|HydroClim Minnesota - October, 2000
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:
- rainfall was much below normal for most of Minnesota during the month
of September. Precipitation totals were one to three inches below
historical averages in almost all communities. Some northwestern Minnesota
counties were exceptions to this general pattern and reported
precipitation totals an inch or more above the norm.
- a significant rainfall event occurred during the evening of September 2 in east central Minnesota. Very heavy thunderstorms formed just to the west of the Twin Cities metropolitan area and dropped three to four inches of rain in less than three hours across portions of Ramsey County. Since that time, precipitation in the metropolitan area has been negligible.
- September temperatures were very close to the historical average
across Minnesota. On September 18th, temperatures climbed into the
mid-80's, setting many maximum temperature records for the date.
Temperatures dropped into the low 20's on September 24th, setting new
minimum temperature records for that date and ending the growing season in
WHERE WE STAND NOW:
- the shortfall of precipitation in September worsened an already
desiccated condition found in an area of central and east central
Minnesota, extending from roughly St. Cloud to the northern suburbs of the
Twin Cities. Intersecting this region is a swath of increasing dryness
found roughly 30 miles either side of a line from Montevideo (west central
Minnesota) to Pine City (east central Minnesota). Additional pockets of
abnormally dry conditions can also be found in far southwestern Minnesota
and along the north shore of Lake Superior. Seasonal rainfall totals
(April 1 - present) in the dry areas are four to nine inches short of
normal, ranking some communities in the lowest 10th percentile when
compared with the historical climate record. By contrast, late summer
rainfalls pushed seasonal precipitation totals in far northwestern
Minnesota to 25% or more above the historical average. This is a
continuation of the wet regime experienced by northwestern Minnesota and
eastern North Dakota over much of the last 10 years.
- as of their September 28 release, the National Drought Mitigation
Center - "U.S. Drought Monitor" shows much of the western one
half of Minnesota in their "D0" category ("Abnormally
Dry"). The NDMC index is a blend of science and subjectivity where
intensity categories are based on six key indicators and numerous
supplementary indicators. The NDMC depiction attempts to describe drought
conditions on a fairly large regional scale, and has difficulty capturing
geographically isolated precipitation deficits such as those currently
found in portions of central, east central and northeastern Minnesota.
- the September 30th Palmer Drought Severity Index (PDSI) depicts most
of Minnesota in the "Near Normal" category. Counties in west
central Minnesota are categorized as experiencing "Moderate
Drought". The Palmer Drought Severity Index is used for assessing
long-term meteorological conditions. One of the inherent weaknesses of the
PDSI is the size of the geographic regions ("climate districts")
covered by the analysis. The persistent dryness found in portions of
central and east central Minnesota is "washed out" by relative
wetness in other counties within the same climate district. Thus in this
case, the PDSI fails to illustrate areas of Minnesota experiencing
significant precipitation deficits. For this reason, it is always useful
to cross-check the PDSI depictions with the State Climatology Office
seasonal precipitation maps.
- the Minnesota Agricultural Statistics Service reports that topsoil
moisture conditions across the state were rated 26% very short, 32% short,
37% adequate, and 5% surplus as of Friday, September 29. This is a large
increase from last month in the amount of acreage categorized as short or
very short. Quantitative soil moisture measurements from University of
Minnesota facilities in Waseca (Waseca county) and Lamberton (Redwood
County) show that available soil water is approximately two inches below
average for this time of year. The data also indicate that the soil near
the surface is extremely dry, with the bulk of the water in the rooting
zone residing in the lower portions of the profile (two to five feet).
- current discharge values for central and east central Minnesota
streams are very low for this time of year. According to the U.S.
Geological Survey and DNR Waters, most streamflows in these regions are
below the 25th percentile, with some streams falling below the 10th
percentile. Low streamflows are also reported in sections of southwestern
and northeastern Minnesota. Conversely, stream discharge ranks in the
"high flow" category in some northwestern watersheds.
- with the exception of northwestern Minnesota, many Minnesota lakes
are at or near low water levels not seen since the aftermath of the
drought of the late 1980's.
- the wildfire danger potential is rated by DNR Forestry as
"high" for a cluster of counties just to the north of the Twin
Cities metropolitan area. The fire danger is considered
"moderate" for sections of northwestern and northeastern
- the 30-day outlook from the Climate Prediction Center calls for near
normal October precipitation across all of Minnesota. Normal October
precipitation ranges from near one inch in northwestern Minnesota, to over
two inches in the southeast. The October temperature outlook is for near
normal conditions in all but southeastern Minnesota. For the southeast,
the outlook leans towards below normal temperatures. Normal October high
temperatures fall from the low to mid 60's early in the month to the upper
40's by month's end. Normal October lows drop from the low 40's early in
the month to the upper 20's by late October.
- the 90-day outlook for October through December indicates near normal
precipitation statewide. The October through December temperature outlook
also calls for near normal conditions throughout Minnesota.
FROM THE AUTHOR:
- the season-long dryness in central and east central Minnesota, and the late-season string of dry weather in other areas has produced significant hydrological imbalances. Because average precipitation values drop off dramatically during October and November, water deficits are unlikely to be ameliorated this late autumn. Receiving normal to above normal precipitation before permanent soil freeze-up in early November would help to replenish parched soils, but will do very little to change surface water conditions this year. Spring snow-melt runoff and early spring rains will determine the extent of wetland, lake, and stream recharge on the near horizon.
NOTES FROM AROUND THE STATE:
- from Bob Weisman, St. Cloud State University
(excerpted from "St. Cloud September, 2000 Weather Summary")
The dry September left St. Cloud with a 2000 growing season (Apr 1-Sep 30) of 12.46 inches, nearly 8 inches below normal. This is the 6th lowest growing season rainfall in St. Cloud in the 109 years of records. Combined with the rainfall deficit from last fall (2.1 inches), St. Cloud is now more than 10 inches of rainfall behind during the growing season since September of last year. 3 of the last 10 years (1992, 1996, 2000) rank in the 7 driest growing seasons to date.
- from Mike Mueller, DNR Waters Area Hydrologist - Cambridge
Total precipitation for September was 0.42" at Cambridge. This coming on the heels of a very dry August, has made numerous wetlands dry for the first time since 1988. Lake levels are also declining and many landowners are experiencing difficulties in removing their boats from the water. Soil moisture seems very low and crop production is likely to be effected. Extensive areas of soybean wilting were observed in late August and there are reports of low yield from early harvests.
On the plus side, the mosquito season was nonexistent this year.
Finally, wetlands are generally not harmed by occasional droughts. Many aquatic plants are adapted to take advantage of exposed soils and shallower waters, by sprouting and quickly covering these areas with lush new growth. A good example of this is wild rice, which has flourished this year, producing a crop that is considered one of the best in many years. Lakeshore owners would be wise to consider establishing buffer areas of native aquatic plants along their shorelines, during this window of opportunity.
UPCOMING DATES OF NOTE:
- October 12, Climate Prediction Center releases 30/90 day outlooks
WEB SITES FEATURED IN THIS ADDITION:
http://climate.umn.edu - Minnesota
Climatology Working Group
Bob Weisman, Meteorology Professor, Earth Sciences Department - St.
Cloud State University
Contributions of information and suggestions are welcome!