January - March 2006

Latest Seasonal Assessment - Abnormally dry weather through the first half of December has led to expanding drought across parts of the Southwest and southern Plains, and prospects look dim for much improvement into the first quarter of the new year. With the latest official precipitation outlook for January-March showing the odds tilting toward the dry side, the risks for drought expansion have increased from Arizona eastward through New Mexico and northern Texas. Some improvement remains on tap for southern and eastern Texas, as well as other parts of the southern Mississippi Valley, but drought should largely persist across Oklahoma, northern Texas and western Arkansas. More significant improvement is indicated for Louisiana and Tennessee thanks largely to heavy thunderstorms falling near the start of the Outlook period in mid-December. Some improvement is also anticipated for the drought affecting Kentucky and southern Ohio, with better odds for improvement for the lingering drought area in North Carolina. Drought should persist in Iowa and Illinois, but some improvement is on the horizon for southern Wisconsin and Michigan. Little change in the drought situation is expected from eastern Wyoming into South Dakota and Nebraska, but some improvement is indicated for the Northwest and northern Rockies.

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 are verifying.

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 time.