Latest Seasonal Assessment -
Since the previous outlook issued on November 20, drought improvement occurred across parts of northern California but protracted extreme to exceptional drought continues
for much of California. Long-term drought also remains entrenched across much of the central and southern Great Plains. Meanwhile, short-term drought intensified across
parts of the lower Mississippi Valley and central Gulf Coast.
The drought outlook valid from December 18, 2014 through March 31, 2015 is based primarily on initial conditions, the CPC January-March (JFM) precipitation outlook, and
climatology. A tilt in the odds towards above-median precipitation during a wet time of year favors additional drought improvement across California. However, it should be
noted that long-term drought conditions are expected to remain beyond March. Snowfall in the Sierras will be critical to ensure adequate water supplies during the spring
and summer. Improvement is also expected across coastal areas of southwest Oregon, while persistence or development is favored for the remainder of the Pacific Northwest
and Idaho. Snow-water equivalent values are generally low across much of the Great Basin and Four Corners region, making persistence more likely. Improvement or removal of
drought forecast across the desert Southwest and southwest New Mexico is consistent with most precipitation tools during JFM.
The relatively dry climatology outweighs the tilt in the odds towards above-median precipitation across the central and southern Great Plains, where persistence is
expected. Large-scale improvement of drought is not anticipated for this region until the convective season begins later in the spring. Prospects are slightly better for
improvement or removal of drought for parts of northeastern and south-central Texas but confidence is low. Farther to the north, a dry climatology favors persistence for
the small drought area across the eastern Dakotas.
Improvement and removal of drought is expected across the lower Mississippi Valley, central Gulf Coast, and Southeast due to expected rainfall in the short-term, the lack
of a consistent dry signal among seasonal precipitation tools, and a typical increase in rainfall during March.
A dry signal among precipitation tools during JFM favors gradual drought development during the next three months across Hawaii.
Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for
January 2015 and January-March 2015,
various short- and medium-range forecasts and models such as the forecast 5-day and 7-day precipitation totals from the Weather
Prediction Center (WPC), the 6-10 day and 8-14 day CPC forecasts, the NAEFS precipitation outlooks,
the soil moisture tools based on the Constructed Analog on Soil Moisture (CAS), dynamical models (CFSv2, NMME, IRI, and IMME), 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. As of December
4, there is an approximately 65 percent chance of El Niño conditions during the Northern Hemisphere winter.
A wet period with multiple storms since late November resulted in above-average precipitation across much of California. The largest 30-day positive anomalies (more
than 4 inches) were observed across northern California. During the first two weeks of December, the capacity of Lake Shasta, one of the larger reservoirs in northern
California, increased from 23 to 31 percent. Despite the more favorable pattern for beneficial precipitation, above-normal temperatures led to relatively high snow
levels. Therefore, snow-water equivalent (SWE) values remain low from the Cascades south to the Sierras. The statewide average of SWE for California is 48 percent of
normal for mid-December. A pattern change is expected along the West Coast during the remainder of December as an upper-level ridge builds across California with
onshore flow shifting north to the Pacific Northwest. Although little or no improvement is expected during the next few weeks, seasonal precipitation tools are
generally consistent indicating a wet signal for California during JFM. Climatology also favors improvement especially across coastal central and southern California
where more than half of its annual precipitation typically occurs from January-March. Drought improvement is expected for California during this outlook period, but
long-term hydrological drought concerns are likely to persist beyond March.
Forecast confidence for California is moderate.
Since the beginning of the wet season, frequent rain and high-elevation snow ended short-term drought across the Pacific Northwest, but long-term drought of varying
intensity persists. According to analysis from the National Water and Climate Center on December 16, SWE values are in the lowest 5th percentile across the Cascades
and mountains of northern Idaho. These low SWE values support persistence of long-term drought across most of Idaho, Oregon, and Washington. The JFM precipitation
outlook indicates increased chances of below-median precipitation across northern Idaho and northeast Washington where development is favored by the end of March.
Meanwhile, additional improvement of drought is expected along the southwest coast Oregon due to heavy rain forecast during the next week and a continued wet
Forecast confidence for Idaho, Oregon, and Washington is moderate.
Persistence is most likely for most of the Great Basin where the snowpack is below-average for the season so far and precipitation signals are weak among tools at
most time scales. However, improvement is forecast for southern Nevada where seasonal precipitation tools are more consistent for a wet signal during January through
Forecast confidence for the Great Basin is low.
A reduction in the coverage of extreme drought occurred across northern New Mexico and southeast Colorado during the past two months. Elsewhere across the Southwest,
drought coverage and intensity remained nearly steady following the end of the summer monsoon. A relatively dry time of year favors persistence across the high Plains
of southeast Colorado and northeast New Mexico, while a deficient snowpack at this time of year near the Four Corners supports persistence for this area of the
Southwest. Odds for above-median precipitation during JFM increase across the desert Southwest where improvement or removal of drought is forecast.
Forecast confidence for Arizona, New Mexico, and southern Colorado is low.
Varying intensity of drought persists across the central and southern Great Plains with exceptional drought centered over southwest Oklahoma and northwest Texas.
Although a tilt in the odds towards above-median precipitation during JFM is forecast for the central and southern Great Plains, a relatively dry climatology favors
persistence on a broad scale. Historically, only 10 to 15 percent of the annual precipitation occurs during this outlook period across Kansas, western Oklahoma, and
northwest Texas. Improvement and/or removal is forecast for the remaining drought areas of Texas where the climatology during JFM is not as dry.
Forecast confidence for the Kansas, western Oklahoma, and northwest Texas is moderate and low for the remainder of Texas.
Short-term drought continues across parts of Alabama, Arkansas, and Georgia, and expanded along the central Gulf Coast. Severe drought, according to the U.S. Drought
Monitor on December 16, exists from southeast Louisiana east to Mobile Bay where 60-day rainfall deficits exceed 6 inches. A low pressure system tracking across the
Southeast during the next week is forecast to bring 0.5 inch to locally as much as 3 inches of rain across the aforementioned drought areas. The JFM precipitation
outlook calls for equal chances of below, near, or above-median precipitation for much of the ongoing drought areas of the Southeast. Due to a weak signal among
precipitation tools during JFM, confidence in drought removal by the end of March is reduced.
Forecast confidence for the Southeast is low.
Abnormal dryness (D0) and moderate drought (D1) expanded across the eastern Dakotas and Minnesota during the past two months. Persistence is likely for the small area
of moderate drought since JFM is a dry time of year.
Forecast confidence for the eastern Dakotas and Minnesota is high.
Small areas of drought exist on Hawaii's Maui and Molokai Islands. Since the seasonal precipitation tools have a dry signal during a wet time of year, persistence and
development of drought is expected.
Forecast confidence for Hawaii is moderate.