HydroClim Minnesota - September 2008

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 9/3/2008

What happened in August:

August 2008 precipitation totals fell short of average by two or more inches in most Minnesota counties. Isolated heavy rain events permitted a handful of communities to match or exceed historical averages for the month. Kittson, Clay, Becker, and Wilken counties reported August rainfall that exceeded the long-term average by more than two inches. Nonetheless, a general pattern of dryness prevailed across Minnesota in August, continuing a trend that began in mid-June.
[see: August 2008 Climate Summary Table]
In spite of the persistent dryness across Minnesota in August, there were two substantial rain episodes during the month. Heavy rain fell on west central and northwestern Minnesota on August 11 and 12. Rainfall amounts ranged from two to four inches during this event. On August 27 and 28, another significant event dropped one to three inches of rain on portions of central Minnesota as well as much of the eastern one-third of the state. Although not included in the August statistics, a substantial rainstorm dropped two to four inches of rain on west central and northwestern Minnesota on September 1 and 2.
[see: Heavy Rain: August 11-12 | Beneficial Rains: August 27-28]
Monthly mean temperatures for August 2008 were very near historical averages. Extreme temperature values for August ranged from a high of 93 degrees on the 3rd at Worthington (Nobles County), to a low of 27 degrees at Embarrass (St. Louis County) on the 25th. As was the case throughout the summer, maximum temperatures above 90 degrees were not common.
[see: August 2008 Climate Summary Table]

Where we stand now:

Much of Minnesota remains impacted by a mid-summer and late summer dry spell. For the eleven-week period during the last two weeks of June and into early September, many Minnesota communities received less than five inches of rainfall. This came at a time of year when rainfall rates average roughly one inch per week. Thus, rainfall deficits over the eleven-week dry spell topped five inches in many areas. Described another way, eleven-week rainfall totals were less than 50 percent of normal for the period. Temperatures over the eleven-week period were very close to historical averages. This held evaporative demand near seasonal norms and mitigated the situation somewhat.
[see: Dry Mid-Summer 2008]
Growing season precipitation totals to date (April 1 through early September) are significantly below normal in a small area of north central Minnesota, and a band that bisects central Minnesota from west to east. Conversely, in some portions of west central, northwestern, northeastern, and southeastern Minnesota, growing season rainfall totals are well above average, surpassing the 95th percentile (one year in twenty) when compared to other April-through-August totals in the historical record.
[see: Weekly Precipitation Maps]
The U. S. Drought Monitor, released on August 26, classified nearly all of Minnesota in the D0 - Abnormally Dry category or worse. Significant portions of the state were placed in the D1 - Moderate Drought classification. The U. S. Drought Monitor index is a blend of science and subjectivity where intensity categories are based on several indicators.
[see: U.S. Drought Monitor]
The U.S. Geological Survey reports that stream discharge values are highly variable across the state. Many Minnesota streams have flows that are below the 25th percentile in the historical distribution for early September. In some northeastern Minnesota rivers, flows rank below the 10th percentile for early September. By contrast, the Red River and many of its tributaries report above-median flows in response to heavy rains that fell in August and early September.
[see: USGS Streamflow | DNR Streamflow]
The Lake Superior water level is up 15 inches from last year at this time and is just below the long-term average for the season. Levels on inland lakes in drought-stricken areas of central and north central Minnesota are low. In some cases, water levels are similar to those observed during the droughts of 2006 and 2007.
[see: Corps of Engineers Great Lakes Water Levels]
The Minnesota Agricultural Statistics Service reports that as of August 29, topsoil moisture was 14% "Very Short", 36% "Short", 50% "Adequate", and 0% "Surplus". Some of the driest topsoil conditions were found in central and north central Minnesota. Fortunately, stored moisture lower in the soil profile supported crop conditions into early September. In the September 2 Crop Progress and Condition Report, 64 percent of Minnesota's corn crop and 65 percent of the soybean crop was rated in good or excellent condition.
[see: Ag. Statistics Service Crop Progress and Condition]
The potential for wildfires is rated by DNR Forestry as "Moderate" in northeastern Minnesota. Elsewhere across the state, the fire danger rating is "Low".
[see: Fire Danger Rating Map]

Future prospects:

The September precipitation outlook offers equal chances of above, near, or below average conditions. 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 leans towards below-normal conditions across nearly all of Minnesota. Normal September high temperatures are in the mid-70's to start the month, dropping to the low to mid-60's by month's end. Normal lows are in the mid-50's 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 indicates no significant tendencies away from climatological probabilities across Minnesota. The September through November temperature projection tilts towards above-normal conditions across the state.
[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:

None

Notes from around the state:

None

Upcoming dates of note:

September 18: National Weather Service releases 30/90 day temperature and precipitation outlooks

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 - Detroit District, US Army Corps of Engineers
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 - Climate Prediction Center, National Weather Service
http://www.crh.noaa.gov/ncrfc - North Central River Forecast Center, National Weather Service

Acknowledgements

None

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