Thunderstorms spawned numerous tornadoes across the Plains Friday, some of which turned violent and destructive in Nebraska and Iowa.

Why it matters: The storms, forecast to be spread across several states, reserved their fury for just two, in an outbreak without a recent precedent.

• The National Weather Service issued at least four tornado emergencies, its most dire type of tornado alert, indicating an imminent threat of potentially catastrophic damage in a populated area.

Threat level: Powerful tornadoes hit near Lincoln and Omaha, Nebraska Friday afternoon.

• The storms are part of a larger, slow-moving weather system that is forecast to bring severe weather, including potentially strong tornadoes, to a vast region from the Texas border with Mexico into the Midwest on Saturday.
• On Friday, social media footage from storm chasers showed wide tornadoes striking communities on the western side of Omaha, Neb., causing major damage.

The latest: Elkhorn, situated about 15 miles west of the center of Omaha, was particularly hard hit, though no fatalities were reported.

• "Many houses are flattened and many houses also have significant damage," Omaha Fire Chief Kathy Bossman said, according to KOLN-TV.

Between the lines: At one point, Omaha had a tornado warning for downtown, a tornado on the ground to its north and another tornado on the ground just to the southeast of the city, all viewed by both weather spotters and Doppler radar.

• One tornado touched down near Omaha's Eppley Airport, with footage shot by a passenger on a jet waiting on the tarmac.
• It was an unusual clustering of tornadic thunderstorms in a relatively small region, owing to the ideal conditions for these storms to form.
• The tornado that hit Elkhorn and then moved to the northeast showed debris lofted to about 25,000 feet above the surface along with radar-observed surface winds consistent with a tornado rated above an EF-4 or greater tornado.

Zoom in: Damaging tornadoes also struck Iowa, including Minden and Harlan.

• "You are in a life-threatening situation. Flying debris may be deadly to those caught without shelter," read the tornado emergency language for Harlan, Iowa, issued at 5:49pm CT.
• "Mobile homes will be destroyed. Considerable damage to homes, businesses, and vehicles is likely and complete destruction is possible."
• The NWS forecast office in Omaha issued at least 40 tornado warnings during this event, as storms erupted throughout its forecast region.

What's next: The National Weather Service notes heightened concern on Saturday for a "widespread" outbreak of severe weather, potentially including powerful tornadoes, across an area much larger than was seen Friday night.

• The severe thunderstorm outbreak will affect tens of millions and multiple cities, including Oklahoma City, Wichita, Des Moines, Kansas City, Dallas and Omaha all the way to Madison, Wis.
• Moisture-rich air flowing northward from the warmer-than-average Gulf of Mexico, combined with slow-moving thunderstorms could yield significant flash flooding as well, particularly in parts of Oklahoma on Saturday.

Go deeper: Severe storms, some with "strong tornadoes," threaten more than 60 million