December 2009 - February 2010

Outlook Graphic: GIF   PDF 

Latest Seasonal Assessment - After the wettest and third coldest October on record (since 1895) across the lower 48 States, November temperatures rebounded but unsettled weather continued in the Pacific Northwest and across portions of the southern Great Plains and Southeast. After a brief period of tranquil weather during early November, abundant moisture from the remnants of Hurricane Ida, coupled with a developing Nor’easter and a stationary front, dropped heavy rains on most of the Southeast, alleviating drought in the Carolinas. Florida was an exception where significant rains bypassed the southern two-thirds of the State, and moderate drought developed in east-central Florida. Light to moderate showers in the upper Midwest erased moderate drought in northern Minnesota, but drier weather to the south maintained drought across northern Wisconsin. After mid-month, heavy rains fell across south-central Texas, providing additional drought improvement. Although the Pacific Northwest recorded stormy weather, areas to the south were left mostly dry, with drought expanding in parts of the Southwest. The outlook for December 2009 through February 2010 indicates drought improvement for California, most of Arizona, southern Nevada, Texas, and Florida. The current moderate El Niño is expected to last through this winter, increasing the odds toward improvement in the aforementioned areas. Ongoing drought with some improvement is forecast for the remainder of the Southwest (northern Arizona, remainder of Nevada, and the Four Corners Region). In contrast, drought should persist in northern Wisconsin and north-central Washington, and develop in the northern High Plains. During El Niño events, the odds favor subnormal winter rainfall across the Hawaiian Islands which should cause worsening conditions for the existing drought regions, and possible drought development over areas that are currently drought free.

Tools used in the Drought Outlook included the official CPC precipitation outlook for December 2009 and the long lead forecast for December 2009 - February 2010, the four-month Palmer drought termination and amelioration probabilities, various medium- and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the soil moisture tools based on the GFS model and the Constructed Analogue on Soil (CAS) moisture, the Climate Forecast System (CFS) seasonal precipitation forecasts, El Niño precipitation and temperature composites for December - February, climatology, and initial conditions.

Short-term dryness has led to drought development in east-central parts of the Florida peninsula. From October 1 – November 30, the rainfall deficit at Melbourne, FL is nearly 7 inches. In the short-term, heavy rain (1 – 5 inches) is expected to fall over the Florida peninsula and may eliminate drought conditions. Beyond the short-term period, the ongoing El Niño strongly favors above-median precipitation during the winter and thus additional improvement is likely. Forecast confidence for Florida is high.

Drought coverage and intensity has decreased in the upper Mississippi Valley, but moderate to severe drought continues in northwest Wisconsin. Due to a lack of any forecast signals for wetter than normal conditions and a relatively dry climatology during the outlook period, drought is expected to persist. Precipitation for this region typically increases later in the spring. Forecast confidence for Wisconsin is low.

Additional relief from the protracted drought affecting parts of southern Texas appears likely during the winter. Forecasts from December through the end of February favor above-median precipitation, and the development of moderate El Niño conditions also favors enhanced precipitation during the outlook period. Forecast confidence for Texas is high.

Short-term dryness earlier during the fall worsened the drought in the desert Southwest and Four Corners Region, especially in Arizona. However, a winter storm at the end of November resulted in locally heavy snow in southeast Arizona. From December 7 – 8, numerical models indicate an increased likelihood for much needed precipitation across Arizona. El Niño composites indicate a tilt in the odds toward above-median precipitation during the outlook period. The CPC seasonal forecast shows slightly increased odds for above-median precipitation for southern Arizona but equal chances for above, below, or near normal precipitation across the reminder of the State. With these considerations, improvement is more likely in southern Arizona. Forecast confidence for the Southwest and Four Corners region is moderate.

Since October 13 when a very strong storm affected northern and central California, drier than normal conditions have prevailed across the State. During the second week of December, a pattern change featuring frequent periods of wet weather is expected. This expected increase in wetness is consistent with a negative Arctic Oscillation (AO) and the current phase of the MJO. El Niño composites along with the CPC seasonal outlook favor above-median precipitation during December – February. Typically, the storm track along the west coast shifts south later in the winter. Due to these considerations, improvement is forecast across California. Forecast confidence for California is high.

Due to rain and snow that occurred during late November and forecasts of above-median precipitation during the 6-10/8-14 day period, the development area in northeast Washington has been removed from the previous outlook. CPC seasonal forecast indicates higher odds for below-median precipitation. Therefore, drought persistence is forecast in central Washington. Forecast confidence for Washington is low.

Abnormal dryness currently exists across parts of Montana. Due to this initial dryness and a few seasonal tools supporting either below-median precipitation or a decrease in soil moisture, drought development is now forecast across parts of the State. Forecast confidence for Montana is low.

Hawaii is forecast to receive below-median rainfall during the upcoming winter, consistent with an ongoing El Niño. Drier than normal conditions will worsen existing severe to extreme drought and likely result in drought expansion across the remainder of the State. Forecast confidence for Hawaii is high.