The mercurial and often strange winter of 2017-18 is about to take a turn for the almost unbelievable. Philadelphia’s high on Tuesday, 72, beat the 70 set in 1939; by comparison, the temperature Tuesday afternoon in Los Angeles was struggling to reach 60.
Wednesday won’t be quite the same in Philadelphia. It could be warmer, with highs perhaps in the mid-70s.
Other records that have stood since 1930 will be threatened throughout the region, routing any remnants of the weekend snowfall. These temperatures would be normal three months from now.
That’s because the atmosphere is behaving like it thinks it’s six months from now, said Paul Pastelok, the long-range forecast specialist at AccuWeather Inc. Just don’t get used to it; in the last several weeks nothing has had staying power.
The impresario of the warm spell is a so-called Bermuda high-pressure system centered off the Atlantic coast, which is bearing mild air on winds from the south, part of the clockwise circulation around its center. Air descends in areas of high pressure, discouraging storms and favoring warmth.
“This is supposed to happen in August and September,” Pastelok said. Boston hit a record 70 on Tuesday, and flood watches were up for most of Vermont and Upstate New York as the surge of warmth goes to town on the considerable snowpack.
As is often the case, mirror-opposite conditions are bedeviling the West, where snow fell in Denver on Monday afternoon with a temperature barely in the teens. In Los Angeles, highs on Tuesday and Wednesday won’t get past the low 60s, about 10 degrees below normal.
All this evidently is being driven by conditions in the tropical Pacific. La Niña, a widespread cooling of surface waters over the tropics, has persisted. For now it is working in tandem with a circulation pattern over the North Pacific to drive up temperatures in the East, Pastelok said.
But the weather this winter has shown all the stability of the stock market, consistent only in its abnormality. Since Dec. 1, only 10 days have had readings within a degree of normal.
Since a two-week cold spell ended in early January, atmospheric traffic has been brisk, which is why temperatures have been so jumpy, and why up to 6 inches of snow fell in the region on the day after the temperature reached 60.
Systems have been moving because there are no “blocks” to stop them, Pastelok said.
Blocks are areas of high pressure that build in a given area and keep systems from moving west to east. Blocks can last a week or longer, and are responsible for prolonged warm and cold spells. And they can retard the movement of storms, like the weekend’s quick-hitter.
When the flow is swift, meteorologists call it “progressive.” Recently, it has been more like fast-forward.
But we’re not done with snow around here. For the first time since December, a block appears to be developing in the North Atlantic that could lead to a return of cold in the East perhaps by early next week, along with storm potential.
“The best shot for snow is the first two weeks in March,” Pastelok said.
Before that happens, records will need updating.
Tuesday’s forecast high of 72 in Philadelphia would beat the nearly 80-year-old record of 70 set in 1939. Records set in 1939 are endangered in Atlantic City, Wilmington, Allentown, Reading, and the Poconos. On Wednesday, Philadelphia is almost certain to beat the 72 registered in 1930, along with setting a new mark for a record-high minimum temperature.
The latest monthly outlook from the Climate Prediction Center sees above-normal temperatures for March, and that forecast will be updated next week. Worth noting is that the updated February outlook, posted on Jan. 31, saw below-normal temperatures for the month.
This month is on track to become the eighth-warmest February on record, according to Walt Drag, meteorologist at the National Weather Service office in Mount Holly, with an average temperature of about 41, better than 5 degrees above normal.
One thing is absolutely certain: This will be the warmest February since last year, which was the warmest on record.