Latest Seasonal Assessment -
The Drought Outlook for October 20, 2011 through January 2012 reflects forecasts and outlooks for periods ranging from the next
few days to the next few months, La Nina composites for the November – January period, and, to a lesser extent, composites of the
small set of La Niña events that immediately followed a previous La Niña episode. Across the southern tier of states and in the
central Plains, drought is expected to persist and expand into adjacent areas. Except for wetness being favored in Colorado and
northern New Mexico for the 6-10 day period, all tools are in remarkable concert, pointing toward drier than normal conditions.
Thus, this is a high confidence forecast. Farther north, both across North Carolina and in a swath from central Illinois through
central Iowa, drought is also forecast to persist and expand slightly, though with less confidence, as the longer-term tools
either barely favor drier than normal conditions or demonstrate no tilt of the odds in any direction. Moving farther to the
north, some improvement is expected across northern Iowa and southern Minnesota while improvement is forecast in the drought
areas in northern Minnesota and Michigan’s Upper Peninsula. Forecast tools trend toward more favorable conditions as one moves
north through the region. Finally, there is no tilt of the odds toward wetness or dryness in Hawaii, but some improvement is
forecast late in the period as the Islands move toward a time of year when La Niña composites favor above-normal precipitation.
Discussion for the Seasonal Drought Outlook
Tools used in the U.S. Drought Outlook (USDO)
included the official CPC temperature and precipitation outlooks for November 2011
and the long lead forecast for November 2011 - January 2012, 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, the four-month Palmer drought termination and amelioration
probabilities, climatology, and initial conditions.
Drought is expected to continue and expand across
the southern tier of states and in the central Plains. All forecast tools, except for the 6-10 day outlook in Colorado and
northern New Mexico, point toward dryness throughout the region. There were some indications that the wetness in the 6-10
day period in the central Rockies could expand into parts of the Plains and Texas, but this appeared less likely than the
official forecast at the time this Drought Outlook was released. Drought development was kept out of parts of Alabama and
Mississippi, where longer-term forecasts for dryness were less confident and where Tropical Storm Lee dropped 5 to locally
12 inches of rain in early September. In addition, drought development was omitted from parts of Florida that received 8 to
15 inches of rain in early October.
Forecast confidence across the southern tier of states and the central Plains is high.
Farther north, drought is also expected to persist
and/or expand slightly in a swath from central Illinois through central Iowas, and across North Carolina. In these areas,
the rest of October looked drier than normal, but most longer-term forecasts and NDJ La Niña composites either leaned very
slightly dry or demonstrated no tilt of the odds toward dryness or wetness. The smaller set of La Niña events that immediately
followed another event leaned dry, however, and this, along with the shorter-term dryness, drove the forecast.
Forecast confidence in both the swath from central Illinois to central Iowa, and through North Carolina, is moderate.
For the small drought area in Kentucky, heavy
precipitation is expected in late October while all other official forecasts were non-committal. However, La Niña events
generally favor wetness in this area, thus improvement was forecast.
Forecast confidence in Kentucky was low.
Some drought improvement was forecast across
northern Iowa and southern Minnesota. Little precipitation is forecast through the end of October, but the November forecast
is neutral while wetness is slightly favored in the official NDJ 2011-12 three-month outlook. The back-to-back La Niña
composites leaned wet. Given the contradictory indicators, some improvement is forecast, most likely later in the period.
Forecast confidence across southern Minnesota and northern Iowa is low.
Improvement is anticipated in the current drought
areas from northern Minnesota into the northern Great Lakes region. Forecasts for all periods are wetter than normal across
northern Michigan, while farther west, a dry end to October is followed by a tilt of the odds towards enhanced precipitation
for November – January. Also, given that much of what falls will likely be snow that covers the ground into spring, the
precipitation should efficiently keep drought at bay by covering any dry land and soil.
Forecast confidence is high in northern Michigan and moderate in northern Minnesota.
Finally, some drought improvement is anticipated
in Hawaii. Drought has recently expanded across the island chain, and none of the official forecasts tilt either drier or
wetter than normal. However, La Niña’s influence generally brings wetter than normal conditions to the state beginning
toward the end of this forecast period, thus some improvement is expected, particularly late in the period.
Forecast confidence in Hawaii is moderate.