Tools used in the Drought Outlook included
the official CPC long-lead precipitation outlook for January-March, the drought
termination and amelioration probabilities for March, various medium and short-range
forecasts and models such as the 6-10 day and 8-14 day forecasts, and the soil
moisture tools based on the GFS model and the Constructed Analogues for the season.
This Outlook depicts drought expansion in
Arizona, New Mexico, and northern Texas to conform to recent drying trends and medium and long-range precipitation
and temperature outlooks. Dryness across the southern tier states would be consistent with the La Niña-like pattern
of sea surface temperature anomalies evolving across the tropical Pacific Ocean. However, current circulation
patterns and some numerical models are consistent with a storm track emanating from the western Gulf of Mexico
toward the northeast. This pattern is bringing moisture from eastern and southern Texas into the lower Mississippi
Valley, and normal to above-normal rainfall is forecast for the Gulf region in the next 2 weeks. This somewhat
more optimistic outlook for the near term coupled with favorable Palmer Drought Index amelioration probabilities by
March continue to imply some drought improvement for the lower Mississippi Valley in keeping with the past several
seasonal drought outlooks.
Heavy thunderstorms on December 14 brought
over 5 inches of rain to the Houston area, and the storms were tracking across Louisiana late in the day. With the
ETA forecast model showing substantial rains exceeding 2 inches in Louisiana by the afternoon of December 15, the
start of the Outlook valid period, an area of green improvement color was added to the southern and eastern portions
of the drought area in that state. The same system was forecast to bring heavy rains to central Tennessee on December
15, resulting in improvement for that drought area as well. Lighter rains are forecast for Kentucky and southern
Ohio, so more limited improvement is shown there.
Farther east, there is broad agreement
from statistical and numerical models that Florida and the southeast Atlantic region should be dry for January-March,
but current soil moisture conditions and wet short-term forecasts argue against introducing drought development at
this time. This area, especially the Florida peninsula, bears watching for indications the long-range forecasts
In North Carolina, the ongoing storm track
favors continued improvement for the remaining drought area in the north-central part of the state.
In the Great Lakes region, this Outlook
is consistent with past Outlooks in showing persisting drought in Iowa and Illinois and some improvement in
Wisconsin and Michigan. Ongoing precipitation trends and numerical models favor improved odds for precipitation
northward from extreme northern Illinois.
This Outlook also continues to depict
persisting drought from eastern Wyoming into South Dakota and Nebraska, as there was no reason to depart from the
earlier Outlooks. Statistical and numerical models tend to show the odds tilting toward more wetness in the
northern Plains and more dryness in the southern Plains, so improvement in this area certainly cannot be ruled out.
There is also the possibility for drought expansion northward from Oklahoma farther into Kansas, but the official
CPC January-March precipitation outlook does not imply much expansion beyond the current northern extent of
drought, so northward development is not indicated on this release.
In the Northwest, northern Intermountain,
and northern Rockies, the recent trend toward less precipitation and stronger western ridging has resulted in
backing off from the more optimistic December 2 Drought Outlook to indicate more limited improvement in this
release. The CFS runs tilt slightly toward wetness for this area, and La Niña composites show some climate
divisions trending wet, but the signals are weak, so a broad-brush, conservative approach seems appropriate at this