Tuesday, July 24, 2007

U.S. seasonal drought outlook from NOAA

The latest seasonal update is available from NOAA's website: Short and long range forecasts favor improvement across much of the South and the East. Showers and thunderstorms are expected in the short range while the seasonal forecast favors above normal rainfall during the August-October period.

Drought conditions are expected to gradually improve across the Tennessee and southern Ohio valleys. However, substantial moisture deficits will likely persist. Year-to-date rainfall deficits range from 10 to 20+ inches in this region. Although these deficits are expected to slowly decrease, the chances of these deficits and their impacts being eliminated are small.

The forecast period covers the height of the hurricane season. The remnants of a tropical system can reduce drought conditions very quickly. However, the occurrence of such events can not be accurately forecast more than a few days in advance. Over the Upper Midwest, moderate to locally severe drought has developed. In the short range, little if any improvement is expected. Drought conditions will likely worsen during the rest of July into early August. This may have a negative impact on agriculture.

As September and October progress, opportunities for significant rainfall and drought improvement will increase. Over the western states, record low precipitation totals for the 2006-07 water year in some areas has resulted in the development of severe drought across the Southwest.

In the northern Rockies, recent heat and dry weather have resulted in drought development. Drought conditions will persist through the period, with possible expansion into northwestern California, Washington, Oregon and central Montana.

In Hawaii, drought is expected to persist across the leeward side of the island chain through October. On the Big Island, Tropical Storm Cosme may generate some significant rainfall during the first few days of the period. The best rains will likely be on the eastern side of the island.

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