It looks like a scene from the movie “The Day After Tomorrow”: sprawling cyclones prowling the north Atlantic and Pacific oceans simultaneously. Each are producing winds at or near hurricane-force, plummeting air pressures, and could whip up waves as tall as an apartment building.
But unlike in the apocryphal and seemingly apocalyptic Hollywood film, these two storms are real, part of Earth’s natural mechanism for distributing heat and moisture.
In the Atlantic, an unusually potent storm is raging between Greenland and the United Kingdom. Wind gusts of 80 to 90 mph and wave heights at times nearing 100 feet are possible on the open ocean beneath the behemoth storm’s core. Sand was even reported on the runway at Egilsstaðir Airport in Iceland.
The storm underwent a familiar process of rapid intensification known as “bombogenesis.” A storm becomes a bomb when its central air pressure falls 24 millibars or more within 24 hours. This low, southwest of Iceland, has dropped from 1,005 millibars on Wednesday to a staggering 929 millibars at present. At its peak strengthening, that nose-dive was near twice the rate needed to qualify as bombogenesis.
The sprawling low will eventually merge with another developing bomb cyclone on its southern flank, potentially becoming one of the strongest storms on record in the North Atlantic.
The joint entity will pass north of Scotland and the U.K., sideswiping them along the way. Named Dennis by government meteorological officials in the United Kingdom and Ireland, the storm will bring up to 3 inches of rain in southwest England. A few spots could top 4 inches in Wales. Wind gusts in excess of 60 mph are possible in coastal Ireland as well.
It’s the second week in a row bomb cyclones have exploded in the Atlantic.
In the Pacific, yet another bomb cyclone is stirring up the seas as it brings 60 mph gusts to the Aleutian chain before lashing southeast Alaska with gusts up to 75 mph. Several feet of snow are possible in the mountains surrounding Denali.
A ripping upper-level jet stream is energizing these tempests. In the Pacific, winds at commercial flight level are zipping west to east at more than 170 mph, while in the Atlantic, a 270 mph jet is possible.
It’s also possible that a few aircraft surfing the jet stream on the trans-Atlantic route will reach ground speeds of 830 mph. The best shot of that is Friday night into Saturday east of Newfoundland. Aircraft that depart from New York on Friday night could potentially arrive in London in record time. (The current subsonic record, set just last week, stands at 4 hours 56 minutes.)
The jet stream in the northern hemisphere is strongest in the wintertime. That’s because temperature contrasts are maximized between the winter-chilled polar regions and the still-balmy warmth of the tropics. The strength of the jet stream is directly related to north-to-south temperature differences. In the summertime, the addition of daylight in the Arctic adds heating, allowing the pole-to-equator temperature gradient to slacken and the jet stream to relax some.
During active stretches with favorable jet stream and temperature patterns during winter, it’s not uncommon to generate storm after storm. The northwest Pacific is known as a factory for this, while the North Atlantic is also an effective manufacturer of its own. Two or three more storms are likely in the next seven to 10 days in the Pacific.
In the summertime, you’re unlikely to get a giant windstorm, nor’easter, or days-long barrage of heavy precipitation and dark skies. That’s because the life-giving jet stream retreats well to the north, dragging the storms with it. Hurricanes can form farther south, but through a completely different process.