VALLEY, Neb. -- Safety alerts related to extreme heat are expiring at the end of Friday night, but that doesn't mean conditions will be significantly cooler immediately.

A total of 38 Nebraska counties are in excessive heat warnings, while another 31 are in heat advisories, all of which are expiring by 9:00 p.m. CT/8:00 p.m. MT.

Excessive heat warnings are in effect for the following counties: Adams, Burt, Butler, Cass, Clay, Colfax, Cuming, Dakota, Dixon, Dodge, Douglas, Fillmore, Franklin, Gage, Hall, Hamilton, Jefferson, Johnson, Lancaster, Merrick, Nance, Nemaha, Nuckolls, Otoe, Pawnee, Platte, Polk, Richardson, Saline, Sarpy, Saunders, Seward, Stanton, Thayer, Thurston, Washington Webster, York

Heat advisories are in effect for the following counties: Antelope, Blaine, Boone, Boyd, Buffalo, Cedar, Custer, Dawson, Frontier, Furnas, Garfield, Gosper, Greeley, Harlan, Hayes, Holt, Howard, Kearney, Knox, Lincoln, Logan, Loup, Madison, Phelps, Pierce, Red Willow, Rock, Sherman, Valley, Wayne, Wheeler

Heat index values have been as high as 115 degrees in some parts of Nebraska. Overnight temperatures could remain high, but extreme temperatures are expected to taper off by Saturday morning. Temperatures are expected to drop below 90 degrees in most places during the weekend, with the possibility of some thunderstorms in various regions.