Wednesday, October 07, 2015

National Drought Summary for September 29, 2015


Although increasingly wet weather has been noted over parts of the East, any rain falling after Tuesday morning (8 a.m., EDT) will be incorporated into next week’s U.S. Drought Monitor. For this week’s analysis, above-normal temperatures prevailed across much of the country, though heavy rain and near-normal temperatures were observed over parts of the Gulf Coast and Southeast. In addition, moderate to heavy rain was noted in western portions of the Corn Belt. In contrast, protracted dryness prevailed over the Northeast, while seasonably dry weather continued over the western U.S.

Alaska, Hawaii, and Puerto Rico

In Alaska, widespread showers over southern and western portions of the state fell outside of the Moderate Drought (D1) areas. In Hawaii, reports from the field supported the removal of the lingering Moderate Drought (D1), with locally more than 6 inches of rain reported on the Big Island. In Puerto Rico, moderate heavy rainfall (2-6 inches) further reduced drought intensity and coverage over the northwestern corner of the island, though like last week, the core Extreme Drought (D3) areas generally missed out on the rain.

Central Plains

Above-normal temperatures accompanied scattered showers, with little widespread change to this week’s drought depiction. Abnormal Dryness (D0) was increased over eastern portions of Colorado, coinciding with locales where 60-day rainfall has tallied 50 percent of normal or less. There were no changes to the Moderate Drought (D1) in Kansas, where this week’s light shower activity (generally 0.5 inch or less) was insufficient for drought reduction.


Locally heavy rain along the Gulf Coast contrasted with increasingly dry, hot conditions farther north. For the period, rain totaled 2 to nearly 5 inches over southern portions of Louisiana and Mississippi, supporting the reduction of Abnormal Dryness (D0) to Severe Drought (D2) from south to north, though rainfall diminished rapidly away from the coast. Meanwhile, Extreme Drought (D3) prevailed and in some cases expanded, with 90-day rainfall totaling locally less than 30 percent of normal.

Mid-Atlantic and Northeast

In advance of the pending moderate to heavy rain, Abnormal Dryness (D0) and Moderate Drought (D1) persisted. Over the Northeast, D1 was expanded from New Jersey into southeastern New Hampshire, where another week without rain pushed 90-day precipitation deficits to 5 to 10 inches. Many of the region’s streamflows are in the 5th percentile or lower, and the Standardized Precipitation Index (SPI) — an objective drought assessment tool — suggests drought is intensifying rapidly. If the region happens to miss out on the pending rain event, additional drought intensification is likely. Farther south in Virginia, 2 to locally more than 8 inches of rain as of Tuesday morning’s data cutoff warranted D0 reductions in southern portions of the state.

Midwest and lower Ohio Valley

Late-season heat and dryness persisted over central and northern portions of the region, while locally heavy rain developed in the western Corn Belt. Temperatures during the period averaged 5 to 10°F above normal, which coupled with a lack of rain led to an expansion of Abnormal Dryness (D0) in eastern North Dakota and neighboring portions of northwestern Minnesota. In these locales, 60-day rainfall has tallied a meager 30 to 50 percent of normal, causing topsoil moisture to diminish rapidly for winter crop establishment and late-season pasture growth. In contrast, moderate to heavy rain (2-6 inches, locally more) over central and eastern Nebraska afforded some localized relief from D0, but generally fell in areas not currently dealing with widespread moisture shortages. There were no changes made to the drought designation in the lower Ohio Valley, as rain falling at the end of the period mitigated short-term moisture losses.

Northern Plains

Hot, dry conditions prevailed, with temperatures averaging more than 10°F above normal. Despite the 90-degree readings and a lack of rain during the period, changes to this week’s drought designation were generally minor. Abnormal Dryness (D0) was expanded over southeastern Wyoming into northwestern Nebraska, where pronounced short-term precipitation deficits (60-day rainfall totaling 30 to 50 percent of normal) has led to locally pronounced topsoil shortages.


Widespread, locally excessive rainfall resulted in significant reductions of drought intensity and coverage, particularly in the Carolinas and Florida. In North and South Carolina, widespread rainfall of 2 to 8 inches (locally more) necessitated 1- and 2-category drought reductions. A similar story was noted on the Florida panhandle, where locally more than 10 inches of rain supported an eradication of Moderate Drought (D1) and Abnormal Dryness (D0). Widespread, locally heavy showers along with additional assessment from the field indicated ongoing drought reduction and removal in southern Florida. Showers and thunderstorms (1-4 inches, locally more) supported localized drought relief from southern Alabama northeastward into northern Georgia, while mostly dry weather elsewhere resulted in little change to this week’s Drought Monitor.

Southern Plains and Texas

Despite areas of beneficial rain in the west and along the Gulf Coast, the overall trend toward intensifying “flash drought” continued. The intensity and coverage of Abnormal Dryness (D0) to Extreme Drought (D3) increased from southern Oklahoma southwestward across central Texas to the Big Bend. Daytime highs reaching into the upper 90s coupled with another dry week continued to accelerate soil moisture losses, with 90-day rainfall tallying a paltry 5 to 20 percent of normal over many of the Lone Star State’s central drought areas. Pronounced short-term dryness has also intensified over central and southern Oklahoma, where 60-day rainfall has totaled mostly less than 30 percent of normal. Meanwhile, widespread showers and thunderstorms (0.4 to 2 inches, locally more) boosted soil moisture for winter crops and pastures on the southern High Plains and eased D0 along the Texas-New Mexico border. Likewise, 1 to 4 inches of rain reduced D0 to D3 in southern and southeastern Texas, though the heaviest rain largely bypassed the core Texas drought areas.

Western U.S.

The overall trend toward drought persistence continued, though isolated showers were noted in the Pacific Northwest and lower Four Corners. After last week’s cool down, much-above-normal temperatures returned to California and the Great Basin. In the north, most of the region’s core Extreme Drought (D3) areas were dry. However, light to moderate showers on Washington’s Olympic Peninsula (mostly an inch or less) coupled with last week’s heavier rain continued to stave off D3 expansion. Across the California and the Great Basin, drought remained unchanged as the region continued through its climatologically dry summer season. However, heat exacerbated the impacts of the region’s historic drought, with daytime highs reaching or eclipsing 100°F from central California into the southern Great Basin. In the Four Corners States, additional assessment from the field in the wake of last week’s locally heavy rain resulted in further reductions of Abnormal Dryness (D0) and Moderate (D1) in southeastern Arizona and southwestern New Mexico.

Looking Ahead

The complex interaction between a blocking high over eastern Canada, a stationary upper-air low over the Southeast, and Hurricane Joaquin (or the remnants of) will bring the threat of heavy rain to the eastern third of the nation. Rainfall may total 3 to 4 inches (locally much more) across the Southeast, Mid Atlantic, and Northeast, pending the final track of Joaquin. Meanwhile, dry weather is expected from Texas into the upper Midwest. Farther west, a Pacific storm system will move ashore, bringing the potential for locally heavy showers from central and northern California into the northern Rockies. Dry weather is expected over the Southwest, though some late-season showers may arrive in the Four Corners at the end of the period. The NWS 6- to 10-day outlook for October 6 – 10 calls for above-normal precipitation and near- to above-normal temperatures nationwide, with drier-than-normal conditions confined to the lower Southeast.

Eric Luebehusen, U.S. Department of Agriculture

Dryness Categories

D0 ... Abnormally Dry ... used for areas showing dryness but not yet in drought, or for areas recovering from drought.

Drought Intensity Categories

D1 ... Moderate Drought

D2 ... Severe Drought

D3 ... Extreme Drought

D4 ... Exceptional Drought

Drought or Dryness Types

S ... Short-Term, typically <6 months (e.g. agricultural, grasslands)

L ... Long-Term, typically >6 months (e.g. hydrology, ecology)

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