April - June 2008

Latest Seasonal Assessment - Although exceptional drought has been eliminated across the Southeast, 12-month precipitation deficits exceed 12 inches across parts of Alabama, Georgia, Tennessee, and the Carolinas. The forecast indicates continued drought improvement across the Southeast, but long-term hydrological impacts will persist as water demand increases by the summer. Some improvement is expected across the southwest Florida peninsula where a wet upcoming week should be followed by a drying trend before the onset of the summer thunderstorm season. Small areas of moderate drought in the eastern Dakotas and Minnesota should experience relief. Some improvement is forecast for the northern high Plains and northern Rockies. Drought persistence or development is forecast for the central and southern high Plains, west Texas, and much of New Mexico. Although the April – June seasonal forecast indicates below normal precipitation for parts of Nevada and Utah, spring snow melt should boost water supplies and result in improvement across the northern Great Basin. Persistence is forecast in southern Nevada, southern California, and southwest Arizona due to a dry climatology.

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for April and April - June 2008, the four-month drought termination and amelioration probabilities, 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 moisture, the CFS seasonal precipitation forecasts, and La Niña composites.

Minor changes made to the previous outlook, released on March 20, were largely based on short and medium range forecasts.

During the winter, the widespread area of exceptional drought was eliminated across Alabama, Georgia, Tennessee, and the Carolinas. However, 12-month precipitation deficits remain above 12 inches in those areas. Lake Lanier, north of Atlanta, reached a record low on December 28, 2007. The lake level has risen, but it remains below normal. The window for winter-spring recharge will end shortly. Although improvement or some improvement is forecast for the southeast, long-term hydrological impacts will likely continue into the summer when water demands increase. Alabama, Tennessee, and Georgia are most likely to experience improvement. Monthly precipitation forecasts indicate lower odds for improvement across the coastal Plain of the Carolinas. HPC’s 1-5 day precipitation forecast shows a widespread area of 1 – 2 inches across the southeast, with more than 3 inches in Tennessee. The CPC 6-10 forecast indicates that above normal precipitation will continue into the second week of April.
Confidence: Moderate

Due to expected wetness during the next two weeks and the upcoming onset of the summer convection later in May, drought development is not expected across Florida. Some improvement is forecast for the southwest Florida peninsula due to variable conditions within the valid period. During the next week, beneficial rainfall (1 – 3 inches) can be expected. During the latter half of April into early May, a brief period of drier weather may prevail before the summer convective rains begin.
Confidence: Moderate

Across the eastern Dakotas and Minnesota, improvement for the two small areas of moderate drought is expected. Climatology with the start of the summer thunderstorm season favors some improvement across the western Dakotas.
Confidence: Moderate

The western Corn Belt is susceptible to dryness during La Niña springs. However, the latest CFS seasonal precipitation forecast indicates above normal precipitation from Nebraska into western Iowa. Development should be limited to the central high Plains where abnormal dryness currently exists.
Confidence: Moderate

A sharp gradient between drier-than-normal and wetter-than-normal conditions currently exists across the Texas Panhandle into north-central Texas. With the above normal precipitation during March, the development area on the March 20 outlook has been reduced in parts of Texas. Seasonal precipitation tools including the official CPC outlook favor a widespread area of persistence or development across the southern high Plains. More than 100 counties in Texas are under burn bans and the expected dryness will likely maintain a high wildfire risk during the spring.
Confidence: High

Since December, a series of winter storms have resulted in drought improvement across the west, especially in the central Rockies. However, drought associated with hydrological impacts persists. Snow-water equivalent values are at or above normal throughout most of the West, including southern Idaho, northern Utah, and parts of Nevada. Despite below normal precipitation in the CPC seasonal outlook, the combination of the upcoming spring snow melt and a few more expected storms in the short to medium range should bring improvement to much of the northern Great Basin. Farther south, in southern California, southern Nevada, and southwest Arizona, persistence is likely due to climatology.
Confidence: Low

In Hawaii, abnormal dryness currently exists. Development is not forecast through June, but longer range forecasts suggest that development could occur later in the summer.
Confidence: Low