Widespread Drought Degradation Despite Active Weather Pattern

An atmospheric river and several fast-moving weather disturbances impacted the West and Northern Tier last week, allowing for some minor improvements to the drought depiction. Dry, unseasonably mild weather prevailed though for the High Plains and the south-central and southeastern U.S. This led to widespread degradation to drought conditions.

Northeast

A series of storm systems moved across the Northeast last week, bringing widespread precipitation. Most of the region reported at least one-half inch of liquid equivalent, with greater amounts extending from Delaware and Maryland’s Eastern Shore through New Jersey, the lower Hudson Valley and southern New England. Temperatures were generally warmer than normal, which caused much of this precipitation to fall as rain. These mild temperatures and rainfall melted away a good portion of the snowpack that had accumulated late in the previous week.

While new precipitation and snowmelt were beneficial, drought reductions were generally limited due to several factors. Across New England, soils and streams have largely frozen over, limiting the potential for new precipitation to substantively alter soil moisture. The precipitation that fell across the Mid-Atlantic did boost topsoil moisture, but the precipitation was largely insufficient to improve groundwater and streamflow conditions.

Abnormal dryness and moderate drought (D0-D1) improvements were limited to portions of eastern Maryland, Delaware, southeastern Pennsylvania and southern New Jersey, where precipitation totals were greater than 1 inch. Some reductions to abnormal dryness and moderate drought were also noted in north-central Pennsylvania and southern New York.

In contrast, severe drought (D2) expanded across the West Virginia Panhandle and western Maryland due to worsening streamflow and groundwater conditions.

Southeast

There was some light to moderate precipitation that fell across much of Alabama, portions of the eastern Florida Panhandle, across the Piedmont and southern Appalachians of Georgia and South Carolina and much of North Carolina and Virginia. Here, rainfall amounts of up to an inch fell, with some locally higher amounts. With temperatures ranging near normal, the precipitation was largely insufficient to yield drought conditions, but it did help prevent further degradations where it fell.

Small reductions were made to abnormal dryness and moderate drought (D0-D1) across southeastern Virginia and northeastern North Carolina, where accumulations exceeded an inch. A small portion of Florida’s Nature Coast also saw improvements to severe drought (D2).

Conversely, drier conditions were noted across parts of northern Georgia, the remainder of Florida and the coastal plain of Georgia and South Carolina. Some drought degradations did occur in these spots. Severe drought (D2) expanded in southeastern Georgia, with abnormal dryness to moderate drought (D0-D1) worsening elsewhere.

South

Unfortunately, the entire South observed subnormal rainfall and above normal temperatures last week, which lead to widespread drought degradations. However, there was a small area of heavier rain that fell across far southern Texas, resulting in reductions of abnormal dryness and moderate drought (D0-D1). There was also some beneficial moisture across parts of Tennessee, where a swath of 1 inch or more rain fell. Abnormal dryness (D0) is currently in place across central Tennessee. Despite this rainfall, short-term precipitation levels remain below average, so no improvements were made this week.

Drought expanded or intensified across the southern Texas plains, Hill Country, the Piney Woods and the Red River Valley. Besides far southern Texas near the Brownsville area, severe to extreme drought (D2-D3) worsened. Degradations were more widespread across the eastern two-thirds of Oklahoma and Arkansas. Severe drought (D2) worsened in northeastern Arkansas. In Arkansas, local observers continue to report drying lakes and ponds, while in Oklahoma, record warmth, strong winds and persistently below normal precipitation promoted expansion of severe and extreme drought (D2-D3).

Midwest

Several clipper-type systems brought snowfall along the U.S.-Canada border, with some lake-effect snow falling across Michigan. Mostly dry conditions were observed for the remainder of the Upper Mississippi Valley, Iowa and western Missouri. Some rain and snow fell east of the Mississippi River, with accumulations increasing towards the east. Overall, only small changes in the drought depiction were made across the region.

There was a reassessment of impacts from prior precipitation that led to some reductions of abnormal dryness and moderate drought (D0-D1) for northwestern Iowa. A localized area in southeastern Iowa and western Illinois saw one-half inch of liquid precipitation this week. This recent precipitation as well as snowfall from early December allowed for some modest reductions of moderate drought (D1). A small reduction of abnormal dryness (D0) also occurred in central Ohio, where accumulations exceed an inch for the week.

At the same time, drier conditions and above normal temperatures led to some degradation to abnormal dryness and moderate drought (D0-D1) across south-central Missouri and far southern Illinois. No change was made to the drought depiction across the Upper Great Lakes region, where streams and soils have mostly frozen over.

High Plains

A lack of snow cover, well above normal temperatures and periods of strong winds led to an unusual amount of winter degradation across the High Plains region last week. Severe drought (D2) expanded across western Nebraska, with expansions of both abnormal dryness and moderate drought (D0-D1) occurring across central and eastern parts of the state. A small area of moderate drought (D1) expanded across southeastern Kansas and across Colorado. Exceptional drought (D4) was introduced to Eagle and Pitkin counties in central Colorado. Abnormal dryness increased in coverage across the Plains of Wyoming.

Drought depictions remained unchanged across the Dakotas, where soils and streams have largely frozen over for the winter.

West

Across the West, a series of atmospheric river events brought copious amounts of precipitation to the Pacific Northwest. Washington and the northern Rockies continue to get pounded with heavy rain and mountain snow, with precipitation also extending further south into western Oregon and northern California.

While the repeated bouts of heavy precipitation continue to ease lingering drought conditions west of the Cascades, the picture is a bit more mixed at higher elevations. Temperatures during the period were above normal, which kept snow elevations higher than average and prevented this above average precipitation from building up substantial snowpacks in the Cascades and northern Sierra Nevada. In fact, snow-water equivalent values remain below 50% of average across the Cascades, northern Sierra Nevada, Blue Mountains and the Bitterroot Range, though conditions have started to improve across the remainder of the northern Rockies. While not an immediate drought concern during the winter months, a lack of snow cover could present problems during the spring and summer melting season.

Based on these considerations, abnormal dryness and moderate drought (D0-D1) were reduced along the western front of the Cascades and across small portions of the Intermountain West. However, drought conditions were maintained across the higher elevations. A small area of abnormal drought reduction was made across northern Montana, where recent storminess brought improvements to short-term drought indicators.

At the same time, little to no precipitation was observed across the Southwest under a large ridge of high pressure. Temperatures also remained well above average. However, recent wet weather the past few months caused conditions to remain status quo.

Looking Ahead

Over the next few days, ongoing atmospheric river activity will bring heavy moisture to the western U.S., with the focus shifting to California for intense coastal rainfall and mountain snowfall. Heavy precipitation will also spread inland to the Great Basin and parts of the Rockies. Later in the week, as the Pacific trough moves ashore and high pressure develops over the northeastern Pacific, a break in atmospheric river activity is expected towards the middle to end of the drought monitoring period. Meanwhile, a strong ridge of high pressure over the central U.S. will result in mostly dry conditions and well above normal temperatures across the Plains.

In contrast, the East will be influenced by a “blocking” ridge of high pressure moving toward Greenland, promoting backdoor cold fronts, cold air damming, and additional precipitation, including winter storms. Much of the Northeast is forecast to receive over an inch of precipitation, with snow or a wintry mix possible into the Mid-Atlantic. The Southeast should remain mostly dry, aside from light rain in the Lower Mississippi Valley.

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Source: U.S. Drought Monitor