June - August 2004

Latest Seasonal Assessment - The drought in the interior West will persist through summer, as the water supply situation stays the same or worsens in coming months due to below-normal snow accumulation during the winter season. The summer thunderstorm season during July and August will likely bring no more than short-term relief from dryness, and the long-term hydrological drought should persist at least until next winter's snow season. In the Pacific Northwest, dry weather in April contributed to low streamflows and decreasing soil moisture, and the June-August forecast for below-normal rainfall and above-normal temperatures has increased the odds for drought development in Washington and Oregon. Since the dryness should have fewer impacts west of the Cascades, drought is not expected to develop in coastal sections. Reservoir levels should not be a problem for most of this area, as Washington was the only western state with above-normal reservoir storage on May 1. Farther east, recent rains have brought significant drought relief to the upper Midwest, and this relief should continue, especially in Minnesota and eastern and central portions of the Dakotas and Nebraska. No more than limited improvement is expected in western Kansas, and there is increased risk of drought development over western and central Oklahoma and portions of southern Kansas and northern Texas, especially during the early part of the forecast period. Drought persists in parts of the Southeast, but much of the affected region should see improvement by the end of August, if not earlier. Nevertheless, with the increase in temperatures, evaporation, and water demand typical of the summer season, drought relief could become more difficult and time-consuming as higher temperatures take hold in the Southeast.

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for June-August, the Palmer Drought Index Probability Projections for August, 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 as the snow season comes to an end and streamflow diminishes in response to below-normal spring snow pack in most states. A fairly stormy pattern developed in May, bringing rain and snow to northern parts of the Rockies, and some central areas as well, and above-normal precipitation should continue at least into late May. Although this may not have a large impact on water supplies, the moisture will benefit agriculture and ease wildfire danger. The forecast map depicts some improvement in Montana and the High Plains in response to the short-term outlook for wetness. The improvement shown is relatively modest as there are some indications—such as shown in the Constructed Analogue Soil moisture forecasts--that a drier and hotter pattern will take hold later in the forecast period across the northern Rockies.

In the Pacific Northwest, there are conflicting signals between the short-term and the long-term forecasts, with normal to above-normal rainfall on tap for the first 2 weeks of the forecast period and abnormally dry and warm weather forecast for the June-August period. The area shown as developing drought shows the area at highest risk based on current conditions and the forecasts for the various time periods. Drought is not forecast along the coasts of Washington and Oregon because of minimal impacts expected this time of the year. Where development is shown, most of the impacts would be on fire danger and non-irrigated agriculture, as reservoirs are generally in good condition.

In the Southwest, the area of some improvement expected across southern Arizona and central and southern New Mexico is 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.

The near-term rainfall forecasts as well as climatic probabilities result in the depiction of continued improvement in the upper Midwest, consistent with the theme of the past several outlooks. Recent rains already eased drought in this region, especially in the Minnesota area, and more rain is expected during the second half of May.

The forecast depiction is more pessimistic for the southern Plains this month, as forecast models show a ridge building up during the last half of May, leading to a dry and hot weather pattern. Since short-term dryness has already been on the increase during May in the Oklahoma area, hot, dry weather during the last half of May would result in a good chance for drought development over parts of Oklahoma and northern Texas by the time June begins. The duration of any such drought is very uncertain, as the seasonal June-August models generally do not support below- normal rainfall in this area.

In the Southeast, the area of increased drought risk shown in the April outlook did see development in April, although heavy rains at month's end and early May brought some relief. Most forecast models are ambiguous about the June-August rainfall prospects for the Southeast, but climatological drought probabilities suggest improvement for much of the affected region by the end of August, and the northern parts of the drought area should see at least normal rainfall during the latter half of May. Increased heat expected with typical summer weather may make further drought relief slow and difficult, and above-normal temperatures are in the June-August forecast. The outlook calls for improvement for this area, but confidence is relatively low.