Latest Seasonal Assessment -
Wet weather overspread northern and central California, Oregon, and Nevada during much of December, but a pattern change
brought drier conditions towards the end of the month. A potent blizzard blanketed parts of the central U.S. with snow,
while stormy conditions prevailed across the eastern third of the U.S. at the end of 2012. Mostly dry weather exacerbated
drought conditions in central Texas, Oklahoma, and southeastern Kansas. During the upcoming three months, a much drier
pattern is expected across the southwestern quadrant of the nation, limiting the prospects for further drought improvements
during the wet season in California and Nevada. In contrast, enhanced probabilities of positive rainfall anomalies across the
Southeast during the remaining winter months increase the chances of drought reduction. Some drought improvement is also
possible across the Midwest and northern tier of the U.S., but general persistence of extreme to exceptional drought is
expected across the Plains states during the dry season. Some improvement of drought conditions is possible in Hawaii during
the winter rainy season, while any benefits of snowfall in the Koyukuk Basin of Alaska would occur beyond this outlook period
with the spring melt.
Tools used in the U.S. Drought Outlook (USDO) included the official CPC temperature and precipitation outlooks
for January 2013, the long lead forecast for January through March 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.
During the previous two weeks, widespread heavy rainfall overspread the long term drought areas of the Southeastern U.S.,
with more than double the normal rainfall amounts falling across central Alabama, northern Georgia, and the western
Carolinas during a climatologically rainy period of the year. These rains boosted streamflows and brought some drought
relief, particularly to areas near the Georgia and Alabama border. During the upcoming week, rainfall is expected to
fall mainly to the south of the core drought areas, but the CPC week 2 outlook maintains enhanced odds of above median
rainfall for the Southeast. The updated January outlook also tilts the odds towards above median rainfall, while the
seasonal forecast maintains equal chances. The latest runs of the CFS version 2 climate model predict significant
positive precipitation anomalies for the southeastern U.S. through February. Based on the November Palmer Hydrological
Drought Indices for the Southeast and climatology, the NCDC indicates that for much of the Southeast, near to slightly
below average precipitation during the December through March period is sufficient to ameliorate extant drought
conditions. Therefore, drought improvement is likely for much of the Southeast.
Forecast confidence for the Southeast is moderate to high.
Despite near to above average precipitation during the previous two week period, drought conditions persisted or
intensified across central North Carolina and Virginia as the heaviest rain and snowfall fell both to the north and south
of the region. The 28 day streamflow averages remained below to much below normal, and the 60 to 90 day SPI values
remained substantially negative. Little additional precipitation is expected during the upcoming week, although the CPC
8 to 14 day outlook predicts enhanced probabilities of above median precipitation. The CPC monthly and seasonal outlooks
both maintain equal chances of above, near or below median precipitation, and the CFS version 2 model predicts no
substantial precipitation anomalies. Climatologically, the January through March period is a drier time of year for this
region. Based on these considerations, some improvement of drought is indicated.
Forecast confidence for the southern Atlantic states is low.
Widespread precipitation during the latter half of December boosted moisture and improved drought conditions across far
eastern Texas and western Louisiana. Additional precipitation is expected during the week 1 period, although amounts are
expected to remain well below an inch. The CPC 8 to 14 day outlook tilts the odds slightly in favor of above median
rainfall, and the 12Z January 2 run of the GFS suggests the possibility of higher accumulations during week 2. The CPC
January updated outlook and the CFS version 2 model both indicate enhanced chances of above median precipitation for
eastern Texas and Louisiana. Based on this guidance and the currently improving drought situation, further improvements
are expected across extreme eastern Texas. Despite current light rainfall, drought persistence is more likely across
southern Texas, where deficits are much longer term.
Forecast confidence for eastern Texas and western Louisiana is moderate to high.
As of the beginning of 2013, snow covered most of the Midwest as far south as Arkansas and northern Texas, with snowpack
depth increasing towards the north. Many streams across Minnesota and parts of Wisconsin have frozen for the winter.
Precipitation anomalies were greatest along a swath from Iowa through Michigan due to a potent blizzard. Light
precipitation is expected across the Great Lakes region during the upcoming week, with locally higher amounts due to lake
effect snowfall. During the week 2 period, enhanced chances for above median precipitation are expected across the Corn
Belt and upper Midwest, while the CPC January outlook tilts the odds towards wet anomalies across the upper Midwest.
Based on this guidance, further improvement or some improvement is expected.
Forecast confidence for the Midwest is moderate to high.
During the second half of December, a potent winter storm brought significant snowfall to western Kansas and most of
Nebraska, while below average precipitation was observed elsewhere across the Plains states. Streams have frozen for the
winter across the Dakotas and eastern Montana under a substantial snow pack. The December through March period is a
climatologically dry time of year for the Plains. Little to no precipitation is expected during the upcoming week. The
CPC 8 to 14 day outlook tilts the odds towards below median precipitation across the southern High Plains, and towards
above median precipitation across the northern Plains. The CPC January outlook maintains the enhanced odds of above
median precipitation for the northern Plains, while the seasonal outlook keeps equal chances. Based on the dry
climatology, drought persistence is expected for most of the Plains. Additional development across the Texas high
plains is possible, while some improvement may be seen across the northern tier, with the greatest benefits occurring
during the spring melt.
Forecast confidence for the Plains is moderate.
Well above average rainfall continued across much of central and northern California and parts of Nevada during the
previous two weeks, while drier conditions prevailed across the Southwest and much of the Pacific Northwest. The CFS
version 2 forecasts have consistently predicted strongly negative precipitation anomalies across portions of the western
U.S. during the winter months, but these forecasts failed to verify as repeated storm systems pushed ashore in California
and Oregon throughout the late autumn and early winter. The phase of the PNA became positive during the last week of
December, however, bringing an end to the story pattern. During the upcoming week, light precipitation is expected along
the Pacific coastal areas, while dry conditions are forecast for the Sierra Nevadas. The CPC 8 to 14 day, January
monthly, and seasonal outlooks all predict enhanced chances of below median precipitation for California and the Four
Corners states during the outlook period. February is the wettest month of the year climatologically for the Central
Valley of California, so significant negative precipitation anomalies during this period have a high impact on drought
conditions in the spring. Based on the dry guidance, drought persistence is expected. Additional development areas have
not been included in this outlook due to the incipient wetness in the region, but may be required in subsequent outlooks
if the dry forecasts verify.
Forecast confidence for the West is moderate to high.
Continued rainfall across the eastern Big Island of Hawaii further improved drought conditions. The CPC January outlook
for Hawaii tilts the odds slightly towards below median precipitation, while the seasonal outlook maintains equal chances
of above, near, or below median rainfall. the January through March period is climatologically wet in Hawaii. Based on
these outlooks and climatology, some improvement is expected across the islands, with the best chances of drought
reduction on the eastern Big Island.
Forecast confidence for Hawaii is moderate.
Persistent dry conditions and low snowpack moisture promoted drought development across the Koyukuk Basin of Alaska. The
CPC January monthly update tilts the odds towards above median precipitation throughout Alaska, but any benefits of
additional snowfall would not be fully realized until the spring melt, which occurs beyond this outlook period. Therefore,
drought persistence is expected.
Forecast confidence for Alaska is moderate.