DANVILLE — Most folks make preparations when a blizzard is headed this way, but not necessarily when there’s a heat wave in the summer.

Area residents, however, are being urged to make preparations now for what is shaping up to be an extended heat wave next week.

The National Weather Service upgraded its excessive heat watch Friday afternoon to an excessive heat warning, which will be in effect from 7 a.m. Sunday to 7 p.m. Friday.

An excessive heat warning is issued when heat index values are expected to reach between 105 and 115 degrees.

Jeff Frame, a professor of meteorology at the University of Illinois, Urbana-Champaign, explained what factors are in play to create this heat wave of exceptionally long duration.

“We’re going to see a ridge of high pressure build over the central plains and the Midwest,” he said. “That will cause a big bubble of warm air in the middle and upper levels of the atmosphere.”

That “bubble” will prohibit cloud formation, so “expect to see a good amount of sunshine,” he said. The bubble also will block any cold front from moving into the region for several days.

“At the surface, we’re going to see persistent winds from the south,” Frame said, adding that the southerly breeze will usher in humidity.

Making matters worse is the corn that is in the height of growing season locally.

“Water evaporates from the corn into the atmosphere, creating more humidity in this area,” he said.

The dew point is the number to watch during this heat wave, Frame said. It will indicate how comfortable it will feel outdoors.

“The higher the dew point is, the more moist it is,” he said. “When it gets above 70, it gets uncomfortable.”

The forecast for next week calls for temperatures in the mid-90s with dew points in the upper 70s, which will combine to create heat index values between 105 and 115 degrees.

Frame said folks also should not expect any relief during the overnight hours next week when temperatures will dip only into the mid- to upper 70s with high dew points.

“It’s going to feel like the air is hanging. It’s going to be oppressive,” he said.

The heat wave also is going to be dangerous.

L. Randall-Hayes, an emergency room physician at Provena United Samaritans Medical Center in Danville, said the elderly, infants and children especially need to take precautions in the heat.

To keep one’s cool during the heat wave, Dr. Randall-Hayes recommends:

• Wear cool, airy-type clothing
• Drink lots of water
• Intermittently go indoors and cool off

She also suggested that family members and neighbors check on the elderly.

“Check to see if they have air conditioning and check for weakness and lethargy,” Randall-Hayes said.

“If they don’t act like they normally do, they need to see a doctor,” she said.

Young, healthy people in high-risk occupations, such as construction, also need to be careful in the heat.

“They need to take 5- to 10-minute cooling breaks every hour, drink lots of water and douse themselves with water,” she said.

“Muscle aches, nausea and vomiting are signs that the heat is affecting them,” she said.

Although no official cooling stations had been designated in Danville as of Friday afternoon, people who need to cool off during the heat wave are welcome to stop by public places such as Provena United Samaritans Medical Center, CRIS Healthy-Aging Center, Danville Public Library and the David S. Palmer Arena.

“Our public areas are open all the time, and we have a cafeteria, too, if they need to come in and cool off,” said Gretchen Wesner, director of marketing at Provena.

Sheri Stevens at CRIS said, “Our center is always considered a cooling center.”

Keep cool

The American Heart Association outlines these symptoms of heat exhaustion: headache; heavy sweating; cold, moist skin, chills; dizziness or fainting; a weak and rapid pulse; muscle cramps; fast, shallow breathing; nausea, vomiting or both.

If a person experiences these symptoms, move to a cooler place, stop exercising and cool down immediately by dousing yourself with cold water and rehydrating. The person also may need to seek medical attention.

Symptoms of heat stroke: warm, dry skin with no sweating; strong and rapid pulse; confusion and/or unconsciousness; high fever; throbbing headaches; nausea, vomiting or both.

If a person experiences these symptoms, seek medical attention right away.