|HydroClim Minnesota - September 2002
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
WHAT HAS HAPPENED
- for the third consecutive month, rainfall totals across much of Minnesota were well above historical averages. August rainfall totals of more than eight inches were reported at a number of locations scattered around the state. Rainfall totals in these areas were four or more inches above the climatological normal. WHERE WE STAND NOW
- intense rainfall events occurred on numerous dates during August. In most cases, the heaviest rain fell over geographically isolated areas. Spotty rainfall patterns are common during August. The most substantial rain event of the month occurred in central and southern Minnesota on the 20th and 21st. A succession of slow moving thunderstorms left a stripe of heavy rain that spanned the width of the state. The heaviest precipitation fell upon southwestern, west central, and central Minnesota where some rainfall totals exceeded five inches. Storm totals of more than five inches were reported in sections of Lac Qui Parle, Yellow Medicine, Chippewa, Meeker, and Rock counties.
- August monthly temperatures were very close to historical averages around the state. A chilly period during the middle of the month was offset by warmer than average temperatures at month's end.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp , http://climate.umn.edu/doc/journal/cool020818.htm
- growing season precipitation totals to date (April 1 - September 3) are very high relative to historical values across northwest, central, and east central Minnesota. In these areas, precipitation totals have exceeded historical averages by more than 50 percent for the season. When compared to all other historical data for the same period (April 1 - September 3), precipitation totals for many communities in northwestern, central, and east central Minnesota are near, or above, all-time record values. By contrast, some sections of northeastern Minnesota are reporting rainfall deficits for the season. In portions of Cook county, growing season precipitation totals have fallen short of the historical average by 30 to 50 percent.
- preliminary data from the Midwestern Regional Climate Center indicate that Minnesota experienced its wettest summer on record. "Meteorological Summer" is defined as the months of June, July, and August. The preliminary state-averaged summer rainfall total for Minnesota in 2002 was 17.61 inches, topping the previous record of 17.16 inches set in 1993. Summer 2002 rainfall totals in the Twin Cities were the fourth highest in the 112 year modern record.
- as of August 27, the National Drought Mitigation Center - U. S. Drought Monitor shows that all Minnesota counties are free of drought designation. The NDMC index is a blend of science and subjectivity where intensity categories are based on six key indicators and numerous supplementary indicators.
- the August 31 Palmer Drought Severity Index map from the Climate Prediction Center places central Minnesota in the "Extremely Moist" category, the wettest designation. East central and northwest Minnesota are in the "Very Moist Spell" category. North Central, south central, and southeast Minnesota fall in the "Unusual Moist Spell" category. Other Minnesota regions are classified as "Near Normal". The Palmer Drought Severity Index is used for assessing long-term meteorological conditions.
- the Minnesota Agricultural Statistics Service reports that as of August 23, the state's topsoil moisture was 20% surplus, 79% adequate, 1% short, and 0% very short. Quantitative soil moisture measurements are rare. However, mid-August measurements from University of Minnesota research locations in southern Minnesota indicate that soil moisture values in those areas were near to above historical averages.
- the U.S. Geological Survey indicates that stream discharge values are high (above the 75th percentile for the date) over much of the state of Minnesota. Some points along the Red River and it's tributaries are at all-time highs for the date. Most stream flows in north central and northeastern Minnesota are near historical averages. Discharge values for some "North Shore" streams in Lake and Cook counties are very low, ranking below the 10th percentile for the date.
- the potential for wildfires is rated as "Low" across nearly all of Minnesota. The fire danger is rated as "Moderate" to "High" in Cook county, and rated as "High" in the blow-down areas of Lake and St. Louis counties.
- the September precipitation outlook from the Climate Prediction Center shows no significant tendencies away from 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 also shows no significant tendencies away from climatological probabilities. 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.
- the 90-day precipitation outlook for September through November shows no significant tendencies away from climatological probabilities. The September though November temperature outlook also shows no significant tendencies away from climatological probabilities.
- the National Weather Service produces long-range probabilistic river stage and discharge outlooks for the Red River, Minnesota River, and upper Mississippi River basins. A hydrologic model is initialized using the current conditions of stream flow and soil moisture across a basin. The model is allowed to run into the future with multiple scenarios using more than 30 years of climatological data. The climatological data are weighted by the 90 day outlooks for temperature and precipitation trends. The model output offers a complete range of probabilistic values of stream stage and discharge for numerous forecast points. The product offers a risk assessment tool which can be used in long-range planning decisions involving flooding or low-flow concerns. These products are part of the National Weather Service's Advanced Hydrologic Prediction Service (AHPS) and are produced near the middle of each month.
FROM THE AUTHOR
- as has been the case all summer, the Upper Midwest remains an oasis of wetness, wedged between drought-ravaged states to the west and east.
NOTES FROM AROUND THE STATE
- the summer of 2002 will be remembered as a summer of heavy rains in Minnesota. 11 significant rain events have been evaluated by the State Climatology Office thus far this season. The State Climatology Office analyzes rainfall events that lead to significant damage, or events where rainfall totals are near or above the threshold established as a one percent probability occurrence. For most communities in Minnesota, a one percent probability occurrence is six or more inches of rain in a 24 hour period. The State Climatology Office is indebted to Soil and Water Conservation Districts in the affected areas for their prompt and thorough response to requests for near-real-time precipitation data. Data are also provided by DNR Forestry and the National Weather Service. We thank Minnesota's many volunteer precipitation monitors, whose diligent efforts make detailed analysis of storm events possible.
- noneUPCOMING DATES OF NOTE
- September 19, Climate Prediction Center releases 30/90 day temperature and precipitation outlooks WEB SITES FEATURED IN THIS EDITION
- Minnesota Climatology Working Group
http://www.drought.unl.edu/ - National Drought Mitigation Center
http://www.cpc.ncep.noaa.gov - Climate Prediction Center
http://www.nass.usda.gov/mn - Minnesota Agricultural Statistics Service
http://water.usgs.gov/cgi-bin/dailyMainW?state=mn&map_type=weekd - U.S. Geological Survey, Minnesota
- Minnesota DNR Waters
http://www.dnr.state.mn.us/forestry/fire/ - Minnesota DNR Forestry
http://www.crh.noaa.gov/ahps/index.html - National Weather Service - Central Region Headquarters
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