October - December 2009

Outlook Graphic: GIF   PDF 

Latest Seasonal Assessment - Heavy early-September rains brought significant and widespread improvements to the drought conditions affecting central and southern Texas for the first time in several months, and the Drought Outlook through December 2009 calls for additional improvements throughout the region. Elsewhere, drought improvement is also anticipated by the end of December across the Carolinas and in most of central and northern Arizona. More limited improvement is forecast for many of the other areas of drought currently affecting the country, including the scattered areas from the western Great Lakes into the northern Plains, eastern New Mexico, east-central and southern Arizona, northwestern Montana, western Washington, much of southeastern Hawaii, and the multi-year drought affecting much of California and Nevada. In contrast, drought conditions should persist in northernmost California, parts of southern and western Oregon, and central and eastern Washington, where below-normal October - December precipitation is anticipated. Drought could expand into more of eastern Washington, where drier than normal conditions are also anticipated through December, and where some moisture shortages have already been observed.

Tools used in the Drought Outlook included the official CPC precipitation outlook for October 2009 and the long lead forecast for October - December 2009, 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 October - December, climatology, and initial conditions.

Drought recently expanded to cover much of the Carolinas, but indications are that improvement is likely by the end of the year. The odds favor above-normal precipitation through the last half of September, and although the October and October - December forecasts show equal chances for above- and below-normal precipitation, the expected development of moderate El Niño conditions by the end of the year could favor increased precipitation late in the period. In addition, the seasonal decline in temperatures and hence evaporation and transpiration means that the precipitation that falls, though typically somewhat less than during other seasons, should increasingly benefit soils, streamflows, and groundwater as the season progresses.
Forecast confidence for the Carolinas is high.

Several areas of drought dot the northern Plains, upper Mississippi Valley, and western Great Lakes region, where some improvement is anticipated by the end of the year. Although September 17 - 21 looks dry for the region, above-normal precipitation is favored to some extent during September 22 - 30. Thereafter, neither the October nor the October - December forecasts favors above- nor below-normal precipitation. Climatologically, the last 3 months of the year are somewhat drier than some other seasons, but with seasonably dropping temperatures, more of the precipitation benefits surface and potentially sub-surface moisture conditions, especially with an increasing proportion of the precipitation falling as snow. Still, the relatively low confidence in the late-September precipitation forecasts and the uncertainty thereafter adds some uncertainty to the forecast.
Forecast confidence for the northern Plains, upper Mississippi Valley, and western Great Lakes is moderate.

A recent heavy rain episode brought the first significant, widespread improvement to the protracted drought affecting Texas in many months, and more improvement looks likely by the end of the year. Although another episode of broadscale heavy rain doesn't appear imminent, all forecasts from late September through the end of December favor above-normal precipitation, and the anticipated development of moderate El Niño conditions also favors enhanced precipitation during the last 3 months of the year.
Forecast confidence for Texas is high.

Some improvement is anticipated for the lingering drought in eastern New Mexico. Moderate to heavy precipitation is expected through the first five days of the period, with near- or below-normal amounts favored later in September. Thereafter, forecasts favor neither above- nor below-normal precipitation during October - December. Based on the precipitation expected in the near-term, seasonably-declining temperatures, and the potential for increased precipitation late in the period related to the expected development of moderate El Niño conditions, at least limited improvement seems most likely, though confidence is not great.
Forecast confidence for eastern New Mexico is low.

Despite near- or below-normal precipitation expected during the last half of September in the drought area covering central and eastern Arizona, improvement is forecast by the end of December in the northwestern half of the region, with more limited improvements expected farther southeast. Above-normal precipitation is anticipated across the northwestern half of the region in October, with equal chances forecast farther southeast. The October - December forecast calls for equal chances of above- and below-normal precipitation throughout the area, but precipitation could increase late in the period if the expected moderate El Niño conditions develop. In addition, as is true throughout the country this time of year, seasonably-declining temperatures allow any precipitation that does fall to be more beneficial for surface and sub-surface moisture conditions, and this is particularly true for snow that accumulates in the higher elevations.
Forecast confidence for central and eastern Arizona is moderate.

Little or no precipitation is anticipated in the near-term for the areas of northwestern Montana experiencing drought, and all forecasts for the region from late September through the end of the year are uncertain at best. Seasonal considerations, including declining temperatures and the increasing potential for precipitation to fall as snow, tilt the outlook toward the expectation of at least limited improvement for the region, but only with considerable uncertainty.
Forecast confidence for northwest Montana is low.

The drought in central and eastern Washington shows no signs of letting up by the end of the year, and some expansion of drought conditions to the east seems likely as well. Below-normal precipitation is expected through the last half of September, and both the October and October - December forecasts favor below normal precipitation. Climatologically, the last 3 months of the year tend to be slightly wetter than other seasons, but even considering this and the fact that temperatures will be dropping, the consistent and fairly confident forecasts for subnormal precipitation make drought persistence and some expansion likely.
Forecast confidence for central and eastern Washington is high.

Some improvement is forecast for the drought in western Washington despite the anticipation of below-normal precipitation from the last half of September through the end of the year. Climatologically, precipitation increases substantially as the last 3 months of the year progress, and even somewhat below-normal totals would represent a significant amount of moisture for the region. However, the below-normal forecasts add some uncertainty to the forecast.
Forecast confidence for western Washington is moderate.

For the remainder of the West, drought is expected to persist across western and southern Oregon and northernmost California while some improvement is expected in most of California and the drought areas covering Nevada. Little precipitation is anticipated through the end of September, which is not unusual for the region, but the odds favor above-normal precipitation across southern California and south-central Nevada during October. For the October - December period, the odds favor drier than normal conditions in northern parts of the region where drought is forecast to persist, with neither above- nor below-normal amounts favored elsewhere. The forecast is based primarily on the October and October - December precipitation outlooks, with some consideration given to climatology, which indicates that October - December is a relatively wet time of year in the northern half of California, across Oregon, and to a lesser extent through northwestern Nevada. In addition, the expected development of moderate El Niño conditions could induce increased precipitation across southern reaches of the region late in the period. However, given the multi-year nature of the drought in most of this area and the uncertainty in late-year precipitation totals for areas south and east of northernmost California, some improvement seems most likely by the end of the year for most of the region, with persistence expected where October - December dryness is favored.
Forecast confidence for central and southern portions of the West is moderate.

Some improvement is expected for the dry areas covering much of the southeastern half of Hawaii, based primarily on climatological considerations. Neither significantly wet nor dry conditions are favored during October - December, but precipitation typically increases somewhat during this time of year in those parts of the state still experiencing drought conditions.
Forecast confidence for southeastern Hawaii is moderate.