Minnesota Drought Situation Report - August 23, 2007

Drought Monitor - August 21, 2007
Drought Monitor Map
Drought Monitor Legend

Drought Status
The latest U. S. Drought Monitor (see map at right) places Minnesota's Arrowhead region and portions of central Minnesota in the Extreme Drought category. Much of the rest of the northern two-thirds of Minnesota falls in the Severe Drought or Moderate Drought designation. Most of northwestern Minnesota is described as being Abnormally Dry. Last weekend's extraordinary rainfall event significantly altered drought designations in southern Minnesota. Conditions in southwestern and south central Minnesota counties improved by two categories over the previous week. These areas now fall in the Abnormally Dry category, a designation often used to describe regions coming out of drought. Southeastern Minnesota counties are very wet and no longer experience drought conditions. The drought situation in the northern one third of Minnesota is the result of the lingering impacts of a very dry 2006, a snow-sparse 2006-2007 winter, and dry 2007 mid-summer weather. The drought situation in the southern two thirds of Minnesota is due to an extremely dry 2007 growing season (see: 12-week U.S. Drought Monitor animation). The U. S. Drought Monitor index is a blend of science and subjectivity where intensity categories are based on several indicators.

Weekly Precipitation Map Last week's weather:
A very large area of southern Minnesota received over four inches of rain this past weekend (see map at left). The rain event led to devastating floods in southeastern Minnesota. In southwestern and south central Minnesota, the heavy rain was widely regarded as beneficial, replenishing soil moisture reserves and elevating levels in surface water systems. In the most drought-stricken regions of Minnesota, last week's rainfall was light to moderate. Central Minnesota areas experiencing Extreme Drought reported rainfall totals of around one inch for the 7-day period ending Monday morning. An additional one or more inches of rain fell in isolated sections of central Minnesota on Monday evening and early Tuesday morning. The rain was welcome, but did not significantly change the drought status in these locales. In the northern one third of Minnesota, rainfall totals were very light last week, generally less than one tenth of an inch. Weekly temperatures were very cool last week, ranging from two to six degrees below the long-term mean.

Mid-summer Dryness (June 5 - August 14):
Dryness was entrenched across Minnesota for much of the mid-summer. Rainfall for the ten-week period from June 5 through August 14 totaled less than four inches in many locations in the southern two thirds of Minnesota (see map below). In these areas, rainfall totals for the period were five or more inches short of the historical average (see map below). When compared with historical rainfall totals for the same ten-week time frame, 2007 values ranked at or below the 5th percentile (one year in twenty occurrence) for many counties (see map below). In a few areas, the June 5 - August 14 rainfall totals were near all-time record low values. The timing of the dry weather was unfortunate. The period from May through September is historically the wettest time of the year in Minnesota. Long-term average rainfall rates during this time interval are around one inch per week. Very dry weather, occurring during a time of year when ample rain is typical, leads to the rapid intensification of drought. The lack of precipitation, along with very high evaporation rates, led to deteriorating crop conditions, lower stream flows and lake levels, and increased wildfire danger.

June 5 to August 14 2007 Precipitation June 5 to August 14 2007 Precipitation Departure Map June 5 to August 14 2007 Precipitation Ranking Map

Growing Season (April 1 to present) precipitation totals, departure, and ranking:
Growing season rainfall totals (April 1 to present) have deviated negatively from historical averages by more than four inches across many northeastern, central, and east central Minnesota counties (see map below). This is roughly the equivalent of missing all of June's rainfall. When compared with other seasonal rainfall totals-to-date in the historical database, this year's rainfall for the season ranks just above the 10th percentile (one year in ten occurrence) in central and east central locales, and in portions of Minnesota's Arrowhead region (see map below).

April 1 to August 20 2007 Precipitation Map April 1 to August 20 2007 Precipitation Departure Map April 1 to August 20 2007 Precipitation Ranking Map

Sector briefs:

More drought information resources are found at http://climate.umn.edu/doc/journal/drought_information_resources.htm.


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URL: http://climate.umn.edu/doc/journal/drought_situation_report_2007_070823.htm
Last modified: August 23, 2007