HydroClim Minnesota - September 2011

A monthly electronic newsletter summarizing Minnesota's climate conditions and the resulting impact on water resources. Distributed on the Wednesday following the first Monday of each month.

State Climatology Office - DNR Division of Ecological and Water Resources, St. Paul
prepared: September 7, 2011

What happened in August 2011:

  • With the exception of those areas impacted by geographically-isolated bands of heavier precipitation, August 2011 was a dry month across much of Minnesota. It was especially dry in northeast and southern Minnesota counties. August rainfall totals in the dry areas fell short of the historical average by one to three inches.
  • Monthly mean temperatures for August 2011 hovered close to the historical average for most Minnesota communities. Extreme temperature values for August ranged from a high of 96 degrees F at Marshall (Lyon County) on the 1st, to a low of 34 degrees F at Embarrass (St. Louis County) on the 21st.

 

Where we stand now:

  • Growing season precipitation totals to date (April through early September) are above average in many northwest and central Minnesota counties. When compared with April through early-September rainfall totals of the past, 2011 ranks above the 95th percentile in some communities. However, the season has not been universally wet across space and time. Rainfall totals for a portion of northeast Minnesota have been quite low, ranking in the lowest 10th percentile historically. Also, rainfall totals for the past six weeks added up to only one to two inches in many southern Minnesota counties, a negative departure from the long-term six-week average of three to four inches. When compared with the same six-week period in the historical database, late-July through early-September rainfall totals rank among the lowest on record in some locales..
  • The U.S. Geological Survey reports that stream discharge values remain high to very high in western and central Minnesota watersheds. The Red River of the North at Fargo fell below flood stage on August 27th. This reporting station had been above flood stage for 150 days in 2011. Conversely, stream flow measurements on far northern Minnesota rivers rank below the 25th percentile when compared with historical data for the date. In northern St. Louis County and northern Lake County, stream flow values rank below the 10th percentile for this time of year.
  • The U. S. Drought Monitor, released on September 1 depicts counties in both southern and northern Minnesota as Abnormally Dry. Portions of St. Louis, Lake, and Cook counties are said to be experiencing Moderate Drought. Stream flow in those areas are low due to the lingering impact of precipitation deficits during the 2010 growing season and spotty rainfall this spring and summer. The Drought Monitor authors will likely present worsening drought conditions in both northern and southern Minnesota in their September 8 release. The U. S. Drought Monitor index is a blend of science and subjectivity where drought categories (Moderate, Severe, etc) are based on several indicators.
  • The Lake Superior water level is two inches above last year's elevation at this time, but down eleven inches from the long-term seasonal average. The water level on White Bear Lake (Ramsey/Washington county border) remains quite low. However, the lake elevation is up by roughly one foot after reaching an all-time record low level mark in November 2010. Some lake levels are quite high relative to historical early-autumn values. This is especially true in west central and central Minnesota lakes. By contrast, lake levels in western Cook, northern Lake, and northern St. Louis counties are low when compared with historical averages for this time of year.
  • As of September 4, the Minnesota Agricultural Statistics Service reported that topsoil moisture was 7% Very Short, 23% Short, 65% Adequate, and 5% Surplus. Topsoil moisture steadily declined through the month of August especially in southern Minnesota. Roughly two-thirds of the corn and soybean crop is considered to be in Good or Excellent condition. In early August, approximately three-quarters of these row crops were rated in the Good or Excellent categories.
  • The potential for wildfires is currently rated by DNR Forestry as Moderate across the northern one-half of Minnesota. Northeast Minnesota has a High wildfire danger rating. All other Minnesota counties are considered to have Low wildfire potential.

 

Future prospects:

  • The September precipitation outlook shows a bias towards below-normal conditions over the southern two thirds of Minnesota, especially the southern two tiers of counties. The rainfall outlook for the northern one-third of Minnesota demonstrates no significant tendencies away from historical climatological probabilities. September precipitation normals range from near two inches in far western Minnesota to around three and one-half inches in eastern sections of the state.
  • The September temperature outlook offers equal chances of above-normal, near-normal, and below-normal conditions. Normal September high temperatures are in the mid-70s to start the month, dropping to the low to mid-60s by month's end. Normal lows are in the mid-50s early in the month, falling to around 40 by late September.
  • The 90-day precipitation outlook for September through November tilts towards above-normal conditions for the far southwestern corner of Minnesota, and no significant tendencies away from historical climatological probabilities elsewhere in Minnesota. The September through November temperature projection leans towards above-normal conditions across Minnesota, especially in the northeast.
  • The National Weather Service produces long-range probabilistic river stage and discharge outlooks for the Red River, Minnesota River, and Mississippi River basins. These products are part of the National Weather Service's Advanced Hydrologic Prediction Service (AHPS).

 

From the author:

  • On July 1, the National Climatic Data Center released new climate normal statistics that summarize data gathered over the period from 1981 through 2010. By international agreement, these statistics are recalculated once each decade. The new normals will be the benchmark measures of central tendency for this decade. In the coming months, the new statistics will be introduced into tables and maps where "departure from normal" measures are offered.