California and National Drought Summary for February 20, 2018
February 22, 2018 - During the past week, large precipitation events affected the Pacific Northwest, Southwest, southern Plains, Midwest, Ohio Valley, Tennessee River Valley, and mid-Atlantic, alleviating drought conditions or preventing further degradations in these areas. An active storm track in the coming week is expected to bring additional precipitation in the central and southern United States, which may result in further drought reductions. Conditions degraded in some areas of the Desert Southwest and Intermountain West that missed out on the heavier precipitation, most notably the Sierra Nevada and the Four Corners.
Over the past week, much of the northeastern United States received precipitation, with the highest amounts (2 inches or greater) falling in West Virginia and western Pennsylvania, and lighter amounts falling over New England. Rain of a half inch to 2 inches in the Baltimore area led to localized improvement out of moderate drought, though other areas remain in moderate drought given low groundwater and rainfall deficits over 90 days. Despite some recent precipitation, abnormal dryness persisted in eastern Pennsylvania.
In the previous week, much of Virginia received .25 inch to 1 inch of precipitation, and the northern third of Alabama and northwest Georgia also received .25 inch to 1.5 inches of precipitation. Moderate drought was adjusted in west-central Georgia, with expansion in the eastern area and reduction in the southern area due to changes in seasonal precipitation deficits. Abnormal dryness was filled in from the I-20 corridor southward because of seasonal precipitation deficits. A separate area of moderate drought in southeast Georgia was expanded toward the South Carolina border because of seasonal precipitation deficits. Moderate drought coverage in south-central Virginia was reduced because of increasing streamflow and lessening mid-range precipitation deficits. Lighter rain amounts (most under a half inch) fell in North Carolina, so no changes to ongoing abnormal dryness and moderate drought were made here. The abnormally dry and moderate drought conditions switched from short term to long term to reflect increasing precipitation deficits at longer ranges. Elsewhere, mostly dry conditions prevailed. Moderate drought and abnormal dryness in the Florida Panhandle and adjacent Alabama Gulf Coast were trimmed because of high streamflow and lessening short-term rainfall deficits. Moderate drought was reduced in southern Alabama because of recent rainfall and improved one-month to seasonal-scale precipitation deficits. Abnormally dry conditions and moderate drought from central to northern Alabama were trimmed because of improved two- to three-month rainfall deficits. Abnormally dry conditions were developing in east-central and south Florida, mostly driven by short-term rainfall deficits. Temperatures in many parts of the Florida Peninsula have been running well above normal in February as well. Winter rye and pastures were beginning to struggle in east-central Florida as a result of this short-term dryness, while hydrologic indicators remained wet in south Florida, likely because of the active hurricane and rainy seasons.
With a warm and moist air mass in place ahead of multiple storm systems affecting the region between Friday and Tuesday morning, heavy precipitation fell over much of the Midwest region, particularly in Missouri, Illinois, and Kentucky. Heavy precipitation persisted beyond the Tuesday morning cutoff along and behind a slow-moving cold front; any precipitation after the Tuesday morning cutoff will be accounted for in next week’s USDM. One-category improvements were made in parts central Illinois because of recent rains and low evaporative demand. Slight reductions in severe and extreme drought were made in south-central Missouri and north-central Arkansas, as streamflow and 90-day rainfall deficits no longer supported severe and extreme drought in the respective improvement areas. Elsewhere in Missouri and Arkansas, seasonal-scale precipitation indicators did not yet support improvements. Because of dry conditions between one and four months in west-central Minnesota, abnormal dryness was expanded there.
Several areas of precipitation fell in Wyoming (ranging from .25 inch to localized 2+ inches); the heaviest precipitation areas were in the Yellowstone/Teton high country and in the Snowy Range. No changes were made in Wyoming, as the snow in the Snowy
Range prevented further degradation there. Precipitation between .50 inch and 1 inch took place in the Dakotas, so no changes were made here, except for an expansion of abnormal dryness along the US 14 corridor in east-central South Dakota where seasonal precipitation deficits persisted. Rains from the aforementioned Midwest storm systems clipped southeast and parts of south-central Kansas with .25 inch to 1.5 inches of precipitation. A small area of .25-.50 inch of precipitation also fell in northwest Kansas. Moderate drought expanded into northeast Kansas because of persistent short- to medium-term seasonal precipitation deficits and abnormally warm temperatures in the last month.
Over the last week, moderate to heavy precipitation from the Midwest storm systems fell over parts of Texas, all of Arkansas, parts of Louisiana, and northern Mississippi. Improvements from abnormally dry conditions took place in parts of western Louisiana and east Texas, where recent rainfall erased precipitation deficits. Abnormally dry conditions in the Bayou crept northward as a result of two-month and longer precipitation deficits. Farther west in southwest Texas, moderate drought and abnormal dryness were reduced, as recent rainfall from last week’s storm system reduced precipitation deficits. In the southern Texas Panhandle, the Friday storm system delivered moderate rainfall, giving some locations their first measurable precipitation in months. In some areas of the southern Panhandle, this was enough to improve conditions from extreme drought to severe drought. Elsewhere, from central Texas southwest to the Edwards Plateau, abnormal dryness to severe drought continued, despite some locales receiving precipitation. Moderate to heavy rain also occurred in parts of western and central Oklahoma, while much of eastern Oklahoma received moderate to heavy rain (which continued after the Tuesday morning cutoff). Drought conditions remained the same in Oklahoma, as the rainfall in western Oklahoma was not enough to improve conditions because of continued long-term precipitation deficits. Drought conditions in central Arkansas improved because of recent rainfall.
A storm system moving through the southwest United States led to moderate or heavy precipitation in parts of New Mexico, Arizona, Utah, and Colorado, with the heaviest Colorado precipitation taking place in the San Juan Mountains. Abnormally dry conditions in south-central New Mexico improved. However, the heavier precipitation missed the Four Corners region, worsening the long-term precipitation deficits. Most of California and Nevada also remained dry this week. Above-normal temperatures over the last few months, combined with precipitation deficits over most of the Southwest, led to the continuation of drought in much of the Southwest region. Moderate drought expanded through parts of the Sierra Nevada, where very low snowfall, short- and seasonal-range precipitation deficits, and warm temperatures so far this winter continued. Some ski areas have even closed because of the lack of snowfall. Abnormally dry conditions expanded through the rest of the Central Valley in California, where precipitation deficits over the water year and streamflow continued to degrade. Moderate drought expanded over south-central Oregon, where short-term and water year precipitation deficits intensified.
Alaska, Hawaii, and Puerto Rico
The Big Island of Hawaii improved by one category because of recent significant rainfall. Alaska and Puerto Rico were status quo for this week.
An active stormy pattern looks to continue in the central and eastern United States as we progress into next week. As a front continues to settle over the central, south-central, and eastern United States, expect moderate to heavy precipitation to continue in these areas late this week. A new storm system this weekend may deliver some rain and snow to parts of the central Plains, Midwest, Great Lakes, and mid-South. Mainly dry conditions are forecasted to persist in Florida, the Carolinas, and most of the low elevation areas of Nevada and California. Some precipitation approaching an inch is possible in the Sierra Nevada. Generally, temperatures in the western United States should fall below normal, while temperatures in the eastern United States will likely be warmer than normal. More variable temperatures are anticipated in the central United States.
Deborah Bathke, National Drought Mitigation Center
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 less than 6 months (e.g. agricultural, grasslands)
L Long-Term, typically greater than 6 months (e.g. hydrologic, ecologic)
National Drought Mitigation Center