The Northeast and Mid-Atlantic: Precipitation continued to bypass most of the region during the past week. Over the last 90-days, 25 to 50 percent of normal precipitation (PNP) has fallen from northern Virginia northward into coastal Maine, with deficits generally between 4 and 8 inches, with 8-12 inch deficits in southern New England and Long Island. The early green-up of trees and vegetation was slowed by the cooler air of recent weeks, but yet many plants have begun to grow, extracting moisture from the soil. According to the USGS, stream flow levels were at near- or record lows for April 17 at 1-, 7-, 14-, and 28-day averages in much of New England and the mid-Atlantic. Most reservoirs, however, were near or at capacity due to the early-season snow melt and thaw, and to wetter conditions in the past (9-12 months ago). Based on considerations above, the AHPS 30-day precipitation deficit map, and local expertise, abnormal dryness (D0) was expanded westward across west-central Pennsylvania, as far as Elk and Jefferson Counties.
The Southeast: Very little precipitation was reported over the Southeast during the past week. AHPS 30-day precipitation deficits of 3 to (as much as) 5 inches are indicated over much of Georgia, Alabama, the Florida Panhandle, and southern Tennessee. One-category degradations were made in much of South Carolina, portions of eastern and southwestern Georgia, and both east-central and far southern Florida. Rainfall deficits of 8-12 inches over the past 180-days are prevalent across Florida, along with Keetch Byram Drought Index (KBDI) values in excess of 550-600 (700 in west-central parts of Florida). Abnormal dryness (D0) was expanded across both northern and northeastern Alabama. An exception to the widespread dryness was an area of moderate to heavy showers and storms (1.5-2.0 inches) along the southeast coast of Florida during the period.
Midwest: Substantial rains (generally 0.5 to 2 inches, locally up to 3 inches) fell across a large portion of the drought area across the upper Midwest/upper Mississippi Valley region during the past week. One-category improvements were made across northern Minnesota (D1 conditions giving way to D0). Minor changes in the direction of improvement were also made in western and southeastern Iowa. A severe weather outbreak last weekend was accompanied by strong, damaging straight-line winds, severe hail, and tornadoes, primarily concentrated across southern Iowa. Temperatures across the region during the past 7-days averaged 2 to 6 degrees above-normal, with the warmest anomalies over Wisconsin. According to the USDA, percent topsoil moisture rated short-very short compared to the 5-year mean was: Illinois (27 current / 7 for 5-yr mean), Minnesota (48/11), and Iowa (27/6). Slight improvements were made to the drought depiction in western Illinois due to recent rains, but abnormal dryness (D0) was expanded northward into northern Illinois amid rainfall deficits over the past 90 days (AHPS) of 1-4 inches and local reports of dusty fields. One-category downgrades have also been made in western and central sections of Kentucky.
Northern and Central Plains: Precipitation amounts varied widely across the region, with amounts generally up to a half-inch observed over the High Plains, and up to 3.5 inches over the lower Plains. Recent heavy rains (up to 3 inches) in southeastern North Dakota justified removal of lingering D0 conditions, with 1-category improvements made over much of eastern South Dakota. In contrast, an expansion of moderate drought (D1) conditions was made in southwestern North Dakota, due to persistent dryness especially over the past 6-months. Moderate drought conditions were also expanded across western portions of Nebraska.
Southern Plains: Moderate to heavy showers and thunderstorms (1-4 inches, locally heavier) fell across portions of northern and central Oklahoma and southeastern Kansas, related in part to a severe weather outbreak which also affected portions of the Mississippi Valley during the past weekend. In northeast Oklahoma, Birch Lake is now slightly into its Flood Pool, while Skiatook Lake has risen by two feet (though capacity is still near 78 percent). The short-term wetness likely outweighs the long-term reservoir deficit in this case, and therefore the D0(L) area in Osage County in northeastern Oklahoma was eliminated. Slight improvements were made in western Oklahoma, though D2 conditions were maintained in extreme southwest parts of the state which are still contending with serious water supply and soil moisture issues. Beneficial wetness in western and southern sections of Texas warranted a number of slight alterations to the drought depiction in those areas.
The West: In Colorado, D1 and D2 conditions were expanded across north-central parts of the state, and a small area of severe drought (D2) was added to Crowley County in the southeast. In contrast, the area of D2 over extreme southeastern Colorado was trimmed back, indicating slight improvement. Severe drought was also expanded from western Colorado into eastern Utah, and from eastern Nevada into western Utah. Little to no precipitation has fallen over these portions of Utah. During the past 30 and 60-days, PNP values range from 10-25 percent of normal. Central Utah is faring much better, having received 0.5-3.0 inches of precipitation in the past 30 days. In California, beneficial late-season precipitation has resulted in a general 1-category improvement across the northern half of the state, and western sections of the southern half of California. Precipitation amounts of 1-4 inches (locally heavier) in the past week have been observed over most of the state. Dryness and drought has been increasing in coverage and intensity across portions of the Southwest. As a result, moderate drought (D1) was expanded across northeastern Arizona into northwestern New Mexico, while severe drought (D2) was expanded from northeastern Arizona to the New Mexico border.
Hawaii, Alaska and Puerto Rico: In Hawaii, some windward locations on Maui, the Big Island, Oahu, and southern Kauai received 1-2 inches of rain, with most other locations reporting less than a half-inch of rain. Fortunately, most of the islands (except the Big Island) received surplus March rainfall, easing any further deterioration there. On the Big Island, however, many northern and leeward locations have reported less than 25 percent of normal rainfall since January 1. Kona coffee growers indicated that leaves are starting to shrivel on their trees and berries are starting to fall. The main hope for the Kona coffee belt is that it is the only area in the state with a summer rainfall maximum. No changes to the drought depiction for Hawaii were deemed necessary this week. There were no drought conditions noted in Puerto Rico and Alaska.
Looking Ahead: Over the next five days (April 19-23), a frontal system is expected to move across the central and eastern US, with an area of low pressure forming along the southern portion of the front over the central Gulf Coast. As the low pressure center tracks northeastward into the Carolinas and Virginia, it is forecast to intensify. As a result, heavy rain (2.0 to 3.5 inches) is expected to significantly mitigate the current drought situation over the East Coast states. To the northwest, across the Great Lakes and Midwest, moderate to heavy rain (1.5 to 2.0 inches) will help alleviate some of the dryness/drought over the Midwest and upper Great Lakes region. Frontal activity is also forecast for the West Coast, though most of the associated precipitation is likely to fall across the coastal portions of the Pacific Northwest, which are currently not experiencing drought problems.
The CPC 6-10 day forecast (April 24-28) has favorable odds of above-normal precipitation across much of the northern border states, and across western sections of southern California. Chances for subnormal precipitation are likely for most other areas of the lower 48 states. Wetter than normal conditions are likely for most of mainland Alaska, with near-normal precipitation amounts expected elsewhere. Temperatures are forecast to be above-normal for most areas in-between the Intermountain West and the Appalachians, as well as for eastern Alaska. Odds favor below-normal temperatures across the West Coast, peninsular Florida, and western Alaska.
Author: Anthony Artusa, Climate Prediction Center/NCEP/NWS/NOAA
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)