HydroClim Minnesota - April 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 4/4/07

WHAT HAS HAPPENED

- March 2007 precipitation totals were above average across Minnesota. This was the second consecutive month of above average precipitation. Monthly precipitation totals ranged from two to four inches statewide, topping the historical average by one or more inches in many communities.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp )
- March 2007 precipitation came primarily from two significant events, one at the start of the month, one at the end of the month. A powerful winter storm lumbered through Minnesota from February 28 through March 2. The storm left a wide swath of twelve or more inches of snow across much of the southern two thirds of Minnesota and along portions of Minnesota's North Shore. Some eastern and central Minnesota counties reported over 18 inches of snow for the event. Strong winds accompanying the storm led to blizzard conditions in the Duluth area and across areas of western Minnesota. During the final days of March, a strong upper level disturbance spiraled through the Upper Midwest and dropped over two inches of rain across much of the southern two thirds of Minnesota.
(see: http://climate.umn.edu/doc/journal/snow070228_070302.htm )
- monthly mean temperatures for March 2007 were above average throughout Minnesota. Mean temperatures for the month ranged from three to six degrees above the historical average. Cool temperatures in early March were more than offset by very warm readings during the last ten days of the month. Numerous records were set on March 25 and March 26 when the temperature soared into the 70's and low 80's in central and southern Minnesota. Extreme values for March ranged from 83 degrees at La Crescent (Houston County) on the 26th, to minus 25 degrees at Embarrass (St. Louis County) on the 6th.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp , http://climate.umn.edu/doc/journal/warm070326.htm )
- warm temperatures in mid-March produced rapid snow melt in many southern and western Minnesota watersheds. In addition to the hasty melt, unusually thick ice created jams in constricted locations along stream courses. The combined result led to isolated moderate to major flooding, the worst of which affected Browns Valley.

WHERE WE STAND NOW

- an early-spring snowstorm on April 3 dropped six to twelve inches of snow across portions of central and northern Minnesota. Cold temperatures during the first week of April will retain this snow cover. An early-April snow cover not unusual in these areas. The average date of the last occurrence of three or more inches of snow depth is on, or after, April 10 for most north central and northeastern Minnesota communities. The average date of the final day of snow cover along the North Shore highlands is April 20.
(see: http://mcc.sws.uiuc.edu/cliwatch/watch.htm )
- at this time, minor to moderate river flooding is underway along the Red River and some of its tributaries. Also, a few locations in the Mississippi and Minnesota river basins are experiencing minor flooding.
(see: http://www.crh.noaa.gov/ahps2/index.php?wfo=fgf , http://www.crh.noaa.gov/ahps2/index.php?wfo=mpx )
- dryness has been entrenched across northern Minnesota for nearly eleven months. While a welcome site, snowfall and rainfall from the early-March and late-March storms only partially eased the situation in the far north. Eleven-month precipitation totals have deviated negatively from historical averages by more than six inches across much of the northern one half of Minnesota.
- the National Drought Mitigation Center (NDMC) - U. S. Drought Monitor released on March 29 continues to indicate that most northern Minnesota counties remain in the "Extreme Drought", "Severe Drought", or "Moderate Drought" categories. The map does not reflect the late-March rains. While this late-March rainfall may improve the drought situation somewhat, a substantial portion of northern Minnesota continues to experience serious drought. The NDMC index is a blend of science and subjectivity where intensity categories are based on several indicators.
(see: http://www.drought.unl.edu/dm/monitor.html )
- the U.S. Geological Survey reports that many stream discharge values are well above the median for this time of year. Stream flow in north central and northeastern Minnesota watersheds remains low.
(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 )
- the soil has lost most of its frost in southern Minnesota. Before the recent cold snap, northern Minnesota soils were thawing from both the top and the bottom, leaving a mid-layer lens of frozen soil to be the last to climb above freezing.
(see: http://climate.umn.edu/doc/observatory.htm , http://www.mvp-wc.usace.army.mil/projects/reservoirs.shtml , http://www.mrr.dot.state.mn.us/research/seasonal_load_limits/thawindex/frost_thaw_graphs.asp )
- many of the larger lakes in the southern one third of Minnesota are now free of ice. Historically, 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, and Detroit Lakes area lakes; and in the final week of April in far northern Minnesota.
(see: http://climate.umn.edu/doc/ice_out/ice_out_status_07.htm , http://www.dnr.state.mn.us/ice_out/ )
- the potential for wildfires is rated by DNR Forestry as "low" across Minnesota. These conditions can change rapidly in response to warm, sunny, and windy weather. Historically, 80 percent of all wildfires in Minnesota occur during April and May.
(see: http://www.dnr.state.mn.us/forestry/fire/ )

FUTURE PROSPECTS

- the April precipitation outlook from the Climate Prediction Center calls for equal chances of below, near, or above normal conditions. April precipitation normals range from one and one half inches in northwestern Minnesota to around three inches in southeastern counties. The historical probability of measurable precipitation for any given day in April ranges from 20 percent in the far northwest to 35 percent in the southeast.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/30day , http://climate.umn.edu/img/normals/precip/precip_norm_04.htm )
- the April temperature outlook offers no strong indications of either above or below normal temperatures in Minnesota. Normal April high temperatures are in the mid to upper 40's early in the month, rising to the low 60's by month's end. Early April normal low temperatures are near 20 in the north, near 30 in the south. By month's end, low temperatures average in the mid 30's in the north, near 40 in the south.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/30day , http://climate.umn.edu/img/normals/temp_norm_adj/temp_norm_adj_04.htm )
- the 90-day precipitation outlook for April through June indicates no significant tendencies away from climatological probabilities across Minnesota. The April through June temperature outlook indicates a tilt towards above-normal conditions throughout the state.
(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/ )

NOTES FROM THE AUTHOR

- northern Minnesota will face many lingering drought issues in 2007. In order to recover rapidly from the 2006 precipitation deficits, spring and summer rainfall totals will need to greatly exceed historical normals. This is possible, but not climatologically likely. The drought was quick to develop, but most likely its impacts will be slow to repair. Some drought concerns for the 2007 growing season in northern Minnesota include:
   * increased wildfire risk
   * streams dropping below protected flow thresholds after the spring melt runoff
   * low lake water levels and associated water access issues
   * ground water levels lowering in lagged response to precipitation deficits. Ground water levels will also respond to increased pumping pressures.
   * inadequate soil moisture conditions further impacting agriculture, especially forage crops
   * inadequate soil moisture conditions further stressing forest communities, making them more vulnerable to pests

NOTES FROM AROUND THE STATE

- none

UPCOMING DATES OF NOTE

- April 19: National Weather Service releases 30/90 day temperature and precipitation outlooks

WEB SITES FEATURED IN THIS EDITION

http://climate.umn.edu - Minnesota Climatology Working Group, Minnesota DNR Waters and University of Minnesota Department of Soil, Water, and Climate
http://mcc.sws.uiuc.edu - Midwestern Regional Climate Center
http://www.crh.noaa.gov/mpx - National Weather Service Forecast Office, Chanhassen
http://www.crh.noaa.gov/fgf - National Weather Service Forecast Office, Grand Forks
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.mvp-wc.usace.army.mil - St. Paul District, US Army Corps of Engineers
http://www.mrr.dot.state.mn.us/research - Minnesota Road Research Section, Minnesota Department of Transportation
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

ACKNOWLEDGEMENTS

- none

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