HydroClim Minnesota - September 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 9/5/2007
WHAT HAPPENED IN
AUGUST
- August 2007 rainfall totals varied tremendously across
Minnesota. August rainfall in the northern one third of Minnesota was quite
light, totaling less than two inches in many places. Rainfall amounts fell
short of average by one to three inches in these locales. August rainfall in
the southern one third of Minnesota was extraordinarily heavy. Many southern
Minnesota locations set all-time August rainfall records. Rainfall totals in
the southern three to four tiers of Minnesota counties topped eight inches
for the month, doubling the historical monthly average. Numerous south
central and southeastern Minnesota communities reported rainfall totals in
excess of 10 inches in August. Many locations set all-time August monthly
rainfall records. Some examples include the Twin Cities (9.32 inches) and
Rochester (14.07 inches). Final August data are still being tabulated,
however it is a certainty that many southeastern Minnesota locations not
only set all-time August monthly rainfall records, but all-time monthly
records for any month. Rainfall totals for these locations will top 15
inches, and a few stations may report August rainfall totals in excess of 20
inches.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp , http://climate.umn.edu/weathertalk/070831.txt )
- a series of thunderstorms moving along a stalled
frontal boundary dropped extremely heavy rain on much of southern Minnesota
on August 18, 19, and 20. The most intense precipitation rates occurred
during the afternoon and evening hours of Saturday, August 18, and the early
morning hours of Sunday, August 19. Over the course of the event, all or
portions of 28 counties received at least four inches of rain. Six-inch
totals were common across the region, and portions of southeastern Minnesota
reported astounding rainfall amounts ranging from 8 to 18 inches. The
heaviest rainfall reports came from Winona, Fillmore, and Houston counties,
where 36-hour totals exceeded 14 inches. The largest multi-day rainfall
total reported (through 8:00 AM, Monday, August 20) was 18.17 inches
observed west of La Crescent in northern Houston County. An official
National Weather Service climate observer near Hokah in Houston County
reported a storm total of 16.27 inches. Of the 16.27 inches, 15.10 inches
fell within the observer's 24-hour observation cycle ending at 8:00 AM on
Sunday, August 19. This is the largest 24-hour rainfall total ever recorded
by an official National Weather Service reporting location in Minnesota. The
previous Minnesota record was 10.84 inches, measured at Fort Ripley in Crow
Wing County on July 22, 1972. The deluge produced flooding tied to seven
fatalities. Major flood damage occurred in many southeastern Minnesota
communities. Hundreds of homes and businesses were impacted. Reports of
stream flooding, urban flooding, mud slides, and road closures were numerous
throughout southern Minnesota. The combination of huge rainfall totals and a
very large geographic extent, make this episode one of the most significant
rainfall events in Minnesota's climate history. A six-inch rainfall total
for a given location in this region over a 24-hour period is said to be a
"100-year" (1% probability) storm. The area receiving six or more inches
during a 24-hour period in the midst of this torrent encompassed thousands
of square miles. Other heavy rainfall events during this decade of
comparable magnitude and spatial coverage include extraordinary rainfalls in
northwestern Minnesota on June 9-10, 2002, and in southern Minnesota on
September 14-15, 2004.
(see: http://climate.umn.edu/doc/journal/flash_floods/ff070820.htm
, http://climate.umn.edu/doc/journal/24hour_rain_record.htm
, http://climate.umn.edu/pdf/flash_flood/ff20020610.pdf ,
http://climate.umn.edu/pdf/flash_flood/ff20040915.pdf
)
- rainfall during the heart of the summer (the twelve-week period from
June 5 through August 28) totaled less than six inches in large sections of
central and northern Minnesota. In these areas, rainfall totals for the
period were five or more inches short of the historical average. When
compared with historical rainfall totals for the same twelve-week time
frame, 2007 values rank at or below the 5th percentile (one year in twenty
occurrence) for many counties. In a few areas, the June 5 - August 28
rainfall totals are near all-time record low values. The timing of the dry
weather is unfortunate. The period from May through September is
historically the wettest time of the year in Minnesota. Long-term average
rainfall rates during this time interval are around one inch per week. Very
dry weather, occurring during a time of year when ample rain is typical,
leads to the rapid intensification of drought. The lack of precipitation,
along with very high evaporation rates, created deteriorating crop
conditions, lower stream flows and lake levels, and increased wildfire
danger.
(see: http://climate.umn.edu/doc/journal/drought_situation_report_2007_070830.htm#mid_summer
)
- monthly mean temperatures for August 2007 were within two degrees
either side of the historical average. Extreme values for August ranged from
a high of 100 degrees at Wild River State Park (Chisago County) on the 10th,
to a low of 28 degrees at Embarrass (St. Louis County) on August
30.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp )
WHERE WE STAND NOW
- growing
season rainfall totals (April 1 - early September) are less than ten inches
in many central Minnesota counties and in Minnesota's Arrowhead region. In
these areas, seasonal rainfall totals have deviated negatively from
historical averages by more than four inches. This is roughly the equivalent
of missing all of June's normal rainfall. When compared with other seasonal
rainfall totals-to-date in the historical database, this year's rainfall for
the growing season ranks near the 10th percentile (one year in ten
occurrence) in many of the drought-stricken counties. In a demonstration of
the state's size and climate variability, rainfall totals in portions of
northwestern and southeastern Minnesota are well above historical averages
for the April 1 to present time frame. Because of the extraordinary August
rains, and despite a very dry June and July, sections of Fillmore, Winona,
and Houston counties are near or above all-time seasonal rainfall records,
with totals topping 30 inches since April 1st.
(see: http://climate.umn.edu/doc/weekmap.asp )
- the U. S.
Drought Monitor released on August 28 places Minnesota's Arrowhead region
and portions of central Minnesota in the "Extreme Drought" category. Much of
the rest of the northern two-thirds of Minnesota falls in the "Severe
Drought" or "Moderate Drought" designation. Most of northwestern Minnesota
is described as being "Abnormally Dry". Substantial August rains led to the
elimination of drought designations in the southern three tiers of Minnesota
counties. The drought situation in the northern one third of Minnesota is
the result of the lingering impacts of a very dry 2006, a snow-sparse
2006-2007 winter, and dry 2007 mid-summer weather. The drought situation in
the central third of Minnesota is due to an extremely dry 2007 growing
season. The U. S. Drought Monitor index is a blend of science and
subjectivity where intensity categories are based on several
indicators.
(see: http://climate.umn.edu/doc/journal/drought_situation_report_2007_070830.htm
, http://www.drought.unl.edu/dm/monitor.html )
- the
U.S. Geological Survey reports that stream discharge values in roughly 30%
of Minnesota's rivers and streams rank below the 25th percentile when
compared with historical data for this time of year. Flow rates in many
north central, northeastern, central, and east central Minnesota watersheds
fall below the 10th percentile for the date. Mississippi River flow
conditions remain very low along the upper reaches of the river. Mississippi
River discharge near Anoka is at roughly the same flow rate as it was during
the 2006 drought, but significantly above the all-time record low for the
date set in 1934.
(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
, http://mn.water.usgs.gov/durationHydrographs/05288500.html
)
- water levels are very low on many Minnesota lakes, exposing
shoreline, and in some cases, making water access difficult. Anecdotal
reports indicate that many lakes in northern, central and east central
Minnesota are a foot or more below average levels for the date. The Lake
Superior water level is near an all-time low for the date and the mean
monthly value will likely be declared as the all-time August low when
statistics are finalized.
(see: http://www.lre.usace.army.mil/_kd/Items/actions.cfm?action=Show&item_id=3886&destination=ShowItem
, http://www.dnr.state.mn.us/lakefind/ )
- the
Minnesota Agricultural Statistics Service reports that as of August 31,
topsoil moisture across nearly 40% of Minnesota's landscape was "Short" or
"Very Short". This is a substantial improvement from the conditions reported
in early August when nearly 85% of the state reported less than adequate
soil moisture conditions. 45% of Minnesota's corn acreage is considered to
be in "Good" or "Excellent" condition. This is up from 25% in early August.
A federal agricultural disaster was declared on August 7 for 24 Minnesota
counties suffering from drought. Farmers and ranchers in an additional 32
adjacent counties are also eligible for drought recovery
assistance.
(see: http://www.nass.usda.gov/Statistics_by_State/Minnesota/Publications/Crop_Progress_&_Condition/index.asp
, http://www.governor.state.mn.us/mediacenter/pressreleases/PROD008255.html
)
- the DNR Division of Forestry classifies current wildfire danger as
"High" or "Very High" across all of the northern one half of Minnesota.
"Moderate" fire danger exists from St. Cloud and the Twin Cities westward to
the South Dakota border. The southern one quarter of the state is depicted
in the "Low" danger category. Burning restrictions are in place in many
northern Minnesota counties.
(see: http://www.dnr.state.mn.us/forestry/fire/ )
FUTURE PROSPECTS
- the
September precipitation outlook from the Climate Prediction Center indicates
no significant tendencies away from climatological probabilities across
Minnesota. September precipitation normals range from near two inches in far
western Minnesota to around three and one half inches in eastern sections of
the state.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/30day
, http://climate.umn.edu/img/normals/precip/precip_norm_09.htm
)
- the September temperature outlook indicates no significant tendencies
away from climatological probabilities across Minnesota. Normal September
high temperatures are in the mid-70's to start the month, dropping to the
low to mid-60's by month's end. Normal lows are in the mid-50's early in the
month, falling to around 40 by late September.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/30day
, http://climate.umn.edu/img/normals/temp_norm_adj/temp_norm_adj_09.htm
)
- the 90-day precipitation outlook for September through November
indicates no significant tendencies away from climatological probabilities
across Minnesota. The September through November temperature projection
tilts towards above-normal conditions in all Minnesota counties.
(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/ )
- until drought
conditions improve in the Upper Mississippi River basin, the National
Weather Service will routinely produce low flow projections for the
Mississippi River near Anoka.
(see: http://www.crh.noaa.gov/crnews/display_story.php?wfo=ncrfc&storyid=9487&source=0
)
NOTES FROM THE AUTHOR
- the Minnesota Drought Task
Force continues to share information among the many entities monitoring and
responding to the 2006-2007 drought situation. Facilitated by the DNR
Division of Waters, this information sharing involves meetings, e-mail
distributions, and Web postings.
NOTES FROM AROUND THE STATE
- none
UPCOMING DATES OF NOTE
- September 20: National
Weather Service releases 30/90 day temperature and precipitation
outlooks
- October 18: 15th Annual Kuehnast Lecture
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://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.lre.usace.army.mil - Detroit District,
US Army Corps of Engineers
http://www.governor.state.mn.us
- State of Minnesota, Governor's Office
http://www.nass.usda.gov - USDA,
National Agricultural Statistics Service
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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