Latest Seasonal Assessment -
Continued abnormally dry weather through the first half of January led to expanding
drought across the Southwest and continued drought over the southern Plains. Beneficial
rains in the southern Mississippi Valley brought some improvement to that region by
mid-January, but severe drought continued over Arkansas and parts of Missouri and
Louisiana. Probabilities for below-normal precipitation and above-normal warmth
enhanced the odds for drought over much of the Southwest at least through April, with a
good chance that drought will further expand. In mid-January, mountain snow pack, an
important source of spring and summer water supplies in the West, was well under one-half
of normal from southern parts of Utah and Colorado southward, and less than 10 percent
of normal over much of Arizona and New Mexico. At lower levels, some impressive dry
streaks had taken hold. As of January 17, Phoenix had reported no rain since October 18. With
the latest official outlook for February-April showing the odds tilting toward below-normal
precipitation from the Southwest into the southern and central Plains, there is an
enhanced risk of drought expanding from the Southwest into the southern and central
Plains as far north as Nebraska. Drought should persist in central Texas, but some
improvement is likely from eastern parts of Texas and Oklahoma into Arkansas and western
Louisiana. No measurable rain had fallen at the Dallas-Fort Worth Airport from December
21 through January 17, but this dry streak looked likely to end soon. More significant
improvement is on tap for extreme eastern Arkansas and eastern Louisiana, as well as the
drought covering parts of Kentucky and Tennessee. Forecasts of below-normal rainfall
during February to April have led to risk of drought development over the Florida
peninsula. To the north, the serious drought affecting northern Illinois and adjacent
Iowa is likely to continue into the spring, but periods of rain or snow should lead to
some improvement. The odds for improvement diminish westward, and drought will likely
persist, or could even expand, from western Iowa into Nebraska. Some improvement is
expected in lingering drought areas of Wyoming and Montana. Recent heavy rain and snow
has finally ended the multi-year drought across the Northwest. In the Pacific, a
drought affecting northern parts of the Hawaiian Island chain should be alleviated.
Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for February-April, the drought termination and amelioration probabilities for April, 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 continues to depict drought expansion in Arizona, New Mexico, and western Texas to conform to recent drying trends, low to non-existent mountain snow packs, and medium and long-range precipitation and temperature outlooks. The latest U.S. Drought Monitor recently expanded drought coverage in Arizona and New Mexico, and also introduced D1 drought into southern Colorado. The Drought Outlook does not extend drought development into southern California because of lingering longer-term wetness in that area as shown by such indicators as the Palmer Drought Index. Also, snow pack in the southern Sierra Nevada was above normal as of mid-January. But the new seasonal temperature and precipitation outlooks for February-April imply an increase in dryness across southern California as well as southern Nevada that should be monitored.
Consistent with the developing La Niña, the seasonal precipitation outlook shows the odds tilting toward below-normal precipitation not only across the Southwest, but also from Texas into Nebraska. This implies that existing drought in western and central portions of Texas and Oklahoma could persist at least through April, and drought could expand into southwest Texas as well as into Kansas and farther into Nebraska and Colorado. As a result, a significant change from last month's Drought Outlook is the indication of enhanced risk of drought in southwest Texas and from Oklahoma through Kansas into central Nebraska. The theme of below-normal precipitation into spring is consistent with a number of both statistical and numerical models, although there are the usual differences in the details. Medium-range forecasts show a pattern of troughs digging southward into the Rockies and Plains that will result in storm systems moving through the central United States during the first 2 weeks of the outlook period, and a few longer-term moisture indices remain quite favorable in the Kansas area. These factors reduce confidence to some extent in drought expansion northward from Oklahoma.
The Outlook is more optimistic from eastern parts of Oklahoma and Texas into the Mississippi Valley. The most recent 6-10 day and 8-14 day forecasts indicate above-normal chances for wetness in southeast Oklahoma and eastern Texas and locations to the east, although models differ on the intensity and extent of the rains, adding uncertainty about western boundary of the area of some improvement. There are mixed signals in the longer-range models, resulting in the monthly and seasonal precipitation outlooks indicating equal chances for wet or dry. The odds for wetness generally increase eastward, consistent with previous Outlooks. The improvement shown for the new drought area in southeastern Louisiana and southern Mississippi is largely driven by the heavy rains expected during the first few days of the forecast period, but improvement is also consistent with the Palmer drought amelioration probabilities for April and a general tendency for recent forecast models to show enhanced northward transport of moisture from the Gulf of Mexico. Of course, there are no sure things in long-range forecasting, and it should be noted that La Niña rainfall composites tend to show some dryness during this time of the year along the Gulf Coast, so a return to a drier pattern cannot be ruled out.
Farther east, dryness over Florida is a fairly reliable La Niña signal, and this Outlook depicts a risk for drought development over those parts of the peninsula that have been recently trending dry. Over the Tennessee and Ohio Valleys, forecasts ranging from the short term to the seasonal are consistent with La Niña composites in showing a strong tendency toward wetness, so the confidence is relatively high that the drought in Kentucky and Tennessee will end or be significantly relieved.
Severe to extreme drought continues in northern Illinois and adjacent parts of Iowa. Although the odds for drought termination by April are negligible, medium and long-range precipitation outlooks, along with recent trends, are consistent with some improvement. La Niña events tend to promote dryness from western Iowa into Nebraska, with Illinois and eastern Iowa more uncertain.
In Hawaii, a small area of drought that has recently developed on the northern islands should see improvement based on long-range rainfall forecasts and the resumption of trade winds and associated showers.