RICHMOND, Va. — Governors in Virginia and North Carolina have declared emergencies ahead of an anticipated intense winter storm that has millions in its path. Virginia Gov. Ralph Northam announced Saturday he'd declared an emergency to help state agencies prepare for a storm that's expected to hit hard the southern part of the state. North Carolina Gov. Roy Cooper issued his declaration Friday and said impacts of the storm would vary across the state. Forecasters are calling for up to 18 inches of snow in the mountains and possible flooding at the coast. "Snow may be beautiful but it can also be treacherous and I urge North Carolinians to take this storm seriously and get ready for it now," Cooper said in a statement Friday. The National Weather Service said Saturday the heaviest snow is expected in northwest North Carolina and southern Virginia. The weather service said a "prolonged period of snow is expected" to begin as early as Saturday evening and lasting until Monday. Winter storm warnings are in effect for areas in northeastern Georgia, northwestern South Carolina, western North Carolina and southwest Virginia, the weather service said. Winter storm watches and winter weather advisories are also in effect for sections of the southern Plains across the Mid-South as well as parts of northern South Carolina and southwest Virginia. The National Weather Service Weather Prediction Center said heavy rainfall was affecting southeastern Texas and Louisiana, and that northwest Texas and central Oklahoma were seeing "wintry precipitation." CBS News As of late Saturday morning, more than 10,000 customers were without power in Texas. Rainfall caused street flooding and spilled over bayous in Southeast Texas. The Harris County Flood Control District said flooding might have impacted homes along Halls Bayou. The county said several bayous are near the top of their banks. They said some creeks and bayous have overtopped their banks. The National Weather Service forecasts that rain will be ending Saturday morning across Southeast Texas. The agency reports some areas in Harris County saw upward of 6 inches of rainfall from Friday morning to Saturday morning. It says other areas saw 3 to 5 inches of rainfall. The airlines have travel waivers in place. As of Saturday morning, 531 flights were cancelled and there were over 700 delays within, into or out of the U.S., according to the flight-tracking service FlightAware. © 2018 CBS Interactive Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.