July - September 2008

Latest Seasonal Assessment - Much of Texas has experienced hot and fairly dry conditions during the past two weeks. Since the start of this year, southwestern and southern Texas have reported only 25 to 50 percent of normal rainfall. Drought conditions will likely persist across most of the state, though the odds for improvement are elevated closer to the Gulf Coast. These improved odds near the coast are based on historical conditions during this time of the year. In the Southwest, little if any rainfall is expected from the Southwest Monsoon during the next two weeks. Although there are no strong indications at this time regarding the strength and duration of this monsoon season, rainfall during July through September typically improves conditions from southeastern Arizona into New Mexico. Farther west, there has been a recent expansion of drought in California, and the official extended range forecasts show little if any precipitation across the state. It is unlikely that California will receive significant improvement during the ongoing dry season. Easing drought conditions are indicated for western North Dakota, which has recently seen beneficial rains after a prolonged dry period. In the Southeast states, improvement is indicated across southern Florida, and over the southern Atlantic coastal plain. Drought recovery is less likely farther inland across the core drought area covering the western Carolinas, northeast Georgia, and far eastern Tennessee. The Hawaiian Islands are likely to experience expanding drought, especially along the leeward slopes.

Tools used in the Drought Outlook included the official CPC precipitation outlook for July 2008 and the long lead forecast for July - September 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 (CAS) moisture, the CFS seasonal precipitation forecasts, and climatology.

Improvement for drought across the interior Southeast has slowed and even reversed during the first half of June as hot, dry weather has taken its toll on soil moisture and stream flows. The Outlook continues to call for improvement over Florida and expands improvement into the coastal Plain of the Southeast from Alabama into the Carolinas and Virginia. This is consistent with the new CPC rainfall outlook for July-September, which shows a slight tilt of the odds toward wetness along the Gulf Coast. The improvement for eastern parts of the Carolinas and over south-central Virginia is based on historical outcomes as shown by the NCDC Palmer probability maps for September. Eastern areas of North Carolina, for example, show at least a 60 percent chance for drought amelioration by September. For the short term, improvement in the coastal zones is also consistent with the June 18-23 QPF, which depicts over 1 inch of rain over the coastal Carolinas. The CAS soil moisture indications for July, August, and September are also consistent with a coastal decrease in dryness. In contrast, from the western Carolinas into northern Georgia, the CAS and the Palmer probability maps show less chance for improvement resulting in Drought Outlook showing a progression from some improvement to persistence. The latest week-2 forecast does show normal to above normal rainfall for the Southeast, so spotty soil moisture improvement is likely at least over the short term. However, hydrological drought indicators such as reservoirs and groundwater are unlikely to improve during the summer absent a significant tropical weather system. The onset of the rainy season in Florida makes the improvement shown there a relatively confident forecast.
Confidence for Florida: High.
Confidence of the interior Southeast: Moderate

Hot, dry weather in June sharply reduced soil moisture in Texas, resulting in drought expanding and intensifying over much of the state. The thunderstorms that tracked southeastward across the state during the night on June 17 despite a strong high pressure ridge over the region illustrate the challenge of making long-range forecasts for this part of the nation. The various forecast tools are not consistent for the coming weeks and months over most of Texas. There is a trend toward cooler weather for the rest of June, and the latest forecast for June 25 to July 1 from CPC shows a broad area of wetness from southern Texas into the Southeast, in marked contrast to the drier 6 to 10 day forecast. For the Drought Outlook, key long range indicators included the Palmer drought alleviation probabilities going through September as well as consideration of monthly normal rainfall totals. These suggested improvement near the Gulf Coast and lower odds for improvement farther inland. The odds for improvement then increase again in western Texas going into New Mexico from the Southwestern monsoon rains which usually begin in July. Short- and long-range forecasts generally indicate increased odds for enhanced rainfall going northward from northern Texas into the central Plains, resulting in improvement from northeast Colorado into North Dakota.
Confidence for Texas and eastern Colorado: Low
Confidence for the Southwest and Nebraska: Moderate
Confidence for North Dakota: High

For the West, the ongoing dry season results in expected persisting drought for the California area, while the CPC July-September outlook indicating a tilt of the odds toward dryness over the Northwest into the northern Rockies contributes to persisting drought from southeast Oregon into southwest Wyoming.

In Hawaii, the drought forecast is unchanged from the preceding forecast, with development expected in many leeward areas due to a seasonal forecast for below-normal rainfall.