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‘Water Year’ Nearing End in Now-Parched West

May 2, 2013 by   - () Leave a Comment

Summary: Periods of locally heavy rain provided drought relief in central and southern portions of the nation, while dry weather with sharp temperature contrasts exacerbated drought from the central High Plains into central and western Texas. The Upper Midwest continued to deal with long-term precipitation deficits despite seasonal spring flooding, while an early end to the western Water Year caused drought to intensify across the Southwest. Short-term dryness was also beginning to have an impact in parts of the Northeast and Mid-Atlantic.

Mid-Atlantic and Northeast: Drier-than-normal weather along with mostly seasonable temperatures prevailed. Over the past 90 days, precipitation deficits of 3 to 7 inches (locally 50%  of normal or less) have caused streamflows to drop below the 20th percentile in many of the newly expanded D0 (Abnormally Dry) areas. Similar streamflow levels were noted in northern West Virginia, where D0 was expanded slightly. Much of the northern Mid-Atlantic and Northeast is dealing with increasingly dry conditions, and will need to be monitored over the upcoming weeks for potential impacts.

Southeast: Locally heavy rain alleviated Moderate Drought (D1) and further eased lingering long-term dryness (D0). Rain was heaviest (1-4 inches, locally more) from northern and eastern Georgia into southern and western North Carolina, which allowed for the removal of D1 in this region. Streamflows continued to exhibit recovery, and were mostly at or above the 20th percentile (D0 equivalent) at the end of the monitoring period. In contrast, northern Florida’s D2 (Severe Drought) area was mostly warm and dry, with declining soil moisture and low streamflows (10th percentile or lower) indicative of the drought’s localized but pronounced impacts. In southern Florida, a wet April coupled with additional showers during the past week eliminated D0 from the region.

Northern Plains and Upper Midwest: Long-term drought lingered despite seasonal snow melt and river flooding, although some improvements were made using updated precipitation data and reports from the field. A narrow band of 0.50 to 1.50 inches of rain eased D0 (Abnormal Dryness) and D1 (Moderate Drought) from south-central North Dakota into northwestern Minnesota. In addition, updated 90- and 180-day precipitation data supported reducing or eliminating areas of D0 and D1 in southeastern North Dakota and neighboring environs, with totals now at or above 100% of normal (locally up to 150%) at both time scales.

Likewise, D3 (Extreme Drought) was reduced in northeast Wyoming and southwestern South Dakota, where near-normal precipitation over the past three months has eased drought impacts. Despite the general consensus that conditions continue to improve, long-term indicators, including the 6-, 9-, and 12-month Standardized Precipitation Indices, show underlying, long-term drought persists in the core D1 and D2 areas of the Upper Midwest. In contrast, short-term dryness has reduced soil moisture in north-central North Dakota, where a small area of D0 was added.

Central Plains and middle Mississippi Valley: Drought intensified over the central High Plains, while rain provided additional drought relief to eastern portions of the region. Widespread showers (0.75-2.0 inches) in eastern Kansas and southwestern Missouri eased drought, with 2-week totals exceeding 4 inches in eastern-most D0 and D1 areas. Meanwhile, above-normal precipitation in northeastern Colorado improved winter wheat conditions, and drought impacts continued to lessen in this area; consequently, Extreme Drought (D3) was mostly eliminated from this corner of the state. In contrast, dry, hot weather (upper 80s and lower 90s, degrees F) prevailed from Nebraska into southeastern Colorado, where drought intensity either held steady or increased. In particular, Exceptional Drought (D4) expanded across southeastern Colorado, where poor pastures and winter wheat conditions reflect the ongoing impacts of protracted dryness (6-month precipitation locally less than 30% of normal); the Colorado winter wheat crop was rated 54% poor to very poor as of April 28, 2013, while Kansas wheat stood at 39%.

South-Central U.S.: Sharp temperature fluctuations were accompanied by rain in the East and South, while unfavorably dry conditions prevailed over the High Plains. From the southeastern Plains into the western Delta, 1 to 3 inches of rain (locally more) eased long-term drought in eastern Oklahoma and northwestern Arkansas; an additional week of rain will likely eliminate the lingering D0 in northwestern Arkansas. Meanwhile, widespread, locally heavy downpours (1-6 inches) eased Moderate to Exceptional Drought (D1-D4) across the southern third of Texas, with totals exceeding 6 inches in western and southern Houston as well as north of Victoria. Meanwhile, scorching heat (highs reaching 97-99°F) extended from the Big Bend northward into eastern New Mexico and the Texas Panhandle. This heat followed an early-period cold snap, when lows dropped into the teens. With no rain and increasing heat, drought intensity and coverage expanded across the southern half of the High Plains. As of April 28, 2013, the percent of the southern Plains’ winter wheat rated poor to very poor stood at 41% in Oklahoma and 68% in Texas, both increases from last week.

Western U.S.: The largely disappointing water year neared an end, with many areas of the West ending the season with bleak spring runoff prospects and increasing drought concerns. Showers were confined to the non-drought areas of the Pacific Northwest, where 1 to 2 inches (liquid equivalent) were reported during the monitoring period. Elsewhere, above-normal temperatures and dry weather maintained or increased drought intensity and coverage.

There was little change from California into the Great Basin and central Rockies. However, D0 (Abnormal Dryness) was expanded up the coast into northwestern California and southwestern Oregon, where 90-day precipitation averaged 35% to 60% of normal. Extreme Drought (D3) was reduced in southwestern Wyoming, where reports from the field indicated conditions have improved in this data-spare area.

Farther south, water-year precipitation shortfalls increased from the southern San Joaquin Valley (40% to 55% of normal) into southern Nevada (30% to 50% of normal) and western Arizona (less than 50% of normal) . The water-year’s disappointing conclusion was further evidenced by the last 3 months, when rainfall tallied less than 20% of normal from the southern California Coast into western Arizona and much of central and eastern New Mexico. Consequently, Moderate (D1) to Severe (D2) Drought was expanded in these locales. In New Mexico, the past 36 months (Apr 2010 – Mar 2013) have been the 4th driest period on record for the state, the driest since the 1950s. Exceptional Drought (D4) was expanded to include much of New Mexico’s Rio Grande Valley as well as portions of east-central and northeastern New Mexico.

Alaska, Hawaii, and Puerto Rico: In Alaska, locally heavy precipitation (liquid equivalent of almost 2 inches) eased D0 in southeastern portions of the state, while updated water-year precipitation values in the 50th percentile or higher supported additional D0 removal in northeastern Alaska. In contrast, D0 was expanded onto central and southern portions of the Kenai Peninsula where water-year precipitation was in the 10th percentile or lower. In Hawaii, there were no changes to the drought depiction despite nearly an inch of rain across the state’s western islands. In Puerto Rico, locally heavy showers (2- 8 inches) boosted streamflows and all but eliminated Abnormal Dryness (D0) from the island.

Looking Ahead: A developing storm over the nation’s mid-section will become cut off from atmospheric steering, causing the system to drift eastward into the Mid-South by week’s end and the Southeast early next week. Five-day precipitation totals could reach 2 to 4 inches across the east-central Plains, upper Midwest, lower and middle Mississippi Valley, and eastern Gulf Coast region. In addition, late-season snow will fall from the central Rockies into the Upper Midwest.

In contrast, little or no precipitation will occur in the Northeast and west of the Rockies. Unusually cool air will trail the storm, resulting in widespread freezes on May 2-3 as far south as the southern High Plains. Warmth will linger, however, from the eastern Corn Belt into the Northeast.

The NWS 6- to 10-day outlook for May 7-11 calls for above-normal temperatures in the West and Northeast, while cooler-than-normal conditions will prevail across much of the Corn Belt and from the central and southern Plains into the Southeast. Meanwhile, near- to below-normal precipitation from the Northwest into the northern Plains and western and northern Corn Belt will contrast with wetter-than-normal weather in the central and southern Rockies, portions of the Intermountain West, and much of the eastern third of the nation.

 

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