|HydroClim Minnesota - March 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
- February precipitation was generally below normal across much of Minnesota. Exceptions were found in some southeastern and central Minnesota counties where heavier precipitation occurred during the month. Moderate to heavy rains fell on some southeastern Minnesota communities on February 18 and 19, with totals ranging one to two inches over a 48 hour period. On February 24, four to eight inches of snow fell in a swath from west central Minnesota to Duluth.
- keeping with a trend established in November and continuing through the winter, February temperatures across the state finished 8 to 13 degrees above average. It was Minnesota's fifth warmest February since 1891. Temperatures in most locations reached into the 50's at least once during the month. Temperatures climbed into the 60's across southwestern Minnesota on February 23.
- the state recorded the 2nd warmest December through February ("meteorological winter") period in the modern record. Some communities reported the warmest meteorological winter ever. Three of the last five winters (1997-1998, 1999-2000, 2001-2002) rank among the seven warmest meteorological winters since 1891.
- the sparse snow cover combined with warm temperatures to contribute to unusual February grassland and peat fires in some areas.
WHERE WE STAND NOW
- snow depths are less than eight inches nearly everywhere in Minnesota. Large sections of northwestern and southern Minnesota report less than two inches of snow cover. The snow depth ranking map indicates that snow depths values over much of Minnesota rank below the 20th percentile for the date. Only in some areas of western and central Minnesota do current snow depths rank near the median.
- as of February 26, the National Drought Mitigation Center designates all but east central and southeastern 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.
- the March 2 Palmer Drought Severity Index (PDSI) from the Climate Prediction Center places south central and 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.
- the U.S. Geological Survey indicates that discharge values for Minnesota streams (where winter reporting is possible) are in the normal to above normal categories for the date. Should late winter snow cover remain below the median, stream flows later in March and into April will fall below average levels.
- soil frost depth data gathered on March 3 by the U.S. Army Corps of Engineers and the University of Minnesota indicate that frost depths, as measured under a sod surface, were 6 to 12 inches in the south, 16 to 24 inches in the west and north. The soil frost layer has deepened over the last 7 to 10 days in response to the recent spell of colder weather.
- on 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. The extraordinarily warm winter has produced relatively thin and unconsolidated lake ice cover. It is probable that lake ice-out will occur ahead of the average dates despite the recent cold snap.
(see: http://climate.umn.edu/doc/ice_out/ice_out_historical.htm )
- the March precipitation outlook from the Climate Prediction Center shows no significant tendencies away from climatological probabilities. March precipitation normals range from near one inch in northwestern Minnesota to around two inches in southeastern counties. March is a transition month when cold, dry continental air masses are gradually replaced by warmer, moist air on a more frequent basis. This is demonstrated by the fact that March normal precipitation is 50 percent higher than February normal precipitation, the greatest percentage increase between any two successive months.
- the March temperature outlook tilts towards above normal conditions. Normal March high temperatures climb from the mid to upper 20's early in the month to the low to mid 40's by month's end. Normal March lows begin the month in the single digits above zero in the far north and near 10 degrees in the south. By late March, normal lows are in the low to mid 20's.
- the 90-day precipitation outlook for March through May shows no significant tendencies away from climatological probabilities. The March though May temperature outlook tilts towards above normal conditions in the north and no significant tendencies away from climatological probabilities in the south.
- 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.
FROM THE AUTHOR
- in the discussions above, I point out that two of the national drought monitoring indices depict portions of Minnesota in developing or ongoing drought categories. The indices reflect the scarcity of winter snowfall and the extraordinarily warm winter temperatures, and attempt to quantify the present climatological anomaly. Precipitation deficits that occur during the Minnesota winter have a profound affect on the winter recreation industry. However, from a water resource standpoint we must recall that on average, the total water volume deposited by winter precipitation is small when compared to annual precipitation. Therefore, below normal winter precipitation has a smaller impact on water resources than deficits established during the growing season.
- 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 moisture situation should reflect the situation found at soil freeze-up.
NOTES FROM AROUND THE STATE
UPCOMING DATES OF NOTE
- March 14, Climate Prediction Center releases 30/90 day temperature and precipitation outlooks
- March 14-21, Probabilistic Flood Outlooks issued by National Weather Service
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
- U.S. Geological Survey, Minnesota
- U.S. Army Corps of Engineers, St. Paul District
http://www.crh.noaa.gov/ahps/index.html - National Weather Service - Central Region Headquarters
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