|HydroClim Minnesota - February 2003
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
- precipitation totals for January 2003 were quite small across all of Minnesota. January precipitation totals were generally less than one quarter inch in most locations, and fell short of the historical average by more than one half inch. This marked the third consecutive month of very light precipitation in Minnesota. In the Twin Cities, the November through January precipitation total was the driest on record. Many Minnesota communities were nearly devoid of snow cover until modest snowfalls covered the ground during the last week of January. An early February winter storm brought more significant snow to portions of central Minnesota.WHERE WE STAND NOW
- January featured wild swings in daily temperatures. Record breaking warm temperatures (=> 50 degrees F) on the 7th and 8th of the month were counterbalanced by seasonal to below-normal temperatures during the last half of January. January temperatures finished around two degrees above normal.
- as of February 5, snow cover across Minnesota was highly variable and was best pictured as an irregular collection of snow belts draped across the state. Bands of six to ten inch snow cover were found across far northern Minnesota as well as a fifty mile wide band dissecting central Minnesota. Elsewhere, snow depths ranged from zero to three inches. For those communities within the snow-sparse areas, snow depths fell below the 5th percentile when compared with historical snow cover for the date. In some locations, snow depths were at all-time lows for the date.
- as of January 28, the National Drought Mitigation Center - U. S. Drought Monitor indicates that nearly all of Minnesota falls within the "D0 - Abnormally Dry" category. Far northeastern Minnesota is judged to be in the "D1 - Drought Moderate" category. The NDMC index is a blend of science and subjectivity where intensity categories are based on six key indicators and numerous supplementary indicators.
- the February 1 Palmer Drought Severity Index map from the Climate Prediction Center places almost all of Minnesota in the "Near Normal" category. Only central Minnesota ("Unusual Moist Spell") falls outside of the "Normal" designation. Winter's dry weather has moved index values lower across all of Minnesota. The Palmer Drought Severity Index is used for assessing long-term meteorological conditions.
- soil surface layers across Minnesota are dry in response to the late autumn and early winter precipitation deficits. Soil moisture values in the mid and lower layers are ample. The soil moisture profile will change very little until the soil thaws.
- the U.S. Geological Survey indicates that stream discharge values for approximately one half of Minnesota rivers (where winter reporting is possible) are in the normal category for the date. Approximately one quarter of Minnesota's streams rank above the 75th percentile for the date. Discharge values for northeast Minnesota streams are low, ranking below the 25th percentile for the date.
- soil frost depths increased rapidly across Minnesota during January. Cold temperatures, combined with limited snow cover, caused soil frost to penetrate beyond 24 inches in depth beneath sod-covered surfaces, and deeper under bare soil. For many locations, soil frost is at the deepest levels observed in more than a decade. Soil frost historically reaches maximum depth in late February.
- Minnesota's lakes and ponds are ice covered. However, many southern and central Minnesota lakes are reporting dangerous patches of open water (see "from the author" below).
- the February precipitation outlook from the Climate Prediction Center shows a tendency towards below normal conditions in the eastern one third of Minnesota, with no significant tendencies away from climatological probabilities elsewhere in Minnesota. Historically, February is Minnesota's driest month with precipitation normals ranging from less than one half inch in northwestern Minnesota to near three quarters of an inch in eastern sections of the state. The median snow cover at the end of February ranges from under 5 inches in the southwest Minnesota, to over 18 inches on the ground in northeastern Minnesota (greater than 30 inches in the Lake Superior highlands). The February temperature outlook indicates a strong bias towards above normal conditions throughout Minnesota. Normal February high temperatures climb from the mid to upper teens early in the month to the mid to upper 20's by month's end. Normal February lows begin the month from near minus 10 degrees in the far north, the single digits above zero in southern Minnesota. By late February, normal lows are in the low single digits above zero in the far north, and near 10 degrees in the south.
- the 90-day precipitation outlook for February through April shows a tendency towards below normal conditions in the northeastern one half of Minnesota, with no significant tendencies away from climatological probabilities elsewhere in Minnesota. The February though April temperature outlook indicates a strong bias towards above normal conditions throughout Minnesota.
- 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 historical climatological data. The climatological data are weighted by 90-day climate outlooks for temperature and precipitation trends. Model output offers a complete range of probabilistic values of stream stage and discharge for numerous forecast points. The product provides 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 are produced near the middle of each month.
FROM THE AUTHOR
- during the month of January, the State Climatology Office received many inquiries regarding Minnesota's lake ice "holes". We offered the following major themes when answering these inquiries:
NOTES FROM AROUND THE STATE
1) the number one issue remains public safety.
2) the phenomenon is relatively rare, and not well studied. DNR staff have offered their thoughts on the subject, but no definitive conclusion has been reached. We may be dealing with the unknowable.
3) some forces creating the phenomenon MAY include:
- the unusual lack of snow cover. High albedo snow cover typically reflects incoming short wave radiation back into space. Lake ice, and the water immediately beneath it, may have adsorbed greater than average solar energy this winter. In spite of cold mid-January temperatures, this energy may have been adequate to melt ice or to keep ice from forming.
- ground water upwelling (which, of course, occurs nearly every year). However, the holes may have formed in areas with historically thinner ice.
- unusually warm early winter weather leading to atypical thermal stratification in the affected lakes.
- some combination of all of the above.
- noneUPCOMING DATES OF NOTE
- February 12, Interagency Flood Planning Coordination Meeting - National Weather Service, ChanhassenWEB SITES FEATURED IN THIS EDITION
- February 20, Climate Prediction Center releases 30/90 day temperature and precipitation outlooks
- February 21, Narrative Flood Outlook issued by National Weather Service (if required)
- February 21-28, Probabilistic Flood Outlooks issued by National Weather Service
- Minnesota Climatology Working Group
http://www.drought.unl.edu/ - 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
- Minnesota DNR Enforcement
http://www.crh.noaa.gov/ahps/index.html - National Weather Service - Central Region Headquarters
- many interesting and useful observations were received from DNR Waters staff and others concerning the lake ice hole phenomenon.
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