California and National Drought Summary for February 17, 2015
Summary
The upper-level circulation pattern during this U.S. Drought Monitor (USDM) week consisted of a persistent ridge over the western CONUS (contiguous United States) and trough in the east. The ridge kept temperatures warmer than normal and blocked significant precipitation, while the trough funneled cold and dry air masses across the CONUS east of the Rockies and well into the Caribbean. Weather systems moving in the upper-level flow brought above-normal precipitation to parts of the Rockies and adjacent High Plains and Upper Mississippi Valley. A large weather system at the end of the week brushed the Ohio Valley as it moved out of the Southern Plains and across the Southeast to Mid-Atlantic coast. It brought rain, snow, sleet, and freezing rain to these areas, but precipitation amounts were mostly below normal for the week.Hawaii, Alaska, and Puerto Rico
North central Puerto Rico has experienced persistently below-normal precipitation, with rainfall deficits exceeding 6 inches over the last 90 days. An area of D0 was added to reflect the precipitation shortages and decreasing streamflow. Warmer- and drier-than-normal weather in Alaska during the last several months has reduced the winter snowpack snow water content percentile, while melting snow has increased the streamflow. Areas of D0 were introduced to the interior regions where precipitation deficits, low snow water content, and modeled soil moisture deficits overlapped. A cold front over the weekend brought rain showers to Hawaii. While not enough to improve the drought and abnormally dry conditions, they prevented further deterioration in the Aloha State this week.The Northeast and Mid-Atlantic
The Northeast and much of the Mid-Atlantic region were locked in a snowy deep freeze this week. Frozen rivers lowered streamflow measurements in some areas. Above-normal precipitation fell in and around Wayne County in New York. This area measured above-normal precipitation for all time scales from the last 7 days to last 12 months, so D0 was contracted in Wayne County. But no change was made to the D0 in the rest of this region.The Plains and Midwest
Portions of the Northern Plains and Upper Midwest received half an inch or less of precipitation this week, but this registered as above-normal due to normal being low during the winter dry season. A handful of stations in Upper Michigan reported more than half an inch of precipitation. Much of the Central Plains to Lower Great Lakes reported little to no precipitation. Precipitation was below normal (half an inch or less) across most of the Great Plains, except portions of Texas and southeast Oklahoma which received an inch or more of precipitation. Although streamflow levels were significantly low, much of Kentucky was buried in 8 to 16 inches of snow this week, with liquid equivalents of an inch or more of precipitation, so no change was made to the depiction over the Bluegrass State. D0-D3 expanded in southwest Texas to the Texas panhandle due to re-evaluation of data.The Southeast and Lower Mississippi Valley
Much of the Southeast has been in a dry pattern for the last 30 to 90 days, with streamflow decreasing and soils drying out. The coastal areas have been wetter than interior regions, but even the coastal areas have been drier than normal for the last month. A winter storm system moving through the Southeast at the end of this USDM week dropped rain in the southern portions and a wintry mix further north. The national snow cover area increased from 25.6 percent of the CONUS covered in snow on February 15 to 48.9 percent two days later, according to the NOAA National Operational Hydrologic Remote Sensing Center. But the storm’s precipitation totals for the week were still well below normal in most areas of the Southeast. One to 2 inches of precipitation was the most reported … in a band from northern Louisiana to northern Georgia and southeast Tennessee, with lesser amounts to the south. D1 expanded in southwest Alabama and southeast Louisiana to reflect 90-day precipitation deficits. D0 expanded in Louisiana, Mississippi, and southern Alabama where weekly precipitation totals were below normal, as well as in western North Carolina and northeast Mississippi, northwest Alabama, and adjacent Tennessee. The expansion of Abnormally Dry (D0) conditions resulted in the joining of some short- and long-term impact areas, so an S impact boundary from southwest Virginia to northeast Mississippi was drawn in to separate the S and SL regions. Severe precipitation shortages were evident in extreme southern Florida for the last week to 4 months, and even extending back over the last 12 months, with several locations having the tenth driest, or drier, winter season (dry season) to date and increasing fire risk. This resulted in an area of D1 being introduced to parts of Monroe and Miami-Dade Counties.The West
Half an inch to an inch of precipitation was reported in a few parts of the West, mainly northwest Washington and portions of the Rockies. Half an inch or less was received in other parts of the Pacific Northwest and Rockies and southeast Arizona, but most of the West received little to no precipitation this week. While storm systems during December and early February helped replenish some reservoirs, the precipitation fell mostly as rain instead of snow, so the mountain snowpack in the coastal ranges remained dismally below normal, severely impacting the ski industry. According to the National Resource Conservation Service (NRCS) SNOTEL network, mid-February snowpack snow water content ranked in the lowest 5 percent of the historical record at many stations throughout Washington, Oregon, California, and Utah, and, in fact, in most western states. Persistent well-above-normal temperatures continued to melt the snowpack, with snow depth decreasing as much as 4 to 12 inches in the last 7 days at many SNOTEL stations in the Pacific Northwest and Rockies. The University of California estimated statewide forage production decreased during January due to the month’s very dry conditions, and the Almond Board of California reported a decrease in almond shipments of about 28 percent in January 2015 compared to January 2014.D0 was pulled back in eastern Washington, and D1 pulled back in Washington’s Lower Columbia Basin, to better reflect water-year-to-date precipitation conditions and soil moisture combined with the low snowpack water equivalent. In Idaho, the south central D3 was eliminated, D0-D2 was pulled back in the southwest and southeast areas, and D3 was expanded in the southwest to better reflect impact conditions and a tighter moisture gradient. D1 expanded in western Colorado, northeast Utah, and southwest Wyoming to better reflect low mountain snow water content and above-normal evapotranspiration due to persistently above-normal temperatures. The impact boundary was adjusted in this area to reflect short-term impacts.
In the Southwest, an area of D3 was added to northwest Arizona to reflect long-term (24-36 month) dryness. The D0 donut holes along Arizona’s Mongollon Rim were reduced in size, and the D0 in north central towards central New Mexico was filled in with D1, to reflect the low SNOTEL snowpack and reservoir situation. D4 was expanded in Mono and Inyo Counties in California and Esmeralda County in Nevada to reflect dryness in the short term (last 7 days to 6 months) and long term (last 48-72 months).
Looking Ahead
The upper-level circulation pattern (of ridge west/trough east) will continue. Above-normal temperatures are expected over the western CONUS and below-normal temperatures east of the Rockies, with weekly temperature anomalies as much as 20 degrees below normal during the next 7 days. Another storm system will develop in the east, bringing an inch or more of precipitation to the Mid-Mississippi and Ohio Valleys and coastal Mid-Atlantic to Northeast. The NWS HPC 7-Day Quantitative Precipitation Forecast (QPF) also calls for half an inch or more of precipitation for February 19-25 across parts of the Rockies and central Plains, eastern portions of the Southern Plains, and most of the country east of the Mississippi River, while half an inch to no precipitation is forecast for the West.The 6-10 day and 8-14 day outlooks expand the area of below-normal temperatures across the eastern CONUS to the Rockies, whileabove-normal temperatures should continue along the West Coast to Alaska. Drier-than-normal weather is expected for February 24-March 4 from the northern Plains to western Great Lakes and southwest Alaska, while precipitation should be above normal from parts of the southern Plains, across the Southeast, to the coastal Northeast. Pacific weather systems undercutting the ridge should bring above-normal precipitation to the West late in the period.
Author(s):
Richard Heim, NOAA/NCDC
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)
