July - September 2004

Latest Seasonal Assessment - The drought in the interior West is forecast to persist, as significant relief from the water shortages cannot be expected until the 2004-05 snow season at the earliest. Nevertheless, showers will aid soil moisture in some areas, benefiting crops and pastures, and reducing the threat of wildfires. The best chances for limited improvement are in western and central Montana, as well as the areas in the desert Southwest typically affected by the summer "monsoon" rains. The odds favor drought development over interior Washington, where a small area of drought already persists, and forecasts call for a tendency toward warm and dry weather during the last half of June and dryness during July-September. Farther east, drought did develop as forecast in western Oklahoma and the Texas Panhandle, but the odds favor some improvement in this area over the coming season. To the north, expected heavy rains near the start of the forecast period, especially during June 17-22, lead to improving prospects for Kansas and central Nebraska. Less improvement is on tap for Nebraska's Panhandle and western parts of the Dakotas. Saturated soils and rivers at or above bankful mean that the odds of drought developing are very small across the Midwest, where drier weather would be welcomed. As suggested in the previous Outlook, the Southeast has seen improving conditions, with 2 to 4-inch and greater rainfall amounts in Georgia and South Carolina during the first half of June significantly boosting soil moisture. With the increase in temperatures, evaporation, and water demand typical of the summer season, and medium and long-range forecasts leaning toward above-normal temperatures, drought relief could become more difficult and spotty as summer progresses, so more limited improvement is indicated in this month's Outlook. Of course, tropical weather systems could quickly relieve the remaining drought at any time, but these are generally not forecast more than a few days in advance.

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for July-September Palmer Drought Index Probability Projections for September various medium and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, and the soil moisture tools based on the GFS model and the Constucted Analogues for the season.

The drought forecast for the interior West continues to call for persisting drought since the snow season is essentially over and there is little chance that the hydrologic drought can improve before the snows fly next winter. However, rains can and do improve soil moisture and crop and pasture prospects during the late spring and summer period, as recently seen in Montana. This month's Outlook shows some improvement in the western half of Montana due largely to medium-range forecasts of normal to above-normal rainfall for the last half of June. The latest CAS soil moisture outlook for the end of September shows near-normal moisture over Montana, with the core dry area extending from California into the Great Basin. With a number of forecast tools showing a tendency toward warmth and dryness in the interior West, the confidence is relatively high that this core area is least likely to see improvement. In the Pacific Northwest, with the CPC long-lead guidance indicating increased odds for below-normal rainfall from Nevada to Washington during July-September, and medium-range forecasts showing warm and dry in Washington, this month's Outlook continues to show an area of drought development in Washington. The area has been reduced from last month due to recent rains. Northeast Washington is currently in D1 drought on the latest U.S. Drought Monitor, and most of the forecast drought area is currently in D0, implying some vulnerability to drought.

In the Southwest, the area of some improvement expected across southern Arizona and central and southern New Mexico continues to be based on typical patterns resulting from the summer monsoon rains, which mostly fall in July and August. Such rains have little impact on water supplies but do benefit fire danger and non-irrigated agriculture. There are no strong forecast signals for either an above normal or below normal monsoon at this time, so the drought outlook is based on historical mean data in the Southwest.

Heavy rains expected to exceed 2 inches in some locations during June 17-22 contributed to the forecast for improvement in the Kansas-Nebraska area, with the 6-10 day and 8-14 day forecasts issued on June 15 suggesting that the wet trend would continue for the central and southern Plains. A number of statistical forecast tools suggested above-normal rainfall in the southern Plains during July-September, but the dynamic models tended to be more ambivalent, and the official long-lead outlook went with equal chances for above or below normal as a result. The conclusion is that there is little evidence that a dry pattern will persist. The picture is mixed for the new drought areas in west Texas, with a building ridge in the near-term not conducive to improvement but some long-range forecast tools showing wetness. Some improvement was indicated as a compromise for this outlook. In the northern Plains, this month's Outlook was somewhat more pessimistic about drought prospects in eastern Montana and the western Dakotas due to some signals from the latest ensemble medium-range models that the large-scale circulation pattern would change during the last week of June, with a ridge building over the Rockies and a trough off the West Coast. Experimental weekly and monthly GSM and RSM runs suggest this pattern could persist through July, so a tendency toward drier and warmer weather in the northern Plains toward the end of June and continuing into July could offset the impacts from beneficial showers expected during the third week of June.

In the Southeast, heavy rains from a tropical disturbance during the second week of June brought significant improvement to the drought area. However, with medium-range forecasts showing a build-up of high pressure and resulting above-normal temperatures, and the July-September temperature guidance from CPC also leaning toward warmth in the northern part of the remaining drought area, the Drought Outlook this month took a slightly more cautious approach to improvement from here on out. Also, the latest CAS soil moisture forecast for the end of September showed a tendency for some dry soils to persist in the Southeast, further reducing the confidence in additional improvement. As always during this time of the year, tropical systems could rapidly relieve the remaining drought anytime between now and the end of September, but these cannot be forecast more than a few days in advance.