Ridiculously Resilient Ridge Rides Rough, Hangs Tough
March 26, 2014
Last weekend weather forecasters were marveling wide-eyed about a potentially unheard-of storm caused by two colliding weather systems that could wallop the entire Northeast with extremely low temperatures and feet of snow. The collision is occurring further out into the Atlantic Ocean as of today, sparing much of the nation, but it will still slap Cape Cod, Boston and eastern Maine, as well as eastern Canada.
So were the forecasters using made-up language—an issue of late, with weather services pasting names on every snow flurry and windy day? Nope, Rex and the bomb are legit meteorological terms.
A “bomb” is when the atmospheric pressure in a weather system drops by more than 24 millibars in 24 hours. For perspective, a typical pressure over the Northeast coast might be around 1,012 millibars, but it doesn’t take much of a drop to intensify a storm. The lowest pressures in the biggest hurricanes on Earth, such as Sandy, reach down to the 940s. So a 24 millibar drop is a lot, and when it happens in less than 24 hours, meteorologists get excited, because that’s rare.
In this case, the storm was fixing to be a Nor’easter—a low-pressure center off the Northeastern coast that circulates counterclockwise, sending winds inland from the Atlantic. So the dynamic duo was termed a Nor’easter bomb. The pressure was forecast to drop to the 980s or even 960s. Whether or not it gets that low, the drop in pressure is steep and confined, which causes strong winds, perhaps greater than 60 mph for the Cape and Maine.
Why did all this happen? The moisture came north in a system from the Gulf of Mexico, but the cold was created by—yep, the Rex block. That term describes an enormous pressure center that can get stuck in place. In this case, that place was over Alaska and the upper West Coast, which forced the jet stream to take a deep dive from the Arctic over the east-central U.S. When that system collided with the moist one from the Gulf, the two combined and began spinning, dropping the pressure inside and pulling up the moisture, turning it into snow. If you want more details about Rex, see a nice blog from last week by Eric Holthaus, a meteorologist who writes for Slate.
This latest bomb is just one more example of the jet stream acting weird, as our climate changes. And as Holthaus notes, although the Northeast is cold, the rest of the planet is not. Average global temperatures are expected to be higher than normal in the next few weeks, he says.
Despite the official start of spring, lingering effects of the winter season will cause planting delays this year.
While the South will be right on schedule weather-wise for prime planting with looming frost concerns, delays will become more and more likely with every mile heading north.
Coming off a frigid, snow-filled winter for areas from the Great Lakes to the Ohio Valley and Northeast, spring will shape up to be mostly cool and wet.
“Damp soil leftover from winter, melting snow and lagging temperatures mean a lot of places are going to have a slow planting period across the Midwest, northern Plains and the Great Lakes,” AccuWeather Senior Meteorologist Dale Mohler said.
With corn and soybeans being the largest crops in the Midwest and Plains, which are planted typically in April and May, one of the most influential factors in when to plant is soil temperature.
“Soil temperatures must be warm enough to support whatever crop you are planting,” Mohler said. “For corn that’s 50 F or above and for soybeans it’s 54 F or above.”
After this year’s harsh winter with record-breaking cold and snow, meteorologists are concerned that because the ground is still frozen in the Ohio Valley and Upper Midwest, it will take longer for the frost to thaw out of the ground and as a result, keep soil temperatures lower longer.
In these areas, the ground is not expected to heat up quickly, as wetness in the early spring and summer is expected across the regions.
The NOAA Weather Prediction Center is calling it “an interesting late cold season weather pattern.” By this time next week, I’ll bet some people will be choosing slightly more colorful adjectives.
The forecast shows a “Rex Block”—named after the first meteorologist to crack this particular pattern—currently forming off the West Coast. Blocking patterns are pretty much what they sound like: quasi-stable arrangement of high and low pressure centers that join forces to gum up the works of the atmosphere, freezing in place—and in some cases, amplifying—the weather du jour. In this case, winter.
Here’s what’s happening: High pressure over Alaska—part of the Rex Block—is forcing the jet stream from Siberia up and over the North Pole. That’s opening the flood gates for extremely cold air to spill southward out of the Arctic and in through the cracks in your bedroom window. A stable low pressure over the Pacific—the other part of the Rex Block—is acting like an anchor to keep the whole thing in place.
The upcoming pattern is a twist on the “ridiculously resilient ridge” that recently plagued North America for months, plunging California into historic drought. In addition to locking the East into (at least) another week of winter, Rex Blocks in the past have been known for their ability to ignite hot and dry Santa Ana winds. Should the pattern drift farther south, that could turn drought-stricken California into a playground of wildfires. Thankfully, that scenario isn’t likely this time around.
However, blocking patterns like this one are also known for their fickle behavior. They could stay in place for three days or 13 days (or more). The most we know right now is that, back East, winter is going nowhere fast.
Reposting: Jennifer Francis and Jeff Masters on Jet Stream, arctic ice, and “stuck” weather patterns.