HydroClim Minnesota - April 2008

A monthly electronic newsletter summarizing Minnesota's 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 4/2/2008 (early release)

What happened in March:

March 2008 precipitation totals were below the historical average in most Minnesota locations. Lower than average snowfall meant that precipitation totals finished one half inch to one inch below the March average. This continued a pattern of below-normal snowfall that was prominent across most of Minnesota this past winter. Because many of Minnesota's volunteer climate observers make morning measurements, the significant rain/snow event of March 31 in southern Minnesota will be included in the April precipitation statistics.
Most of March's precipitation came from three snow or snow/rain events that occurred during the last two weeks of the month.
[see: March 31 Snow and Rain | March 21-23 Snow | March 17-18 Snow]
Keeping with a season-long trend, monthly mean temperatures for March 2008 were below historical averages. March temperatures ranged from three to five degrees below normal across Minnesota. Extreme values for March ranged from a high of 56 degrees on the 14th at a handful of locations in southwestern Minnesota, to a low of minus 33 degrees at Embarrass (St. Louis County) on the 8th. Some low temperature records were set on March 7 when temperatures dropped to near minus 20 degrees in western Minnesota.

Where we stand now:

The snow depth map to be prepared on April 3 will show that snow cover remains in place across much of Minnesota. The deepest snow cover is found in the northern tier of Minnesota counties. A significant snow cover stubbornly holds on along the Lake Superior highlands. Snow depths exceeding 12 inches are reported in many of those areas.
[see: Snow Depth Maps]
The U. S. Drought Monitor, released on March 25, continues to place a small area of west central and central Minnesota in the "Moderate Drought" category. Portions of northwestern and north central Minnesota remain designated as "Abnormally Dry". This is an acknowledgement of some lingering precipitation deficits. All other Minnesota locales are deemed to be free of drought conditions. The U. S. Drought Monitor index is a blend of science and subjectivity where intensity categories are based on several indicators.
[see: U.S. Drought Monitor]
The U.S. Geological Survey reports that stream discharge values, for observation points where measurements are possible despite the influence of river ice, are near or below the historical median for the date in most locations. The lone exception is far southeastern Minnesota where stream flows are above the 75th percentile for the date.
[see: USGS Streamflow]
The Lake Superior water level is up seven inches from last year at this time. While the Lake Superior water level is no longer near the all-time seasonal low, it remains below the long-term average.
[see: Corps of Engineers Great Lakes Water Levels]
In their final report of 2007, the Minnesota Agricultural Statistics Service reported that despite the dry November weather, mid-November topsoil moisture was "Adequate" across 83% of Minnesota's landscape. Topsoil moisture deficits should not be a concern in most areas at the start of the 2008 growing season.
[see: Ag. Statistics Service Crop Progress and Condition]
Soil frost remains in solidly in place in many Minnesota locations. Frost depths generally range from 18 to 36 inches. In those locations that experienced deeper and less compacted snow cover through the winter, especially northeastern Minnesota and far southeastern Minnesota, frost depths are much shallower. In areas with deep frost, the soils will thaw rapidly as the sun angle increases, the days get longer, and warm rain acts as a heat transfer mechanism. On average, the soil profile thaws by late March to early April in the south, early April to mid-April in the north. The soil thaws from both the top and the bottom, leaving a mid-layer lens of frozen soil to be the last to climb above freezing.
[see: National Weather Service River Forecast Center | U of M Climate Observatory | Ag. Statistics Service Ag News | MnDOT Road Frost Depths]
All of Minnesota's larger lakes remain ice covered. 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: Lake Ice-out Status]
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: Fire Danger Rating Map]

Future prospects:

The April precipitation outlook tilts towards above normal conditions, especially in northwestern Minnesota. 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: Climate Prediction Center 30-day Outlook | April Precipitation Normal Map]
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: Climate Prediction Center 30-day Outlook | April Temperature Normal Map]
The 90-day precipitation outlook for April through June indicates no significant tendencies away from climatological probabilities across Minnesota. The April through June temperature projection offers equal chances of above, near, or below average conditions.
[see: Climate Prediction Center 90-day Outlook]
No significant snowmelt induced flooding is expected this spring along Minnesota's rivers. 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: National Weather Service River Forecast Center]

From the author:

None

Notes from around the state:

None

Upcoming dates of note:

April 17: 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 U of M Dept. of Soil, Water, and Climate
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.lre.usace.army.mil - Detroit District, US Army Corps of Engineers
http://www.nass.usda.gov - USDA, National Agricultural Statistics Service
http://www.mrr.dot.state.mn.us - Minnesota Department of Transportation, Office of Materials
http://mndnr.gov/forestry - Minnesota Department of Natural Resources, Division of Forestry
http://www.cpc.ncep.noaa.gov - Climate Prediction Center, National Weather Service
http://www.crh.noaa.gov/ncrfc - North Central River Forecast Center, National Weather Service

Acknowledgements

None

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