Several weather systems traversed the contiguous U.S. (CONUS) in the fast-moving upper-level flow during this U.S. Drought Monitor (USDM) week. Upper-level troughs, surface fronts, and surface low pressure systems brought above-normal precipitation to parts of the Southwest, parts of the Pacific Northwest to Great Lakes, and parts of the Southeast, Upper Ohio Valley, and Northeast. But the speed and tracks of the weather systems left much of California and other parts of the West, most of the Central to Southern Plains, parts of the Southeast and Northeast, much of the Mid-Mississippi Valley, and Mid-Atlantic coast drier than normal. Temperatures averaged cooler than normal in the West under the influence of the troughs, while the dominance of ridging east of the Rockies resulted in above-normal temperatures. As noted by the U.S. Department of Agriculture (USDA), the persistence of the unseasonably warm weather east of the Rockies has ushered winter wheat out of dormancy up to a month ahead of normal. The warm temperatures and unusually early green up have increased evapotranspiration and heightened the need for soil moisture in areas wrestling with winter-time drought, at a time when crop-water demands are typically minimal. As reported by the National Weather Service, vegetation has responded rapidly to the unusually warm temperatures, with flowers and trees blooming or in full bloom across east-central Georgia and central South Carolina. Drought conditions continued to improve in California, as the hydrologic systems responded to the precipitation of recent weeks and months, and in the Northeast. Drought and abnormally dry conditions expanded from the Southern Plains and Midwest to the Southeast and Mid-Atlantic coast, reflecting precipitation shortages that have developed over the last one to three months as well as, in the Southeast, worsening hydrological conditions and long-term dryness…
Central to Northern Plains
Bands of precipitation fell across the Central to Northern Plains. Much of Kansas and parts of the Dakotas received a tenth of an inch or less of precipitation, while a snowstorm dropped 0.3-1.0 inch of precipitation across parts of Nebraska and southwest South Dakota. D1 expanded across eastern Kansas, while D0-D1 contracted in northwest Nebraska and western South Dakota. According to February 27 USDA reports, 56% of the subsoil and 55% of the topsoil in Kansas, and 30% of the subsoil and 25% of the topsoil in Nebraska, were short to very short of moisture, while 21% of the winter wheat in Kansas was in poor to very poor condition…
Two or more inches of precipitation fell across parts of the northern California coast, the Sierra Nevada, and San Diego County regions, while less than an inch was recorded in other areas. The typical interior rainshadow areas had less than half an inch of precipitation. Drought improvement occurred in three regions.
The D0-L in the San Joaquin Valley was removed due to improving hydrological (aquifer) conditions. There are two types of aquifers: confined and unconfined. Unconfined aquifers are characterized by a geology where water can seep into the aquifer from the ground surface directly above. Confined aquifers have a geology in which an impermeable layer of dirt or rock exists above the aquifer which prevents water from seeping into it from the ground surface directly above. Confined aquifers are recharged by water seeping into them from farther away where the impermeable layer doesn’t exist. Most of the USGS well groundwater stations in the San Joaquin Valley were showing significant recharge occurring, while those that were still quite low were probably confined aquifers which may take months or years to recharge.
D1 was pulled back along the Coastal Range to Santa Barbara County. The lake levels of the reservoirs in Santa Barbara and Ventura Counties continued to rise but, since the rains let up, they were not rising as quickly. Lake Cachuma’s reservoir was at 87,466 acre-feet on February 26, which equates to 45.2% of capacity versus 42.4% a week ago; Lake Casitas was at 43% compared to last week’s 42.3%; and Lake Piru was at 33.7% versus last week’s 31.7%. D2 was kept in place in this region to reflect the continued low, but recovering, reservoirs. However, the recent rains have not improved the situation on the offshore islands. With below-normal precipitation this week and continued groundwater shortages, D2 was added to Catalina Island.
Rain during the last day of this USDM week gave southern California and southwest Arizona a good soaking, with rainfall amounts 0.5-2.0 inches over parts of Arizona and over 5 inches over parts of San Diego County in California. In the mountains of San Diego County, Palomar Observatory reported 9.04 inches of precipitation. D0-D1 was pulled back one category in San Bernadino, Riverside, and San Diego counties, and the adjacent D2 was trimmed a bit. The rain should result in rapid responses in local reservoirs. The San Diego River reached 14.2 feet, which is the third highest stage ever and slightly higher than December 2010 and 1980…
Rest of the West
One to 4 inches of precipitation fell across coastal Washington and Oregon and parts of the Northern to Central Rockies, the Great Basin, and Arizona. Less than an inch of precipitation fell across other parts of the West, with some areas receiving a tenth of an inch or less. D1 was deleted and D0 contracted in eastern Oregon and western Montana to better reflect precipitation and snowpack conditions. D0-D1 was trimmed in southwest Arizona and D0 pulled back in east-central Montana. D0 was added over the southwest mountains of Montana to reflect low snowpack water content (SWE) and subnormal precipitation at the 7-day to 3-month time scales, and D0 was expanded over northeast New Mexico to better reflect soil moisture and streamflow conditions…
In the 2 days since the Tuesday morning cutoff time of this week’s USDM, a frontal system dropped 1-2 inches of rain, and locally more, across parts of the Ohio Valley D0 area, with half an inch or more falling across parts of the Southeast. For March 2-9, 3-5 inches of precipitation, and locally more, is forecast for north coastal California to western Washington; 1-2 inches over parts of the Northern Rockies; and a tenth of an inch or more across the rest of the Northwest into the Great Basin. Precipitation is expected across parts of the Southern Plains to Southeast, Northern Plains to Great Lakes, and along the Eastern Seaboard, with amounts ranging from a few tenths of an inch across most of these regions, to an inch or two across southern Texas, the Gulf Coast, and northern Great Lakes. Most of the Southwest into the Central Plains should be dry. Above-normal temperatures are expected for most of the CONUS, with the greatest departures in the Central Plains, while below-normal temperatures may linger in the Pacific Northwest. Odds favor the temperature anomaly pattern persisting through March 10-15, with cooler-than-normal temperatures expected for Alaska. March 10-15 projections favor a continuation of the precipitation anomaly pattern with below-normal precipitation from the Southwest to Central Plains and along the Gulf of Mexico coast to Mid-Atlantic States, with above-normal precipitation favored for the rest of the CONUS. Odds favor drier-than-normal weather in southern Alaska and wetter-than-normal conditions in northern Alaska.
Click on a thumbnail graphic to view a gallery of drought data from the US Drought Monitor.