Minnesota Drought Situation Report - August 2, 2007
Drought Monitor - July 31, 2007
The latest U. S. Drought Monitor(see map at right) places
portions of northeastern Minnesota, and most of the southern one half of Minnesota, in the
Severe Drought category. With the exception of northwestern
counties, the remainder of Minnesota is classified as experiencing a Moderate Drought or
depicted as being Abnormally Dry. The drought situation in the northern
one third of Minnesota is the result of the lingering impacts of a very dry 2006, and a snow-sparse 2006-2007 winter. The drought situation
in the southern two thirds of Minnesota is due to a 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.
Last week's weather:
Precipitation last week was generally light across the most drought stricken areas of Minnesota (see map below). Most of these
locations received less than a quarter inch of rain for the seven-day period ending Monday morning, July 30. Significant rainfall was reported in just a few areas.
Rainfall exceeding one inch fell in a relatively small portion of south central and southeastern Minnesota. One-inch rainfall also fell along a narrow band
from Park Rapids to Duluth. Weekly temperatures were well above the long-term mean last week, enhancing evaporation rates.
Maximum temperatures topped 90 degrees at least once last week in nearly every Minnesota community. Historically, the last two weeks of July and the first week of
August are the warmest of the summer.
Seasonal weather overview:
Dryness has been entrenched across the southern two thirds of Minnesota for much of May, June, and July. Rainfall for the eight-week
period from June 5 through July 30 totaled less than three inches over much of the southern two thirds of Minnesota (see map below).
In most of these areas, rainfall totals for the period were four or more inches short of the historical average (see map below).
When compared with historical rainfall totals for the same eight-week time frame, 2007 values rank at or below the 5th percentile for many central and
southern Minnesota counties (see map below). In a few areas, the June 5 - July 30 rainfall totals are near all-time record low values.
The timing of the dry weather is 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, has led to deteriorating crop conditions, lower
stream flows and lake levels, and increased wildfire danger.
Growing Season (April 1 to present) precipitation totals, departure, and ranking:
Rainfall totals since April 1 are less than nine inches across much of the southern one half of Minnesota (see map below). Growing season rainfall totals
have deviated negatively from historical averages by more than four inches across many central, east central, southwestern, and south central
Minnesota counties (see map below). This is roughly the equivalent of missing all of June's rainfall. Seasonal rainfall deficits exceeding
six inches are reported in a band that extends from Litchfield in central Minnesota eastward into portions of the Twin Cities metropolitan area. Six-inch
shortfalls are also in place in some southwestern and south central Minnesota counties. When compared with other seasonal rainfall totals-to-date in the historical database,
this year's rainfall for the season ranks below the 20th percentile (one year in five occurrence) in most southern Minnesota counties (see map below).
Agriculture - The
Agricultural Statistics Service reports that as of July 27, topsoil moisture across nearly 80% of Minnesota's landscape was "Short" or "Very Short". Corn and soybean
conditions in many areas continue to decline in response to the diminishing soil moisture reserves. Only 30% of Minnesota's corn acreage is considered to be in "Good"
or "Excellent" condition, a 10% decrease from the previous week. Governor Pawlenty has requested
the U.S. Department of Agriculture - Farm Service Agency to begin a formal damage assessment as the first step toward a possible disaster declaration.
Stream flow -Stream discharge in roughly
45% of Minnesota's rivers and streams is below the 25th percentile when compared with historical data for this time of year.
Flow conditions in many northeastern, central, and east central
Minnesota watersheds fall 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 heart of the 2006 drought.
Lake levels -
Lake levels continue to drop throughout Minnesota, exposing shoreline, and in some cases, making water access difficult.
Quantitative lake level data are difficult to obtain in real time. However, anecdotal reports indicate that many lakes, especially in central and east central Minnesota,
are a foot or more below average levels for the date. The Lake Superior water level is
near an all-time low for the date and could fall below the all-time seasonal low by early autumn.
Wildfire Danger - The Department of Natural Resources - Division of Forestry classifies current
wildfire danger as High or Very High across much of central,
east central, and northeastern Minnesota. Most of the remainder of the state is depicted in the Moderate Danger category.