Winter Weather Update III
There's a New Sheriff In Town
I feel like it is time for another weather update. So let’s do a quick review, and then take a look at the next few weeks.
My most recent discussion focused on what I anticipated would be — and did become — an “amplified” weather pattern in the broad scale. That basically means there was opportunity for the northern jet stream to dip deep into the Lower 48, bringing the mother lode of cold air with it, along with multiple opportunities for snow. This certainly happened, culminating with the folks in Louisiana experiencing record, debilitating snowfall. We also got some snow in the Mid-Atlantic, although not as much as could materialize in such a pattern. The reason for the relatively modest precipitation is the depth and magnitude of the intrusion of cold air. In basic terms, the cold air pushed all the storms to the south and east. As a result, Louisiana saw much more snow than did, say, southeast Pennsylvania. Multiple storms developed well off of the eastern seaboard, of concern to no one but fishermen and shipping interests. I thought one or two of those might form a little closer to the coast than they ultimately did. C’est la vie. As I wrote before, the specifics of where storms will develop on the eastern flank of these jet stream anomalies are very difficult to predict. But the storms did develop.
All of that is now changing — thus this post. The graphic below tells the general story.
Gone is that drunken, misbehaving northern jet stream, which is now the model of sobriety. There’s a new sheriff in town, and he’s keeping the good guys and the bad guys on separate sides of town. The northern jet has retreated to its more normal neighborhood in the northern plains states and southern Canadian provinces. For now, there are no signals for it to get any serious ideas about reamplifying. I’m sure it will happen again this season, just probably not in the next couple weeks.
But don’t you sulk, snow bunnies! These more sober and boring patterns can still produce abundant precipitation — potentially good news for those hoping for more drought relief on the east coast. “How’s that?” you ask. Well, let’s think about that and take a quick look.
If you consider the situation in the graphic above, you have a large body of cold air to the north and a large body of warm air to the south. Think of it as World War I — two deeply entrenched sides, with nothing really happening in the big picture, but plenty of action where the two sides interact. In the atmosphere, that interaction often takes the form of “overrunning” events. Warm air is lighter than cold air. If it is forced to interact (for reasons that need not concern us), moist warm air rises over the cold air, where it necessarily cools and can no longer hold the moisture — which then falls through the cold air and lands on your car. The form it takes when it lands depends on the thickness of that cold layer of air, ranging from rain to freezing rain to sleet to graupel to wet snow to the powder favored by very crazy people with death wishes. Predicting exactly what will fall is the business of people who predict weather for a living. Since, understandably, nobody is willing to pay me for what I do in the weather realm, I leave those near-term predictions for those other lucky people, blessed with the brains and the good looks required to stand in front of a green screen. If I stood in front of a green screen, a troll convention would erupt. And nobody needs that.
Anyway…
So let’s look at what might happen over time when a meterological no man’s land forms, as it is about to do from sea to shining sea. Here’s a good example, this valid for 2/5/25:
Ya see what I mean? A disturbance on the warm side is making some trouble. And when that warm air strays a little too far north, flakes can fall. Am I predicting precipitation for Wednesday? Well, actually, yes. But per above, I have no idea what form it will take to start. It all depends on where that line between the warm and cold air sets up. That said, it does seem like the warm air will win on Thursday, turning whatever frozen precip that might fall to rain by 2/6.
Let’s look ahead a few more days, to Saturday evening (2/8) into 2/9 (a.k.a., Super Bowl Sunday):
Again, you can see that mischief is brewing along the demarcation line between the two atmospheric armies, except this time the armies look more serious and better equipped — another frozen precip to rain event, as things look now. But, again, much will change, and I leave the details as an exercise for the glamour geeks who get paid to analyze such things.
And let’s look ahead further still, to the 2/12 time frame:
Similar deal, but notice the subtle change — the northern jet is trying to assert itself again just a liiiitttle bit in the midwest. This changes the overrunning equation enough that the cold air is likely to win the battle, and the event will likely be mostly snow in some places. You can see this redevelop the next day, into what would be a decent Mid-Atlantic snowstorm:
Of course, the odds of all that actually happening as described are low. I am simply trying to illustrate that the atmospheric pattern is shifting, and we are now in a persistent regime of overrunning events — any one of which could bring much-needed precipitation to a broad swath of the country at mid latitudes.
For winter precip lovers, the moral of the story is that the weather last month was a high-risk, high-return type of situation. With the dynamics of a highly energetic northern jet intruding deep into the lower 48, big storms were likely to develop (ask Louisiana). But those same dynamics can also sweep the serious action well out to sea (ask Pennsylvania). In contrast, the new pattern is more likely to produce events that tend to be smaller (though not always!), but more frequent, and with higher probability. In sum, as we get into the new week, those east of the Mississippi can expect some sort of precipitation event every few days for the next couple weeks. And, boy, we can use it…
Thanks for reading.