Minnesota Drought Situation Report - September 20, 2007
Drought Monitor - September 18, 2007
The latest U. S. Drought Monitor (see map at right)
places portions of 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. This week's Drought Monitor map includes one notable change from the
previous week's map. The Severe Drought polygon in north central Minnesota was
extended westward to depict the very dry conditions reported in these areas since mid-July.
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 central third 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.
This week's weather:
The data deadline for the weekly U.S. Drought Monitor is Tuesday mornings at 7:00 AM CDT. Therefore, this week's Drought Monitor was
produced without accounting for heavy rains on Tuesday, September 18 and Thursday, September 20. Precipitation totals of one to four inches
have been reported in some of the most drought-stricken areas of Minnesota. It is still raining in these areas as of this writing. Next week's
Drought Monitor will reflect these events and categorical improvements are likely. Radar-based rainfall estimates for this week's events can
be viewed at http://water.weather.gov
Last week's weather:
Rainfall totals for the week ending Monday morning, September 17 were generally less than one third of an inch in most Minnesota
communities (see map at left). Sections of far northern Minnesota and far southeastern Minnesota
received more than one half inch of rain. Long-term average rainfall rates rainfall totals are beginning to drop off at this time
of year to around one half inch per week.
Temperatures last week were very cool,
averaging eight to ten degrees below normal. Most locations reported their first frost of the autumn last week.
Summer Dryness (June 5 - September 17):
Dryness has been entrenched across north central, northeastern, west central, and central Minnesota for much of the summer. Rainfall for the fifteen-week period from June 5
through September 17 totaled less than six inches for many locations in west central and central Minnesota (see map below).
In these areas, rainfall totals for the period were seven or more inches short of the historical average (see map below).
When compared with historical rainfall totals for the same fifteen-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 - September 17 rainfall totals were near all-time record low values.
The period from May through September is historically the wettest time of the year in Minnesota. Long-term average rainfall rates during the heart of the summer 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.
Agriculture - The
Agricultural Statistics Service reports that as of September 14, topsoil moisture across nearly half of Minnesota's landscape was "Short" or "Very Short".
This is an improvement from the conditions reported in early August when nearly 85% of the state reported less than adequate soil moisture conditions. Due to last week's
frost, the growing season has essentially ended for Minnesota's row crops. Because the plants will not longer be consuming water, rainfall that occurs during the
remainder of the autumn will be very effective at replenishing the soil moisture profile.
Stream flow - Stream discharge in
27% of Minnesota's rivers and streams remains below the 25th percentile when compared with historical data for this time of year.
Flow conditions in many north central, northeastern, central, and east central
Minnesota watersheds rank below the 10th percentile for the date. Mississippi River flow conditions remain very low along the upper reaches of the river.
Mississippi River discharge near Anoka is at roughly the same flow rate as it was during the 2006 drought, but well above the all-time record
low for the date set in 1934. National Weather Service projections
indicate that flow in the Mississippi through the Twin Cities will rise in response to this week's rains.
Lake levels -
Water levels are very low on many Minnesota lakes, exposing shoreline, and in some cases, making water access difficult. Anecdotal reports indicate that many lakes in northern,
west central, central, and east central Minnesota are a foot or more below average levels for the date. The
Lake Superior water level is expected to be at an all-time low
for September when the final statistics are calculated.
Wildfire Danger - The Department of Natural Resources - Division of Forestry classifies current
wildfire danger as Low across Minnesota.
More drought information resources are found at http://climate.umn.edu/doc/journal/drought_information_resources.htm.
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Last modified: September 20, 2007