As has been the case throughout the month of September, the latest weekly drought update shows that drought conditions have tightened their grip on the Plains States and Western U.S., and the overall drought footprint expanded to encompass 65.45 percent of the lower 48 states, up from 64.8 percent on Sept. 18. This represents the highest areal coverage in the 12-year history of the Drought Monitor analysis, topping last week's record.
As of Sept. 25, the worst categories of drought — extreme to exceptional drought conditions — encompassed nearly one quarter of the lower 48 states. Nearly all of Nebraska, with the exception of a sliver in the southeastern corner of the state, is suffering under extreme to exceptional drought conditions — 98 percent, to be exact.
U.S. Drought Monitor as of Sept. 25, 2012. Click on the image for a larger version.
Since September 18, the area of the “Cornhusker State” experiencing exceptional drought grew from 70.9 percent to 73 percent. Other states with a large footprint of the worst drought categories include Kansas, where 5 percent of the state is suffering from exceptional drought, and Oklahoma, where exceptional drought has enveloped 17 percent of the state, an increase from the Sept. 18 data. According to The Weather Channel, the “exceptional” drought extents in Nebraska and Kansas are both records for those states.
The most recent U.S. Drought Outlook, which was issued on Sept. 20, calls for the drought to persist from the High Plains all the way to the West Coast, including the Pacific Northwest, where drought conditions are expected to develop through December 31. Some relief is likely from Texas eastward to Georgia, and in South Central states and the Ohio Valley. Texas is still suffering from drought conditions after a record drought struck in 2011. On Wednesday the Texas A&M Forest Service announced that the drought has killed about 301 million trees across the state, although it emphasized that forests will recover once conditions improve.
According to data from the National Oceanic and Atmospheric Administration (NOAA), parts of the Midwest and Plains states need upwards of 15 inches rain to climb out of the drought, and the projected weather pattern for the late fall and winter is not likely to favor such above average rainfall in those areas.
Map showing the amount of rainfall that would be necessary for parts of the U.S. to climb out of drought conditions. Click on the image for a larger version.
The drought forecast for the next few months is being shaped by the expected influence of a developing El Niño event in the equatorial tropical Pacific Ocean. Such events are characterized by warmer than average sea surface temperatures, which can profoundly reshape weather patterns in the U.S. and elsewhere. El Niño winters tend to be wetter than average in the South and the Ohio Valley.
As Climate Central has reported, the government’s official climate outlooks failed to accurately anticipate the drought’s development in the late spring to early summer, and did not forecast the extraordinarily hot summer across the lower 48 states, where it was the third-warmest summer on record. July was the warmest month of any month on record in the contiguous U.S., and the year is on track to become the warmest year on record in the U.S. (Global temperatures, while much warmer than average, are not likely to set an annual record.)
The hot weather aggravated the drought by leading to greater evaporation of moisture from soils, which in turn led to even higher temperatures.
Some computer models, did capture both the drought and heat well in advance, but these were outlier predictions that were discounted in favor of the consensus view from many other models.
The drought is the worst to strike the U.S. since the Dust Bowl era of the 1930s and lengthy droughts of the 1950s. It came on suddenly and largely without warning, and although the main trigger was most likely the pattern of water temperatures in the Pacific and Atlantic Oceans, the drought was exacerbated by extremely hot temperatures during the spring and summer. Climate studies have shown that the odds of severe heat waves are increasing due to manmade climate change.
Drought Grows, Forecast to Persist Through Early Winter
Scientists Seek Insights Into Outlier Drought Predictions
Lack of Warning on Drought Reflects Forecasting Flaws
U.S. Has Third-Warmest Summer, Warmest Year to Date