Heat advisory in effect Thursday; more storms possible through weekend


Morning thunderstorms will make way for heat and humidity Thursday afternoon, with temperatures rising into the lower 90s in the Twin Cities.

Showers and thunderstorms will exit to the east Thursday morning as a warm front pushes through. A hot and muggy air mass will move in, pushing afternoon heat indices up to 90 to 105 degrees (map below), the National Weather Service says. Additional storms are possible Thursday afternoon and evening, especially in southeastern Minnesota.

The high heat index has prompted the weather service to issue a heat advisory from 12 p.m. to 8 p.m., the hot conditions may lead to a heightened risk of heat-related stress and illness, especially with the young and elderly.

People outside, like those attending the first day of the Minnesota State Fair, should remember to wear light-weight, loose-fitting clothing and drink plenty of water – coolers are allowed at the State Fair, which can help keep your drinks cold.

This steamy tropical air mass will increase occasional thunderstorm chances for the first few days of the fair, Paul Huttner wrote on the MPR News Updraft blog, saying Friday will be the best time for a dry day at the big event.

Early morning storms

Thunderstorms rolled through central and southern Minnesota Thursday morning, dumping heavy rain and gusting winds throughout the area.

Here's a look at some of the rainfall totals from the storm:

Wind gusts between 35 and 40 mph were reported with the storms west of Rochester, the National Weather Service says, and there were reports of some wind damage.

A second round of storms is expected to move through southeastern Minnesota late Thursday afternoon, the National Weather Service says. The storms could produce localized flooding, large hail and damaging winds. Additional storms are also possible Friday and through the weekend, with temperatures forecasted to be in the 80s.

Huttner says late night thunderstorms, like the ones that moved through Minnesota early Thursday, are more common towards the end of August as the nights get longer. He explains why:

"Late August warm fronts in Minnesota ... often bubble north at night, and fire so called 'nocturnal' thunderstorms. These storms like to develop as the nights get longer. The upper atmosphere has more time to cool off after our earlier late August sunsets. Advancing warm air near ground level cuts underneath cooler air above, increasing instability."

The result is thunderstorms as the sun starts to rise, Huttner says.

Urban heat islands

Do cities often feel hotter than neighboring rural areas? That's because most of the time they are – and Minneapolis is among the cities with the most intense "urban heat islands," according to a report.

An urban heat island is a phrase used to describe a metropolitan area that is significantly warmer than its surrounding rural areas. This can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, along with heat-related illness and mortality, the Environmental Protection Agency says.

Climate Central, an independent organization that reports on the changing climate, says Minneapolis is among the cities where the temperature difference between the urban and rural areas is the greatest.

The organization took the average daily temperature differences between urban and rural areas over the past decade to come up with the 10 most intense summer urban heat islands – Minneapolis ranks No. 9 with a temperature difference of 4.3 degrees.

Climate Central notes Minneapolis can get up to 22 degrees hotter than surrounding rural areas.

The top 10:

  • Las Vegas – 7.3 degrees
  • Albuquerque – 5.9 degrees
  • Denver – 4.9 degrees
  • Portland – 4.8 degrees
  • Louisville – 4.8 degrees
  • Washington, D.C. – 4.7 degrees
  • Kansas City – 4.6 degrees
  • Columbus – 4.4 degrees
  • Minneapolis – 4.3 degrees
  • Seattle – 4.1 degrees

Climate Central put together this interactive on the rankings, which explains more about each city's temperature changes:

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