Happily wrapped in fleece and drinking a hot beverage, you suddenly realize it's that time - the season of the shivery swim for charity.
And the region's biggest, the Maryland State Police Polar Bear Plunge at Sandy Point State Park in Annapolis, is coming in two weeks.
It's a rite of passage for some, a dare for many and a good deed for all. The quick foray into the frigid waters of the Chesapeake Bay benefits Special Olympics, and thousands now wade in.
So, how can one stay healthy and safe during this short but extremely cold act of momentary insanity?
From the medical community and event organizers, here are the quick "don'ts": drink and dive; stay in the water too long; wear too many clothes; barrel over your fellow plungers; ignore instructions.
Some "dos": Strip down to a bathing suit just before dip time; keep your head above water; wear shoes to protect your feet; get into warm clothes right after you get out of the water.
And, of course, organizers say, have fun.
"It really has grown from a small group of idiosyncratic individuals to a large family event that raises significant money for Special Olympics," said Kevin Gerold, a doctor who has plunged multiple times and helps provide medical care at the event.
"Over the years, it's been a really safe event," said Gerold, an assistant professor in the Johns Hopkins University's department of anesthesiology and critical care and the tactical medical director for the Maryland State Police.
At this year's event, the 12th annual, there will be more emergency personnel on land, in the water and on boats looking out for the participants, expected to exceed the 7,400 who plunged last year. There also will be more heated tents for changing clothes and more medical tents.
Some plungers have received minor cuts in past years from ice in the water, and there have been problems with people stepping on each other. Last year, there also was a spinal-cord injury suffered by someone who dove into shallow water. It was the worst and only serious injury Gerold could recall.
Organizers continue to discourage diving, and even ask participants to refrain from completely submerging themselves in the cold water because it's harder for emergency personnel to keep watch.
Also this year, alcohol has been banned on the beach to control what's become tailgate-like festivities. Organizers have other entertainment for plungers and the thousands who come to watch. That entertainment includes a pig race.
More than organizers' fear of plungers suffering hypothermia is their worry that people may be trampled. So this year the event has been split into two plunges, at noon and 3 p.m., said Greg Shipley, communications director for the state police and an event co-founder.
"Frankly, it was getting a little crowded on the beach," he said. "We've made some changes to reduce what minimal risk there was."
Participants have to raise a minimum of $50, and registration is taking place online, at plungemd.com. There also will be registration on the day of the plunge. There's no age limit, but those younger than 18 need a waiver signed by a parent.
Last year, the event raised $2.4 million, and organizers say they hope to bring in $3 million this year. Shipley says he believes it's the largest of the many plunges across the country for Special Olympics and for other groups that now host cold-water dips. The state police also host a plunge in February at Wisp Resort in Garrett County.
Shipley, who has plunged for the past 11 years, said his strategy is to get in and get out.
"It happens very quickly," he said. "Once you're back to your towel, you'll be surprised at how much more fun it is than you think it will be. It's not a terrible thing, but an extreme amount of fun."
That is not to say that hypothermia is not an issue.
Water is dangerous even in the 70-degree range. The bay water temperature this time of year is in the 40s. The Mayo Clinic says people can tolerate water temperatures of 32.5 degrees to 40 degrees for 15 to 30 minutes before they become exhausted or unconscious. They will die in 30 to 90 minutes.
Water that is 40 to 50 degrees will cause exhaustion or unconsciousness in 30 to 60 minutes and death in one to three hours.
But most people stay in the bay water only long enough to get their picture taken, generally a minute or less, said Tyler Cymet, head of the family medicine section at Sinai Hospital and an assistant professor in the Johns Hopkins University's School of Medicine.
Cymet, who is not affiliated with the plunge but who has treated a toe injured at the event, said he wouldn't recommend it for little kids, seniors and those with a heart condition. Cold water can make the heart skip beats or have a lot of extra beats.
He also warned against drinking before plunging, saying alcohol impairs people's judgment and gives them a false sense of warmth.
"There isn't much danger from staying in the water for five minutes," he said. "If you're turning colors, it's not good and a clue you need to get out."
Some people do seem hardier than others, he said.
Cymet said a patient told him about one of the most severe of these type of swims - put on by the South Pole 300 Club. It's a tradition for newcomers to Antarctica.
At midwinter, when the temperature dips below minus-100 degrees, participants sit in a sauna until the temperature reaches 200 degrees. Then they run outside naked except for shoes and maybe a scarf and head to the geographic South Pole for the shock of the 300-degree change. Many don't make it the whole way without frostbite and damaged lungs.
Although it's hard to predict the weather weeks away, conditions won't be nearly that severe at Sandy Point. Former Gov. Robert L. Ehrlich Jr. is a regular Polar Bear Plunger who is readying for this year, longtime aide Henry Falwell said. "When Governor Ehrlich sees how so many Special Olympic athletes benefit from the event, the last thing on his mind is the cold," Falwell said.
Cymet, who is a native of Florida, said he doesn't understand why anyone would volunteer to get into water colder than 91 degrees, the human comfort zone.
"Personally, I prefer the hot-tub plunges," he said. "[They're] much more comfortable and probably could raise just as much money."
TAKE THE PLUNGE
Maryland State Police Polar Bear Plunge
Jan. 26 at noon and 3 p.m.
Sandy Point State Park
Participants take a dip in the Chesapeake Bay to benefit Special Olympics
Maryland State Police Deep Creek Dunk
Feb. 23 at 2 p.m.
Wisp Resort in Garrett County
Participants take a dunk in Deep Creek Lake to benefit Special Olympics
Strip down to a bathing suit. Wet clothes will hold the cold water on your skin.
Wear shoes to protect your feet in the water.
Get in and out. Forty-degree water can cause exhaustion and unconsciousness in as little as 15 minutes.
Don't completely submerge yourself. The cold water may be too shocking.
Those with heart problems should consult their doctors before plunging.
Don't dive in because the water could be too shallow.
Try not to run over fellow plungers on the way in or out of the water, and keep a lookout for those in distress.
Change into warm clothes as soon as possible after you leave the water.