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Climate Prediction Center


December 2012 - February 2013


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Latest Seasonal Assessment - During the past two weeks, heavy rain has fallen across the Pacific Northwest, including northern California, with heavy snow in mountainous areas. The Four Corners region, northern Great Plains, the Mississippi and Ohio Valleys, the Tennessee Valley, parts of the central Gulf region and the Northeast all received moderate amounts of precipitation (0.5 to 2 inches), which helped ease drought conditions in some areas. In the West, abundant precipitation is predicted across northern and central California in the next few weeks, likely continuing the process of easing the drought. In the Pacific Northwest, the most significant precipitation is expected over the coastal ranges and Cascades, areas which are not currently in drought. Some improvement in long-term drought conditions is also anticipated over the northern Plains and a significant portion of the Mississippi Valley. Persistence of drought is deemed the best bet across central and southern portions of the Intermountain Region, the Rockies, and the Plains. Persistence of existing drought, or the development of new drought areas are expected in Texas. CPC's December 2012 and December-February 2012/13 precipitation outlooks show a tilt in the odds towards above-median precipitation across portions of the interior Southeast, the Tennessee Valley, parts of the Ohio Valley, and south-central portions of the Mississippi Valley. In the short-term (next 5-days), an upper-level trough is expected to bring light to moderate precipitation (up to 2 inches) to portions of the southern Atlantic Coast region. Up until recently, dry weather had dominated across the Hawaiian Island chain, but within the past few days the return of the trade winds resulted in decent rainfall to favored windward slopes. Some improvement is favored for most areas, except for the Big Island where persistence of drought is thought to be the best bet.

Discussion for the Seasonal Drought Outlook

Tools used in the U.S. Drought Outlook (USDO) included the official CPC temperature and precipitation outlooks for December 2012, the long lead forecast for December 2012 through February 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. To some degree, negative PDO (Pacific Decadal Oscillation) composites were also considered in this Drought Outlook.

Heavy rainfall and high elevation snowfall persisted across the Pacific Northwest and northern Rockies during the first ten days of November. During this same period, temperatures started off above-normal but ended up below-normal. On November 10th, Great Falls, Montana reported a maximum temperature of 10 degrees F, which is 36 degrees below normal for the date, as unusually cold air for this early in the season pushed southward and eastward across the northern Plains. A wet pattern is predicted through the ensuing two-week period across the Northwest, including northern and central California. Recent CFSv2 forecasts for December 2012 precipitation and December-February 2012/13 precipitation generally favor a somewhat wetter pattern than what they were predicting several weeks ago. The CPC monthly outlook for December 2012 and the winter seasonal outlook for December-February 2012/13 anticipate equal chances (EC) over the Pacific Northwest, though the seasonal outlook favors below-median precipitation across northern and central California.
Forecast confidence for the Northwest is moderate.

Since the start of November, up to 2 inches of precipitation has fallen over much of the Four Corners region, with locally heavier amounts reported over higher elevation areas. For the next two weeks, a drier pattern is expected. CPC's monthly and seasonal forecasts call for EC across this region, due to weak and conflicting climate signals. Based on the dry trending guidance in the shorter-term and uncertainty in the 30-day and 90-day periods, coupled with diminishing chances of a substantive El Nino event, drought reduction during the rainy season becomes less likely.
Forecast confidence for the Southwest is moderate.

Moderate precipitation (0.5 - 2.0 inches) fell over Montana, North Dakota, and eastern sections of the central and southern Great Plains during the past two weeks, helping to ease regional drought conditions. Less than 0.5-inch of precipitation was reported elsewhere. Recent precipitation should help to recharge soils before the ground freezes. For the upcoming two weeks, model guidance is generally trending drier across the Great Plains. The CPC monthly and seasonal outlooks are indeterminate regarding the precipitation anomaly sign. In Texas, drier conditions are favored in association with a negative PDO (Pacific Decadal Oscillation). Therefore, odds favor persistence for the areas of drought in eastern and southern Texas, and two areas of developing drought were introduced in central and south-central Texas.
Forecast confidence for the Plains is moderate.

Much of the Mississippi River Valley received moderate precipitation (0.5 2.0 inches) during the past two weeks, with 2.0 3.0 inch amounts observed over central portions of both Arkansas and Mississippi, southeastern and north-central Missouri, and eastern Iowa. Though little precipitation is predicted for the ensuing week, there is a tilt in the odds for above-median precipitation across the upper Mississippi Valley during the Week 2 period. For the December and DJF outlooks, the area favored for above-median precipitation shifts southward to the south-central Mississippi Valley, and extending eastward from there across the Tennessee and portions of the Ohio Valleys. As a result, improvement is anticipated across the D0 and D1 areas encompassing western Tennessee, southeastern Missouri, and small portions of adjacent states.
Forecast confidence for the Mississippi-, Tennessee-, and Ohio Valleys is moderate to high.

Most of the Southeast received little to no precipitation during the past 2 weeks, with the exception of northwestern and central Georgia which received moderate rainfall (0.5 2.0 inches). In the short term (next 5 days), an upper-air disturbance is likely to bring up to an inch of rain to the southern Atlantic Coast states, helping to ease some of the drought in this area. CPC's 6-10 day precipitation outlook shows enhanced odds of above-median precipitation for the Carolinas. At monthly and seasonal time-scales, the best chances (though still modest) for above-median precipitation are centered over the southern Appalachians/eastern Tennessee region. Negative PDO composites favor drier conditions closer to the Gulf Coast. Elsewhere, EC is predicted.
Forecast confidence for the Southeast is moderate.

During the past 14-days, heavy precipitation (2.0 inches or greater) fell over a significant portion of the mid-Atlantic and upper Ohio Valley region, with moderate amounts (0.5 2.0 inches) over the lower Ohio Valley and southwestern Virginia. After a relatively wet start to the period, climate signals become weak and conflicting. Therefore, EC is deemed the best bet for the 30-day and 90-day precipitation outlooks.
Forecast confidence for the mid-Atlantic region is moderate.

In Hawaii, mostly dry weather prevailed earlier this past week, but trade wind showers and a nearby upper-air trough brought precipitation to windward locations late in the week. As we progress into the rainy season, it is thought that some improvement is most likely for most of the Islands, with the exception of the Big Island, where persistence of drought is favored.
Forecast confidence for Hawaii is moderate.


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NOAA Center for Weather and Climate Prediction
Climate Prediction Center
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Page Author: Climate Prediction Center Internet Team
Page last modified: November 15, 2012
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