California and National Drought Summary for April 21, 2015
Summary
During the past 7-days, moderate to heavy rain (generally 0.5-3.0 inches, locally greater) fell across portions of the Southeast, the Gulf Coast, the Great Plains, and the Ohio Valley. These areas of precipitation occurred in proximity to several slow-moving/stationary fronts and mid-level troughs. By far the heaviest precipitation totals were observed near the Gulf Coast, where numerous coastal counties from southeastern Texas to the extreme western Florida Panhandle received 5-10 inches during the past week. Precipitation amounts were generally light (0.5-inch or less) in the interior Pacific Northwest, the Southwest and the northern Plains.Hawaii, Alaska and Puerto Rico
No changes were made to the Hawaiian depiction this week. In the southern half of southeastern Alaska, dams are generally in good shape. However, a lack of snow melt in this area (especially if summer turns out to be warmer and drier than usual) could negatively impact stream volume and fishing. In Puerto Rico, abnormal dryness (D0) was expanded across central and east-central sections of the island, due to stream flows in the lowest quartile of the historical distribution, and the lack of substantial rain across much of this area. Climatologically, April represents the tail end of the dry season in Puerto Rico, before the approach of the late spring/early summer ITCZ (Inter-Tropical Convergence Zone) and its associated showers and thundershowers.The Midwest
Moderate rain (1-2 inches) fell over western portions of the abnormal dryness (D0) area in eastern Iowa over the weekend, resulting in minor trimming of the drought depiction. In west-central Iowa, about 1.5 inches of rain fell this past week, prompting the elimination of the small area of abnormal dryness (D0). In northern Minnesota, variable temperature and precipitation conditions occurred throughout the week. Dry, warm and windy conditions prevailed early in the week, while cooler temperatures, reduced evaporation and precipitation amounts ranging from 0.3-1.0 inch occurred late in the week. Despite the rain, stream flows in northwestern and north-central Minnesota remain within the lowest quartile of the historical distribution. For now, no degradations were made to the drought depiction in Minnesota.The Northeast and Mid-Atlantic
About an inch of rain fell Monday night and Tuesday morning across much of Massachusetts. This precipitation, along with rebounding reservoirs and a boost in stream flows (following snow melt), supports a slight trimming of the southern margin of the abnormal dryness (D0) area in both Berkshire and Franklin Counties in northwestern Massachusetts. In north-central Pennsylvania and south-central New York, abnormal dryness (D0) was eliminated, due to sufficient precipitation (2-4 inches) in the past two weeks. Heavy rain (generally 4-7 inches in April so far, with isolated greater amounts) fell across the mountains of southwestern Virginia. Stream flows in the region are mostly within the 95th to 98th percentile of the historical distribution. The area of abnormal dryness (D0) was therefore removed from the drought depiction.The Plains
In North Dakota, light rain fell during the past 7-days, offsetting further deterioration of conditions. Temperatures also fell significantly (below freezing in some areas), keeping evaporation rates low. In South Dakota, only slight adjustments were made to the drought depiction. In north-central South Dakota, moderate drought (D1) was extended slightly northward into Walworth and Edmunds Counties. In southeastern South Dakota, moderate drought (D1) was expanded slightly southward to include eastern Hutchinson, central Turner, and northern Lincoln Counties. Most other areas of the state received enough rain this past week (a quarter-inch to an inch) to offset additional deterioration of conditions, but not enough to justify improvements. In the southern portion of the Nebraska Panhandle and nearby southeastern Wyoming, abnormal dryness (D0) was eliminated due to a recent storm system that produced about 2 inches of precipitation (liquid equivalent), much of which fell as wet snow. The region is finally beginning to experience spring green-up. The improved conditions also warranted the removal of abnormal dryness (D0) in the northern Laramie Range in southeastern Wyoming. During the past week in the Sand hills region of north-central Nebraska, 2-4 inch rainfall surpluses and good soil moisture infiltration prompted a 1-category improvement to the depiction. In northeastern Nebraska, despite receiving decent moisture over the past 2 weeks, significant deficits still linger at the 30-, 60-, and 90-day time periods. Therefore, the depiction remains unchanged in this area, pending reassessment next week. In Kansas, respectable rains (mostly 0.5-2.0 inches, locally greater) helped to offset any additional degradation. Surface water supplies are still low, and runoff is minimal. No alteration was made to the Kansas drought depiction this week.The southern Great Plains also experienced a mix of both improvements and degradations. In Oklahoma, 1-category degradations were made in the western Panhandle, as only 1.0-1.5 inches of rain fell during the past 30-days. There were reports of dust storms and dead dryland wheat across much of this area. In west-central Oklahoma, a swath of 4-8 inch rains prompted a 1-category improvement from about Roger Mills County northeastward to Major County. In extreme northeastern and northwestern Roger Mills County, and most of adjacent Ellis County, no good runoff rains were reported, suggesting status quo for those areas. In Texas, widespread 1-category improvements were made to the drought depiction after recent rain fell over many areas that needed it. Stream flows are improving in southern and south-central Texas, and there is continued reservoir improvement in the Dallas area. In the Panhandle region, some of the wheat crop is expected to be salvaged, but it is unlikely the crop will return to normal.
The Southeast and lower Mississippi Valley
Several quasi-stationary fronts draped across the Southeast contributed to heavy rain (generally 2 inches or greater) near the Gulf Coast, with 3-10 inch totals common from southeastern Texas to the extreme western Florida Panhandle. Stream flows across this region are well above-average (90th-98th percentile of the historical distribution). Accordingly, areas of abnormal dryness (D0) and moderate drought (D1) were eliminated from eastern Louisiana and southern Mississippi, and a general 1-category improvement was rendered to the drought depiction in central and southern Alabama. Widespread moderate to heavy rain (1-4 inches) across Georgia and the Carolinas, stream flows at or above the 90th percentile, and support from CPC’s short- and long-term drought blends prompted the elimination of all remaining abnormal dryness (D0) across the Carolinas and much of Georgia. In southern Florida, timely rains resulted in a 1-category improvement (the removal of D0) for Glades, northern Hendry, and the northwestern half of Palm Beach Counties. In contrast, a 1-category downgrade was rendered to the depiction in much of Miami-Dade, Broward, Monroe, and eastern Collier Counties (including Big Cypress National Preserve). The KBDI (Keetch-Byram Drought Index), a drought index specifically designed for fire potential assessment, is at an extremely high value of 650-700 (and higher) in this area. For reference, the maximum value of this index is 800.The West
Moderate precipitation (0.5-2.0 inches, liquid equivalent) fell in much of the Upper Colorado River Basin this past week, though not enough to greatly improve snowpack or stream flows. This region will be monitored for possible improvements next week. In parts of northeastern Colorado, where 1-3 inches of rain have fallen so far this April, 1-category upgrades were made. This includes Cheyenne County in extreme eastern Colorado, and near the northern border with Wyoming. In southern New Mexico, moderate drought (D1) was removed from southwestern Chavez and all of Otero Counties due to good moisture conditions. The Pecos River Valley is doing well on the eastern side of the state, with full reservoirs and commencement of irrigation. Conditions are not as promising though for the Rio Grande Valley.In northeastern California, exceptional drought (D4) was expanded across the northern Sierras this week, while in northern Modoc County, a one-category improvement (from D4 to D3) was rendered to the depiction to more accurately reflect local conditions. In east-central California near Yosemite National Park, the average surface elevation of Mono Lake stood at 6378.9 feet, as of April 15th. This is the lowest surface elevation of the lake since early 1996. The target elevation is 6391 feet. For the past two weeks, extreme to exceptional drought (D3-D4) covered two-thirds of California. In northern Nevada, a one-category degradation was made to northwestern Elko County, while in southwestern Montana, small improvements were made to the drought depiction in Gallatin County.
In Washington state, record/near-record low snowpack supports the expansion of moderate drought (D1) across the northern Cascades, and the introduction of moderate drought in northeastern Washington.
Looking Ahead
For the ensuing 5-day period, April 23-27, northern New England, portions of Georgia and Alabama, and southern Florida are expected to receive 1.0-1.5 inches of precipitation, which would help in the mitigation of existing dryness/drought. Up to about 2 inches of rain is forecast for the easternmost portions of the drought region in both Oklahoma and Texas, during this period. Light precipitation (0.25-inch or less) is anticipated for most of the Dakotas and upper Mississippi Valley, though western South Dakota is expected to receive 1.0-1.5 inches of rain. Between 1.0-1.5 inches of precipitation (liquid equivalent) is predicted for parts of the West.For the 6-10 day period, April 28-May 2, there are enhanced odds of near- to below-median precipitation across most of the contiguous U.S. Odds favor above-median rainfall from the central and eastern Gulf Coast region northeastward across the Southeast, mid-Atlantic, and southeastern New England.
Author(s):
Anthony Artusa, NOAA/NWS/NCEP/CPC
Dryness Categories
D0 ... Abnormally Dry ... used for areas showing dryness but not yet in drought, or for areas recovering from drought.Drought Intensity Categories
D1 ... Moderate DroughtD2 ... 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)
