Weather whiplash. Temperature roller coaster. Choose whichever overused expression you like, they all apply. So far this February has been one wild ride.
The month started with a low of 10 degrees in Boston. Just four days later, temperatures soared to a record-tying 65 degrees.
The big question—why the dramatic changes? The answer is multifaceted.
The Cold Extreme: The Polar Vortex
At the start of the month, temperatures plunged to 50 below in the Midwest. Here in New England, we got a taste of that cold in the early days of February. But only a taste.
The cold came straight from the Arctic, thanks to the Polar Vortex.
The Polar Vortex is a ribbon of fast moving air high in the atmosphere. It usually flows in a circular motion around the North Pole, basically keeping the cold near the surface locked up.
When the air high above the Arctic warms up, the winds weaken. That allows the low-level cold to spill out towards the United States, hence all the talk of the Polar Vortex across the country.
So essentially we can thank our cold end of the extreme scale to warming over the Arctic that sent brutally cold air diving south.
The Warm Extreme: Storm Track
Once the Polar Vortex retreated back to the north, we briefly saw seasonable temperatures around Greater Boston. Remember that ‘normal’ for this time of year is a high temperature in the upper 30s.
But by Monday and Tuesday of this week, we were off to the races with temperatures in the 60s.
For that, we can thank a westward storm track, something that has been in place since last fall.
Remember how the Autumn was a record wet one? That’s because the jet stream was configured in a way that brought storm after storm through New England, each loaded with moisture from the south.
That same westward storm track has continued into winter.
When storms pass to the west of Boston, they bring winds out of the south. That’s a warm direction. Air from the Gulf of Mexico or Southeastern United States surges in.
If we had a storm track that brought storms to the south and east of Boston, storms would arrive with a northeast wind in Boston. That’s why we refer to those storms as Nor’Easters, which this time of year can bring cold and big snows to the city.
So, essentially each time a storm, be it big or small, comes at us this year we are popping into this warm sector as it passes by. Hence the frequent, but quick, bursts of warmth.
New Few Days
We’re going to see another example of this Thursday night into Friday, as a weak storm passes through New England, again to the west of Boston. Temperatures will briefly surge into the 50s before dropping again this weekend.
There is a lot of research to suggest that these types of extreme shifts in temperature will only become more common in the future as the world continues to warm overall.
Of course extremes have always happened—in fact, ‘normal’ is just an average of extremes—but the frequency of these shifts is on the rise.