|HydroClim Minnesota - March 2001
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 above normal across
Minnesota. February precipitation totals topped one inch in most
locations, and exceeded two inches in some areas of southern, central, and
northeastern Minnesota. February 2001 precipitation doubled or even
tripled the historical average in this traditionally dry month. Much of
the February precipitation fell during a procession of storms that dropped
heavy snow, sleet, and rain throughout the weekend of February 23 - 25.
Snowfall totals of over 12 inches were reported in west central and
central Minnesota during these storms, and snowfall amounts approached 24
inches in portions of Minnesota's Arrowhead region.
- February temperatures were cold, finishing four to
eight degrees below normal. It was the coldest February since 1994, and
for some communities, the coldest February since 1989.
WHERE WE STAND NOW
- most of Minnesota reported more than 18 inches of
snow cover as of March 1st. Snow depths across a large swath of Minnesota,
extending from west central Minnesota into northeastern Minnesota, were
greater than 24 inches. Snow depths in the southern two thirds of
Minnesota ranked above the 95th percentile for the date, and snow depths
for the remainder of Minnesota were above the 60th percentile. For some
areas of west central and southwestern Minnesota, snow depths were at or
near all-time record values for the date.
- snow water equivalent data gathered by the
National Weather Service and the Army Corps of Engineers show that the
snow pack across Minnesota generally contained three to five inches of
water as of March 6. Some areas within the Minnesota River basin reported
five to six inches of snow water equivalent. Portions of the upper reaches
of the Red River basin report snow water content of four to five inches,
but the snow pack over the majority of the Red River watershed contains
less than three inches of water. Snow densities vary across the state but
are generally around 20% (approximately one inch of water for each five
inches of snow cover).
- soil frost depths across the state range from
near zero to 12 inches in areas receiving early and persistent snow cover,
24 to 40 inches in areas blown free of snow.
- stream discharge values are difficult to determine
during the frozen water season. However, for gauging locations that
provide winter data, the U.S. Geological Survey indicates that many points
in the Red River basin are above the 90th percentile when compared to
historical values for the date. Stream flows in other areas of the state
are near average for the date.
- as of their March 1 release, the National Drought
Mitigation Center - "U.S. Drought Monitor" shows Minnesota to be
free of any drought designations. 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 3 Palmer Drought Severity Index (PDSI)
depicts much of Minnesota as experiencing an "Unusual Moist
Spell". Many counties in southern, central, and northwestern
Minnesota fall in this grouping. Counties in the rest of the state are
categorized as "Near Normal". The Palmer Drought Severity Index
is used for assessing long-term meteorological conditions.
- the 30-day outlook from the Climate Prediction
Center shows no significant tendencies (equal chances of below, near, and
above normal) in March precipitation for Minnesota. March precipitation
normals range from three quarters of an inch in northwestern Minnesota to
near two inches in the southeast. The March temperature outlook tilts
towards below normal values. Normal March high temperatures are just below
freezing early in the month, rising to the low to mid 40's by month's end.
Normal March lows average around ten degrees to start the month and climb
to the mid 20's as the month ends.
- the 90-day precipitation outlook for March through
May tilts towards above normal precipitation. The March through May
temperature outlook calls shows no significant tendencies away from
- the National Weather Service now produces
long-range probabilistic river stage and discharge outlooks for the Red
River and Minnesota River basins. A hydrologic model is initialized using
the current conditions of the river, water equivalent of the snow cover,
soil moisture, and soil temperature. The model is then 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 Services (AHPS) and will be
produced near the middle of each month. The AHPS service will be available
for the Mississippi River Basin in the autumn of 2002.
FROM THE AUTHOR
- the heavy late-season snow cover inflates the risk for spring snow-melt flooding this year. Those with interests in flood-prone areas should carefully monitor National Weather Service flood outlooks and flood forecasts (see the description of the AHPS system in "Future Prospects" above and the flood outlook schedule in "Upcoming Dates of Note" below). The National Weather Service offices with forecast responsibilities for Minnesota's rivers offer excellent Web sites which present the latest flood outlook and forecast information. Look for the "Rivers/Hydrology" section of the following Web sites:
> Red River basin - (NWS Grand Forks) http://www.crh.noaa.gov/fgf/
NOTES FROM AROUND THE STATE
UPCOMING DATES OF NOTE
- March 9, Flood Potential Numerical Outlook from
the National Weather Service
WEB SITES FEATURED IN THIS EDITION
- Minnesota Climatology Working Group
Contributions of information and suggestions are welcome!