Bloomberg News

Seasonal Drought Outlook for July 19 to Oct. 31, 2012 (Text)

July 19, 2012

Following is the text of the U.S. Seasonal Drought Outlook as released by the National Weather Service in Camp Springs, Maryland:

Latest Seasonal Assessment - Dryness and drought, exacerbated by above-normal temperatures, have been increasing both in extent and intensity across much of the central and northern U.S. Based upon the July 10 U.S. Drought Monitor, nearly 61 percent of the contiguous U.S. was in drought (D1-D4), the highest such value for the U.S. Drought Monitor since its inception in 2000. The drought and heat arrived at a critical time for Midwestern agriculture, especially corn. The combination of heat and dryness has severely reduced the quality and quantity of the corn and soybean crop, with 38 percent of the corn and 30 percent of the soybeans rated as poor or very poor as of July 15 by NASS/USDA. Some states, such as Kentucky, Missouri, and Indiana, had over 70 percent of their corn adversely rated. Unfortunately, drought is expected to develop, persist, or intensify across these areas, and temperatures are likely to average above normal. Some widely-scattered relief may come in the form of cold front passages or organized thunderstorm clusters (MCSs), but widespread relief for much of the area is not expected. In the Southeast, recent widespread thunderstorm activity has slightly eased drought there, and the 3-month outlook favors increased odds for above normal precipitation along the central Gulf. This is due to the greater likelihood of a tropical system affecting these areas and from sea-breeze triggered thunderstorms. Therefore, some improvement is expected across the Deep South, from coastal Texas eastward to South Carolina. Across the Southwest, the odds favor an active (wet) southwest monsoon in both the 1- and 3-month precipitation outlooks. As a result, improvement is anticipated across much of Arizona and western New Mexico as the summer monsoon continues, with some improvement in other parts of the region. Drought persistence is the best bet across the remaining portions of the Western U.S. since late summer and early fall are typically dry. In Hawaii, subnormal seasonal rainfall is expected which should maintain drought on the leeward (west) sides while expanding it toward the windward (east) sides. Lastly, an El Niño Watch continues, with the forecaster consensus reflecting increased chances of an El Niño beginning in July-September.

Discussion for the Seasonal Drought Outlook

Tools used in the U.S. Drought Outlook (USDO) included the official CPC temperature and precipitation outlooks for August 2012 and the long lead forecast for August through October 2012, various medium- and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the most recent 384-hour GFS total precipitation amounts, the soil moisture tools based on the Constructed Analog on Soil (CAS) moisture, the Climate Forecast System (CFS, versions 1 and 2), the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions.

After receiving heavy to excessive rains (1 to 3 feet) from Tropical Storms Beryl and Debby, drought was alleviated from most of Florida and southern Georgia by late June. Since then, rainfall totals have decreased to more typical amounts (1 to 3 inches) during the past few weeks. In the remainder of the Southeast, June was mostly dry with near or slightly below normal temperatures. Since July 1, however, widespread thundershowers have dropped moderate to heavy rains from the Carolinas to Tennessee and on the lower Mississippi Valley, producing some drought relief. The extended-range forecasts (6- 10 day and 8-14 day) anticipate elevated odds of subnormal median rainfall across the Southeast, although the 384-hour GFS predicts decent rains for the mid-Atlantic and southern Atlantic Coast. Though CPC’s updated August outlook calls for Equal Chances (EC) of below-, near-, and above-median precipitation across much of the Southeast (except for below normal odds for Arkansas and western Tennessee), the seasonal outlook for August-October, as well as the CFSv2 model, favors wetter-than- median conditions over the central Gulf Coast region. In addition, the odds for at least some improvement are elevated closer to the coast which is often affected by sea-breeze induced thunderstorms and the “wild card factor” - tropical systems - where ASO are usually the peak months. In addition, it is difficult to sustain a drought in an area where the normal annual precipitation is 40 to 50 inches (e.g. Georgia, Alabama, and Tennessee) and evenly distributed per month. Monthly and seasonal temperature outlooks also favor above-normal temperatures, especially in northern regions, with decreasing odds as one heads south and east to the Gulf and Atlantic. In short, drought should persist in the north and show some improvement in the south. Forecast confidence for the Southeast (including lower Mississippi and Tennessee Valleys) is moderate.

During the past 2 weeks, light rainfall (1-2 inches) in the Northeast and mid-Atlantic, combined with triple-digit heat in the later region, have caused some deterioration (D0 and D1) in both areas. The Delmarva Peninsula remained in D2 as significant precipitation continued to bypass this area in both the long and short term. Although the short and medium-term models predict some moderate to heavy rain amounts in the mid-Atlantic and lower temperatures, there are no clear indications in the August and ASO precipitation outlooks for dry or wet odds (equal chances). But since most of the D0 and D1 have recently developed in the Northeast and mid-Atlantic (short-term), a brief period of wet weather could alleviate the accumulated deficiencies (2 to 4 inches at 30- and 60-days) - hence the Some Improvement label. Farther west, however, the deficits are larger, and the August and ASO temperature outlooks favorably tilt toward above-normal temperatures and subnormal precipitation. Accordingly, development was added to the far eastern Ohio Valley and central Appalachians. Forecast confidence for the Northeast and Mid-Atlantic regions is moderate.

Since July 1, much of the Midwestern Corn Belt experienced subnormal rainfall and abnormal warmth, further increasing the drought and adversely impacting agriculture. 17-day deficits ranged between 1.5 to 3 inches from the central Great Plains to the eastern Ohio Valley, and temperatures averaged well above normal. Triple-digit heat was common during the first week of July. Current NLDAS soil moisture anomalies (Ensemble Mean LSM, total column) reveal widespread moisture deficits on the order of 5 to 8 inches. Current root-zone (top 1-meter) soil moisture deficits range from 3 to 6 inches across this region. The CPC 6- 10 day, 8-14 day, August, and ASO Outlooks call for enhanced chances of below-median rainfall and above-normal temperatures for most of the region. An exception is the upper Midwest which may see decent rains in the short-term. Unfortunately, the self- perpetuation of regional drought conditions, with very dry soils and very limited evapotranspiration, tends to inhibit widespread development of or weaken existing thunderstorm complexes. It would require a dramatic shift in the weather pattern to provide significant relief to this drought, and most tools and models do not forecast this. Accordingly, drought was maintained across the Midwest, and expanded northward and eastward to encompass parts of the Dakotas, upper Midwest, and extreme eastern Ohio Valley. Forecast confidence for the Midwest (including Ohio Valley) is moderate.

During the past 2 weeks in the Plains, surplus rainfall was limited to the extreme southern Great Plains (southern and southeastern Texas), central High Plains (eastern Colorado), and portions of the northern Plains (central Dakotas and southeastern Montana). During the last 60 days, most of the Plains (except the Dakotas, parts of Colorado, and Texas Panhandle) recorded subnormal precipitation, with deficits of 4 to 8 inches (locally even greater) accumulated from extreme southern Texas northward into north-central Kansas. For the first 5-days of this outlook, an upper-air ridge will continue to steer moisture and storms around its periphery, resulting in little to no rainfall for the central and southern Plains. Instead, the arc-shaped moisture corridor favors monsoonal moisture heading northward through the southern and central Rockies and northeastward across the Dakotas and upper Midwest. The CPC extended-range precipitation forecast maintains unfavorable odds for rainfall in the southern half of the Great Plains. CPCs 30-day outlook favors a slight tilt in the odds for subnormal precipitation in the central and northern Great Plains, with equal chances elsewhere. CPCs 90-day precipitation outlook has no odds either way (equal chances). Climatologically, the northern and southern Plains reach their normal wet time of the year during the late spring and early summer, so by the fall their precipitation is waning. Unfortunately, all indicators (short and medium-term, August, and August-October) favor above normal temperatures. With much of the Plains already in drought, above normal temperatures expected into the fall, and a dry short-term and 30-day forecast, the drought should persist, with some possible development in the northern Plains. Forecast confidence for the Plains is moderate.

In the Southwest and southern High Plains, the June-September period is critical for producing monsoonal rains. In parts of Arizona, New Mexico, western Texas, and eastern Colorado, a large majority of its normal annual precipitation occurs during these 4 months. Therefore, a forecast for above normal monthly and seasonal precipitation during this period may bring drought- relieving rains. Since July 1, the southwest monsoon has been generous across much of the Southwest, with most areas also reporting surpluses out to 30-days, and some portions (most of Arizona and southeast California) out to 60 and 90 days. CPCs precipitation outlook suite for the extended-, monthly-, and seasonal ranges (including the seasonal CFSv2 forecast) all favor near- to above-median rainfall across this region. With most tools and models in agreement, improvement is forecast for Arizona and western New Mexico, with some improvement for the remainder of the Southwest. Forecast confidence for the Southwest is moderate to high.

Widespread moderate to severe drought covers the rest of the western U.S. except for the Northwest. While the southwestern monsoon can bring moisture throughout the Four Corners States, southeastern California, and southern Nevada, the summer is climatologically dry across the Great Basin, the rest of California, and the Northwest. In addition, persistent wet weather in the Northwest during the past several months has accumulated surpluses at 1 to 6 months out, making it difficult for drought to develop anytime soon. CPCs extended range forecasts strongly tilt toward subnormal precipitation, while the monthly and seasonal outlooks favor slightly enhanced odds of below-median precipitation over the Northwest, and equal chances in the Great Basin and northern Rockies. Therefore the seasonal drought forecast calls for the existing drought to continue without any areas of improvement or new development. Forecast confidence for the West is high.

The summer months are climatologically dry in Hawaii, but as the fall commences rainfall normally increases. The latest Hawaiian monthly and seasonal outlooks (from dynamical models) slightly tilt toward subnormal rainfall. Therefore, drought is expected to persist in existing areas (mainly leeward sides), and slowly spread eastward (toward the windward sides), especially later in the period. The exception is Kauai where D1 covers the eastern portion, with drought development expected to push westward. Forecast confidence for Hawaii is moderate to high.

SOURCE: National Weather Service

To contact the reporter on this story: Stephen Rose in Washington at srose31@bloomberg.net

To contact the editor responsible for this story: Marco Babic at mbabic@bloomberg.net


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