In most places, save for areas of the central Plains, and across the southwestern U.S., parts of the deep South and southeastern U.S., drought conditions began and rapidly intensified during the Summer of 2012.
After beneficial and timely rainfall during the early to mid-Spring season, a rapid shift to much drier conditions, exacerbated by extended spells of record or near-record setting daily as well as monthly temperatures, set the stage for rapid drought development.
Analyses comparing the current drought with those of the 1930s are ongoing. However, across much of the central U.S., the current drought onset is similar to the drought of summer, 1988.
La Niña (cooling of oceanic water temperatures in the central Pacific) was largely responsible for the multi-year drought and intensification of conditions on the Southern and Central Plains. In 2011, the worst one-year drought on record in Texas occurred during a La Niña event that began in the previous year and ended by summer. Spells of historic heat-wave conditions exacerbated drought severity, too.
Blame El Nino
The return to neutral ocean conditions in the equatorial Pacific, or "normal" water temperatures, and over the summer season the arrival of weak El Nino conditions (warming of those same waters) suggests little change to sensible weather throughout much of the Heartland over the next several weeks, if not longer.
Summer and early autumn arriving El Nino's typically generate a much drier, hotter-than-usual pattern. However, signs of a shift to above normal rainfall are seen across much of the southern tier of the U.S. due in part to a strengthening sub-tropical current of air aloft. And, while tropical activity usually lessens in El Nino years due to that same strengthening of winds aloft, the current set-up may not be strong enough to fully impact the tropics. So there may still be a fair number of features that may increase rain systems through the southern and perhaps the eastern U.S. Some may recall that it was the remnant features of a couple tropical systems that started the end demise to the Great Drought of 1988. Additionally, expect drier conditions in the Ohio Valley, much of the Midwest, as well as the northern and central Plains.
At the height of the drought during the summer season, at one time moderate to exceptional drought covered almost 65% of the contiguous U.S when the U.S. Drought Monitor, developed in 1999, was used as a benchmark tool. The U.S. Drought Monitor is collaboration between NOAA, the U.S. Department of Agriculture, and the National Drought Mitigation Center, located at the University of Nebraska-Lincoln, and represents an assessment of drought conditions drawn from hundreds of indicators and peer-reviewed by experts in the field.
According to weekly Palmer Drought severity indices -- a single index that has a longer history and larger data set to reference, at one time drought conditions covered about 60% of the U.S. For the Palmer Drought Severity Index, which has data back to 1895, droughts in 1934, 1939, and 1954 had aerial extents of 79.9%, 62.1%, and 60.4%, respectively.
The impacts of the drought have been extraordinarily dramatic and far-reaching. Economic research groups have shown that between 40% and almost 50% of the country's agricultural land is in some sense of severe or worse drought. That fact alone would make the 2012 drought more extensive than any since the 1950s.
Its impact has affected more than 60% of farms at one time, more than ¾ of summer crops, and almost that of cattle areas. The July portions of drought caused water supply and quality issues for municipal utilities, dying trees, grasshopper and other insect infestations, and curtailed barge traffic on the Ohio and Mississippi Rivers. At mid-Summer, livestock producers began taping winter hay stocks and started preparation for herd reductions
So, how long will it last?
One set of data suggests lingering or intensifying drought over most of the U.S. through late October, while other methodologies suggest a duration well into November before a modest improvement begins to materialize across the southern Plains and Midwest. Outlier forecast tools even suggest that varying degrees of a multi-year drought is underway -- one that has comparisons to the western U.S. drought pattern back in the late 1990s.
In any event, exceptions to this later- versus sooner- approach to ending this year's drought are found in of all places…the Southwest and Southeast, where improvement is suggested by lingering, late-season monsoonal showers, and tropical-oriented features, respectively. Some drought improvement is also suggested around the lower Great Lakes and upper Ohio Valley locales, but here, it's largely dependent on the movement of tropical systems from the Gulf coast or southeastern U.S.
Here's what to look for in your area:
Mild, warm Northwest, unsettled Southwest
The Pacific Northwest and intermountain West will see an upper air pattern that generates rather mild to periodically warm and dry weather. Several outbreaks of cold appear to be confined to late fall. Little in the way of early cold weather-related livestock stress or early frost/freeze issues is foreseen. Harvest delays should be kept to a minimum, with the exception of drought-related issues, including ongoing wildfires.
As for California and the Southwest early-on, temperatures and weather may vary greatly week-to-week as north Pacific storm systems swing northward or to the southeast, all driven by El Nino. A late-running monsoon season looks promising in the Southwest. The track of features would suggest average precipitation totals across the far northern Sacramento Valley, while wetter-than-usual conditions build across the remainder as weakening monsoonal showers yield to organized features via the Pacific.
Trend towards wetter on the Southern Plains
Blistering and blazing heat across southern areas of the Plains diminishes early-on, but temperatures still remain above average in the wake of one of the hottest summers ever recorded. Mild to unseasonably warm weather should be the rule until late Fall on the northern and central Plains and much of the western Corn Belt south of Interstate 80. Harvest delays (assuming there's something to harvest in southern areas) will be minimal.
The same applies to winter wheat seeding. Deeper into the fall season, rather challenging periods of weather are ahead, but who'll complain about frequent moisture in southern areas. Issues regarding wide temperature swings and a frequency of storm systems are ahead. Farther north, including the western Corn Belt, fall fieldwork and harvest delays will be minimal, along with soil moisture gains. So, there is some promise of re-charge in the worst of the drought regions of the southern Plains.
Wide swings in temperatures and precipitation across the South
Early in the season, periodic spells of cooler-than-average temperatures are expected across the Southeast and mid-Atlantic region; due in part to tropical systems tracking northward across the Eastern States or the western Atlantic that in turn buckles the jet stream southward allowing cooler air to follow-in behind. Meanwhile, from Texas, east-northeast through the mid-South and at times the mid-Atlantic region, mild, late Summer-like warm episodes early in the season will yield to more seasonal readings, and perhaps more frequent cold air intrusions late in the season across the Deep South. However, early season frost and freeze potential still looks minimal.
As for precipitation, there'll be plenty of it, especially east of the Delta and particularly in the Southeast and mid-Atlantic region early in the season, followed by a trend towards much drier-than-average weather towards the start of winter. Drought areas may show significant improvement from the lower Mississippi Valley, westward as large-scale upper air troughiness takes hold. Areas to the east, as well, should see modest drought improvement, at least early in the season.
Cool start, then warmer and wetter in the Northeast
As for the Northeast and New England, the area will progress towards a far more active pattern, aided by tropical systems making their turn into the northwestern Atlantic. This is turn allows lobes of cool air to settle southward. Early-season frosts and light freezes are possible. Thereafter, rather broad southwest flows aloft will frequently occur, this allowing spells of frequently milder-than-usual weather to dominate. Not until late in the season, very near the start of Winter will the area experience longer-lasting spells of cold weather, but no worse than near-seasonal temperatures.
As for precipitation, normal to above normal amounts are ahead much of the Fall, but also intertwined with multi-week periods of dry weather allowing a seasonal pacing to Fall fieldwork and clean-up duties.
Colder, wetter across Eastern Corn Belt
Finally, across the Midwest and Great Lakes Corn Belt, a challenging mid- to late-Fall weather pattern is expected, but not before a mild to warm start and extended spell early in the season. Cold air outbreaks will be few and far between. This, however, will not be rule advancing deeper into the season. Temperatures will build a range to below-normal to well-below normal, but with some fluctuations from the lower Great Lakes to the Ohio Valley. Several early-Winter-like cold wave episodes are likely.
As for precipitation, there's good news from the standpoint that normal to above-average frequency and amounts of moisture are ahead, especially from the Ohio Valley to the Great Lakes region of the Corn Belt. This may also include early-season snowfalls in the upper Great Lakes. The early start to harvest due to the summer's impact of heat and drought should keep mid- to late Fall harvest delays to a minimum, although other fieldwork operational delays are likely to materialize later in the season.
- Soulje is an agricultural meteorologist and writes from Illinois. He's also a regular on the weekly ag-focused television show - This Week in Agribusiness - hosted by Max Armstrong and Orion Samuelson.