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Drought Monitor: Warm Western Temps Raise Concerns of Snow Melt

Ernst Undesser
Edited by Ernst Undesser with Information from Eric Luebehusen of USDA February 26, 2016

Drought Monitor: Warm Western Temps Raise Concerns of Snow Melt

Summary

Increasingly warm weather prevailed across much of the nation, with beneficial rain observed from Texas to the central and northern Atlantic Coast. Seasonable dryness over the Great Plains accompanied temperatures averaging 10 to 15°F above normal, with numerous daily record highs noted over southern portions of the region. Out west, progressively warmer weather heightened concerns of early snow melt, with early-week rain and mountain snow falling short of weekly normals and doing little to ease long-term drought.

 

Western U.S.

Despite some welcomed rain and mountain snow at the beginning of the weekly drought assessment period, a return to dry, warmer weather by week’s end renewed concerns of a sub-par Water Year even with the ongoing strong El Niño. There were localized improvements to drought intensity and coverage, but the overall trend was toward maintaining or increasing the West’s multi-year drought.

In northern portions of the region, additional rain and mountain snow continued the locally favorable Water Year in the Northwest and resulted in further reductions of Abnormal Dryness (D0) across southwestern Oregon, eastern Washington, and northern Idaho. Farther east, Moderate Drought (D1) was likewise reduced in south-central Montana (Big Horn County) to reflect near- to above-average reservoir storage and Water Year precipitation.

In contrast, Wyoming’s snowpack Snow Water Equivalent (SWE) remained below the 10th percentile (40 to 70 percent of average) in the Bighorn Mountains and below the 20th percentile (50 to 85 percent of average) in the River Range, where Severe (D2) and Moderate (D1) Drought were introduced, respectively.

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Farther south, there were small changes to the dryness/drought depiction from the Great Basin into the Four Corners Region. In the D1 and D2 areas around Great Salt Lake, reservoir storage hovered near or below 60 percent of average for the date, reflecting the lingering impacts of the region’s long-term drought.

D0 was expanded over central Arizona and southeastern New Mexico, where the favorable first half of the Water Year has given way to protracted dryness over the past 90 days (generally less than 50 percent of normal, locally less than 40 percent). Furthermore, the initially favorable snowpacks in the lower Four Corners have begun to rapidly diminish, with SWE near or below the 20th percentile (less than half of normal) from central Arizona into western New Mexico.

In the core drought areas of California and western Nevada, welcomed early-week rain and mountain snow gave way to warm, dry weather. Despite locally impressive precipitation totals during the 7-day period (ending Tuesday morning at 4 a.m., PST) , wetter-than-normal conditions for the week were confined to the northern-most counties in California as well as portions of the Sierra Nevada.

Extending back another 7 days, precipitation over the past two weeks — even with this week’s rain and snow — has fallen well short of normal over most of the state. Nevertheless, a boost to northern California’s SWE and reservoir storage led to a small reduction of Extreme Drought (D3). However, the recent overall trend toward warmer, drier weather — despite the ongoing strong El Niño — has raised concerns over increasing short-term drought impacts in addition to the region’s ongoing long-term (“L” Impact) drought.

To illustrate, a pronounced pocket of short-term dryness extends from the foothills of the San Jacinto Mountains southeast of Los Angeles northwestward to Santa Barbara, where rainfall has averaged a meager 33 to 50 percent of normal during the current Water Year (since October 1).

Southern Plains and Texas

After early-week heat, increasingly wet weather resulted in a significant reduction of Abnormal Dryness (D0) and Moderate Drought (D1) over much of the region. Early in the period, daytime highs topped 80°F across Texas and Oklahoma, with readings touching 90°F over the southern High Plains and Deep South Texas.

While the hot, windy conditions sparked wildfires and increased concerns over “flash drought”, widespread, moderate to heavy rain (1-3 inches, locally more) during the latter half of the period reduced or eliminated a wide swath of D0 and D1 over central and southern portions of Texas and neighboring Oklahoma.

In contrast, persistent short-term dryness necessitated expansion of D0 and D1 in Deep South Texas.

Central Plains

Sunny skies and above-normal temperatures prevailed across this drought-free region, with daytime highs reaching 90°F in central and southwestern Kansas and upper 70s to lower 80s elsewhere. While still within the central Plains’ climatologically dry season, the recent abnormal warmth hastened winter wheat out of dormancy and will heighten the need for topsoil moisture over the upcoming weeks.

Northern Plains

Spring-like warmth was observed over the northern Plains, with daytime highs reaching the upper 60s (°F) in southern Montana and lower 70s in southern South Dakota. Light precipitation was observed across much of the region, though amounts were again insufficient to offer relief from Abnormal Dryness (D0) and Moderate Drought (D1).

Midwest and lower Ohio Valley

Warm, mostly dry conditions prevailed in this drought-free region, though a major winter storm was impacting the region during the middle of the last week of February.

Delta

Increasingly heavy rainfall put an end to a pronounced short-term dry spell. Rain was heaviest across southern Arkansas and western Louisiana, where amounts totaled 2 to 3 inches. At the end of the drought assessment period (Tuesday morning, 7 a.m., EST), additional heavy rain was falling in the region, with late-season snow in northern portions of the Delta.

Southeast

Warmer albeit unsettled conditions kept the Southeast free of drought. Abnormal Dryness (D0) remained over southern Georgia as rain bypassed most locales in the lower Southeast, although rain overspread southern portions of the region after the latest drought monitoring period ended Tuesday morning.

Mid-Atlantic and Northeast

Widespread rain and northern snow (1-2 inches, liquid equivalent) afforded the region significant reduction in Abnormal Dryness (D0), and to a lesser extent Moderate Drought (D1). However, the heaviest precipitation once again bypassed the primary D1 areas from northern Connecticut into Massachusetts and southeastern New Hampshire. Temperatures moderated during the period, replacing recent bitter cold and accelerating snow melt.

Alaska, Hawaii, and Puerto Rico

Much-above-normal temperatures prevailed over Alaska, though the state remained covered by a seasonal snowpack.

In Hawaii, notably drier-than-normal conditions over the past 90 days have increased stress to pastures, particularly on the island of Maui where Severe Drought (D2) was introduced.

In Puerto Rico, unseasonably heavy rain led to a notable reduction in drought intensity and coverage. Rain tallied 2 to locally more than 6 inches, raising the 3-month precipitation to above average across the western half of the island as well as the island’s eastern tier. Puerto Rico’s lingering drier-than-normal conditions are now mostly confined to areas from San Juan to the southern coastline, where local streamflows remain below the 10th percentile.

Looking Ahead

Stormy, occasionally cold weather in the East will contrast with warmth and dryness across much of the west. A potent winter storm will march northeastward across the Great Lakes, producing additional locally heavy showers across the Atlantic Coast States as well as moderate to heavy rain and snow in the Midwest. In the storm’s wake, briefly chilly conditions east of the Mississippi will give way to a rapid warm up by early next week.

Generally tranquil weather will prevail from the Plains into the upper Midwest, though here, too, increasingly warm conditions will develop into next week.

Unfavorably warm, dry weather will persist from California and the Great Basin into the lower Four Corners Region, while periods of rain and mountain snow continue farther north from the Northwest into the northern and central Rockies.

The NWS 6- to 10-day outlook for March 1 – 5 calls for above-normal temperatures across western and central U.S. as well as much of the Northeast, with cooler-than-normal conditions confined to the upper Midwest. Meanwhile, below-normal precipitation is anticipated from the central and southern Pacific Coast eastward onto the High Plains and upper Midwest.


Source: : http://droughtmonitor.unl.edu/

Ernst Undesser
Edited by Ernst Undesser with Information from Eric Luebehusen of USDA February 26, 2016