California and National Drought Summary for March 31, 2015
Summary
Rain was heaviest across the nation’s mid-section as well as parts of the Northwest and eastern U.S., while intensifying dryness was noted in the Southeast and from the northern Great Lakes and Upper Midwest to the central and southern Pacific Coast, including the Great Plains. Much-above-normal temperatures accelerated crop-water demands on the Plains and further reduced already-dire mountain snowpacks over much of the West. Dryness also increased in the Northeast, though lingering cold mitigated the impacts of the precipitation deficits somewhat.Alaska, Hawaii, and Puerto Rico
There were no changes made to the drought depiction in Alaska and Puerto Rico this week, and only minor adjustments in Hawaii. In Alaska, much-above-normal temperatures (10-15°F above normal) maintained concerns over dwindling mountain snowpacks; these will need to be monitored closely over the upcoming weeks as the region heads into the warmer months. In Hawaii, a small reduction of Abnormal Dryness (D0) was made on the Big Island due to reported improved conditions at farms in these areas. In Puerto Rico, scattered light to moderate showers (mostly less than 2 inches) fell outside of the island’s remaining D0, where streamflows still remained below the 20th percentile.Central Plains
Dry, unseasonably warm weather maintained or worsened drought over the central Plains for a second consecutive week. With sunny skies and temperatures approaching or topping 80°F from southeastern Colorado into Kansas and central Nebraska, drought conditions remained or intensified. In particular, pronounced dryness over the past 6 months (30-50 percent of normal) across south-central and northern Nebraska supported the expansion of Moderate (D1); the Standardized Precipitation Index (SPI, a station-based drought indicator) over the same time period in these locales averaged -1.0 to -1.7 (D1-D3 equivalent) indicating conditions may rapidly deteriorate if rain fails to materialize soon. Elsewhere, light showers (generally less than half an inch) in eastern portion of the region afforded little – if any – drought relief.Mid-Atlantic and Northeast
Chilly conditions were accompanied by highly variable rainfall, with locally heavy showers in southern portions of the region contrasting with increasing short-term dryness over New England. Abnormal Dryness (D0) expanded northward over much of New York and encompassed significant portions of Vermont, New Hampshire, and Maine. Despite light showers (generally less than half an inch) during the period, precipitation over the past 60 days has tallied locally less than 50 percent of normal. Even with melting snow, streamflows in many of the newly-expanded D0 areas were in the 10th percentile or lower, and soil moisture for warm-season growth continued to decline. In contrast, locally more than an inch of rain further eased D0 in southwestern Virginia.Midwest
Chilly weather prevailed, with moderate to heavy showers in southern portions of the region contrasting with increasingly dry conditions elsewhere. Rain totaled more than an inch from southeastern Nebraska into central and western Ohio, while totals farther north were generally less than half an inch. Widespread pronounced precipitation deficits (15-50 percent of normal) are noted over most of the Midwest during the past 90 days, while 6-month precipitation stood at a meager 35 to 70 percent of normal from the Dakotas and parts of Nebraska into the central Great Lakes region. Likewise, declining soil moisture and streamflow percentile rankings indicated rapidly worsening conditions over the Midwest’s newly-expanded Abnormal Dryness (D0) and Moderate Drought (D1) areas. In addition, the Standardized Precipitation Index (a station-based drought indicator) depicted D1 or worse conditions from the Dakotas into southeastern Michigan and northwestern Ohio, though lingering below-normal temperatures have mitigated the impacts of the dryness somewhat.Northern Plains
Light to moderate rainfall on the northern-most Plains was in sharp contrast to increasing dryness and drought farther south. Locally more than an inch of rain in North Dakota was sufficient to prevent further expansion of Abnormal Dryness (D0) or Moderate Drought (D1), though precipitation over the past 6 months remained well short of normal (30-60 percent of normal). Farther south, above-normal temperatures (daytime readings in excess of 80°F) and a lack of much-needed rain resulted in expansion of D1 in southern South Dakota; precipitation in South Dakota’s new D1 area averaged 25 to 50 percent of normal over the past 6 months, which equated to a Standardized Precipitation Index (SPI, a station-based drought indicator) equivalent over the same time period of D1. Likewise, soil moisture rankings remained unfavorably low over much of southern and eastern South Dakota, and streamflows – which benefited from recent snow melt – have begun to drop rapidly.Southeast and Delta
Mostly dry, mild weather overspread much of the region, resulting in an eastward expansion of Abnormal Dryness (D0). Pronounced short-term dryness caused D0 to increase from southern North Carolina into South Carolina and Georgia, where precipitation over the past 90 days has totaled 60 to 75 percent of normal. Streamflows in the expanded D0 areas were generally at or below the 30th percentile (D0 equivalent), and were below the 10th percentile from northern Georgia into western North Carolina. Moderate Drought (D1) likewise increased across southern Alabama, coinciding with 90-day rainfall averaging 25 to 60 percent of normal; the Standardized Precipitation Index (SPI – a drought intensity indicator) depicted D1 (or worse) over the past 3 to 6 months in this region. In Florida, seasonably heavy showers eased D0 and D1 near Lake Okeechobee, while protracted short-term rainfall deficits and above-normal temperatures maintained low water levels and high salinity in the Everglades’ Severe Drought (D2) area. Farther west, locally heavy showers (1-3 inches) eased D0 and D1 in the northwestern Delta, while near- to above-normal streamflows and soil moisture supported the removal of D0 in eastern Arkansas and western Tennessee, though drier-than-normal conditions are still apparent over the longer term.Southern Plains and Texas
Worsening drought in the north contrasted with heavy rain and drought reduction in the south and east. Across western Oklahoma and northern Texas, sunny skies, daytime highs approaching or topping 90°F, and occasionally gusty winds caused Moderate (D1) to Extreme (D3) Drought to intensify. Soil moisture and streamflow rankings remained at or below the 5th percentile in the southern Plain’s core drought areas, while the satellite-derived Vegetation Health Index indicated rapidly declining conditions from the Texas Panhandle into northern Oklahoma. Farther east, locally more than an inch of rain afforded some relief from drought in northeastern Oklahoma. Farther south, additional assessment from the field indicated some reduction of Abnormal Dryness (D0) was warranted near Victoria, Texas, while drought coverage and intensity remained unchanged northwest of Austin as reservoir levels struggled to rebound due to a pronounced long-term drought impacts.Western U.S.
The overall trend toward drought persistence continued, with drought intensification noted over the eastern Great Basin and central Rockies. The west continued to cope with much-above-normal temperatures, further depleting already-dire snowpacks and reducing spring runoff prospects over much of the region.In the north, additional Pacific moisture and weekly average temperatures up to 10°F above normal resulted in moderate to heavy showers (1-4 inches, locally more) in orographically favored portions of the Cascades and northern Rockies. However, plentiful water-year precipitation (since October 1) in the Northwest remained in sharp contrast to virtually non-existent snowpacks, with the snow-water equivalents less than 25 percent of normal (locally less than 10 percent) across Oregon as well as southern and northwestern Washington. The lack of snow maintained concerns for spring and summer water supplies despite the generally favorable 2014-15 water year.
Across the Great Basin and Four Corners States, drought intensified in northern portion of the region but remained unchanged elsewhere. In particular, Severe Drought (D2) expanded over northeastern Nevada, where water-year precipitation (since October 1) has averaged less than 50 percent of normal the northwest; the Standardized Precipitation Index (SPI, a station-based drought indicator) over the same time period in this location averaged -1.3 to -2.0 (D2-D4 equivalent) indicating conditions will likely deteriorate further if rain and mountain snow fail to materialize soon. In Colorado, D2 was increased as low SNOTEL percentiles, low snowpack, and high temperatures are having an impact in the state; snow-water equivalent (SWE) in the state’s D2 areas are now consistently at or below the 10th percentile, and locally below the 5th percentile. Meanwhile, conditions remained unchanged in the southern Four Corners Region, where Water Year precipitation has been generally higher than locales farther north.
In California, there were no changes to this week’s depiction as the state entered a fourth consecutive year of drought. With temperatures averaging more than 10°F above normal for the week, snowpacks continued to dwindle; as of April 1, the state’s total snowpack stood at a meager 5 percent of average. Indicative of the virtually non-existent snowpack, streamflows have dropped into the 5th percentile or lower over much of California. In addition, the 2014-15 Water Year has ended on an abysmal note, with precipitation over the past 30 days totaling a mere 10 percent of normal or less from Redding southward. Even with some precipitation in the forecast across central and northern California, any rain and mountain snow – while welcomed – would likely do little to improve the state’s dire drought prospects.
Looking Ahead
Rain from the lower and middle Mississippi Valley into New England will contrast with mostly dry conditions across the Southeast and Gulf Coast as well as from the Plains into the Southwest. A strong cold front will bring temporary relief from unseasonable warmth over the Plains, though above-normal temperatures will return by the weekend. Rainfall associated with the front will be light on the Plains, and generally confined to central and northern-most portions of the region. However, rain will intensify as the cold front marches east, with 5-day totals of 1 to 3 inches possible from the northern Delta into the Ohio Valley and Northeast. In contrast, dry conditions are expected from the Carolinas to the immediate Gulf Coast. Out west, some showers and high-elevation snow will overspread the Northwest during the weekend, while the Southwest and Four Corners Region remain dry. The NWS 6- to 10-day outlook for April 7–11 calls favorably cooler- and wetter-than-normal weather from the Pacific Coast into the Great Basin, including California. Likewise, wetter-than-normal weather is also expected from the Mississippi Valley and Gulf Coast States into the Northeast. In contrast, drier-than-normal conditions will prevail across the Rockies and Great Plains. East of the Rockies, abnormal warmth over southern portions of the Corn Belt and Mid-Atlantic States will contrast from cooler-than-normal weather across the northern Great Lakes and New England.Author(s):
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 DroughtD2 ... 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)
