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Climate Prediction Center


November 2009 - January 2010


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Latest Seasonal Assessment - Heavy rains and mountain snows during the first half of October brought significant relief to many of the drought areas across the country, especially California. Much of Texas has seen elimination of short-term drought conditions due to the recent rains, though longer-term, hydrologic impacts will remain for a while, especially in southern Texas. A series of frontal systems have brought heavy rains to the East Coast states, resulting in substantial mitigation of drought conditions. The same is true of the upper Midwest, though long-term drought areas of northwestern Wisconsin and northern Minnesota still need significant rain or snow. For the most part, improvement is forecast for areas east of the Rockies during the Outlook period. West of the Divide, the situation is less clear. Improvement is predicted for California and southern Arizona, with the odds tilted toward some improvement for central and northern Arizona, northwest Nevada and Washington's Olympic Peninsula. Despite precipitation expected during the last half of October, drought persistence is indicated for central Washington and northwest Montana.

Discussion for the Seasonal Drought Outlook

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

Within the past two weeks, several frontal systems have pushed across the Southeastern states, as far south as north-central Florida. Much of South Carolina and Georgia have received rainfall surpluses during this period ranging from 2 to 4 inches, and locally as much as 5 inches. However, a significant portion of North Carolina has 1 to 2 inch deficits for the same two week period, which equates to only 10 to 25 percent of their normal rainfall. From a historical standpoint, stream and river flow values throughout much of the state currently fall within the lowest quartile. From a different, more optimistic perspective, the latest (Oct 11) USDA topsoil moisture maps reveal that approximately 14 percent of North Carolina is reporting short-very short conditions, compared with 33 percent for the past 5-year mean. CPC precipitation forecasts in general support additional improvement in drought conditions in the Carolinas. Elsewhere, dry conditions have largely dominated the central Appalachians for at least the past few weeks, with spotty relief for a few areas. One to two inch rainfall deficits have been noted, and stream flow values for the period are within the lowest quartile in western portions of Virginia. HPC's precipitation forecast for the next five days calls for 2 inches of rain across the central Appalachians.
Confidence for the East Coast states: High

For the Southern Great Plains, the main headline has been the recent rains in Texas and Oklahoma, which essentially wiped out the short-term drought in many areas. It is important to note, however, that longer-term drought still exists in southern Texas and more rain will be needed to replenish groundwater supplies and reservoirs. Rainfall surpluses for the past two weeks across central and eastern portions of both Texas and Oklahoma (excluding southern Texas) has generally been 2 to 3 inches, with 4 inch or greater surpluses over a fairly wide area. In contrast, 1 to 2 inch rainfall deficits dominated southern Texas, and somewhat smaller deficits continued across eastern New Mexico. Stream flows generally registered near or above normal across the lower (eastern) southern Plains, but below normal across the southern High Plains. CPC's extended and long-range precipitation forecasts call for above median precipitation across the southern Plains. In the central Plains, slight dryness persisted across extreme southeastern Nebraska, which has helped with late season harvesting of corn and other crops. Most of Nebraska, however, has done well (in terms of rainfall) relative to climatology. The Northern Plains have also benefited from recent rains during the past two weeks. One to two inch precipitation surpluses brought some relief to the Dakotas, with 2 to 3 inch surpluses reported in eastern South Dakota. Very modest surpluses were noted in southwestern North Dakota. Stream flows were at or above the 90th percentile across the eastern Dakotas, and close to normal for western areas.
Confidence for the southern Plains: High

Across the Upper Midwest, welcome rains have fallen across a large portion of the drought areas. A broad area of 2 to 4 inch (or more) surpluses across central and southern Minnesota, northwestern and northeastern Wisconsin and western upper Michigan, has made a substantial dent in the drought in these areas. Northern Wisconsin still needs significantly more rain to bring this long-term drought (of well over a year) to an end. The northern portions of Minnesota have missed out on these recent rains, showing deficits between 0.5 and 2 inches for the past 2 weeks. Streams and rivers are generally running near to below average from the Arrowhead region of northern Minnesota southeastward across northern Wisconsin and adjacent upper Michigan. The HPC QPF rainfall forecast for the next five days calls for light rain (0.25 inch or less) across the driest areas of northern Minnesota and northern Wisconsin, but between 0.5 and 1.0 inch for most of the remaining upper Midwestern areas. The Constructed Analog Soil Moisture (CAS) forecast shows continued dryness for the region at the end of November 2009, and dryness/drought is predicted to be even more pronounced by the end of January 2010. USDA short-very short topsoil moisture values for the uppermost 6 inches of soil indicates Minnesota's current state value of 17 percent is only slightly drier than the 5-year mean of 14 percent. For Wisconsin, a state-wide value of 26 percent is actually slightly wetter than the previous 5-year mean of 31 percent. CPC's 30-day and 90-day outlooks indicate equal chances of below-, near-, and above median precipitation. Given this uncertainty, as well as the tendency this area has had for missing out on the heavier precipitation amounts, it is thought that some improvement may be the best forecast for portions of northwestern Wisconsin and northern Minnesota.
Confidence for the Upper Midwest: Moderate

Recent heavy rain and mountain snow in the northern Rockies has helped considerably in trimming back D0 dryness in southwestern Montana. Slight precipitation deficits for the past two weeks were noted in northwestern Montana and northern Idaho, with 1 to 2 inch deficits for western parts of Washington and Oregon. Stream flows were predominantly normal in the interior Pacific Northwest, and below normal near the Pacific Coast and northern Idaho. CPC's extended-range forecasts out through the next two weeks calls for near to above median precipitation across the Northwest, but below median for the 30-day and 90-day outlooks. Overall, the odds appear tilted toward persistence of dryness/drought for the region, though the area of drought development which was indicated on the previous Outlook over east-central Washington looks too risky, especially given short- and extended-range predictions of near to above median precipitation.
Confidence for the Pacific Northwest/Northern Rockies: Moderate

Recent heavy rain and mountain snow in northern and central California has brought some relief to the region unusually early in the rainy season, but ongoing reassessment will be needed to determine exactly how much mitigation has occurred. CPC's monthly forecast for November 2009 calls for equal chances of below-, near-, and above median precipitation, but for the upcoming Nov-Dec-Jan 2009/10 season, CPC's outlooks call for wetter than median conditions across the state. The weak to moderate El Nino anticipated this upcoming winter does not provide much help in tilting the odds towards wet or dry. Up until the last 5 or 10 years, it was common for strong warm events to be connected to unusually heavy precipitation events in California, especially later in the winter season, but recently this correlation has not been very cooperative. Across the Southwest, drought has been expanding and intensifying during the summer and into early autumn. For the past 90-days, 2 to 6 inch rainfall deficits have mounted, primarily because of an unusually weak summer monsoon. For Arizona as a whole, this corresponds to 25 to 50 percent of normal rainfall. Northern Arizona in particular has received only 10 to 25 percent of its normal rainfall. The CAS tool predicts the drought to continue through November 2009 and even throughout the Nov-Dec-Jan 2009/10 season. A consensus of various soil moisture models/tools from the CFS (experimental), the NASA NSIPP model, the University of Washington VIC model, and CPC ENSO Soil Moisture Composites, provides at least reasonable (but by no means unanimous) support for this Drought Outlook.
Confidence for California and Arizona: Low to moderate

For Hawaii: With the approach of the rainy season, most areas are expected to see at least some improvement.

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Page Author: Climate Prediction Center Internet Team
Page last modified: October 15, 2009
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