I am someone who reflexively shirks the adaptation and rapid proliferation of new terminology, even if that terminology has existed in other circles for quite some time. This has been extremely common over the last 15-20 years in the weather community, from the Polar Vortex to a Bomb Cyclone to the Atmospheric River. I shirk because, to an item, when they hit the popular zeitgeist, and are uniformly misused.

I’m coming around on the usage of some of these terms though. I have a friend who works closely in science communication, and she has expressed an appreciation for terms like these, which can either clearly indicate what is going on for the lay person, in terms of impacts and importantly, how to prepare of these storms. When the Weather Service is using this terminology, it’s good, when Jimmy Fallon is using the terminology, it’s probably not good.

So with all that said, I head a national meteorologist describe the recent and deadly weather in the Pacific Northwest as a “double whammy” that included a Bomb Cyclone followed by an Atmospheric River. This is fine with me, as we have the expectation that a bomb cyclone will bring very strong winds, and an atmospheric river brings heavy rain. That’s what happened, that’s what residents of the area prepared for, and in the interest of being complete pedantic, was meteorologically misleading.

It wasn’t so much a double whammy as one really big whammy. First, let’s make sure we have a basic definition of what each are. An atmospheric river is a jet stream that flows from the Pacific Ocean to the west coast. In a bygone era, we may have called this the Pineapple Express for example, but the atmospheric river nomenclature is applied to any jet streak intersection with the west coast. The jet is always a conduit for moisture, but because of a semi permanent ridge off the California coast, doesn’t always intersect with the west coast, making it more remarkable.

A bomb cyclone is an area of low pressure (an extratropical cyclone) develops explosively, specifically by dropping an average of 1 mb an hour as the low pressure deepens. This doesn’t happen often, and when it does, in encourages very strong winds. Bomb cyclones are almost always developed over the sea, where friction doesn’t inhibit the development, which means winds also reach some pretty extraordinary velocities.

One important component to a bomb developing is a strong jet streak. Low pressure develops on the left side of a jet at th point the wind starts to decelerate, if you are following the course of the wind, particularly in trough environments. In fact, the jet is often interpreted at the surface as a cold frontal boundary, trailing the low pressure.

So an overwater cyclone develops with the help of a strong overwater jet streak. If the cyclone moves inland, it is very possible, even likely the jet will follow. At atmospheric river, in this parlance, is an ingredient in the development of a bomb cyclone. The bomb cyclone then moves inland, with the atmospheric river in close pursuit.

The terms make sense, and I don’t have a problem with their usage, but now there is a little bit of background for you.

It’s mid-November, and temperatures are getting cooler and days are getting shorter. Certainly, both are factors in making things a little depressing. The cold keeps us inside, and the lack of daylight makes things dark, quite literally.

But even in the daylight, it can often seem more grim. When it’s sunny, that usually means it’s colder in the morning, but another huge factor is the lower Lifting Condensation Level (LCL) that comes with winter. The LCL is level at which air lifted from the surface would reach the condensation point in the atmosphere. In practice, this is the height at which the bases of clouds form.

A given “parcel” of air will see temperatures drop at a known rate with height, based on established atmospheric physics. As we know with fog and clouds, moisture can only be retained in air to a certain temperature before it condenses. This is also why we have dew in the morning – that is when temperatures are coolest, and the air can’t hold the moisture any longer.

Cold air holds less moisture, and the atmosphere is colder in at all levels in the winter. As air at the surface is generally warmer than air aloft, it is prone to rising until it meets the LCL, at which point clouds start to form. Clouds are more likely in the cooler weather because the air can’t hold moisture, and the LCL is lower because the change in temperature from the surface to the point which the air can’t bear as much water is smaller, so those clouds are going to have low bases. There will be more clouds, and they will be lower to the ground. It’s dingy and claustrophobic, even in the day time.

But at least night comes earlier. At least spring is only 6 months away.