HydroClim Minnesota - September 2009

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 Waters
compiled 9/10/2009 (late distribution)

What happened in August:

August 2009 rainfall totals varied widely across Minnesota. Monthly rainfall totals in central and east central Minnesota topped historical averages by two or more inches and brought welcome relief to drought-affected areas. In some locations, August rainfall totals were near, or above, all-time records for the month. Conversely, August rainfall totals fell short of historical averages across much of north central Minnesota and along the southern tier of Minnesota counties. Monthly rainfall deficits in these areas amplified a dry situation that began early in the growing season.
[see: August 2009 Climate Summary Table | August 2009 Precipitation Departure Map | Wet August]
Two significant rainfall events in August were responsible for the bulk of the welcome precipitation that fell on central and east central Minnesota. On August 7, a sequence of thunderstorms dropped four or more inches of rain along a band that extended from west of Willmar to the southern suburbs of the Twin Cities. The largest 24-hour total reported was 6.20 inches at Chaska. On August 19, a 50-mile wide area extending from the northern Twin Cities suburbs to north of Duluth received two to five inches of rain. Some of the heaviest rain fell on drought-stricken counties such as Anoka, Kanabec, Chisago, Pine, and Carlton.
[see: Heavy Rain - August 7 and 8 | Heavy Rain - August 19 and 20]
Monthly mean temperatures for August 2009 were cool, averaging two to four degrees below the historical average. Many Minnesota reporting locations failed to reach 90 degrees during the month of August. The seasonally cool temperatures maintained a trend of below-normal conditions that persisted throughout the summer. Extreme temperature values for August ranged from a high of 96 degrees at Moorhead and Marshall on the 12th, to a low of 27 degrees in Embarrass (St. Louis County) on the 31st. Many low temperature records were set in northern Minnesota during the mornings of the August 30 and 31. As was the case throughout the summer, cooler-than-normal temperatures reduced evaporation and transpiration rates, and partially counterbalanced the precipitation deficits.
[see: August 2009 Climate Summary Table]

Where we stand now:

The U. S. Drought Monitor, released on September 10, placed areas of east central Minnesota in the Severe Drought category. Portions of north central, west central, east central, and southeastern Minnesota were designated as experiencing Moderate Drought. Large portions of the rest of Minnesota were considered to be Abnormally Dry. The drought designations are the result of two spells of dry weather, one during this year's growing season, and one longer-term. The shorter-term dryness began in April 2009 and persisted through September over nearly all of Minnesota. April through August precipitation totals in many locations fell short of the historical average by more than five inches. The longer-term dry spell commenced in mid-June 2008 and most profoundly affects east central Minnesota. In this area, 15-month precipitation deficits of ten or more inches have led to a significant impact on hydrology. The U. S. Drought Monitor index is a blend of science and subjectivity where drought categories (Moderate, Severe, etc) are based on several indicators.
[see: Drought 2009]
DNR Waters and the U.S. Geological Survey report that stream discharge values for roughly one-quarter of all Minnesota measurement sites ranked below the 25th percentile in the historical distribution for early September Some measurements fell below the 10th percentile when compared with historical early-September values. Some of the lowest flows, relative to historical data, are observed along the Mississippi River and in tributaries to the Minnesota River in south central Minnesota.
[see: USGS Streamflow | DNR Streamflow]
The Lake Superior water level is up two inches from last year at this time but remains below the long-term average. Water levels on many central and east central Minnesota lakes are very low.
[see: Corps of Engineers Great Lakes Water Levels | Lake Minnetonka Water Level]
The Minnesota Agricultural Statistics Service reports that as of September 6, topsoil moisture was 3% "Very Short", 24% "Short", 71% "Adequate", and 2% "Surplus". Topsoil moisture shortfalls exist in pockets scattered through central and southern Minnesota. In the latest survey, 72 percent of Minnesota's corn crop and 68 percent of the soybean crop was rated in good or excellent condition. Row crop development is approximately 10 days behind the historical average and these commodities remain vulnerable to an early frost.
[see: Agricultural Statistics Service Crop Progress and Condition]
The potential for wildfires is currently rated by DNR Forestry as "Low" across Minnesota.
[see: Fire Danger Rating Map]

Future prospects:

The September precipitation outlook offers equal chances of above, near, and below normal rainfall across the northern three-quarters of Minnesota. The monthly precipitation outlook for the southern one-quarter of Minnesota tilts towards above-normal rainfall. 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.
[see: Climate Prediction Center 30-day Outlook | September Precipitation Normal Map]
The September temperature outlook depicts no significant tendencies away from historical climatological probabilities. 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.
[see: Climate Prediction Center 30-day Outlook | September Temperature Normal Map]
The 90-day precipitation outlook for September through November shows no significant tendencies away from climatological probabilities. The September through November temperature projection indicates equal chances of above, near, and below normal conditions nearly everywhere in Minnesota. In far northeastern Minnesota, the three-month outlook leans towards above-normal temperatures.
[see: Climate Prediction Center 90-day Outlook]
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).
[see: National Weather Service River Forecast Center]

From the author:

The DNR Division of Waters prepares a monthly product providing general information on the quantitative status of water resources across Minnesota. The monthly Hydrologic Conditions Report places current measurements of precipitation, stream flow, lake levels, and ground water levels in historical context.
[see: DNR Waters Monthly Hydrologic Conditions Report]

Notes from around the state:

None

Upcoming dates of note:

September 17: National Weather Service releases 30/90 day temperature and precipitation outlooks
October 15: 17th Annual Kuehnast Lecture

Web sites featured in this edition:

http://climate.umn.edu - Minnesota Climatology Working Group, Minnesota DNR Waters and U of M Dept. of Soil, Water, and Climate
http://www.drought.unl.edu - National Drought Mitigation Center
http://water.usgs.gov/cgi-bin/dailyMainW?state=mn&map_type=weekd - U.S. Geological Survey
http://mndnr.gov/waters - Minnesota Department of Natural Resources, Division of Waters
http://www.lre.usace.army.mil - US Army Corps of Engineers, Detroit District
http://www.nass.usda.gov - USDA, National Agricultural Statistics Service
http://mndnr.gov/forestry - Minnesota Department of Natural Resources, Division of Forestry
http://www.cpc.ncep.noaa.gov - National Weather Service, Climate Prediction Center
http://www.crh.noaa.gov/ncrfc - National Weather Service, North Central River Forecast Center

Acknowledgements

None

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