Call it the ghost of the polar vortex, the polar-vortex sequel or the polar vortex's revenge. Meteorological purists may tell you it's not a polar vortex at all.
However you choose to refer to the looming weather pattern, unseasonably chilly air is headed for parts of the northern and northeastern United States at the height of summer early next week.
Bearing a haunting resemblance to January's brutally cold weather pattern, a deep pool of cool air from the Gulf of Alaska will plunge into the Great Lakes early next week and then ooze toward the East Coast.
Of course, this is July, not January, so temperatures forecast to be roughly 10 to 30 degrees below average won't have quite the same effect.
But make no mistake, in parts of the Great Lakes and Upper Midwest getting dealt the chilliest air, hoodies and jeans will be required. Highs in this region could well get stuck in the 50s and 60s — especially where there is considerable cloud cover.
Wednesday morning's lows might drop into the 40s over a large part of the central United States. Remember, this is July!
The heart of the chilly air mass will probably just skirt the East Coast, but temperatures are likely to be about 10 degrees below normal. Highs could struggle to reach 80 in Washington on Tuesday and Wednesday, with widespread lows in the 50s (even 40s in the mountains).
Note that, as with any extended forecast, there is some uncertainty here. If the cool air mass loses some punch, highs might still reach 80 to 85 around the District of Columbia, with lows in the 60s rather than the 50s.
The pattern might last only a few days but will probably set some records, especially around the Plains and Great Lakes — where water temperatures are still depressed from the frigid winter in which ice remained on Lake Superior into June.
What's behind this unusual winter weather pattern primed for the dog days of summer? A lot of it is simply chance (randomness), but Weather Underground meteorologist Jeff Masters says Japan's typhoon Neoguri is playing a role in the pattern's evolving configuration:
"The large and powerful nature of this storm has set in motion a chain-reaction set of events that will dramatically alter the path of the jet stream and affect weather patterns across the entire Northern Hemisphere next week.
"Neoguri will cause an acceleration of the North Pacific jet stream, causing a large amount of warm, moist tropical air to push over the North Pacific. This will amplify a trough of low pressure over Alaska, causing a ripple effect in the jet stream over western North America, where a strong ridge of high pressure will develop, and over the Midwestern United States, where a strong trough of low pressure will form."
Most amazing about the pattern is not so much the forecast temperatures, but the uncanny similarities in the weather patterns over North America seen in both the heart of winter and heart of summer. All the same features apparent in January are on the map in mid-July: low pressure over the Aleutians, a large hot ridge over the western United States, the huge cold low or vortex over the Great Lakes, and then the ridge over northeastern Canada.
It's not at all clear what this means or what, if anything, it portends. Weather patterns cycling through a certain circulation regime can repeat (and we've seen this pattern multiple times since November and December), but with El Niño forecast to develop, the global configuration of weather systems is likely to change.
As news of this cool-air episode breaks, you might notice meteorologists bickering over whether this is a "polar vortex" event or not. For their part, several National Weather Service offices are using the term.
But Larry Cosgrove, an energy meteorologist, says that while the looming cool air mass is "admittedly impressive," calling it a polar vortex is hogwash.
"It's insane," Cosgrove wrote on his Facebook page. "Poor wording combined with misunderstanding of the term make a mockery out of synoptic meteorology."
Cosgrove's argument is that the air mass doesn't meet the "polar vortex" standard — its pressure isn't low enough and the air isn't sufficiently cold and truly Arctic in origin (i.e. not below freezing at 5,000 feet). "[On] TWO counts we fail to reach the standard for calling such an upper low a vortex," he said.
The middle road might be the best one: Call it a "poor man's polar vortex."