Latest Seasonal Assessment -
The update to the Seasonal Drought Outlook posted on December 2 reflected improved soil moisture conditions in the
Southeast and more pessimistic prospects in the Southwest and southern Plains. Thanks to good November rains and
prospects for more rain in December, the latest Outlook no longer indicates drought development in the
Southeast, although the odds still favor below-normal rainfall during the winter season for Florida and the South
Atlantic coast. Farther west, soils have continued to dry out from Arizona into Texas and the lower Mississippi
Valley, as combined October-November rainfall totaled less than 60% of normal for most of this region, and less than
40% of normal from northeast New Mexico to northern Texas and into Oklahoma, east Texas, and Mississippi. The new
Drought Outlook indicates enhanced risk for drought development across Oklahoma, north Texas, and eastern New
Mexico, as well as over southern Arizona. In contrast, some improvement is forecast for southern and eastern Texas
into Arkansas and Louisiana. The odds tilt toward improvement in Kentucky and Tennessee, as well as North Carolina
and much of the Northwest and into the northern Rockies, including western Wyoming. A number of reservoirs will
continue to measure below-normal storage in the Northwest despite recent rain and snow. More limited improvement is
foreseen in the Great Lakes region and central Wyoming, with little change expected from eastern Wyoming into Iowa
Tools used in the Drought Outlook
included the official CPC long-lead precipitation outlook for December 2005 - February 2006, the drought termination
and amelioration probabilities for February 2006, 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 November 17 Drought Outlook was updated on December 2 mainly to account for improved drought prospects in the Southeast and the deteriorating situation in the southern Plains and the Southwest.
Rains during November eliminated most of the D0 dry areas in Georgia, Alabama, and northwest Florida on the U.S. Drought Monitor, and forecast models suggest more rain is on the way for the first half of December. Since there are still a number of long-range indicators pointing to below-normal rainfall this winter in the region, the threat of drought development has not been eliminated, but the odds have diminished enough to warrant removing the development area from the map at this time. The potential for development will be considered again when the next regularly scheduled CPC long-lead temperature and precipitation outlooks, as well as the Drought Outlook, are released on December 15.
Elsewhere, November rainfall totaled less than one-quarter of an inch over central and western Oklahoma and western Texas, with under one-tenth of an inch in eastern New Mexico and southeastern Arizona. The Drought Monitor recently added an area of D1 drought to the Texas Panhandle, and D0 dryness covers a broad area from southern and northern Arizona eastward through central Texas. With CPC indicating a tilt of the odds toward below-normal rainfall for December in the updated monthly outlook from Arizona to Texas and Oklahoma, odds have increased for drought to expand across northern Texas and over much of Oklahoma and parts of New Mexico, and the updated Drought Outlook indicates such an expansion. A number of numerical models are consistent with continued dryness or drought in this region, including the CFS monthly and seasonal forecasts for precipitation and soil moisture. Such model results are roughly consistent with the ongoing SST pattern in the Pacific Ocean. Whether or not we officially enter a La Nina situation this winter, the pattern of cold water seen recently in the eastern tropical Pacific is not conducive to an active subtropical jet and accompanying heavy rains across the southern states.
If the next CPC seasonal precipitation outlooks indicate below-normal rainfall for January-March, the odds for drought development will increase over a broader area of the Southwest. Over the shorter term, December may see some beneficial precipitation in eastern Texas and over the southern Mississippi Valley, as Gulf moisture overruns high pressure to the north. As a result, some drought improvement is anticipated over southern and eastern Texas and eastward into Arkansas and Louisiana.
For areas from the Rockies westward to the Pacific Coast, substantial precipitation during the cold half of the year is critical. Ideally, snow piles up on the higher elevations before melting slowly as spring progresses, refilling the streams, rivers, and reservoirs that serve as the region’s primary water sources. So far, the 2005-2006 water year is off to a good start in most areas currently experiencing moderate to severe drought (as depicted in the Drought Monitor). Snow water content is at least slightly higher than normal as of early December, with 110 to 150 percent of normal over most of Oregon, western Washington, central and southern Idaho, and southwestern Montana. However, the water recharge season is only about 8 weeks old, and with a vast majority of the season still to come, the current short-term wetness will mean little if below-normal precipitation occurs during the next few months. Therefore, precipitation from the Rockies westward during this forecast period is critical and will be closely monitored. The updated CPC monthly outlook indicates wetness for much of the Northwest in December, and this, along with wetness in the short-term forecasts, suggests the odds tilting toward continued improvement in the Northwest into the Rockies. In addition, a number of long-range forecast tools, including the latest CFS runs, tilt toward wetness through the winter across the region. Reservoir contents, however, will likely remain below average for at least the next few months in some areas, and the latest week 2 forecasts indicate dryness for the region.
Farther east, drought is forecast to persist in a swath from the Wyoming High Plains eastward through most of the northern tier of Illinois, where drier than normal conditions are expected during the next 2 weeks. There are no strong indicators for either above- or below-normal December – February precipitation per se, but since this is a relatively dry time of year (particularly in the High Plains) and there are no indicators strongly pointing toward wetter than normal conditions, substantial drought relief seems unlikely by the end of February.
In the central and southern Great Lakes region, climatology indicates that a substantial reduction of long-term moisture deficits is unlikely by February, and the next 2 weeks are expected to be drier than normal. However, winter precipitation climatologically accounts for a larger proportion of the annual total here than in areas farther west, and additionally, with lake-effect and lake-enhanced snowfall relatively common, it seems likely that at least a temporary reduction of some drought impacts should occur over the course of the next few months.
Drought has improved somewhat with recent rains in North Carolina, although short water supplies and water usage restrictions remain in place for several locales. The objective indicators are generally neutral for the next 3 months, but two or more storms during the first 10 days of December should bring considerable precipitation to the remaining drought area, leading to improvement, albeit accompanied by continued below-normal reservoir levels.
Finally, the drought area in Kentucky and Tennessee has seen recent improvement and short-term conditions favor additional beneficial precipitation, especially in eastern areas.