The temperature should come close to 100 degrees Sunday in the Tri-Cities, according to the National Weather Service.
That's about 10 degrees above normal for this time of year, and the mercury is expected to keep climbing. Highs should hit 105 or 106 degrees Monday and Tuesday in the Tri-Cities.
There will be little relief at night. Lows are expected to be in the range of 69 to 72 degrees Sunday through Wednesday nights. Normally lows average about 60 degrees in July in the Tri-Cities.
Temperatures should cool a little later in the week, but remain unseasonably warm with a high of about 100 degrees Wednesday and 98 degrees for the Fourth of July.
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By the end of the week temperatures should be closer to normal with highs in the low 90s and lows of about 60 degrees.
The Tri-Cities could see a repeat of Saturday's thunderstorms on Monday. But while thunderstorms are possible, the chance is low, according to the weather service.
A series of thunderstorms rolled across the Mid-Columbia Saturday, putting on spectacular lightning displays but also sparking fires. However, rain aided firefighters in quickly extinguishing most of them.
A lightning strike midmorning is believed responsible for a blackened swath of land across the east side of Badger Mountain. Hiking on the mountain was stopped temporarily as about 30 acres burned.
Benton Fire District 1 also was called to a two-acre fire on Badger Canyon Road, and a haystack burned in the Horn Rapids area of Richland.
The thunderstorm also brought hail to some areas of the Mid-Columbia, including north of Prosser. Herald reader Harriet Mercer took pictures of three-quarter inch hail stones that fell just before 8 a.m.
The weather service's storm spotters also reported hail ranging in size from nickels to quarters five miles east of Sunnyside and one mile south of Prosser.
With temperatures hitting the triple digits, public agencies are issuing recommendations to stay cool and avoid heat stress.
Excessive heat has caused more deaths in recent years than all other weather events, according to the American Red Cross.
It recommends postponing outdoor activities, slowing down and avoiding strenuous exercise during the hottest part of the day. If you are working outside in excessive heats, use a buddy system and take frequent breaks, the Red Cross advises.
Check on those vulnerable to the heat, such as the elderly, if they do not have air conditioning. Libraries, theaters and malls can offer some air conditioned relief during the hottest parts of the day.
At the first signs of heat illness -- dizziness, nausea, headaches or muscle cramps -- move to a cooler location, rest for a few minutes and slowly drink a cool beverage, says the Washington State Department of Health. If you do not feel better, seek medical help.
Extreme temperature changes also are hard on the elderly and small children, according to the Department of Health. A cool shower immediately after coming in from hot temperatures can give them hypothermia.
It also warns that a sunburn can slow the skin's ability to cool itself.
Pets also are vulnerable in the heat. They need shade and plenty of cool water if left outside, but they may need to be brought indoors during the hottest hours of the day. They should not be left in a parked vehicle.