|HydroClim Minnesota - September 2001
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
- continuing a dry spell that commenced during the second half of June and continued through July, August precipitation totals were below average across much of the southern two thirds of Minnesota. Rainfall amounts during August generally fell short of historical averages by one to two inches in these areas. Scattered sections of northwestern and southeastern Minnesota finished the month with above normal precipitation, but August was generally dry from a statewide perspective.
- mid and late summer rainfall was below historical averages in all but far northern Minnesota. In the eleven-week period from June 19 through September 4, rainfall totals fell short of normal by two to four inches across large areas of the state. For a significant number of Minnesota counties, the dry spell led to precipitation deficits of four to eight inches for this time interval. The dryness was especially acute in sections of central and southwestern Minnesota, where June 19 through September 4 precipitation totals ranked below the 5th percentile when compared to historical records for the same time span.
- as mentioned, the dry spell was not universally distributed across the state. Mid to late summer precipitation across most of the northern tier of Minnesota counties was adequate to abundant, in some cases ranking above the 90th percentile for the period.
- August average temperatures finished above historical averages by two to three degrees. Most of Minnesota suffered through episodes of extreme humidity and heat on July 30 through August 1, and then again August 4 through August 8. During these sultry spells; temperatures climbed into the 90's, dewpoint temperatures reached the upper 70's, and heat index values exceeded 100 degrees.
WHERE WE STAND NOW
- as of September 4, growing season precipitation totals (beginning April 1) continue to exceed normal across much of the state. In most of these areas, the near to above normal growing season rainfall totals reflect the lingering impact of an extremely wet spring. Mid and late summer precipitation shortfalls are counterbalancing the early season deluge in many areas and growing season precipitation shortfalls are expanding in intensity and area, especially in central and southwestern Minnesota.
- as of August 28, the National Drought Mitigation Center classifies a swath of counties through central Minnesota in their "DO" category ("Abnormally Dry"). The NDMC index is a blend of science and subjectivity where intensity categories are based on six key indicators and numerous supplementary indicators.
- the September 1 Palmer Drought Severity Index (PDSI) depicts all of Minnesota in the "Near Normal" category. The Palmer Drought Severity Index is used for assessing long-term meteorological conditions.
(see: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_monitoring/palmer.gif )
- the Minnesota Agricultural Statistics Service reports that topsoil moisture as of Sunday, September 2 was rated 4% surplus, 54% adequate, 29% short, and 13% very short. As of September 2, crop conditions were primarily rated as fair to good. However in areas with seasonal precipitation deficits, and for crops planted in coarse textured soils; crop stress is evident and row crops are reaching physiological maturity prematurely.
- the U.S. Geological Survey indicates that stream flows across much of Minnesota fall in the normal category for the date (ranking between the 25th and 75th percentile). Stream flows in some northwestern, north central, and northeastern counties fall above the 75th percentile for this time of the year. Surface water levels are historically at their lowest point during the month of September.
- the potential for wildfires is rated as "moderate" in some central and eastern central counties, as well as significant segments of northeastern and northwestern Minnesota. Elsewhere across Minnesota, fire danger is characterized as "low".
- 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 and Minnesota 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 will be produced near the middle of each month. The AHPS service will be available for the Mississippi River Basin in the autumn of 2002.
for the Red River basin, http://www.crh.noaa.gov/mpx/ahps/
for the Minnesota River basin)
FROM THE AUTHOR
- thus far the growing season of 2001 has been divided into two very distinct precipitation regimes. The period from April 1 until the third week of June was extraordinarily wet, ranking among the wettest springs on record. During the third week of June, the jet stream abruptly pushed north of the international border. The shift in the storm track has stubbornly persisted to this date, causing many storm systems to miss the state or to brush only the northern tier of counties. Most of Minnesota's surface hydrology, including soil profiles, were maintained this summer by reserves built up during the wet early season. The bank account is now running short in many areas, and adequate fall recharge will be critical in maintaining surface water levels.
NOTES FROM AROUND THE STATE
UPCOMING DATES OF NOTE
- September 13, Climate Prediction Center releases 30/90 day temperature and
WEB SITES FEATURED IN THIS EDITION
http://climate.umn.edu - Minnesota Climatology Working Group
http://enso.unl.edu/ndmc/ - National Drought Mitigation Center
http://www.cpc.ncep.noaa.gov - Climate Prediction Center
http://www.nass.usda.gov/mn/ - Minnesota Agricultural Statistics Service
- U.S. Geological Survey, Minnesota
http://www.dnr.state.mn.us/forestry/fire/ - Minnesota Department of Natural Resources - Division of
Forestry http://www.crh.noaa.gov/fgf - National Weather Service Forecast Office - Grand Forks
http://www.crh.noaa.gov/mpx - National Weather Service Forecast Office - Chanhassen
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