Potentially life-threatening cold had the region in its grip Monday, one of the 10 coldest days on record for a Jan. 21 in Philadelphia, dating to 1874, according to the National Weather Service.

The high for the day was just 19 degrees, after a morning low of 10, with wind chills as low as 10 below zero during the day. It wasn’t quite Jan. 21, 1985 — when the high was 8 and the low 6 below zero — but Monday decidedly qualified as bone-chilling.

But Tuesday could feel like a breath of spring, with temperatures making a run possibly all the way to near 30. And on Wednesday, highs in the 40s could be accompanied by rain.

The deep freeze Monday affected mass transit, with SEPTA reporting in the morning that service on the Cynwyd Regional Rail Line was suspended for a time due to switch problems and that trains on the Market-Frankford Line all ran as locals.

SEPTA also announced special schedule for the Paoli/Thorndale Line, affecting some trains to Bryn Mawr and express trains, and later reported delays of up to 30 minutes due to a broken rail. PATCO canceled two trains Monday morning.

Philadelphia city officials had declared a code blue on Sunday, which opens all available beds in the city’s shelter system and sends 24-hour outreach teams to find people who are homeless and get them inside. Anyone who sees someone in need of shelter is asked to call the city’s homeless outreach hotline at 215-232-1984.

Officials also advised pet owners to not to let their animals outside too long.

Up in Bucks County, self-avowed storm chaser Ray Leichner posted on his Twitter feed a steamy video of what happens when boiling water is tossed into air when temperatures are near the single digits.

The Philadelphia region in the meantime caught a break over the weekend, when the snowstorm initially feared to hit the area instead tracked 20 to 30 miles north, dumping snow north of the Lehigh Valley.