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Severe weather and record rains

Turbulent Start to September

September 3-4 (Wed-Thu) brought severe weather to many parts of central Minnesota.  There were at least 20 reports of large hail, ranging in size from 0.5 inch diameter to 2.75 inch diameter, with piles of hailstones reported near Waverly, MN.  In addition there were many reports of damaging winds, ranging from 50 mph to over 84 mph.  Around Todd and Wadena Counties many trees were blown down, and some building roofs damaged by winds. 

Several observers reported over 1 inch of rainfall, with much of it coming in less than one hour.  In addition there were some new daily record amounts reported at several climate stations.  On September 3rd, St Cloud reported a new daily record with 2.94 inches.  Cook in St Louis County reported a record 1.12 inches on that same day, as did Dawson with 1.13 inches.  More new daily records of rainfall were reported on September 4th, including 4.26" at Onamia, 3.64" at Little Falls, 3.52" at Pelican Rapids, 3.35" at New York Mills, 2.35" at Mora, 2.22" at Aitkin, 2.12" at Rush City, 2.11" at Ottertail, 2.06" at Sandstone, 1.50" at Milaca, and 1.44" at Forest Lake.  The rainfall of 4.26 inches at Onamia represents the largest single day rainfall in September since 9.48 inches was measured on September 23, 2010 at Amboy. Many other locations reported large amounts of rainfall but lacked historical records for comparison.  For example, Askov (Pine County) reported 3.80 inches, a huge daily quantity for the month of September, but they have no climate record for historical context.

As a result of the heavy rainfalls the National Weather Service had to issue a number of flash flood warnings, and many roads and highways were closed for a time, including portions of Hwy 210.  Fortunately it looks like showers will not return to the area until next Monday or Tuesday, thus providing an opportunity to dry out.

High dew points and a heat burst

September 3-4 brought very high dew points to many parts of the state, with readings of 70 degrees F or higher.  Montevideo reported a 73 degrees F dew point on the 3rd and 77 degrees F on the 4th, while the University of Minnesota-St Paul Campus reported a dew point of 75 degrees F on the 3rd and 79 degrees F on the 4th of September.  These are near record values for the date.  On Thursday (Sept 4th) the high dew points pushed the Heat Index readings into the 90s F by afternoon for many southern Minnesota communities, making for a very uncomfortable day.

In addition early in the morning hours on September 4th, decaying thunderstorms over western portions of Minnesota and eastern portions of South Dakota brought an overnight "heat burst" for some areas. This is produced by compressional heating of sinking air from aloft, and is usually accompanied by higher wind gusts.  The graphic below (provided by SD State Climatologist Dr. Dennis Todey) shows the short term temperature spike at Brookings, SD  between 4:00 and 5:00 am. In Marshall, MN the air temperature at 5:00 am was 66 degrees, but rose to 72 degrees F by 6:30 am, while at Slayton, the air temperature was 66 degrees F at 4:00 am and rose to 72 degrees F by 4:30 am.

Lack of 90 F temperatures

Greg Spoden, Minnesota State Climatologist reported this week that MSP has reported only 2 days with temperatures of 90 degrees F or higher during 2014.  This is rare in the historical record.  Having 2 or less days with 90 F temperatures has only happened 8 other years back to 1873.  Morris, Albert Lea, Duluth, and Rochester have not reported a single day with 90 degrees F this year, also quite rare in their historical records.  Cooling Degree Days (CDD) used to measure the need for air conditioning during the summer were around 25 percent less than normal this summer in many places.

Weekly Weather potpourri:

A recent drought briefing from Brad Rippey of the USDA World Agricultural Outlook Board offers these major points:
-During the four-week period ending on September 2, 2014, contiguous U.S. drought coverage decreased slightly to 32.78% -- a 1.16 percentage point drop.  Coverage reached its year-to-date peak of 40.06% on May 6, but subsequent rainfall across the nation’s mid-section and the Southwest has reduced drought’s overall imprint.  During August, statewide decreases in drought coverage of 10 to 20 percentage points were noted in Kansas (from 92 to 72% in drought), New Mexico (from 82 to 70%), and Kentucky (from 19 to 7%).
-Nevertheless, drought still covers a substantial portion of the central and southern Plains and the western U.S.  On September 2, the highest level of drought ­D4, or exceptional drought­ was noted in portions of California (58%), Nevada (12%), Texas (3%), and Oklahoma (2%).  California also led the nation with 82% coverage of extreme to exceptional drought (D3 to D4).

Hurricane Norbert in the Eastern Pacific Ocean was bringing heavy rains and high surf to Baja California this week.  Wind gusts were over 90 mph and sea wave heights exceeded 25 feet. By early next week clouds and rain from this storm may reach parts of the southwestern USA including southern California.

Environment Canada reported a snow storm in southern Alberta this week southwest of Calgary.  The snow made for some difficult driving conditions and comes earlier than normal in September.  The snow is not expected to last as temperatures will rebound into the 60s and 70s F over the coming weekend.

MPR listener question: 

I heard you report how extremely variable the August rainfall was around the state.  Did anybody set a record for wettest or driest month of August in Minnesota?


Good question.  The wettest places in the state from the NWS Cooperative Observer Network were Minnesota City (Winona County) with 8.59 inches (4th wettest August in their historical records), and Rushford (Fillmore County) with 7.95 inches (2nd wettest August in their historical records).  Other observers without lengthy climate records had large amounts of rainfall in August as well, like Onamia with 8.20 inches and Cannon Falls with 8.05 inches.  On the low end of the rainfall spectrum for August, Eveleth (St Louis County) reported their driest August in history with just 0.89 inches, and International Falls reported their 5th driest August in history with just 0.90 inches.

Twin Cities Almanac for September 5th:

The average MSP high temperature for this date is 77 degrees F (plus or minus 10 degrees F standard deviation), while the average low is 57 degrees F (plus or minus 8 degrees F standard deviation).
 Average dew point for September 5th is 55 degrees F, with a maximum of 78 degrees F in 1990 and a minimum of 31 degrees F in 1929.

 MSP Local Records for September 5th:

MSP weather records for this date include: highest daily maximum temperature of 98 degrees F in 1922; lowest daily maximum temperature of 57 degrees F in 1873; lowest daily minimum temperature is 36 degrees F in 1962; highest daily minimum temperature of 77 F in 1912; record precipitation of 2.57 inches in 1946; and there has been no snow on this date.

All-time state records for September 5th:

The state record high temperature for this date is 103 degrees F at Tracy (Lyon County) in 1922. The state record low temperature for this date is 23 degrees F at Park Rapids (Hubbard County) in 1885. State record precipitation for this date is 3.72 inches at Ely (St Louis County) in 1912 and at Austin (Mower County) in 1946; and no measurable snowfall has occurred on this date.

Past Weather Features:

September 5, 1885 brought a season-ending frost to northern parts of the state, especially the Red River Valley where temperatures fell into the mid to upper 20s F.  Ground frost was reported in southern counties as well with a temperature reading of only 34 degrees F at Albert Lea.

One of the strongest and longest September Heat Waves in state history occurred over September 1-8, 1922.  Day after day brought 90 F temperatures with little or no rainfall until the 8th.  Sixteen communities saw the mercury reach the century mark, and it was 96 degrees F as far north as Babbitt.  Following that warm start to the month some observers reported frost on the 11th which ended the growing season.

Strong thunderstorms brought heavy rains and street flooding to Rochester, Austin, and Grand Meadow over September 5-6, 1946.  Austin reported a total of 6.74 inches of rain, while Grand Meadow reported 4.37 inches.  The same storm system delivered a record amount to the Twin Cities of 2.57 inches.

A damaging frost occurred on September 5, 1962 before the corn and soybean crops had reached maturity.  This unusual early frost affected areas around Luverne, Waseca, Farmington, Theilman, and Montevideo. 

Severe thunderstorms with heavy rain visited the state over September 5-6, 2004.  Over 20 climate observers reported 3 or more inches of rainfall, and areas of northern Minnesota around Fergus Falls, Detroit Lakes, and Moorhead received over 4 inches.  This brought relief to many dry areas of the state, restoring some watersheds which had been running low.


Mostly sunny weekend with cooler than normal temperatures.  Increasing cloudiness on Monday with a chance for showers and thunderstorms into Tuesday and somewhat warmer temperatures.  Another chance for showers by Thursday next week followed by even cooler temperatures heading into next weekend.

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