Latest Seasonal Assessment -
The Drought Outlook for November 3, 2011 through January 2012 reflects forecasts and outlooks for periods ranging
from the next few days to the next few months, La Niña composites for the November – January period, climatology
and, to a lesser extent, composites of the small set of La Niña events that immediately followed a previous La
Niña episode. In a broad area across the Southeast and along the southern tier of states, drought is forecast to
persist and expand. In this region, the November – January outlook and La Niña composites favor below-normal
precipitation for the period as a whole, even though the first half of November should bring near- to above-normal
precipitation to the lower Mississippi Valley, northern and eastern Texas, central and western Arizona, and
southeastern California. Farther north, at least some improvement is anticipated from central Arkansas and
northeastern Oklahoma northward through the rest of the eastern Plains and adjacent Mississippi Valley. Monthly
and seasonal outlooks lean wet in northern parts of this area. Farther south, heavy precipitation over the next
two weeks is expected to keep drought conditions in check through the remainder of the period. Rainfall may total
several inches in the east-central Plains by mid-November. Meanwhile, the various tools almost unanimously favor
subnormal precipitation on all time scales across eastern Colorado and the western halves of Oklahoma and Kansas,
where drought should persist. In Hawaii, no tilt of the odds toward dryness or wetness is discernible for
November – January, but some improvement is anticipated later in the period as the Islands progress toward a time
of year when La Niña conditions 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 forecast to persist in
the Southeast and expand to cover eastern South Carolina and most of Florida. Between 0.5 and 1.5 inches of
rain is forecast across the central Carolinas during November 3 – 7, but for the rest of the period, most
tools favor drier than normal conditions. Odds lean toward below normal precipitation across the southeastern
half of the region during November 8 – 14, with neither drier nor wetter than normal conditions favored across
the interior Southeast. On longer time-scales, the November and November – January outlooks, as well as the
La Niña composites, all favor subnormal precipitation throughout the region.
Given the agreement among the vast majority of tools, forecast confidence for the Southeast is high.
Drought is forecast to persist and
expand along the southern tier of states from the central Gulf coast through southeastern California, and to
persist in the southern half of the central and western Plains. Overall, the forecast tools are not in
overwhelming agreement, as was the case for the last Drought Outlook issuance. Short-term indicators through
the first half of November are a mixed bag, varying with time frame and location. For the first five days of
the period, November 3 – 7, only light precipitation is expected in most areas, but moderate totals of 0.5
to 1.5 inches are forecast from northern Texas through central Oklahoma and in a swath across central Arizona.
For November 8 – 16, drier than normal weather is generally favored from central sections of Texas, Oklahoma,
and Kansas westward across the areas of drought in Colorado and New Mexico, but enhanced chances for surplus
precipitation exist across the lower Mississippi Valley, southeastern Plains, and western sections of the
desert Southwest. Longer-term outlooks are more in concert, with the November outlook favoring dryness from
the High Plains eastward while the November – January outlook and the La Niña composites show enhanced
chances for below-normal precipitation throughout the region. Finally, the deep and protracted nature of the
ongoing drought was also considered. Deficient precipitation dates back more than a year through this region,
and shortfalls of 12 to more than 24 inches for the current calendar year are common across many sections of
Oklahoma, Texas, and Louisiana. Given these large long-term precipitation deficits -- and the fact that
indicators valid for the bulk of the November – January forecast period point toward more dryness –- any
moderate to locally heavy rains during the first half of November should have little impact on the overall
overall drought picture.
All things considered, forecast confidence for the southern tier of states from the central Gulf Coast
through southeastern California, and for the southern half of the central and western Plains, is high.
In contrast to areas farther south
and west, precipitation during the first two weeks of November could have a significant and lasting impact on
some of the drought areas in the eastern Great Plains and adjacent Mississippi Valley from central Arkansas,
northeastern Oklahoma, and east-central Kansas northward. Improvement is expected through most of this region,
with relatively small areas of more limited improvement in southwestern and east-central sections of the broad
region. The forecast is driven by two different factors divided by latitude. The 3-month forecast leans wet
from northwesternmost Iowa and eastern South Dakota northward through Minnesota and the Upper Peninsula of
Michigan, driving the forecast for improvement there. Farther south, heavy rainfall is expected during the
first half of November in a swath from central Arkansas and parts of eastern Kansas and Oklahoma
northeastward, with at least moderate precipitation indicated as far north as central Iowa by some tools.
Several inches are likely to fall on parts of the east-central Great Plains and middle Mississippi Valley. In
contrast to the situation farther west in the Plains and along the southern tier of the country, precipitation
deficits here, though steep in some areas, do not date back as far, and fairly widespread calendar-year
precipitation shortfalls exceeding 8 inches can only be found in the southeastern quarter of Kansas, northeast
Missouri, central Iowa, and near the Canadian border. Therefore, the heavy precipitation over the next two
weeks should have a significant impact on the overall drought picture, enough to keep drought
re-intensification in check through the end of January even though the 3-month forecast leans toward dryness
from Kansas and Missouri southward. The areas of some improvement were differentiated based on lesser expected
precipitation totals during the first 2 weeks of November, relatively large 90-day and/or year-to-date
precipitation anomalies, and to some extent the areas where the 1-month and 3-month outlooks indicated
enhanced chances for below-normal precipitation.
Because of the inherent uncertainly associated with one or a few weather events and their eventual effect
on drought impacts, forecast confidence is moderate in the eastern Great Plains and adjacent Mississippi
Valley from central Arkansas, northeastern Oklahoma, and east-central Kansas northward through southern Iowa,
and high from central Iowa northward to the Canadian border.
Finally, some drought improvement is
anticipated in Hawaii. Drought has recently expanded across the island chain, and none of the official
forecasts tilts either drier or wetter than normal. However, La Niña conditions generally favor wetter than
normal conditions across 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.