Severe hydrologic drought in Upper Green
by Jim Fahey, Wyoming NOAA hydrologist
April 30, 2010
Here is the latest information on drought conditions across Wyoming (as of April 30th, 2010)
- Severe hydrologic drought conditions developed over the winter for the Snake--Upper Yellowstone--Shoshone--and Upper Green Basins.
- Below to well below normal precipitation totals for rangelands/basins across northern and western Wyoming for water year 2010 (October 2009 - April 2010).
- Above to well below normal precipitation totals for rangelands/basins across south central and southeastern Wyoming for water year 2010 (October 2009 - April 2010).
Near normal mountain snowpack averages across southeastern Wyoming for water year 2010--below average mountain snowpack averages across the rest of Wyoming.
Major reservoirs across Wyoming continue to maintain storage increases from water year 2009.
Synopsis
3 key ingredients define the overall drought picture for Wyoming: Rangeland Precipitation---Water Supply---Mountain Snowpack
Rangeland/Watershed Precipitation
Precipitation across Wyoming’s pasturelands/rangelands during the first 7 months of water year 2010 (October 2009 - April 2010) varied from below to well below average across the northern and western areas of Wyoming--to above to well above average across the south central to southeastern areas of the state. Above to well above precipitation totals across the major river basins across southeastern Wyoming; but below to well below average precipitation totals across the rest of the major watersheds in Wyoming. Specifically, precipitation averages across Wyoming’s major watersheds varied from 67 to 131 percent of average during the first half water year 2010.
Water Supply
Total reservoir storage in early April across Wyoming continued to be above water year 2009 storage totals. Most importantly, storages at the big reservoirs along the North Platte River have continued to maintain storage increases that were seen during water year 2009. Seminoe and Pathfinder reservoirs continued to maintain at 60 to 70 percent of capacity by early April. Boysen Reservoir also maintained 80 to 90 percent of capacity during the first half of the current water year.
Streamflows across Wyoming during the earliest part of the runoff were near normal to above normal.
Mountain Snowpack
Mountain snowpack averages across Wyoming are not as high as what has been seen in the past 2 water years. Snow water equivalent (SWE) trends for water year 2010: Below to much below average SWEs across the Upper Yellowstone, Snake, Shoshone, and Upper Green Basins---Near normal SWEs across the rest of Wyoming’s major basins.
Overall Drought Picture // and What Does the Future Hold?
Severe hydrologic drought developed during the winter across the Upper Yellowstone, Snake, Shoshone, and Upper Green Watersheds. The Big Horn and the Upper Wind Basins saw moderate drought conditions develop over the winter. Major deficits in snowpack across northern and western Wyoming are the driving factor in the hydrologic drought conditions. Spring precipitation may allow drought conditions to improve somewhat; but spring precipitation is usually concentrated across areas east of the continental divide. So, current drought conditions are expected to persist across Wyoming through the middle of summer.
Near normal precipitation averages are expected for most of Wyoming---from the rest of spring to early fall. Extreme southeastern Wyoming is expected to see above normal precipitation averages for the rest of the spring and into the summer months. Generally, above average temperatures are expected during the summer for most of Wyoming.
Reservoir storages are the one bright spot in the overall drought picture for Wyoming. However, gains made in reservoir storages during the past 2 water years may be in jeopardy if Wyoming experiences a dry and warm summer.
For the complete drought report with graphics (in .PDF format)---Please go to:
http://www.crh.noaa.gov/images/riw/hydro/drought_info.pdf
for additional drought graphics and information---please refer to:
http://www.crh.noaa.gov/riw/hydro/drought.php
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