September - November 2010

Outlook Graphic: GIF   PDF 

Latest Seasonal Assessment - The weather pattern for much of the summer has featured a subtropical ridge across the southern tier of the U.S. and an active storm track across the Northern Plains and Upper Midwest. Anomalously warm temperatures and suppressed convective coverage underneath the subtropical ridge has led to increasing drought conditions from the mid-Atlantic and the Southeast westward to the Southern Plains. In the Upper Mississippi Valley, several episodes of thunderstorms this summer has resulted in beneficial relief to protracted drought conditions, although recent dryness in the Dakotas has led to a small area of moderate drought in northern South Dakota. An active late-July and early August monsoon has reduced drought coverage in the Southwest, but since August there has been little drought relief in northern Arizona. Climatologically dry conditions have resulted in a persistence of moderate to severe drought across the Great Basin and the Northern Rockies, while moderate to exceptional drought continues across Hawaii. The forecast for the SON 2010 season calls for drought improvement for the Northeast, the coastal mid-Atlantic region, the Upper Mississippi Valley, the Dakotas and the southeast. Drought is expected to persist in the West, Southwest, the Southern Plains and Hawaii. While some improvement is forecast for northern Louisiana and the interior mid-Atlantic, drought is also forecast to develop or persist in the lower Ohio and middle Mississippi Valleys.

Tools used in the U.S. Drought Outlook (USDO) included the official CPC precipitation outlook for September 2010 and the long lead forecast for September - November 2010, 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, La Niña composites for the September - November season, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions.

Recent rainfall has helped to alleviate moderate drought conditions in the Northeast, although a small area of moderate drought continues to affect parts of central and eastern Maine. Five-day precipitation forecasts show potential for beneficial rains in this region. The medium-range, monthly and seasonal forecasts favor near-average precipitation in the 6-10/8-14 day period, and equal chances in the monthly and seasonal outlooks. There is a climatological increase in precipitation in the Northeast during the fall months. Based on these factors, improvement is forecast for this region.
Forecast confidence for the Northeast is moderate.

Drought has persisted across much of the Mid-Atlantic states due to above-average temperatures and spotty rainfall. Moderate drought exists in areas closer to the Atlantic coastline, while severe drought continues across eastern West Virginia, central Virginia into east-central North Carolina. In the short-term, outer rainbands associated with Hurricane Earl may affect parts of the mid-Atlantic coastline. Showers are also expected in the short-term associated with a frontal boundary in eastern West Virginia the Virginia and North Carolina piedmont. CPC's 6-10 and 8-14 day forecast favors near average precipitation closer to the coastline, with below-median precipitation in the interior. CPC's monthly forecast also shows a slight tilt in the odds toward above-median precipitation closer to the mid-Atlantic coastline. Improvement is forecast closer to the coast where greater prospects for precipitation coincide with areas where drought is less severe. Across interior areas, drought is less likely to improve given the dry medium-range forecasts but some improvement to conditions may be expected.
Forecast confidence for the Mid-Atlantic and the southeast is low to moderate.

Small areas of moderate drought continue across parts of Georgia, Alabama, and central Florida. Five-day precipitation forecasts for this region indicate only isolated precipitiation is expected in this region. CPC's medium-range and seasonal forecasts show near-average precipitation in this region, while the September forecast shows a slight tilt in the odds toward above-median precipitation. The potential for tropical cyclone activity early in the seasonal period supports drought improvement in this region. Increasing dryness associated with La Niña conditions during the winter months would suggest that further improvement to these drought areas would become increasingly less likely.
Forecast confidence for the Southeast is moderate.

In the upper Mississippi Valley and Great Lakes, long-term drought has diminished in severity and in areal coverage due to the effects of several rainfall episodes that have taken place this summer. Further west into the Dakotas, Recent dryness in the Dakotas has developed into moderate drought across a small portion of northern South Dakota. Short-term (0-5day) and medium-range (6-10 and 8-14 day) forecasts continue to show a tilt in the odds toward above-median precipitation across the northern Plains and Great Lakes region. The monthly and seasonal precipitation forecasts indicate equal chances for above or below-median precipitation in the upper Mississippi Valley, with a slight tilt in the odds toward above-median precipitation across the Dakotas. Drought is forecast to improve in the upper Mississippi Valley and the Dakotas.
Forecast confidence for the Dakotas, upper Mississippi Valley and Great Lakes region is moderate.

Moderate drought has now developed across parts of northern and central Arkansas into southern Missouri, while drought continues across the remainder of the mid-Mississippi and lower Ohio Valleys. A cold front pushing across the region may bring some precipitation in the short-term. However, CPC's 6-10 and 8-14 day forecast and the latest monthly and seasonal outlooks favor above-average temperatures and below-median precipitation across this region. In addition, La Niña composites for the September - November season show a signal for below-median precipitation. Several of the soil moisture forecasts continue to show mixed signals. The combination of CPC's forecasts favoring continued warm temperatures and the La Niña composites lead to a forecast of drought persistence in areas where D1 or greater drought currently exists, with developing drought conditions in western Arkansas.
Forecast confidence for the mid-Mississippi and lower Ohio Valley is low to moderate.

While a wet pattern in mid-August led to a substantial reduction in drought coverage in south-central Louisiana, moderate to extreme drought conditions continue in northern Louisiana, with moderate drought in eastern Texas. CPC's 6-10 and 8-14 day forecasts indicate enhanced probabilities for below-median precipitation, while the monthly and seasonal forecasts show equal chances for above or below-median precipitation. La Niña conditions would also lead to increasing dryness near the end of the period. The potential for tropical cyclone activity early in the seasonal period in the central Gulf Coast would support improvement, but it is not certain that a tropical cyclone would make landfall in the region. If a tropical cyclone were to make landfall in the central Gulf Coast, improvement would be more likely. Some improvement is forecast for northern Louisiana and eastern Texas.
Forecast confidence for northern Louisiana and eastern Texas is low.

Warm temperatures and dry conditions have led to expanding drought across Oklahoma and Texas. Though some precipitation is possible in the short-term across parts the drought area, the medium-range forecasts favor dryness in this region as the subtropical ridge persists across this region. The monthly and seasonal forecasts also do not show signals for improvement. Based on these forecasts, drought persistence is indicated.
Forecast confidence for the southern Plains is moderate.

An increase in late-spring precipitation in the Northern Rockies and the Great Basin resulted in beneficial drought improvement. Small areas of moderate to severe drought remain across the Northern Rockies, while an area of D1/D2 drought continues in the Great Basin. There is little change in the forecast reasoning regarding drought tendency in the northern Rockies from the previous outlook. Climatological dry conditions and monthly and seasonal precipitation and streamflow forecasts favoring dryness lead to a forecast of drought persistence.
Forecast confidence for the Great Basin and the Northern Rockies is high.

Although there has been some monsoon activity in the southwest since the previous outlook, the precipitation has not resulted in significant improvement to ongoing drought in northern Arizona. As the North American Monsoon climatologically ends in September, additional rainfall becomes increasingly less likely. CPC's latest medium to long-range forecasts also favor dry conditions in this region. Thus, drought persistence is forecast for the Southwest.
Forecast confidence for the Southwest is moderate.

Moderate to exceptional drought (D1 to D4 designations) continues across the leeward sides of the Hawaiian Islands. Forecasts for these areas call for below-median rainfall during September - November, leading to a forecast of drought persistence. Precipitation does show a climatological increase later in fall, and La Niña conditions would tend to favor above-average precipitation during the winter months. This suggests drought improvement could become more likely beyond this forecast period.
Forecast confidence for Hawaii is high.