Latest Seasonal Assessment -
A series of storm systems late in November helped to reduce drought coverage and intensity across southern Texas
and across parts of the Florida Panhandle. In a potential harbinger of things to come, an extended Pacific jet
stream in early December brought periods of much-needed precipitation into parts of central and southern
California, and a major winter storm brought heavy snow into parts of southern Utah, Colorado and northern
Arizona. The outlook for January through March 2010 indicates improvement to drought conditions across central and
southern California, the Four Corners Region, southern Nevada, Texas, and Florida. The current El Niño is
expected to continue through at least early spring, increasing the odds toward improvement in the aforementioned
areas. More limited drought improvement is forecast over northern Nevada, northern California and southern Oregon,
as the storm track shifting further to the south later in winter is expected to lower precipitation chances. In
contrast, drought is forecast to persist in northern Wisconsin and east-central Washington. Drought development
is forecast during the period from parts of Montana into the western High Plains, as well as over Ohio. With
moderate El Niño episodes favoring below median winter rains over Hawaii, severe to extreme drought in the state
is expected to continue or worsen, with the potential for drought to develop across the remainder of the Hawaiian
Islands during the period.
Discussion for the Seasonal Drought Outlook
Tools used in the Drought Outlook
included the official CPC precipitation outlook for January 2009 and the long lead forecast
for January 2009 - March 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 January - March,
climatology, and initial conditions.
Areal coverage of drought
conditions in the Florida peninsula has decreased due to increases in precipitation in recent weeks.
Short-range forecasts suggest potential for near to above-median precipitation during the next two weeks.
Long-range forecasts also favor drought improvement in Florida as well, as the ongoing El Niño strongly
favors above-median precipitation during the winter months.
Forecast confidence for Florida is high.
Moderate to severe drought
continues in northwest Wisconsin. Soil moisture anomalies in this area currently remain negative, and most of
the short, medium, and longer-range forecast guidance do not suggest potential for wetter than median
conditions in this region. Drought is therefore expected to persist in this region. Precipitation for this
region typically increases later in the spring.
Forecast confidence for Wisconsin is low.
Continued relief from the
protracted drought affecting parts of southern Texas appears likely through much of the forecast period.
Short and medium-range forecasts suggest wetter than median conditions, and the latest CPC seasonal forecast
indicates wetter than median conditions for January through March. The forecast of at least a moderate El
Niño and its associated potential for wetter than usual conditions across Texas also argues for improvement
of drought conditions here.
Forecast confidence for Texas is high.
A series of recent storm systems
has resulted in increased streamflows across parts of the drought area over the Southwest and Four Corners
region, with some improvement in soil moisture conditions especially noted over southern and south-central
Arizona. Latest medium-range guidance indicates equal chances for below, above or near-median precipitation
in this area. CPC’s latest seasonal forecast for January through March indicates a slight tilt in the odds
for wetter than median conditions across southern parts of Utah and Colorado into northern Arizona, with
increasing odds for wetter than median conditions across central and southern parts of Nevada and Arizona.
Despite latest long-range soil moisture forecasts which argue for drought persistence, the ongoing El Niño
and its associated wet conditions for this region suggests drought improvement for this drought area.
Forecast confidence for the Southwest and Four Corners region is moderate.
Recent storminess has resulted in
some decrease in drought intensity across California, southern Oregon and northwestern Nevada, with
significant improvement in streamflows across coastal locations of central and southern California. CPC’s
6-10 day and 8-14 day precipitation forecasts call for normal amounts over California and southern Oregon,
with a slight tilt in the odds for above median precipitation over northern Nevada. El Niño composites along
with the CPC seasonal outlook favor above-median precipitation during January through March across central
and southern California. Typically, the storm track along the West Coast shifts south later in the winter.
The CPC seasonal forecast is also slightly less optimistic for above median precipitation over northern
California, northern Nevada and southern Oregon, where equal chances for above, below or near median
precipitation are indicated for these areas. With these considerations in mind, improvement during this
period is more likely across central and southern California, with some improvement of drought conditions
over northern California, southern Oregon and northern Nevada.
Forecast confidence for central and southern California is high, and forecast confidence for northern California, northern Nevada and southern Oregon is moderate.
Ongoing drought conditions continue
across parts of east-central Washington. Also, due to a lower than usual snowpack, there are concerns for
drought development over northern Idaho as well. Conflicting evidence exists amongst the short, medium and
long-range precipitation guidance in these areas. Latest short to medium-range forecasts suggests near to
above median precipitation chances over east-central Washington and northern Idaho. However, El Niño
composites for January – March indicating dryness argue for drought development in northern Idaho and drought
persistence in east-central Washington. This is consistent with both CPC’s latest seasonal precipitation
forecast (indicating higher odds for below-median precipitation), as well as seasonal soil moisture
forecasts. Due to the conflicting evidence, drought persistence will remain forecast for east-central
Washington and drought development will not be drawn on the map for northern Idaho at this time.
Forecast confidence for Washington and northern Idaho is low.
Abnormal dryness currently exists
across parts of Montana. There are a few seasonal forecasts which suggest continued decreases in soil
moisture over this region. A decrease in soil moisture is also forecast by the seasonal tools from the
western Dakotas into northeast Wyoming. Precipitation forecasts from the short, medium, and long-range
suggest equal chances for below, above, or near median precipitation over eastern Montana, northeast
Wyoming and the western Dakotas, with a slight tilt in the odds for below median precipitation over
west-central Montana. Based on the seasonal tools, as well as minimal precipitation amounts over the first
2 weeks of the period, drought development is forecast for parts of Montana and is expanded south and
eastward into the western Dakotas and northeast Wyoming.
Forecast confidence for Montana is low.
Over Ohio, despite current near to
above normal streamflow levels, parts of eastern Ohio and southern Ohio currently are observing below normal
soil moisture levels. Latest short, medium, and seasonal precipitation and soil moisture guidance favor
drought development over Ohio during this period. This is consistent with the El Niño composite for
January – March, which favors below median precipitation here. Therefore, drought development is now
forecast for this period over Ohio. Large uncertainties over precipitation forecasts during the first 2
weeks of the period further reduce confidence levels for drought development. Any such development, should it
occur, would take place later in the period.
Forecast confidence for Ohio is low.
As is consistent with an ongoing
El Niño, Hawaii is expected to receive below-median precipitation during this period. These dry conditions
will likely exacerbate ongoing areas of severe to extreme drought over Hawaii and also provide support for
drought development over the remainder of the Hawaiian Islands.
Forecast confidence for Hawaii is high.