towards wet conditions for the Gulf Coast, which may bring some relief to the southern portions of the drought areas, but this relief may only serve to offset the current expansion of the drought. Therefore, only modest improvement, if any, is expected for the Southeast. Forecast confidence for the Southeast is low.
An extratropical transitioning Hurricane Sandy made landfall along the mid-Atlantic coastline, bringing devastating storm surge, strong winds, and widespread rainfall to the region. Areas of drought along the Delmarva and the Northeast were wiped out over a period of three days, while significant improvements were made to lingering drought regions in the Ohio Valley. As the remnants of Sandy continue to drift across the northeastern quadrant of the nation, further drought reduction is expected. During the week 2 period, a new storm system is forecast to develop across the Midwest and traverse the Ohio Valley and Northeast. Based on this short term wetness, continued drought improvement is expected for the small remaining drought areas of the mid-Atlantic and Ohio Valley. Forecast confidence for the mid-Atlantic and Ohio Valley is moderate to high.
Previous outlooks for Hawaii depicted drought persistence and expansion based on the expectation of a weak to moderate winter El Niño, and a near consensus for dry seasonal precipitation anomalies across Hawaii among the long range models comprising the National Multi-Model Ensemble. El Niño conditions have failed to materialize, however, and current outlooks predict a borderline or even ENSO neutral winter season. Recent runs of the CFS version 2 have also backed off on the dry signal, and now maintain little to no seasonal precipitation anomalies. Therefore, with the Hawaiian rainy season approaching, the chances for drought reduction have improved. Some of these drought regions have been present for several years, however, illustrating a difficulty in completely eradicating extant drought from Hawaii in the absence of a high impact event, particularly across the eastern islands. Therefore, some improvement is forecast for the western islands of Hawaii, where the winter rains have the highest probability of ameliorating the drought. Persistence is maintained for the western islands for the time being, but this may need to be revisited in the next outlook. Forecast confidence for Hawaii is moderate.
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