Drought Monitor: South-central U.S. hit with locally heavy rain

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Summary:  Locally heavy rain provided drought relief to the south-central U.S., while dry conditions returned from central California into the Four Corners Region.  Unfavorable dryness persisted in the Southeast.

Mid-Atlantic and Northeast:  Light to moderate rain and snow (locally more than 1 inch liquid equivalent) from western Pennsylvania into central New England contrasted with increasingly dry conditions on the lower Delmarva.  Locally heavy lake-effect snow showers eased D0 (Abnormal Dryness) downwind of Lake Ontario.  However, precipitation has totaled locally less than 50 percent of normal over the past 90 days from northern New York into western and northern Maine, where the D0 designation was expanded.  Meanwhile, unfavorable dryness continued to cause declining streamflows on the lower Delmarva Peninsula, where the updated 3-month Standardized Precipitation Index (SPI) likewise supported the introduction of Moderate Drought (D1).  In addition, a 60-day precipitation shortfall (50-70 percent of normal) along with streamflows in the lowest 30th percentile in southern Virginia resulted in a northward expansion of D0 in this locale.

Southeast:  Dry, warmer-than-normal weather prevailed, resulting in an increase in drought designation from central and eastern portions of North Carolina into southern Georgia as well as southern Florida.  Moderate (D1) to Extreme (D3) Drought was expanded northeastward over the Coastal Plain of North and South  Carolina, with ongoing dryness (50 percent of normal or less over the past 90 days) causing a further decline in streamflows (gauges closest to the coast are in the lowest 10th percentile) and soil moisture.  Abnormal Dryness (D0) was also introduced to central and northern North Carolina to reflect developing precipitation deficits (60-day rainfall averaging 50-75 percent of normal).   In Georgia, the sharp contrast between northern drought-free areas and southern Exceptional Drought (D4) further intensified.  In northern Georgia, additional showers – albeit light (amounts generally less than an inch)- kept soils favorable moist.  Meanwhile, little if any rain fell across southern Georgia, where Exceptional Drought was expanded to correspond with the greatest 6-month rainfall departures (locally less than 50 percent of normal) and the lowest streamflows (5th percentile or lower).  In Florida, light showers (0.25 to 0.5 inch) were reported across the panhandle.  Dry weather prevailed across the remainder of the state, which led to declining streamflows, elevated fire danger, and increasing short-term precipitation deficits.  Severe Drought (D2) was expanded southward across Gainesville to the northeastern Gulf Coast, with soil moisture and streamflows in the 10th percentile or lower.  Farther south, Moderate Drought (D1) was expanded from Fort Meyers east to West Palm Beach, with the 3-month Standardized Precipitation Index (SPI) and Soil Moisture percentile rankings supporting the increase.  Much of central and northern Florida remains a strong candidate for additional drought expansion over the upcoming weeks if rain does not soon materialize.  

Delta:  Heavy rain further eased drought in southern and western portions of the Delta.  The precipitation - which tallied 2 to 4 inches (locally more) - resulted in widespread drought reduction in central Louisiana and southern Mississippi.  Coastal locations remained largely unchanged, with rainfall totals significantly less (mostly less than an inch).  The same held true for northern Louisiana and southwestern Arkansas, where rain amounts were generally an inch or less.  Long-term precipitation deficits are still reflected in the 9- and 12-month Standardized Precipitation Indices (SPI), which continue to depict D1 (Moderate Drought) to D4 (Exceptional Drought) in southern and western portions of Louisiana.

South-Central U.S.:  Locally heavy rain across central and eastern drought areas contrasted with unfavorably dry, warm weather elsewhere.  A soaking rain (2-4 inches, locally more) fell from San Angelo northeastward across Dallas-Fort Worth into southeastern Oklahoma and northwestern Arkansas.  A second, smaller but locally heavier band of rain (1-6 inches) was observed from San Antonio and Austin eastward across Houston into Beaumont-Port Arthur.  Consequently, widespread reductions in drought were made - in some case up to 2 categories - as a result of the heavy rain.  However, reservoirs remained unfavorably low across the northeastern quarter of Texas; consequently, despite 2 to 3 inches of rain, relatively small improvements were made to D0 (Abnormal Dryness) to D2 (Severe Drought) in these locales.   Meanwhile, above-normal temperatures (4-10°F above normal) and increasing dryness led to drought intensification across southern and western portions of Texas as well as neighboring portions of eastern New Mexico.  Precipitation over the past 60 to 90 days has trended well below normal, especially from the Rio Grande Valley northward into southeastern New Mexico and west-central Texas.

Central and Northern Plains:  Unseasonably warm, dry conditions returned, melting much of the region’s protective snow cover and offering areas under Abnormal Dryness (D0) little if any relief.  The 3-month Standardized Precipitation Index (SPI) continued to exhibit varying degrees of dryness (D0-D3) from Nebraska northward into the Dakotas and eastern Montana, although shorter-term (30-60 days) precipitation has tallied near to above normal across the northern Great Plains.  Dryness is most protracted in northeastern North Dakota (where Moderate Drought – D1 – was expanded) and from southeastern portions of South Dakota into north-central Nebraska.  Drought areas of southern Kansas and southeastern Colorado were likewise dry and warm (10°F or more above normal), although an approaching storm offered some hope for relief over the next several days.   

Midwest:  Drought areas of the Midwest - which extend from northwestern Iowa into Minnesota and Wisconsin - reported dry weather and unseasonable warmth (temperatures 9 to 18°F above normal) during the past week.  There were no changes to drought designation, with cold-season impacts still relatively minor.  This area will have to be closely monitored over the upcoming weeks, with the potential for rapid drought intensification if precipitation does not materialize soon.

Western U.S.:  After last week’s much-needed precipitation, dry weather returned from central California into the Four Corners Region.  From southern California into southern Nevada and northwestern Arizona, Moderate Drought (D1) was introduced to reflect very low water-year-to-date precipitation (locally below 25 percent of normal) as well as declining snow water percentiles.  The new D1 area also corresponds with the latest 3- and 6-month Standardized Precipitation Indices (SPI), which depict D1 conditions or worse in these same locales.  Additionally, Abnormal Dryness (D0) was expanded to include much of southern California, where seasonal rainfall has totaled less than 50 percent of normal.  Despite beneficial snowfall in the Sierra last week, snow water equivalent remained in the 20th percentile or lower, indicating this region may fall rapidly back into Severe Drought (D2) if additional snow does not fall soon.

In northern portions of the region, another round of moderate to heavy mountain snow (2-10 inches liquid equivalent) maintained favorable spring runoff prospects from the Klamath Mountains northward into the Cascades.  However, the core Moderate Drought (D1) area received little if any precipitation, with no change made to this area.  Additional snow (0.5-2.5 inches liquid equivalent) boosted snow water equivalents (SWE) in central and northern Idaho above the 40th percentile, although the D0 (Abnormal Dryness) area of southeastern Idaho – where SWE remained in the 20th percentile or lower – was mostly dry.  In Montana, D0 was expanded into the southwestern quarter of the state to reflect SWE that ranged from the 10th to the 30th percentile.  Northwestern Montana – in particular Flathead County – was a candidate for D0 introduction due to SWE locally in the 20th percentile or lower, but much-needed precipitation (1-4 inches liquid equivalent) provided a reprieve.  There were no changes made to the drought designation in the central Rockies following last week’s introduction of Moderate Drought; this region will be reassessed pending the final result of an approaching storm system.

Alaska, Hawaii, and Puerto Rico:  In Alaska, bitterly cold conditions continued, with temperatures averaging 15 to 25°F below normal.  Snow continued to fall across the southern half of the state, with no concerns for drought.  In Hawaii, much of the state remained dry.  Additional assessment for Molokai indicated pastures are in very poor condition, resulting in a degradation to D3 (Extreme Drought) over the western third of the island.  Likewise, dry conditions and additional assessment led to the introduction of Severe Drought (D2) on Lanai.  There were no concerns for drought on Puerto Rico.

Looking Ahead:  A disturbance will race across the southeastern quarter of the nation, producing light to moderate rain over the central and southern Atlantic Coast States.  However, rain is expected to rapidly diminish as it approaches the drought areas of southern Georgia and Florida.  Meanwhile, an upper-air disturbance will trigger light to moderate snow across the central and northern Rockies.  As this feature reaches the Plains, a storm will rapidly develop and intensify, generating increasingly heavy rain and snow from the central Plains into the Corn Belt, while a trailing cold front triggers showers and thunderstorms from central Texas into the Delta and interior Southeast.  Little if any precipitation is expected in Florida and from California into the southern Rockies.  Likewise, drought areas of the Upper Midwest will also remain dry.  The CPC 6-10 day forecast for February 7-11 calls for drier-than-normal conditions from the Pacific Coast States eastward into the mid-Mississippi River Valley and Southeast, with wetter-than-normal conditions confined to southern Texas and the eastern Great Lakes.  Warmer-than-normal weather from the central and northern Plains to the Pacific Coast will contrast with below-normal temperatures in the Gulf and southern Atlantic Coast States.

Author: 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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