June - August 2006

Latest Seasonal Assessment - Scattered heavy showers eased the fire danger over Florida in mid-May, and the Drought Outlook calls for more improvement as the thunderstorm season gets underway during late May and June. Drought areas in the Carolinas and along the Gulf Coast are also likely to see improvement. In contrast, hot, dry weather is expected to contribute to persisting or worsening drought over the High Plains from Texas to Wyoming near the beginning of the outlook period. Although the forecast for June-August does not show a strong indication for below-normal rainfall in the Plains, it appears that the drought will largely persist well into summer. The odds for improvement increase farther east, and some additional relief is anticipated from eastern Oklahoma into Missouri. In the Southwest, where the near-failure of the winter rain and snow season resulted in severe to extreme drought over much of Arizona and New Mexico, the summer monsoon rains in July and August will reduce the fire danger, although reservoir levels may continue to drop. The best odds for short-term drought relief extend from southern Arizona into New Mexico.

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for June-August, the drought termination and amelioration probabilities 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 Constructed Analogues for the season.

Mid-May thunderstorms brought significant drought relief to Florida, with some spots recording over 4 inches of rain. The anticipated start of the thunderstorm season toward the end of May should bring additional relief from dryness and drought, so the Outlook indicates improving drought conditions for the Florida peninsula. Climatological probabilities for drought relief are also high in the Carolinas, so improvement is also expected in this region. La Niña soil moisture composites are also consistent with increased moisture in this area for the summer relative to normal. Although the La Niña has ended, such composites often remain useful some months after the ENSO event has ended. In the Gulf Coast region, various degrees of improvement are depicted from Texas to Mississippi. This is consistent with recent trends and medium-range forecast models suggesting increased convective activity by early June in the Gulf, resulting in the strong possibility that tropical moisture will surge northward. The May 16 2-week soil moisture forecast from CPC also shows increased moisture in southern Louisiana. That same forecast shows a strong trend toward decreasing soil moisture across the Great Plains, and the most recent official 6-10 day and 8-14 day forecasts indicate a large area of warmth and dryness related to high pressure ridging aloft over the central U.S. With the demise of the La Niña and the onset of summer, the rainfall outlook for June-August becomes quite uncertain for the Plains, but the likely intensification of the drought from Texas northward during the early part of the Outlook period tilts the odds toward drought persistence for the High Plains into summer. There is even a good chance that drought could redevelop across those areas of western and central Texas that have seen recent relief. The confidence that a developing drought would persist into August is not high, given that the CPC long-lead outlook depicts equal chances of above or below-normal rainfall in the Plains states. This Drought Outlook stays with the theme of indicating better chances for improvement in the lingering drought areas in the Mississippi Valley, although the area of partial improvement is smaller this month in response to the drier medium-range forecasts. The latest available GFS model does bring some moisture northward into the eastern Plains and Mississippi Valley and, although the model may be overdoing the rainfall amounts, this is consistent with the idea of some improvement from eastern Oklahoma into Missouri.

Medium and long-range models continue to show better odds for rainfall in the northern Plains and upper Midwest than farther south, so some improvement is indicated for Montana and South Dakota.

The Outlook for the Southwest mainly hinges on the area expected to pick up the most rains from the upcoming monsoon season, which typically begins in July over Arizona and New Mexico. The greatest impact of the rains will likely be the reduction of fire danger in July and August. In contrast, unless the quantity of rainfall is impressive, most of the reservoirs will continue to drop. Elephant Butte storage in southern New Mexico, for example, will probably hit 5 percent of normal by September, the lowest point since October 1971. The confidence in delineating the areas prone to improvement is low. This Outlook considers both the NCDC drought alleviation probabilities for August, which show much of New Mexico as improving, and the seasonal statistical precipitation model for the Southwest produced by the Earth System Research Laboratory (the former Climate Diagnostics Center).