We're all about to freeze to death at the hands of an angry Alaskan sea bomb! Or, that's what it sounds like when you scroll through Twitter, anyway. What is this "bomb" everyone is talking about? Just how cold will it get and for how long? That question and more, answered below.

What's going on?

Let's go back a few days. The western Pacific saw a pretty strong typhoon earlier this week, named Super Typhoon Nuri (pictured above). The storm reached the equivalent of category five status as it stayed east of land; the fact that it didn't make landfall anywhere is why you didn't hear about it unless you're a hardcore weather geek.

As previously explained on The Vane (1, 2), many tropical cyclones eventually undergo a transition late in their life cycle from a tropical cyclone to an extratropical cyclone. Extratropical cyclones are the common low pressure systems that we see almost every day in North America—they create cold and warm fronts, and they're responsible for most of the interesting weather that occurs over the continental United States.

While tropical cyclones derive their energy from intense thunderstorms that forms around the storm's eye, extratropical cyclones strengthen by tapping into strong winds on certain sides of the jet stream.

Nuri is experiencing its extratropical transition as it approaches a very strong streak within the jet stream, allowing the storm to further intensify into a monster. The latest run of the GFS (American) model shows the storm's minimum pressure bottoming out at 929 millibars, which is what one would typically see in a category five hurricane.

The monster-formerly-known-as-Nuri will produce winds well in excess of hurricane force, along with waves 50 or more feet (!) high, as it spins in the Bering Sea.

Is this that "meteorological bomb" I've heard about?

Yes. A "bomb" in weather terms refers to a process called "bombogenesis," or the explosive intensification of a low pressure system over a short period of time. Bombogenesis occurs when an extratropical cyclone's minimum pressure drops 24 millibars in 24 hours. If a storm's minimum pressure drops from 980 millibars to 956 millibars over the period of one day, it underwent bombogenesis—it bombed out, or was a bomb, as they like to say.

This particular system deepened from 990 millibars last night to 962 millibars this morning, and the pressure will continue to drop through tomorrow.

Since we're all sensitive to hype, let's get this out of the way: calling a storm a bomb isn't really hype if A) it fits the definition, and B) the article or newscast goes out of its way to define what the term means for viewers. Just as the polar vortex is an actual meteorological phenomenon, bombogenesis is a real thing that has the potential to be taken out of context.

What does this have to do with our weather in the U.S.?

This storm will set off a chain reaction in the jet stream, as the Capital Weather Gang characterizes it, that allows a deep trough to dig through the United States. When the jet stream dips south during the cold months, it can allow cold Arctic air to spill south into Canada and the United States.

Over the next week, a series of low pressure systems over Canada will work together to help drag down this cold air from the north. An intense area of high pressure will build in thanks to the cold air, locking it in place for an extended period of time.

The cold weather will begin on Monday in the far north, with the chill working its way south through the week. The cold front should pass through the eastern states on Wednesday and Thursday.

Of course it's cold, stupid. It's November. No big deal, right?

Models are forecasting high temperatures 10 to 20 degrees below normal for this time of the year. November has a reputation for getting cold, sure, but it's still a shock to the system for many that highs won't climb out of the 30s or 40s for an extended period of time. Highs in Chicago, for instance, could sit in the low- to mid-30s from Wednesday through Sunday and possibly longer than that.

For a more extreme example, this Sunday could be the last time Minneapolis sees the north side of freezing for a week or longer. Of course, the record low maximum (coldest high temperature) in the month of November in Minneapolis is 4°F above zero set in 1985, so highs not budging out of the upper-20s or low-30s for a week or longer is a cakewalk. It's all relative.

In any event, if you live east of the Rockies and away from the Gulf Coast, expect a prolonged period of relatively cold temperatures. It'll feel like winter. It's unusual for this time of the year, but it's been worse before.

Is this the polar vortex?


Why is there so much coverage of this storm?

It's an interesting story and people are always interested in unusual and extreme weather. Plus, after the polar vortex panic last winter, people are going to be super sensitive to cold snaps this year. Measured articles talking about the facts are beneficial to the conversation—people are hyping and panicking enough, as it is.

Am I really going to die?

Some day, yes, but unless you get hypothermia, use a grill or generator inside and pump your home full of carbon monoxide, or slide off the road because of ice, probably not.

[Images: Peanuts Online via YouTube, CIMSS, NWS EDD]

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