Storminess Continues:Strong thunderstorms moved over portions of northern and central Minnesota during the past week, especially on July 11-12 (Mon-Tue). Rainfall totals from 5-7 inches occurred over portions of 10 central Minnesota counties, causing widespread flash flooding. Tornadoes caused some damage to homes, businesses, and farms in Meeker and Stearns Counties. Large hail was reported in 4 Minnesota Counties, the largest, 2.5 inch diameter near Mora.
According to the Minnesota State Climatology Office the storm on July 11-12 was the largest mega-rain event since the Duluth flood of June 19-20, 2012. A mega-rain event is classified as a six-inch rainfall that covers at least a 1000 square miles, with a central core value of at least 8 inches. There have been only 13 such storms documented in Minnesota history, but 6 of these have occurred since 2002. You can read more about this weeks storms at the MN State Climatology Office.
The largest rainfall reported from the storm this week was 9.34 inches at Cloverton in Pine County. Several climate observers reported a new daily rainfall amount for July 11th, including:
7.51 Inches at Rice (Benton County)
6.38 inches at Brainerd airport (Crow Wing County)
6.36 inches at Bruno (Pine County)
5.50 inches at Moose Lake (Carlton County)
2.93 inches at Madison (Lac Qui Parle County)
2.63 inches at Saint Cloud (Stearns County)
2.27 inches at Duluth (St Louis County) tied record from 1914
2.00 inches at Wheaton (Traverse County)
With the large amount of rainfall, flood warnings were still being issued at the end of the week for parts of Pine, Aitkin, Kanabec, and Crow Wing Counties. Many areas of the state have already seen 5-7 inches of rainfall in July and the month is barely half over.
Weekly Weather Potpourri:According to a press release from NOAA this week, June of 2016 was the warmest of record for the contiguous 48 states since records began in 1895. It surpassed the record warmest June of 1933. Minnesota was warm in June, but only modestly, ranking 31st warmest in 122 years.
NOAA also recently released an assessment of billion dollar weather-related disasters so far this year across the USA. There have been eight. Dominated by flooding, wind, and hail events , most of the insured losses have been in the Southern Plains or Southeastern states so far. You can find an assessment at the NOAA web site.
An interesting paper this week from the University of Oxford examines the famous Heat Wave of August 2003 in Europe and how much of it might be attributed to anthropogenic causes. They even differentiate the death tolls in France and the United Kingdom based on anthropogenic factors.
MPR listener question:What is the average number of days with thunderstorms in Minnesota and how does this number compare with other states?
Answer:The average number of days with thunderstorms each year varies across Minnesota, from about 30 days in northern counties to over 40 days for those counties along the Iowa border. This is considerably more than west coast states and the northeastern states, but less than most southern states. The state with the largest number of annual thunderstorm days is Florida, where some central counties record 100 days with thunderstorms each year. This features is the result of convergence of the sea breezes coming off both the east and west coasts, which induces lift in the warm, humid air and development of cumulonimbus clouds. The second highest frequency of thunderstorm days is found in the Rocky Mountain Front Range through portions of Wyoming, Colorado, and New Mexico. In this region, topography plays an important role and helps produce 60-70 days with thunderstorms each year.
Twin Cities Almanac for July 15th:The average MSP high temperature for this date is 84 degrees F (plus or minus 7 degrees F standard deviation), while the average low is 65 degrees F (plus or minus 6 degrees F standard deviation).
MSP Local Records for July 15th:
MSP weather records for this date include: highest daily maximum temperature of 102 degrees F in 1988 and again in 1974; lowest daily maximum temperature of 63 degrees F in 1962; lowest daily minimum temperature is 49 degrees F in 1912; highest daily minimum temperature of 79 degrees F in 1988; record precipitation of 1.87 inches in 1907; and no snowfall has occurred on this date.
Average dew point for July 15th is 59 degrees F, with a maximum of 77 degrees F in 1988 and a minimum of 43 degrees F in 1920.
All-time state records for July 15th:The state record high temperature for this date is 112 degrees F at Beardsley (Big Stone County) in 1931. The state record low temperature for this date is 30 degrees F at Alborn (St Louis County) in 1930. State record precipitation for this date is 7.17 inches at New Ulm (Brown County) in 1916; and no measurable snowfall has occurred on this date.
Words of the Week: Sulfurous readingsThis terminology is intended to evoke an image of heat and humidity like that found in natural geothermal sulfur springs used at some health spas. Meteorologists may include such terminology in their forecast discussions, particularly when heat and humidity are expected to prevail for long periods of time, producing Heat Index values of 100 degrees F or greater. Though many people relish an exposure of several minutes to such conditions in a health spa, exposure to this type of outdoor climate for hours and days is not healthy for anybody.
Past Weather Features:Strong thunderstorms brought 2-5 inches of rain to many parts of southern Minnesota over July 14-15, 1916. In addition large hail ruined many crop fields in southern Minnesota.
On a statewide basis the hottest July 15th in history occurred in 1931. At least 35 Minnesota cities reported afternoon temperatures of 100F or higher. The temperature at Winona that day never dipped below 80F.
July 15, 1995 brought an end to a 3-day Heat Wave that caused widespread turkey losses in the state, as hundreds of thousands of birds died of heat stress. This was also the end of the lethal Chicago Heat Wave that killed over 600 people there.