HydroClim Minnesota - April 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

compiled 4/3/02


- March precipitation was generally near normal across much of Minnesota. In some west central and central Minnesota counties, March precipitation totals finished above normal by about one half inch. After a three month period lacking in significant snow events, March compensated for the shortfall by bringing three substantial snow storms to Minnesota. During the three day period, March 7 through March 9, two major winter storms dropped heavy snow on central and northeastern Minnesota, rain and damaging freezing rain on southeastern Minnesota, and generated high winds nearing 50 mph in many areas. The third major winter storm swept through Minnesota on March 14 and 15. Snowfall totals from this event topped 15 inches along a 70 mile wide band from Canby to Hinckley. Six or more inches of snow was reported over much of the remainder of the southern two thirds of Minnesota. In some areas of south central and southeastern Minnesota, the storm produced freezing rain that coated surfaces with one quarter to one half inch of ice.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp , http://climate.umn.edu/doc/journal/snowstorm020308.htm , http://climate.umn.edu/doc/journal/snowstorm020314.htm )
- in sharp contrast with a winter-long trend of unusually warm weather, March temperatures finished significantly below normal. Temperatures across the state were four to nine degrees lower than historical averages. In a unique juxtaposition, the March mean temperature was colder than any of the preceding winter months in many communities.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp , http://climate.umn.edu/doc/journal/warm020110.htm )


- snow depths at the end of March were generally less than four inches in all but east central and northeastern Minnesota. Large sections of northwestern and southeastern Minnesota reported almost no snow cover. The March 28 snow depth ranking map indicated that snow depth values ranked near the historical median in a one hundred mile wide band extending from southwestern to northeastern Minnesota. Elsewhere, snow depths ranked below the 20th percentile for the date. Early April snows, not depicted in the late March snow maps, exceeded six inches in some east central Minnesota communities.
(see: http://climate.umn.edu/doc/snowmap.htm )
- as of March 26, the National Drought Mitigation Center designates much of western and northern Minnesota as "Abnormally Dry". The remainder of the state is free of any 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.
(see: http://enso.unl.edu/monitor/monitor.html )
- the March 30 Palmer Drought Severity Index (PDSI) from the Climate Prediction Center places northwestern Minnesota counties in the "Moderate Drought" category. Other areas are categorized as "Near Normal". 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 U.S. Geological Survey indicates that the majority of discharge values for Minnesota streams (where winter reporting is possible) are in the normal category for the date. Some streamflows in scattered areas around the state are below normal.
(see: http://water.usgs.gov/cgi-bin/dailyMainW?state=mn&map_type=weekd )
- soil frost depth data gathered on April 1 by the U.S. Army Corps of Engineers and the University of Minnesota indicate that frost depths, as measured under sod-covered surfaces, were 6 to 16 inches in the south, 16 to 28 inches in the west and north. Frost depths across Minnesota are highly variable depending on the amount of snow cover and soil type. For some locations, frost is near maximum depth for the season. Soil frost typically reaches maximum depth in late February and is gone by the first week of April in the south, mid-April in the north. Soil frost will thaw from both above and below, leaving a mid-profile ice lens to thaw last.
(see: http://www.mvp-wc.usace.army.mil/projects/reservoirs.shtml )
- the extraordinarily warm weather during December, January, and February led to relatively thin and unconsolidated lake ice cover. It appeared certain that lake ice-out would arrive early this spring. However, the cold March temperatures delayed ice-out progress, and the outlook for ice-out dates is unclear. Long-term average lake ice-out occurs during the first week of April in the southern tier of Minnesota counties; near the end of the second week of April in the Twin Cities metropolitan area; towards the end of the third week of April for Brainerd, Alexandria, Detroit Lakes area lakes; and during the final week of April in far northern Minnesota.
(see: http://climate.umn.edu/doc/ice_out/ice_out_historical.htm )


- the April precipitation outlook from the Climate Prediction Center shows no significant tendencies away from climatological probabilities. April precipitation normals range from one and one half inches in northwestern Minnesota to around three inches in southeastern counties.
- the April temperature outlook also shows no significant tendencies away from climatological probabilities. Normal April high temperatures are in the low to mid 40's early in the month, rising to near 60 by month's end. Normal April lows are near 30 to start the month and climb to around 40 as the month ends.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/multi_season/13_seasonal_outlooks/color/seasonal_forecast.html )
- the 90-day precipitation outlook for April through June shows no significant tendencies away from climatological probabilities. The April though June temperature outlook also shows no significant tendencies away from climatological probabilities.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/multi_season/13_seasonal_outlooks/color/seasonal_forecast.html )
- 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 will be produced near the middle of each month.
(see: http://www.crh.noaa.gov/ahps/index.html )


- heavy late November rainfall and snowfall brought relief to areas affected by precipitation deficits established during the later part of the 2001 growing season. Because the considerable November precipitation fell before soil freeze-up, the soil moisture profile was amply recharged in most areas of the southeastern three fourths of Minnesota. Soil moisture changes relatively little while the soil is frozen, therefore the early spring soil moisture situation should reflect the situation found at soil freeze-up. The primary area of concern for dry soils at this time is northwestern Minnesota. Many areas in the Red River Valley were missed by the late autumn precipitation. Snowfall in these areas was sparse throughout the winter, and wind erosion has been a concern.
- in the coming months you may hear a great deal about the onset of an "El Niņo". The El Niņo phenomenon is a semi-regular (every two to seven years) warming of the sea surface in the eastern equatorial Pacific. There are no known connections between El Niņo and Minnesota's growing season weather. However, El Niņos are often associated with warm and relatively snow free winters in Minnesota. I would like to emphasize that El Niņo is not presently in place, but there are indications that it may evolve later in the year.


- none


- April 18, Climate Prediction Center releases 30/90 day temperature and precipitation outlooks
- April 18-25, Probabilistic Flood Outlooks issued by National Weather Service


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://water.usgs.gov/cgi-bin/dailyMainW?state=mn&map_type=weekd - U.S. Geological Survey, Minnesota
http://www.mvp-wc.usace.army.mil/projects/reservoirs.shtml - U.S. Army Corps of Engineers, St. Paul District
http://www.crh.noaa.gov/ahps/index.html - National Weather Service - Central Region Headquarters


- none

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