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Climate Prediction Center

 
 
 

July - September 2009

 

Outlook Graphic: GIF   PDF Adobe PDF Reader

 

Latest Seasonal Assessment - Continued hot, dry weather will likely lead to an expansion of drought across eastern Texas during the latter part of June. Farther south, some moisture may benefit South Texas, but no significant relief is forecast for the historical drought covering south-central Texas. The odds for improvement increase in northern Texas, where prospects range from limited improvement to more significant improvement. The best chance for improvement extends from western Texas into New Mexico. Above-normal rains are forecast early in the period for this area, and the summer thunderstorm season that runs from July into September is expected to offer additional relief. Shower activity is forecast to bring some improvement to the Oklahoma Panhandle, while small drought areas in central Oklahoma are forecast to merge. In the West, unseasonable rains during the first half of June brought some drought relief, especially for Oregon and Idaho. Although above-normal rains are forecast for the latter part of June over the Northwest, amounts are expected to be less than observed earlier in the month, and the July-September period is typically not favorable for drought relief. As a consequence, drought should largely persist from California and Nevada into southern Oregon. The long-standing drought in northern Wisconsin and southeastern Minnesota is forecast to improve, thanks in part to heavy rains forecast for the early stages of the forecast period. Drought in Hawaii is likely to continue to expand.

 
Discussion for the Seasonal Drought Outlook
 

Tools used in the Drought Outlook included the official CPC precipitation outlook for July 2009 and the long lead forecast for July September 2009, the four-month Palmer 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 Climate Forecast System (CFS) seasonal precipitation forecasts, and climatology.

In Wisconsin and Minnesota, the 5-day QPF for the start of the forecast period depicted 1.5 to more than 2 inches of rain. CPC extended-range forecasts (6-10 and 8-14 days) indicated that above-median rain was likely beyond the 5-day period. The CPC soil moisture models indicated a 20-40 mm reduction in the deficits over the drought area by the end of week 2. These positive developments are enough to swing the Outlook from some improvement to improvement despite continued uncertainty about the July-September precipitation outlook.
Forecast confidence for Wisconsin and Minnesota is moderate.

For Texas, the first half of June was unusually dry across southern and eastern Texas into Louisiana. Houston reported a mere trace of rainfall from June 1-16, with temperatures mid-month rising into the upper 90s. Hot, dry weather during the first 5 days of the forecast period is expected to exacerbate dryness, but a wetter pattern for southern and eastern Texas is forecast for the extended-range forecasts. Above-normal rainfall is forecast for Louisiana in the extended range. Drought is forecast to expand eastward in Texas, but the likelihood for significant rains in Louisiana keeps the development area out of Louisiana. Model forecasts for the extended range indicate a surge northward of moisture that could bring showers to Deep South Texas toward the end of June, so some improvement is indicated for this area, expanded slightly to the west from the previous Outlook due mainly to the 2-week soil moisture forecasts. The bulk of the drought area in south-central Texas is depicted to persist, as climatology suggests reduced odds for significant improvement this time of the year. El Nino analogs played no more than a very minor role in this Outlook, given that impacts this time of the year are generally considered minor, but it is noted that one of the 3-month soil model forecasts driven by historical El Nino events shows increased odds for dryness in south-central Texas compared to all historical years. Also, the CFS model shows enhanced odds for below-normal rainfall for southern Texas. Farther north, the Drought Outlook continues to indicate some improvement for northern Texas, with improvement farther west. This is consistent with various seasonal precipitation and soil moisture forecasts and is similar to the previous Outlook. The confidence for improvement over west Texas and into New Mexico is relatively high, given consistency between short range and long-range precipitation forecasts. The official CPC July-September precipitation outlook shows equal chances for wet, dry, or median for the southern Plains except for extreme western Texas and Oklahoma.
Forecast confidence for southern, central, and eastern Texas is moderate. Confidence for West Texas is high.

The Outlook continues to show improvement for the Southwest, with especially high expectations for improvement for the New Mexico area and adjacent Texas as a surge of moisture out of Mexico was evident on satellite imagery at the time this Outlook was prepared. Given this initial rainfall, plus the typical improvement from summer thunderstorms during July-September, prospects for improvement look favorable. The CPC official seasonal outlook shows the odds tilting toward above-median rainfall across much of the Southwest, further adding to confidence in the drought outlook.
Forecast confidence for the Southwest is high.

In far western Oklahoma, the odds for improvement increase toward the west based on climatology and the seasonal rainfall outlook. Some improvement continues to be shown for the Panhandle. The two small areas of drought in central Oklahoma are expected to persist based on short term and extended range forecasts showing below-median rainfall and above-normal temperatures, as well as climatological considerations.
Confidence for Oklahoma is moderate.

This Outlook replaces the area of some improvement in northern California, Oregon, and Idaho with persisting drought. Although an upper-level trough is expected to bring above-median rainfall to much of the Northwest during the latter half of June, rainfall amounts are not expected to be as high as those received earlier in June. In addition, the Outlook period covers the time of the year when drought improvement is unlikely. Confidence in the Outlook is reduced because of the possibility that the short-term moisture could have more of an impact than expected.
Forecast confidence for the West is moderate.

The area of drought shown for northern Washington continues to be depicted as persisting. Extended-range forecasts indicate above-median rains, but actual rainfall amounts in the drought area are expected to be light. In addition, the CPC long-lead monthly and seasonal outlooks show the odds leaning toward warmth and dryness for Washington. To the east, above-median rainfall amounts are expected during the last half of June over Montana, and some improvement is indicated for the small area in northern Montana due to favorable prospects for beneficial rains in the short-term. The CPC long-lead outlooks depict the odds tilting toward below-normal rainfall for July and July-September, reducing the likelihood for continued improvement.
Confidence for Washington and Montana is moderate.

The Outlook for the small drought area in southern Alaska is more optimistic due to extended-range forecasts of above-median rainfall. With neither the CPC long-lead monthly nor seasonal outlooks showing below-normal rainfall, the odds now favor improvement.
Forecast confidence for Alaska is moderate.

In Hawaii, with the dry season in progress, persisting and expanding drought continues to be forecast. Below-normal rainfall is forecast for the extended range. Long-range forecasts are more uncertain for this period, so the confidence in the drought outlook is not as high.
Forecast confidence for Hawaii is moderate.


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Page Author: Climate Prediction Center Internet Team
Page last modified: June 18, 2009
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