Meteorologists with the National Weather Service (NWS) are urging some New Yorkers to postpone their travel this weekend as heavy snow moves into the area.

The NWS has been monitoring the possibility of lake effect snow in parts of New York this weekend, and the Buffalo office issued a winter storm warning earlier this week. On Wednesday afternoon, forecasters upgraded the watch to a lake effect snow warning for this weekend for Wyoming, Chautauqua, Cattaraugus and southern Erie counties, as well as the eastern Lake Ontario region.

“Heavy lake snowfall is expected. The most persistent lake snowfall is likely to produce several feet of snow over the weekend,” the warning said. “The highest accumulations will occur near the Tug Hill plateau. Snowfall rates are likely to exceed 5 cm per hour at times.”

Once the snowfall rate exceeds 2 inches per hour, snowplows have a difficult time clearing roads, said NWS meteorologist David Thomas Newsweekmeaning roads will quickly become buried if the snow falls this fast or faster. This could lead to extremely dangerous driving conditions or roads could be temporarily closed in some locations, although it is too early to say which roads may be affected.

“Travel will be very difficult and at times almost impossible. The dangerous conditions will certainly impact the Friday evening commute,” the warning reads. “With lake effect snow, weather can vary from locally heavy bands of snow with severely reduced visibility to dry conditions just a few kilometers away. Be prepared for rapid changes in weather, visibility and road conditions.”

The safest course of action is to postpone travel until after the storm or leave before it arrives.

“If you must travel, drive with extreme caution. Leave plenty of space between you and the motorist in front of you and allow extra time to reach your destination,” the warning says. “Avoid sudden braking or acceleration and be particularly careful on slopes or when turning.”

The lake effect snow warning goes into effect on Friday at 7 a.m. local time and lasts until 7 a.m. Monday. Poor driving conditions could impact Thanksgiving travelers heading home or Black Friday shoppers.

The warning comes as nearly 80 million Americans nationwide are expected to travel for the Thanksgiving holiday.

Elsewhere in New York, a winter storm warning issued by the Albany office warned of heavy snowfall of 7 inches or more that began falling Wednesday evening and continued into Thursday night. The snow could make roads difficult for last-minute travelers.

“Roads, particularly bridges and overpasses, are likely to become slippery and dangerous. Plan for slippery road conditions,” the station said. “The dangerous conditions could impact travel around the Thanksgiving holiday.”