Get out now while you still have the chance!

A blizzard warning has been issued for New York City and much of the tri-state area beginning at midnight Tuesday as Winter Storm Stella threatens to dump as much as 18 inches of snow.

Whiteout conditions are expected to make travel extremely dangerous and power outages are likely amid crippling wind gusts of 20 to 40 mph, according to AccuWeather senior meteorologist Tom Kines.

“Travel will be poor at best, if not impossible,” Kines told The Post on Monday. “If you have the option tomorrow of staying put, I would definitely recommend that. And if you try to fly by air tomorrow, forget it — not happening.”

The blizzard warning — which will be in effect for 24 hours — will cover New York City and Long Island as well as Fairfield, Westchester, Rockland, Bergen, Hudson, Essex, Union, Monmouth and Ocean counties.

Snow will begin around 3 a.m. and continue throughout Tuesday before tapering off in the evening, Kines said.

The city is expected to get at least a foot of snow and 16 to 18 inches could get dumped on western and northwestern areas of the city. Eastern Long Island could be spared with just 6 to 8 inches.

Temperatures will hover in the low 30s and drop into the lower 20s Tuesday night.

Gov. Andrew Cuomo activated the state Emergency Operations Center as of Monday night and directed state agencies to be on heightened alert.

“I encourage all New Yorkers in affected regions to plan ahead and avoid any unnecessary travel as the storm progresses,” Cuomo said in a statement, adding that commuters should expect road closures, delays and cancellations.

Service updates from Metro-North Railroad and the MTA were unavailable Monday morning, according to spokesman Aaron Donovan, who said Cuomo will be providing information later in the day.

New York City issued a hazardous travel advisory for Tuesday — expecting snowfall rates of up to 2 to 4 inches per hour Tuesday morning and afternoon, with strong wind gusts and temperatures in the upper 20s.

Alternate-side parking was also suspended Tuesday and Wednesday.

“We’re preparing for a significant storm on Tuesday, and New Yorkers should also prepare for snow and dangerous road conditions,” Mayor Bill de Blasio said in a statement.

“Besides the snow, it will be cold. We urge you to avoid unnecessary travel and help keep roads clear for sanitation crews and first responders,” he said.

The city’s Department of Sanitation is pre-deploying 689 salt spreaders across the five boroughs. PlowNYC will be activated and more than 1,600 plows will be dispatched when more than 2 inches of snow accumulates.

The department — which has 283,000 tons of salt available — will assign 2,400 workers per shift. Workers were to be assigned to 12-hour shifts beginning at 7 a.m. Monday.

A coastal flood advisory also will be in effect from 8 a.m. to noon Tuesday for lower New York Harbor, Newark Bay and portions of northeastern New Jersey.

The Port Authority of New York and New Jersey was installing hundreds of pieces of snow equipment at the three New York area airports.

Southwest Airlines warned of cancellations, delays and diversions until Wednesday. Delta Air Lines told travelers they could book alternative flights without fees, AFP reported.

Hundreds of flights were canceled ahead of the storm, according to the tracking service FlightAware.

Stella’s expected conditions are staggering — but not all that uncommon.

“We do get snow in March. The fact we’re getting snow shouldn’t be a surprise,” Kines said. “The fact that we’re getting a foot or more — yeah, that’s becoming less and less common.”

Though Stella may be colossal — covering the East Coast from Washington, DC, to Maine — she might not be a record-setter.

The biggest March snowstorm on the books for our area was in 1888, when 21 inches of snow fell between March 12 and 14, Kines said.

With Post wires