April - June 2009

Outlook Graphic: GIF   PDF 

Latest Seasonal Assessment - Heavy rains during mid-March benefited drought areas in the southern Plains and Southeast. Nevertheless, severe drought continued in Texas and parts of Oklahoma, with burn bans in 171 Texas counties as of March 18. An improving trend will continue over parts of the region, with the best odds for reduced drought in central and eastern portions of both states. Recently-developed drought on the Colorado plains and over southern New Mexico is likely to persist, with a good chance drought may expand northward in New Mexico and westward into southern Arizona. Drought recently intensified in Florida, where dry-season rainfall deficits approached a foot in some locations. As of mid-March, nearly two-thirds of the pastures were rated in poor to very poor condition. Pond and lake levels were dropping and wildfire danger was a major concern. Drought is expected to persist over the state into May, and could expand over the eastern Panhandle. The start of the thunderstorm season later in May should begin to ease drought conditions, and some improvement should continue in June, as seasonal rains increase. Farther north, drought is expected to continue in southern Georgia, but there should be a tendency toward improvement to the north into the Appalachians. Groundwater and lakes remain low in parts of Georgia and South Carolina due to the long-term drought. It is unlikely enough rain will fall to get water supplies back to normal before the impact of warm weather hits, so some water shortages are likely to continue into summer. In the mid-Atlantic region, unseasonably low streamflow and well levels in early spring will lead to drought unless heavy rains fall. Drought development is forecast from northern Virginia into New Jersey. Drought areas in the Upper Midwest and parts of the Northwest should see improvement, while the bulk of the improvement is likely over for California and the Great Basin as the wet season winds down. Rain and snow forecast for later in March will keep California on pace for a near-normal water year, but will not be enough to make up for the multi-year deficits.

Tools used in the Drought Outlook included the official CPC precipitation outlook for April 2009 and the long lead forecast for April – June 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 California and the Great Basin, the wet season is winding down, making additional drought relief more difficult. Unlike last year, the storms have continued into March, and at least one more beneficial storm is forecast only a few days into the forecast period. The additional rain and snow will keep California and adjacent parts of Nevada on pace for a near-normal water year, but the forecast precipitation from this storm and potentially from additional events into April will likely not be sufficient to make up for the deficits accumulated during the past 3 years. Forecast spring-summer streamflows remain below normal, and the large reservoirs in the north will not fill up despite the marked improvement seen since the stormy period began in February. As a result, the Drought Outlook indicates persisting drought for most of California and the Great Basin, except for a small area in northern California where spring storms should have the most impact. The CPC long-lead precipitation forecast for April-June leans toward below normal precipitation for the northern Great Basin, and this contributed to a somewhat more negative outlook for that region. The limited improvement shown for southern Idaho is mainly based on the wet forecast for the first 2 weeks of the forecast period in addition to indications from several seasonal soil moisture models.
Forecast confidence for California and the Great Basin is high.

Increased moisture forecast by the medium-range models supports the improvement shown for the small drought areas in Washington and Montana. For the longer term, below-normal forecast temperatures offset to some extent the slight tendency for below-normal precipitation depicted in CPC’s long-lead outlook for April-June in Montana.
Forecast confidence for Washington and Montana is moderate.

The drought expansion depicted in the Southwest in Arizona and New Mexico is based on initial dry areas, dry medium-range forecasts, and a warm and dry monthly forecast for April from CPC. La Niña composites for New Mexico tend toward below-normal rainfall during April-June. Runoff and soil moisture forecasts from the 3-month Ensemble Streamflow Prediction (ESP) model based on both climatology and La Niña analogues support some drought expansion.
Forecast confidence for Arizona and New Mexico is moderate.

The persisting drought forecast for Colorado and western parts of the drought affecting Oklahoma and Texas is consistent with La Niña soil moisture composites, the June Constructed Analogue Soil (CAS) moisture forecast, and the April long-lead outlook for temperature and rainfall. The 2-week soil model forecast indicates drying in Colorado and western Kansas, as does the CFS soil moisture change map for June. Improving conditions are shown for eastern parts of the drought area extending into central Texas. This is based on the CFS soil moisture for June, the 2-week soil moisture forecast, the NASA seasonal soil moisture forecast, and climatology. May and June tend to be wet months for Texas, especially in the east. The area shown in green was in marginal drought to begin with, so most susceptible to eradication. (Part of this area was removed from D1 drought status in the final March 17 Drought Monitor after the Drought Outlook was completed.) The forecast for expansion in western Kansas shown in the March 5 Drought Outlook was removed due to wetter seasonal and medium-range forecasts for this area. There is considerable uncertainty about the location for improvement in the drought region given the range of possible weather developments into June. La Niña composites tend to show below-normal rainfall for southern Texas during April-June, consistent with the persisting drought area shown on the Outlook map.
Forecast confidence for the central and southern Plains is low.

For the central Gulf Coast, generally normal rainfall is forecast during the first 2 weeks of the period. Longer term, the CPC April forecast and several seasonal forecasts, such as the CAS and La Niña rainfall composites, imply below-normal rainfall and continued drought. The depiction shows some improvement due to expected variability during the upcoming season, with better odds for improvement early on.
Forecast confidence for the central Gulf Coast is low.

In Florida, drought has been intensifying in agreement with previous drought forecasts. The La Niña appears to be having an influence in steering storm systems to the north. Confidence for persisting or worsening drought is quite high early in the forecast period for the Peninsula, given the reliability of La Niña rainfall signals, but the onset of the warm season thunderstorm season later in May means that some improvement is likely to begin by then, accelerating into June. The Outlook map could have indicated this temporal variability by depicting an area of some improvement, but the drought impacts should be serious for a significant part of the forecast period, and this warranted the more pessimistic depiction on the map. As of mid-March, 65 percent of pastures were rated poor to very poor, and topsoil moisture rated 82 percent short to very short in Florida. Wildfires and water shortages were a very real risk. The drought could easily expand toward the northwest and also into coastal South Carolina based on medium-range rainfall forecasts, La Niña soil moisture composites and the CAS forecast for June.
Forecast confidence for the South Atlantic Coastal Region is moderate.

To the north, heavy mid-March rains eased dryness in Alabama and Georgia and much of the interior Southeast. This was the second major rainfall event this month. Wells in parts of Georgia and in northwestern South Carolina remained low for this time of the year due to the long-term rainfall deficits. Lake Lanier levels in northern Georgia were around 10 feet below normal, despite rising 7 feet since December 1. Various long-range rainfall forecasts and La Niña composites as well as medium-range rainfall forecasts are consistent with rainfall increasing and dryness decreasing northward from Florida. As a result, the Outlook depicts improving conditions northward into the western Carolinas. Nevertheless, some water shortages are likely to continue into summer, as it is too late in the recharge season to expect lakes and wells to recover before water demand increases with the warm weather.
Forecast confidence for the interior Southeast is low.

The mid-Atlantic region got off to a slow start this year, with precipitation since January 1 only about one-half of normal in Washington DC, Baltimore, Philadelphia, and Newark. As a result, streamflow and groundwater were unseasonably low in March. Without a large boost in moisture, the region could go into the warm season with serious groundwater deficits and continued low streamflows. With medium-range forecasts showing normal to below-normal rainfall, and a tendency for La Niña springs to be dry, the odds support drought development for the region. However, one or two wet storms could turn the situation around, so the confidence that any drought will persist into June is low. Elsewhere, low streamflows extend westward into southern Ohio and parts of Indiana. There is heightened risk for drought in the Ohio Valley, but medium-range forecasts as well as the April forecast are not as dry as in the mid-Atlantic region, so development is not depicted in this area at this time.
Forecast confidence in the mid-Atlantic is low.

Long-range rainfall forecasts continue to point to improving drought conditions in Hawaii, so the Outlook again shows improvement in the scattered drought areas remaining on several of the islands.
Forecast confidence in Hawaii is moderate.