Sunday, March 29, 2015

National Drought Summary for March 24, 2015

Summary

Rain across southern-most portions of the nation provided drought relief, while dry weather maintained or worsened drought from California into portions of the Rockies, Plains, and Upper Midwest. In addition, above-normal temperatures further reduced already-dire mountain snowpacks over much of the West and accelerated pasture and crop-water demands in the nation’s mid-section. Dryness also increased in the Northeast, though below-normal temperatures mitigated the impacts of the precipitation deficits.

Alaska, Hawaii, and Puerto Rico

There were no changes made to the drought depiction in Alaska, Hawaii, and Puerto Rico this week. In Alaska, persistent warmth (5-10°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, scattered light showers (mostly less than half an inch) afforded little if any relief to the state’s Moderate Drought (D1) areas. In Puerto Rico, the heaviest rain (greater than 2 inches) fell west of the island’s remaining D0, where streamflows still remain below the 20th percentile.

Central Plains

Dry, unseasonably warm weather maintained or worsened drought over the central Plains. With temperatures approaching or topping 80°F from southeastern Colorado into Kansas as well as little if any rain, drought conditions remained or intensified. In particular, pronounced short-term dryness (25 to 50 percent of normal over the past 90 days) across central and southern portions of Kansas supported the expansion of Moderate (D1) to Severe Drought (D2). Soil moisture continued to decline, and many streamflows were in the 10th percentile or lower.

Mid-Atlantic and Northeast

Cold, mostly dry conditions were observed across the region, with Abnormal Dryness (D0) expanded northward across eastern New York and western Vermont, where precipitation over the past 60 days has tallied locally less than 50 percent of normal. Despite the dryness, temperatures averaging more than 10°F below normal have resulted in little – if any – impacts from the dry conditions, as many surface water features remain frozen. In contrast, near- to above-normal precipitation continued over the southern Mid-Atlantic, easing D0 in southwestern Virginia.

Midwest

Chilly but dry conditions in eastern portions of the Midwest contrasted with warm weather and areas of light rain in western portions of the region. In the Great Lakes, Abnormal Dryness (D0) was introduced in southeastern Michigan and northwestern Ohio as well as central and northern portions of Michigan and Wisconsin. Precipitation in these locales has totaled locally less than 50 percent of normal over the past 90 days, reducing soil moisture for spring growth.

Northern Plains

Despite pockets of light rain, unseasonable warmth (up to 10°F above normal) coupled with increasingly dry conditions over the past 90 days led to the expansion of Abnormal Dryness (D0) and Moderate Drought (D1) in the western Dakotas. Over the past 90 days, precipitation has totaled 60 to 75 percent of normal (locally less) in the newly-expanded D0 areas of the northern Plains, while the D1 area of South Dakota has received less than 50 percent of normal precipitation. The dryness coupled with rapid snow melt and temperatures well into the 70s in South Dakota have accelerated water demands for emerging pastures and greening winter crops. In addition, reports from the field indicate dry soils are becoming an underlying issue.

Southeast and Delta

Locally heavy rainfall led to reductions in drought coverage and intensity in the mid-South, while mostly dry, warm weather caused a minor increase in Abnormal Dryness (D0) in the Carolinas and the introduction of Severe Drought (D2) in southern Florida. Moderate to heavy rain (1 to 3 inches) fell across the Gulf Coast States, though the immediate Gulf Coast remained dry except in far western Florida. Consequently, D1 (Moderate Drought) and D0 were reduced from the central and northern Delta into the Florida Panhandle. In contrast, the South’s soaking rainfall bypassed south-central North Carolina, where D0 was expanded to reflect short-term dryness and streamflows locally below the 10th percentile. Likewise, protracted short-term dryness and above-normal temperatures have caused low water levels and high salinity in the Everglades, where D2 was added.

Southern Plains and Texas

Worsening drought in the north contrasted with heavy rain and drought reduction in the south. Across Oklahoma and northern Texas, most areas received less than 0.5 inch of rain during the monitoring period, which coupled with daytime highs in the upper 70s and lower 80s (degrees F) afforded no relief from drought. In areas where rain was sparse or non-existent, Severe to Exceptional Drought (D2-D4) expanded as streamflows continued to decline well below the 10th percentile. Soil moisture likewise rapidly diminished as the unseasonable warmth increased crop- and pasture-water demands. Meanwhile, moderate to heavy rain (1 to 4 inches) from southern Oklahoma into central and southern Texas reduced drought coverage and intensity, with the most notable improvements occurring between San Antonio, Texas, and the Big Bend. Despite the soaking rainfall, little change was made to the drought coverage and intensity northwest of Austin, where reservoirs levels struggled to rebound due to a persistent, pronounced long-term drought.

Western U.S.

The overall trend toward drought persistence or intensification prevailed, with relief confined to a few scattered locales in the Four Corners Region and southeastern California. 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, a steady influx of Pacific moisture and weekly average temperatures up to 7°F above normal resulted in moderate to heavy showers from the Cascades into the northern Rockies. However, plentiful water-year precipitation (since October 1) in the Northwest was 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.

In the Four Corners, drought worsened in the northwest while conditions improved somewhat in southeastern portions of the region. In particular, Severe to Extreme Drought (D2-D3) expanded over northern Utah to account for water-year precipitation averaging 30 to 45 percent of normal; the Standardized Precipitation Index (SPI) – a measure of drought severity – depicted values at or below -1.75 (D3 equivalent) in this same area . In addition, snow-water equivalents southeast of the Great Salt Lake were near or below 50 percent of normal (3-10th percentile). In New Mexico, however, improving conditions were noted in the southern Rockies, where locally more than an inch of rain and high-elevation snow afforded relief from Moderate Drought (D1).

In California, changes to this week’s depiction were generally minor as the state entered a fourth consecutive year of drought. Locally more than an inch of rain was noted in the Cascades and in the Coastal Range, but the moisture fell well short of supplying drought relief. Even with this week’s rain, precipitation deficits over the past two weeks exceeded 2 inches in these same locales. In the D4 areas of the Cascades and southern San Joaquin Valley, water-year precipitation has averaged 30 to 50 percent of normal, and locally less than 50 percent of normal over the past 3 years. Short-term moisture has been somewhat more plentiful in northern California, though even areas north of Sacramento are dealing with significant long-term precipitation deficits (70-75 percent of normal over the past three years) that will take considerable time to erase. Despite the generally worsening conditions, a small reduction in Extreme Drought (D3) was made in southeastern California’s Mojave Desert, where the wildflower bloom has responded favorably to showers.

Looking Ahead

Warm, mostly dry weather over the west will contrast with chilly, wet conditions east of the Mississippi Valley. The greatest likelihood for drought-easing rainfall will be from Texas and the northern Delta into the Northeast. Spotty showers are expected over the Rockies and Northwest, though the light rain coupled with persistent warmth will not ease drought or aid spring runoff prospects. Mostly dry, warm weather is expected over California and the Southwest. The NWS 6- to 10-day outlook for March 3 – April 4 calls for near- to above-normal temperatures nationwide, except for colder-than-normal conditions across the nation’s northeastern quadrant. Meanwhile, above-normal precipitation from the northern Plains and Upper Midwest into the Great Lakes and Northeast will contrast with drier-than-normal conditions in the south, particularly from California into the Four Corners and southern Plains.

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 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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