HydroClim Minnesota - September 2007

A monthly electronic newsletter summarizing Minnesota 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 9/5/2007


- August 2007 rainfall totals varied tremendously across Minnesota. August rainfall in the northern one third of Minnesota was quite light, totaling less than two inches in many places. Rainfall amounts fell short of average by one to three inches in these locales. August rainfall in the southern one third of Minnesota was extraordinarily heavy. Many southern Minnesota locations set all-time August rainfall records. Rainfall totals in the southern three to four tiers of Minnesota counties topped eight inches for the month, doubling the historical monthly average. Numerous south central and southeastern Minnesota communities reported rainfall totals in excess of 10 inches in August. Many locations set all-time August monthly rainfall records. Some examples include the Twin Cities (9.32 inches) and Rochester (14.07 inches). Final August data are still being tabulated, however it is a certainty that many southeastern Minnesota locations not only set all-time August monthly rainfall records, but all-time monthly records for any month. Rainfall totals for these locations will top 15 inches, and a few stations may report August rainfall totals in excess of 20 inches.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp , http://climate.umn.edu/weathertalk/070831.txt )
- a series of thunderstorms moving along a stalled frontal boundary dropped extremely heavy rain on much of southern Minnesota on August 18, 19, and 20. The most intense precipitation rates occurred during the afternoon and evening hours of Saturday, August 18, and the early morning hours of Sunday, August 19. Over the course of the event, all or portions of 28 counties received at least four inches of rain. Six-inch totals were common across the region, and portions of southeastern Minnesota reported astounding rainfall amounts ranging from 8 to 18 inches. The heaviest rainfall reports came from Winona, Fillmore, and Houston counties, where 36-hour totals exceeded 14 inches. The largest multi-day rainfall total reported (through 8:00 AM, Monday, August 20) was 18.17 inches observed west of La Crescent in northern Houston County. An official National Weather Service climate observer near Hokah in Houston County reported a storm total of 16.27 inches. Of the 16.27 inches, 15.10 inches fell within the observer's 24-hour observation cycle ending at 8:00 AM on Sunday, August 19. This is the largest 24-hour rainfall total ever recorded by an official National Weather Service reporting location in Minnesota. The previous Minnesota record was 10.84 inches, measured at Fort Ripley in Crow Wing County on July 22, 1972. The deluge produced flooding tied to seven fatalities. Major flood damage occurred in many southeastern Minnesota communities. Hundreds of homes and businesses were impacted. Reports of stream flooding, urban flooding, mud slides, and road closures were numerous throughout southern Minnesota. The combination of huge rainfall totals and a very large geographic extent, make this episode one of the most significant rainfall events in Minnesota's climate history. A six-inch rainfall total for a given location in this region over a 24-hour period is said to be a "100-year" (1% probability) storm. The area receiving six or more inches during a 24-hour period in the midst of this torrent encompassed thousands of square miles. Other heavy rainfall events during this decade of comparable magnitude and spatial coverage include extraordinary rainfalls in northwestern Minnesota on June 9-10, 2002, and in southern Minnesota on September 14-15, 2004.
(see: http://climate.umn.edu/doc/journal/flash_floods/ff070820.htm , http://climate.umn.edu/doc/journal/24hour_rain_record.htm , http://climate.umn.edu/pdf/flash_flood/ff20020610.pdf , http://climate.umn.edu/pdf/flash_flood/ff20040915.pdf )
- rainfall during the heart of the summer (the twelve-week period from June 5 through August 28) totaled less than six inches in large sections of central and northern Minnesota. In these areas, rainfall totals for the period were five or more inches short of the historical average. When compared with historical rainfall totals for the same twelve-week time frame, 2007 values rank at or below the 5th percentile (one year in twenty occurrence) for many counties. In a few areas, the June 5 - August 28 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, created deteriorating crop conditions, lower stream flows and lake levels, and increased wildfire danger.
(see: http://climate.umn.edu/doc/journal/drought_situation_report_2007_070830.htm#mid_summer )
- monthly mean temperatures for August 2007 were within two degrees either side of the historical average. Extreme values for August ranged from a high of 100 degrees at Wild River State Park (Chisago County) on the 10th, to a low of 28 degrees at Embarrass (St. Louis County) on August 30.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp )


- growing season rainfall totals (April 1 - early September) are less than ten inches in many central Minnesota counties and in Minnesota's Arrowhead region. In these areas, seasonal rainfall totals have deviated negatively from historical averages by more than four inches. This is roughly the equivalent of missing all of June's normal rainfall. When compared with other seasonal rainfall totals-to-date in the historical database, this year's rainfall for the growing season ranks near the 10th percentile (one year in ten occurrence) in many of the drought-stricken counties. In a demonstration of the state's size and climate variability, rainfall totals in portions of northwestern and southeastern Minnesota are well above historical averages for the April 1 to present time frame. Because of the extraordinary August rains, and despite a very dry June and July, sections of Fillmore, Winona, and Houston counties are near or above all-time seasonal rainfall records, with totals topping 30 inches since April 1st.
(see: http://climate.umn.edu/doc/weekmap.asp )
- the U. S. Drought Monitor released on August 28 places 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". Substantial August rains led to the elimination of drought designations in the southern three tiers of Minnesota counties. 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. The U. S. Drought Monitor index is a blend of science and subjectivity where intensity categories are based on several indicators.
(see: http://climate.umn.edu/doc/journal/drought_situation_report_2007_070830.htm , http://www.drought.unl.edu/dm/monitor.html )
- the U.S. Geological Survey reports that stream discharge values in roughly 30% of Minnesota's rivers and streams rank below the 25th percentile when compared with historical data for this time of year. Flow rates in many north central, 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 2006 drought, but significantly above the all-time record low for the date set in 1934.
(see: http://water.usgs.gov/cgi-bin/dailyMainW?state=mn&map_type=weekd , http://climate.umn.edu/dow/weekly_stream_flow/stream_flow_weekly.asp , http://mn.water.usgs.gov/durationHydrographs/05288500.html )
- 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, 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 the mean monthly value will likely be declared as the all-time August low when statistics are finalized.
(see: http://www.lre.usace.army.mil/_kd/Items/actions.cfm?action=Show&item_id=3886&destination=ShowItem , http://www.dnr.state.mn.us/lakefind/ )
- the Minnesota Agricultural Statistics Service reports that as of August 31, topsoil moisture across nearly 40% of Minnesota's landscape was "Short" or "Very Short". This is a substantial improvement from the conditions reported in early August when nearly 85% of the state reported less than adequate soil moisture conditions. 45% of Minnesota's corn acreage is considered to be in "Good" or "Excellent" condition. This is up from 25% in early August. A federal agricultural disaster was declared on August 7 for 24 Minnesota counties suffering from drought. Farmers and ranchers in an additional 32 adjacent counties are also eligible for drought recovery assistance.
(see: http://www.nass.usda.gov/Statistics_by_State/Minnesota/Publications/Crop_Progress_&_Condition/index.asp , http://www.governor.state.mn.us/mediacenter/pressreleases/PROD008255.html )
- the DNR Division of Forestry classifies current wildfire danger as "High" or "Very High" across all of the northern one half of Minnesota. "Moderate" fire danger exists from St. Cloud and the Twin Cities westward to the South Dakota border. The southern one quarter of the state is depicted in the "Low" danger category. Burning restrictions are in place in many northern Minnesota counties.
(see: http://www.dnr.state.mn.us/forestry/fire/ )


- the September precipitation outlook from the Climate Prediction Center indicates no significant tendencies away from climatological probabilities across Minnesota. 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: http://www.cpc.ncep.noaa.gov/products/predictions/30day , http://climate.umn.edu/img/normals/precip/precip_norm_09.htm )
- the September temperature outlook indicates no significant tendencies away from climatological probabilities across 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: http://www.cpc.ncep.noaa.gov/products/predictions/30day , http://climate.umn.edu/img/normals/temp_norm_adj/temp_norm_adj_09.htm )
- 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 in all Minnesota counties.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/90day/lead01/index.html )
- 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: http://www.crh.noaa.gov/ncrfc/ )
- until drought conditions improve in the Upper Mississippi River basin, the National Weather Service will routinely produce low flow projections for the Mississippi River near Anoka.
(see: http://www.crh.noaa.gov/crnews/display_story.php?wfo=ncrfc&storyid=9487&source=0 )


- the Minnesota Drought Task Force continues to share information among the many entities monitoring and responding to the 2006-2007 drought situation. Facilitated by the DNR Division of Waters, this information sharing involves meetings, e-mail distributions, and Web postings.


- none


- September 20: National Weather Service releases 30/90 day temperature and precipitation outlooks
- October 18: 15th Annual Kuehnast Lecture 


http://climate.umn.edu - Minnesota Climatology Working Group, Minnesota DNR Waters and University of Minnesota Department 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://www.dnr.state.mn.us/waters - Minnesota DNR Waters
http://www.lre.usace.army.mil - Detroit District, US Army Corps of Engineers
http://www.governor.state.mn.us - State of Minnesota, Governor's Office
http://www.nass.usda.gov - USDA, National Agricultural Statistics Service
http://www.dnr.state.mn.us/forestry - Minnesota DNR Forestry
http://www.cpc.ncep.noaa.gov - Climate Prediction Center, National Weather Service
http://www.crh.noaa.gov/ncrfc - North Central River Forecast Center - Chanhassen, National Weather Service


- none

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