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April - June 2009

 

Outlook Graphic: GIF   PDF Adobe PDF Reader

 

Latest Seasonal Assessment - Above normal rainfall in March helped ease drought conditions over eastern Texas, along the Gulf coast, and parts of the southeast. Nevertheless, severe drought continued in parts of Texas and Oklahoma. 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. The abnormally dry area along the Gulf Coast and over southern Alabama and Georgia has seen significant relief. In fact some of these areas are currently undergoing flooding. A wetter than normal pattern is expected to continue along the eastern Gulf Coast and over parts of the Southeast in the short and medium range. Heavy snow has offered some relief for the drought area over Colorado. Additional heavy snow is possible over the region during the beginning of the current forecast period. Further south over southern New Mexico little rainfall fell during March. Medium and longer range forecasts indicate near to below normal rainfall over the region so there is a good chance drought may expand northward in New Mexico and westward into southern Arizona. Drought has been intensifying over most of Florida, especially the central and southern part of the state. Drought is expected to persist over the central and southern parts of the state during May. On the other hand, heavy rainfall has ended drought over the Florida Panhandle and parts of northern Florida. The start of the thunderstorm season later in May should begin to ease drought conditions, elsewhere in Florida. Farther north, drought is expected to continue to improve over the interior Southeast. In the mid-Atlantic region, a dry winter and early spring has lead to unseasonably low streamflow and well levels and the development of moderate drought over part of the area. Rainfall is forecast to increase over the region during the short and medium ranges which would result in some improvement. 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 early in April will keep California on pace for a near-normal water year, but will not be enough to make up for the multi-year deficits.

 
Discussion for the Seasonal Drought Outlook
 

Tools used in the Drought Outlook included the official updated CPC precipitation outlook for April 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, 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 later in 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 updated CPC monthly forecast for April indicates equal chances for above or below normal precipitation over most of the region except for southeastern California and southern Nevada where below median precipitation amounts are forecast. 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.
Forecast confidence for California and the Great Basin is high.

Increased moisture forecast by the short -range models supports the improvement shown for the small drought areas in Washington and Montana. Medium-range models indicate mostly near normal precipitation with a slight tendency for below median precipitation for part of the area. The CPC updated monthly forecast for April forecasts equal chances for any particular precipitation category over the region. The CPC long-lead precipitation forecast for April-June leans toward below normal precipitation for these areas which is offset to some extent by the expectation that temperatures will be below normal.
Forecast confidence for Washington and Montana is moderate.

The small area of drought over Wisconsin is expected to see improvement due to light to moderate precipitation forecast over the next 5 days, forecasts of mostly near normal precipitation during the medium-range, and forecasts of equal chances for a given category in CPC's updated monthly forecast for April, and the long lead forecast for April-May-June.

The drought expansion depicted in the Southwest in Arizona and New Mexico is based on initial dry areas, forecasts of little to no precipitation in the short range, near normal precipitation in the medium range, above normal temperatures and below normal precipitation during April, and above normal temperatures with near normal precipitation during April-May-June. La Niña composites for New Mexico tend toward below-normal rainfall during April-June.
Forecast confidence for Arizona and New Mexico is moderate.

The area of some improvement forecast for Colorado, southern Kansas, central Oklahoma, and central Texas is based on short and medium range forecasts of near to above normal precipitation for those regions offset by the CPC forecasts of equal chances for any given precipitation category during April, and equal chances or below median precipitation during April-May-June. Improving conditions are shown for eastern parts of the drought area extending into central Texas. This is based on the monthly CFS volumetric soil moisture change from initial anomalies forecasts for April, May and June, forecasts of equal chances for any given precipitation category in CPC's updated monthly forecast for April and the long lead forecast for April-May-June, 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. 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. The persisting drought area forecast for western Oklahoma and west/central Texas is based on La Niña soil moisture composites, the CPC updated forecast for April which depicts a likelihood of near to below median precipitation, and medium range forecasts which suggest near normal precipitation amounts for southern and western Texas. The medium-range forecast indicates above median precipitation for parts of Oklahoma and the Panhandle of Texas, which reduces confidence in the forecast of drought persistence for those regions.
Forecast confidence for the central and southern Plains is low.

For the central Gulf Coast, recent very heavy precipitation has alleviated the drought. Short and medium range forecasts suggest a continuation of the wetter than normal pattern for the region so that drought re-development over the region during the forecast period seems unlikely.

In Florida, drought has been intensifying over the central and southern part of the state. The La Niña appears to be having an influence in steering storms to the north. Confidence for persisting or worsening drought is quite high for the central and southern parts of the Peninsula. This idea is supported by the forecast of only light precipitation in the next 5 days, the forecast of near normal precipitation during the medium range, and below median precipitation for these areas in the CPC updated monthly forecast for April, and the CPC long lead seasonal forecast for April-May-June. With the onset of the warm season thunderstorm season later in May 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. Wildfires and water shortages are a very real risk. Recent heavy rains have eased dryness over the Florida Panhandle and reduced drought over northern parts of the state. Additional heavy rain is expected over the Florida Panhandle and northern Florida.
Forecast confidence for Florida is moderate.

To the north, heavy March rains eased dryness in Alabama and Georgia and much of the interior Southeast. Streamflows have recovered to close to normal over much of the area, and are actually above normal over southern Alabama and southern Georgia, although 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 still around 10 feet below normal. Rainfall is expected to be above normal over the next 5 days, especially over the southern part of the region. Medium range forecasts and the CPC updated monthly forecast for April indicate the likelihood that the wetter than normal pattern will continue. La Niña composites also are consistent with rainfall increasing and dryness decreasing northward from Florida. As a result, the Outlook depicts improvement over northern Florida, southeastern Georgia, and for the areas north of there. Nevertheless, some water shortages may continue into summer, as it is too late in the recharge season to expect lakes and wells to fully recover before water demand increases with the warm weather.
Forecast confidence for the interior Southeast is moderate.

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, and Philadelphia. Some rainfall is expected over the next 5 days, and medium range forecasts indicate above median precipitation for much of the area. Streamflows remain very low over the region especially over the Maryland, Delaware and Pennsylvania. The CPC updated monthly forecast for April and the CPC seasonal forecast for April-May-June indicate equal chances for both temperature and precipitation categories. La Niña composites tend to show drier than normal over the area for spring. For these reasons a forecast of some improvement was specified for the region.
Forecast confidence in the mid-Atlantic is low.

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


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Page last modified: April 2, 2009
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