Heat alerts covered parts of 16 states early Wednesday — largely in central and southern parts of the United States — including a population of about 55 million from coast to coast.

Excessive-heat warnings are in effect for Oklahoma City, much of south-central and southwestern parts of that state and into northwestern Texas. The Weather Service warns of dangerously hot conditions, with heat indexes — a combination of heat and humidity — up to 110 or 115 forecast Wednesday afternoon.

“Working or exercising in direct sunlight will stress your body in about 15 minutes,” it wrote.

Farther south, Dallas and Waco in Texas, New Orleans, Gulfport, Miss., Valdosta, Ga., and Pensacola, Fla., are included in heat advisories, for heat indexes up to 105 or 110. Additional heat advisories are in place for Jacksonville, Fla., Savannah, Ga., Raleigh, N.C., and Philadelphia, where heat indexes of 105 and higher are anticipated.

In the West, Palm Springs and the Coachella Valley in California are also under excessive-heat warnings for temperatures likely to surpass 110 on Wednesday and Thursday.

Major Level 3 out of 4 heat risk, as forecast by the Weather Service, covers a large region Wednesday from the central Plains and Iowa southward through much of the southern Plains to the Mississippi Valley, then across a swath of the South. Sizable chunks of Oklahoma, Arkansas, Georgia and Florida are included in extreme Level 4 out of 4 heat risk.

As a cooler batch of air passes the U.S. Northeast late in the week and this weekend, trailing cold fronts will push the highest heat southward at times. The heat also looks to surge hard in between, so even if cooler air shows up, it is likely to be short lived.

Where the heat is most intense Wednesday

A brief bout of high-end heat overtakes the Mid-Atlantic on Wednesday, with readings 10 to 15 degrees above normal and widespread highs in the mid-90s to around 100. Heat indexes are also set to reach 100 to 105 or so.

Parts of the South will also witness temperatures rising near 100 on Wednesday, particularly in Georgia and South Carolina. Southwestern Oklahoma and northwestern Texas could see widespread highs of 105-plus. These temperatures are a good 10 to 15 degrees above average in much of both regions, including around Oklahoma City and Dallas.

Highs nearing 90 are expected as far north as the border with Canada from Washington state through Montana, along with widespread high temperatures that hot or hotter in the Great Basin. Deserts in the Southwest rise to about 110 to 120.

Where hot spots are ahead

Much of Oklahoma and a big chunk of Texas should spend the rest of the workweek dealing with highs of 100 to 105. Breaks with weak cold fronts passing by are generally expected to last only a day or two and remain north of the Red River.

Dallas could see 100 or higher through the week, with temperatures rising next week. It’s likely back into the 100s early next week across Oklahoma, after a brief weekend cool-down.

Across the Desert Southwest, highs around 110 will be common in Phoenix to southeastern California — maybe a few degrees lower around Las Vegas. Death Valley should pass 120 on several occasions. The forecast is for 123 there next Tuesday. By that point, 105 or close is forecast through the Central Valley of the Golden State.

Near and east of the Mississippi River, heat focuses on the South, with mid-90s or higher common. The Midwest and Mid-Atlantic will probably see occasional pulses of higher heat amid cooler conditions than recently.

What to know about records this week

Record highs were set or tied Tuesday in St. Louis (103), Albany, Ga. (103), Birmingham, Ala. (101) and Tallahassee (101), among other locations.

On Monday, records were logged from parts of Nebraska, then running southeast to Arkansas and eastward across the South. Monday records include Salina, Kan. (106), Scottsbluff, Neb. (104), Baton Rouge (100) and Wilmington, N.C. (99).

Wednesday’s focus will be across the Mid-Atlantic, then perhaps sporadically into the Appalachians and South. Temperatures approaching 100 could threaten or topple daily maximums from Charlottesville into the D.C. and Baltimore areas. Highs around 100 may also test a few records from Alabama to the Carolinas.

Although it stays hot into the weekend, especially across the South, record-high potential may be minimized for a time. Very intense heat will still occur. For instance, Amarillo in the Texas Panhandle is forecast to reach 107 on Friday, which would flirt with a record for the date of 108 in 1998.

A (too soon) look at Independence Day and the rest of July

As the hottest month of the year on average, July will doubtless be toasty. The Weather Service is forecasting a hotter than normal one, especially in the East and parts of the interior West.

While July should open with cooler-than-average air in much of the northeastern quadrant of the contiguous United States, that’s destined to be short lived as warmer-than-normal conditions probably move north again through the Independence Day period.

On and around the Fourth, the resident heat dome seems likely to be stretching from the Desert Southwest to the Southeast. Hotter-than-average conditions are currently a decent bet for most places other than maybe the northern tier of the Lower 48. A chance for storms riding the northern periphery of the heat dome will need monitoring for states from the northern Plains to the Northeast and Mid-Atlantic.