MINNEAPOLIS (WCCO) – Residents in more than 50 Minnesota counties are encouraged to keep cool and drink plenty of fluids if they’re outside Thursday afternoon, when heat indexes are expected to soar to 115 degrees.

The National Weather Service has issued an excessive heat warning for much of the state. The only parts not affected are northwestern and northern Minnesota.

The warning will remain in effect until Friday evening, but officials say the most dangerous heat will occur Thursday, when temperatures will rise well into the 90s and dew points will be in the sopping low 80s.

Related: Extreme Heat Resources

The combination of high humidity and summer heat increases the risk of heat-related illnesses, such as heat stroke and heat exhaustion. Officials encourage those spending time outside to take frequent breaks, drink plenty of water, wear light clothing, and schedule strenuous activity to the morning or evening hours.

(credit: CBS/Climate Central)

(credit: CBS/Climate Central)

In Minneapolis, there are several places around the city that are designated as cooling centers. These are movie theaters, malls, libraries and Salvation Army locations. In St. Paul, city officials say such cooling areas are also available, and city pools will be open longer than usual.

Also in effect in the Twin Cities metro is an air pollution advisory, which goes from 11 a.m. to 9 pm. The combination of sun, heat and light winds increase the amount of ground-level ozone, officials say, and it can affect those with respiratory and cardiovascular problems.

The weekend looks to bring some relief from the heat, as dew points will drop. Still, the highs will be in the 80s, and Saturday night could bring severe storms.