March - May 2009

Outlook Graphic: GIF   PDF 

Latest Seasonal Assessment - Heavy rain and snow during mid-February raised river levels and boosted snow pack in drought-affected areas of California, but major reservoirs remained well below normal. The seasonal drought outlook indicates improving conditions for northern and central parts of the state due to expected above-normal rain and snow into early March. However, it is highly unlikely that water shortages will end before the dry season sets in, given the long-term deficits that have accumulated over nearly three years. Much more precipitation is needed to get the critical snow water content levels up to normal by April, when snow pack typically peaks. Water storage in mid-February ranged from 44 to 83 percent of normal in the largest reservoirs, suggesting that California has a long way to go to see relief from its hydrologic drought. In the southern Plains, moderate to exceptional drought is forecast to continue in Texas and parts of Oklahoma due to forecast below-normal rainfall during March through May. The same dry forecasts also lead to the continued outlook for drought development in southwestern Texas and southeastern New Mexico. Below-normal rainfall expected for March-May also results in a forecast for drought to persist or expand across the Florida Peninsula and into southeastern Georgia and southern South Carolina. Drought affecting parts of Louisiana, Alabama, and North Carolina should also continue. The lingering drought in the southern Appalachians should see improvement toward the northwest in the eastern Tennessee area, but less improvement toward the southeast in the western Carolinas. Areas of drought in Montana and northern Wisconsin are forecast to improve. Lingering drought in parts of Hawaii should also ease.

Tools used in the Drought Outlook included the official CPC precipitation outlook for March 2009 and the long lead forecast for March – May 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 seasonal precipitation forecasts, and climatology.

The recent Pacific storms brought beneficial moisture to drought-affected California, and more relief is on the way. The storm forecast for the first weekend of the valid period (February 21-22) should bring over 2 inches of precipitation to the Sierra and northwestern parts of the state. The previous storm delivered widespread 2 to 7 inches, boosting streamflows and mountain snow pack. The official 6-10 day and 8-14 day forecasts indicate above-normal precipitation for much of the state. The Drought Outlook shows improvement where the expected precipitation amounts in the first two weeks of the forecast period are highest, and where the seasonal forecast models show less chance of a return to drier weather during March-May. Nevertheless, it is important to point out that the expected improvement is unlikely to end the hydrological drought affecting the state. The largest reservoirs showed storage levels on February 17 ranging from 44 to 83 percent of normal, and just 30 to 49 percent of capacity. With the major reservoirs less than half full, it would be difficult to get enough moisture before the dry season begins to fill the reservoirs. Another concern is the March-May precipitation forecast, as the majority of the dynamic models indicate below-normal precipitation across the southern half of the state. This is one reason for depicting persisting drought across southern California.
Forecast confidence for California: Moderate

Improvement elsewhere in the West could be more difficult, although the water supply situation is not as serious as in California. The expected storm track during the first 2 weeks is sufficient to bring at least some improvement for the northern Great Basin, but the official CPC 3-month precipitation outlook tilts the odds toward below-normal totals from eastern Nevada toward the southern Plains.
Confidence for the Great Basin and Intermountain region: Low

The small drought area in southeastern Colorado is switched from some improvement to persist because the forecasts for all time periods from 5 days to 3 months are dry. In the same vein, forecasts from short term to seasonal time periods indicate below-normal rainfall for Texas and New Mexico, so the Outlook continues to depict drought expansion westward into New Mexico. Expansion into the Texas Panhandle is more muted because both recent moisture and heavy rain in August and October make it more difficult for drought to develop, as indicated by the University of Washington Ensemble Streamflow Prediction models, which show relatively low odds for development in the Panhandle. Despite some indicators not showing imminent drought, winter wheat is in poor condition. Given the continuing La Niña into late winter or early spring and warm and dry forecasts, the area from Texas northward into western Kansas needs to be monitored.
Confidence for the southern Plains: High

Medium-range forecasts and climatology favor improvement for the small drought areas in Montana and the long-term drought in northern Wisconsin and adjacent Michigan. The area shown as some improvement in the prior Outlook changed to straight improvement in this forecast due mainly to the expected storm track and the spring climatology. The NCDC Palmer drought amelioration maps indicate better than a 60 percent chance for amelioration by the end of May.
Confidence for the Upper Midwest: Moderate

The latest CPC monthly and seasonal forecasts show the odds tending toward dry for the South and Southeast, and persistence is indicated for the scattered drought areas in those regions. Near-normal rainfall is forecast for the first 2 weeks of the period, so there may be temporary improvement.
Confidence for the South and Southeast outside of Florida: Moderate

The long-term drought in the northern Georgia-western Carolinas area has not gone away despite some beneficial moisture this winter. Short, medium, and long range forecast models show a wet-to-dry transition from the Ohio Valley toward the South Atlantic coastal plain. Improvement is shown for eastern Tennessee to reflect these forecasts, with more limited improvement in the western Carolinas and northeast Georgia.
Confidence for the Appalachians: Moderate

Florida has seen some periods of rain in recent weeks, but the overall trend has been toward increasing dryness, especially in the southern Peninsula, where impressive dry season rainfall deficits have developed. With medium range, monthly, and seasonal forecasts all pointing toward below-normal rainfall, the Outlook continues to depict persisting and expanding drought across the Peninsula and into southeastern Georgia. Wildfire danger could become a major concern before the onset of the wet season if these forecasts are correct.
Confidence for Florida: High

In Hawaii, the Outlook continues to indicate improvement due to seasonal forecasts and climatology. A few seasonal dynamic models show below-normal rainfall over the southern islands, and this decreases the confidence levels to some extent.
Confidence for Hawaii: Moderate