Stormy Weekend: August 7-8, 2009

rainfall map

It was a rainy weekend over parts of central and southern Minnesota. There were three rounds of rain. Below is a synopsis of the most stormy and rainy weekend of the year (so far) in the Twin Cities.

Round one, during the morning and early afternoon of Friday, August 7.

The first rain event was a thick band of showers and thunderstorms that moved from west to east across much of central and southern Minnesota during the morning and early afternoon hours on Friday. This band dropped anywhere from a half to over an inch of rain. The rain ended by early afternoon in the Twin Cities with some gusty southeast winds. In general this was a good soaking rain.

Round two, late Friday, August 7 to early morning hours of Saturday August 8.

The heaviest rain fell with strong thunderstorms that developed near a warm front draped over southern Minnesota around 10pm Friday, August 7. These storms moved tot he north east and formed an east to west line from Montevideo to the southern half of the Twin Cities. The storms then began drifting east and dropped torrential rains. This caused street flooding in spots including Shakopee. The highest 24 hour total was 6.20 inches in Chaska. This included 1.34 inches that fell in the first wave during the day on Friday, and the 4.86 inches for the late Friday into early Saturday. Other thunderstorms developed in the early morning hours on Saturday to the northwest of the Twin Cities and dumped heavy rain at St. Cloud. The heavy rains were most welcome to areas that were under a moderate or severe drought.

Round three, Saturday night, August 8

For the first time this summer, truly tropical air reached the Twin Cities. The dew point temperature slowly climbed throughout the afternoon on Saturday and was 75 degrees by 8pm, the highest so far for the Twin Cities in 2009. For a time it looked like the risk of severe weather had passed by the Twin Cities. Then at 7pm an tiny cluster of storms developed in Wright County. These storms rapidly intensified and moved east and north east. An EF1 tornado was reported in Minnetrista and moved northeast through Orono and Long Lake and ended over the southwest portion of Plymouth. By 11pm the storms had moved across the St. Croix River into Wisconsin.

For more information contact: climate@umn.edu