Matt Lanza

Northeast snow this weekend, a big, complex storm next week, and what’s the deal with the polar vortex?

One-sentence summary

Today’s post goes in deep on this weekend’s winter storm in the East, previews next week’s potentially major storm in the Eastern half of the U.S., and discusses what stratospheric warming and the polar vortex actually means.

This weekend’s storm: Snow chances highest north and west of I-95

Back on Tuesday, we laid out the groundwork for this weekend’s storm. There’s been a lot of hype surrounding this, and we tried to cut through some of it to show that the highest odds of significant snow would be north and west of the I-95 corridor, with the exception of New England. So what has changed since?

Not a whole lot. I love these IQR plots from Tomer Burg’s site. In simple terms they’re showing you the uncertainty within the modeling. When it comes to storms like this, you have to use ensemble guidance. Recall, the ensembles are 30 to 50 runs of a model with some tweaks each time, so you get a more realistic spread of possibilities. Often, when you’re watching the TV news or you see a loud post on social media, they’re showing you deterministic guidance, or what we often call the operational models. That’s the whole GFS vs. Euro thing you hear about sometimes.

But back to Tomer’s plot. On Tuesday, I noted “the European ensemble shows a number of storm tracks on either side of the Benchmark with several rather close to the coast. This means uncertainty is high.” Then, as a meteorologist, I looked to see what our cold air supply looked like, and it’s meager. All this to say that it made sense to think that snow would stay mostly north and west of the I-95 corridor, with the exception of New England, where the storm track may favor more snow. That’s a lengthy introduction to say, here we are today:

Most ensemble members are at or northwest of the 40/70 Benchmark, and with a lack of much cold air supply, this probably means the heaviest snow will focus inland of the major I-95 cities. (Tomer Burg)

Since Tuesday, uncertainty has dropped, and we’re seeing a coalescing of ensemble members at or north and west of the 40/70 Benchmark. With this type of track and a distinct lack of much cold air, the focus of snow will likely be inland for this event, with rain or a mix at the coast. With track forecast confidence comes snow forecast confidence to a point. If we look at today’s odds of 3″ or more of snow from the European ensemble, here’s what we get:

Odds of plowable snow are high in New England, Upstate New York, far North Jersey, and much of interior Pennsylvania. (Weather Bell)

Back on Tuesday, Washington, DC had about a 40 percent chance of 3″ or more snow. Today, that is less than 10 percent. For Philly, we were around 40 to 50 percent on Tuesday, and we’re down to about 20 to 30 percent today. New York City was 50 to 60 percent on Tuesday and may be about 75 percent today. Boston and most of Southern New England were 60 to 80 percent on Tuesday and near 100 percent today. So, over the last couple days, as the models have sort of nudged things north some, the snow cutoff has nudged with it, with lower odds in Philly and DC and higher odds in New England (as you might expect with the storm closer).

Let’s ratchet things up to 6 inches. What do those odds look like?

Odds of 6 inches or more of snow this weekend are near zero from Trenton south to DC, but they increase substantially north of there. (Weather Bell)

The 6 inch probabilities are interesting, and you can begin to see where the highest uncertainty may be. From Philly south through DC, the odds of 6″ of snow are extremely low, if not close to zero. This looks like a snow to rain or mix event there. My homeland of Southern New Jersey is in the same boat. Things get much trickier though once you get into areas north and west of Philly up into New York. The “gradient” of snow percentages increases dramatically over a short distance. For example, you have about a 10 to 20 percent chance of 6″ of snow on Staten Island but about a 50 percent chance in the Bronx. Similar style gradients exist in North Jersey and near coastal New England. That’s according to the European model. In reality, with cold air lacking, I think these odds may even be a bit too high on the southern end, and I am going to assume that most of NYC will see some wet snow to a mix or rain. The NWS in New York City highlights the chance of interior snow, with a very low chance that the city sees accumulating snow.

The storm summary from the National Weather Service office in New York City. (NOAA)

For New England, the battle line becomes the coast, with the typical problem areas from a forecasting perspective coming to fruition this time as well. Despite the cheery view of the Euro in Boston, the actual odds are probably a bit less than shown for 6″ or more snow there, and the NWS Boston image below shows this, with about a 50 to 60 percent chance for the city.

The current storm situation for southern New England from NWS Boston, with low confidence in details for coastal New England into Boston proper. Also note the chance of strong winds. (NOAA)

All in all, we’re likely looking at a storm with the greatest odds of meaningful snow from portions of interior Pennsylvania through northwest New Jersey, the Catskills, Litchfield Hills, perhaps to Hartford and Worcester, southern Vermont, New Hampshire, and Maine. For the northwest suburbs of NYC and for Boston, it will be a closer call.

Don’t overlook the wind and coastal impacts with this storm either. A pretty healthy period of wind is possible from about Long Beach Island, NJ up through Long Island and coastal southern New England. This will likely cause some minor coastal flooding and possible beach erosion as well.

Next week: A major interior U.S. winter storm with big wind possible

It’s still a bit too soon to get into the finer details, but we are likely to see a much more significant storm next week across the interior U.S. Modeling has been consistently indicating the odds of a deep, strong area of low pressure tracking from Texas into the Ohio Valley and Ontario and Quebec. This storm is going to have it all: Heavy rain, severe weather, heavy snow, and powerful winds. Here’s a quick overview of what we’ll be watching.

Heavy rain: A swath of heavy rainfall is likely on the warmer, Eastern side of this storm from the Gulf Coast up through the interior Southeast, Mid-Atlantic, and possibly the Northeast. The Weather Prediction Center already has a slight risk on day 5 (Monday) for the central Gulf Coast, which is level 2 of 3 at this timeframe.

A slight risk of excessive rainfall is possible next Monday for the Gulf Coast, with heavy rain also possible north of there. (NOAA WPC)

Severe weather: The Storm Prediction Center is highlighting the chance for severe weather on Monday from Texas to the Florida Panhandle and on Tuesday in Florida and Georgia.

Severe weather is possible in the Deep South and Gulf Coast into Florida from next week’s storm on Monday and Tuesday. (NOAA SPC)

It’s too early to speculate on details, but just know that severe weather is a possibility early next week.

Heavy snow: There is an increasing chance of heavy snow for somewhere between Kansas and Missouri into Iowa, Illinois, perhaps Indiana, Michigan, Ontario, and Quebec. Current European ensemble model odds of 6″ or more snow are relatively high in Kansas, Illinois, northwest Indiana, and Michigan into Canada.

There are increasing odds of accumulating snow in parts of the Plains and Midwest into Canada early next week. (Weather Bell)

It’s far too early to speculate on details, but it’s apparent that someone will get a good bit of snow from this storm. One of the challenges again in this storm is a lack of cold air. There will be significant cold dumping into the Western US, but the Plains and Midwest have decidedly blah cold air available at this time. A lot of time to sort this out still.

Strong winds: In my opinion, the heavy rain in the East and the strong potential winds from this storm are the most serious looking elements next week. Modeling is at least implying the risk of a wide area of 30 to 40 mph or higher winds from the southern Plains into the Southeast, Ohio Valley, East Coast, and Great Lakes. Expect this storyline to become more noteworthy in coming days as the details of this storm get sorted out.

Is the polar vortex coming?

I want to close by addressing something that’s got a lot of people spooked or excited or more aware than usual of winter weather. There has been a lot of speculation on social media about the polar vortex coming later this month. The reasoning is attributed to a sudden stratospheric warming event (SSW) that displaces the polar vortex from the Pole and dumps cold air into the mid-latitudes where most people live. It sounds pretty terrible, unless of course you love cold. So what’s the deal, really?

Every winter, the polar vortex strengthens over the North Pole. It basically houses the coldest air in the Northern Hemisphere. It’s never perfectly still, but it’s usually confined to the North Pole. Every so often, the polar vortex can be disrupted, allowing cold to leak out of the polar region and toward the mid-latitudes, where most people live.

An example of a stable polar vortex that is typically seen in winter (left) and a disrupted polar vortex (right), which happens from time to time during winter. (NOAA/UCAR)

The image above lays out, broadly how this happens. For example, this winter has been a mild one for most of the U.S. so far, and it’s not a shock that the polar vortex has been fairly strong.

One of the pathways to displace or split the polar vortex is by what we call a sudden stratospheric warming. What is that, and why does it matter? When we talk about the “polar vortex,” most meteorologists are actually referring to the stratospheric polar vortex. We’re looking about 10 miles and higher up in the atmosphere. That’s the actual polar vortex. When you think of the polar vortex, you’re likely thinking of blobs of intense cold that periodically drop into the U.S. during winter. So, they’re two fundamentally different things. Related, but different.

During some winters, there will be a disruption of the stability in the stratosphere that happens via a sudden warming event, where the strong westerly winds locking the polar vortex over the Pole can weaken or even reverse. When that happens it can release some of that cold from the polar region into the mid-latitudes, impacting the U.S. or Europe or Asia.

Stratospheric warming is ongoing, which may be enough to qualify as a lower-end sudden stratospheric warming event. (NOAA)

But that’s not a guarantee. No two SSWs are identical, and not every SSW will lead to a “release the hounds” cold air outbreak over the U.S. (or Europe or Asia). There’s a lot that we don’t completely understand about these events and what causes one to produce big cold or another to do little to nothing. But the bottom line here is that this year we are seeing a minor SSW event ongoing. This will do some work on the polar vortex, and it should allow for a relatively wavier jet stream heading into later January. That does not mean a repeat of the February 2021 or December 2022 cold events in Texas, but it could mean some pushes of stronger cold than we’ve seen so far this winter.

One hurdle right now is that snowfall across North America is running a good bit below normal.

Snowfall across North America is struggling mightily this year. (Rutgers University)

Snow cover is below average in the West, Canada, the Midwest, and Plains. Cold air modifies and moderates as it comes south, and when it travels over less snowy ground, it can moderate faster. This can change in the coming weeks, but will it happen in the Plains? That’s TBD.

The takeaway from all this is that a SSW event does *not* guarantee strong cold air. There are complicating factors involved that can prevent strong cold from materializing. However, an SSW event does tend to weaken the polar vortex and increase the odds that colder air could emerge from the polar regions at times in a few weeks. That does not necessarily mean a repeat of February 2021 (Uri). These types of situations occur several times a decade and most do not produce historic cold air like we saw in that event. But they can produce some of the coldest air of a given winter. So our advice: Sell the hype. But don’t be surprised if the forecast later this month turns a bit colder than we’ve seen so far this winter.

An East Coast storm is likely this weekend, but whether you see snow or mostly a mix depends on a lot of things

One-sentence summary

A significant storm is likely this weekend along the East Coast, but there are a number of complexities to it that will determine who sees snow, a mix, or mostly rain.

What’s happening?

As we jump start 2024, the weather pattern will begin to kick into high gear, bringing storminess, not atypical for an El Nino winter. What I want to do in this post is table set what’s happening, and what it may or may not mean. Social media has been ripe with speculation over everything between snowstorms in the Northeast Corridor to sudden stratospheric warming events that can potentially lead to a weather pattern conducive to cold and snow. What should we actually be watching? Let’s jump in.

Through Friday

Nationally, things look mostly quiet through the end of the week, with some rain and mountain snow in the West, and at least some widespread rain over the Southeast or Gulf Coast from a quick moving system.

Weekend storm

A storm on Thursday will get going over the Rockies and emerge into Texas on Friday, delivering some widespread rain and at least a slight chance of strong to severe storms on the Gulf Coast. By Saturday evening, there is good agreement that low pressure will be centered near the East Coast between Delmarva and the Outer Banks of North Carolina.

Low pressure plots and interquartile range differences from the 51 member European ensemble show that low pressure is likely on Saturday evening off the Mid-Atlantic coast, but there is still about a 250 mile spread in possibilities, creating low confidence on specifics. (Tomer Burg)

There is still a considerable spread in details and specifics based on that. But we can look at this and make some assumptions. Let’s roll it forward to Sunday morning. When we talk about Northeast storms, you’ll occasionally hear reference to “the Benchmark.” The Benchmark refers to the 40 degree latitude/70 degree longitude point south of New England. In general, when storms track near this point, it’s a favorable setup for snow in the Northeast Megalopolis (Boston-DC). There are a lot of other factors that play into this, but if you want an old school, quick and dirty idea of snow chances, that’s about as good as you can do. So on Sunday morning, this storm tracks, broadly, toward the Benchmark.

The European ensemble mean (black lines) shows low pressure centered south of the Benchmark on Sunday morning. But a closer inspection shows a number of ensemble members with low pressure hugging the coast or even farther away. This indicates high uncertainty in forecast details. (Tomer Burg)

So the European ensemble shows a number of storm tracks on either side of the Benchmark with several rather close to the coast. This means uncertainty is high. Let’s ask the next question. Is cold air available? The answer is…not entirely.

Temperature anomalies around 5,000 feet up in the atmosphere show a distinct lack of colder than normal air that you’d probably prefer to see with a storm like this to get snow in the major cities. (Pivotal Weather)

The air may be cold enough for snow, but there’s a lack of any real Arctic air, a lack of colder than normal air, and a storm track that’s tenuously close to the Benchmark. This does not give me warm and fuzzies for I-95 or coastal snow. You can see this reflected in European model probabilities of 3 inches or more snow (what I would deem “plowable” snow).

Snow chances of 3″ or more are highest in New England and notably lower from New York through DC. This has the feel of a snow to mix or rain type storm for much of the I-95 corridor. (Weather Bell)

Odds of 3″ or more snow are currently sitting around 60 to 80 percent in much of New England, around 50 to 60 percent in New York City, and around 40 to 50 percent in Philly. You can see some lollipops of higher odds in the mountains of West Virginia through Pennsylvania, New Jersey, just south of the Catskills, and the Litchfield Hills in Connecticut.

What this says to me, as someone who grew up with this stuff: Probably a thump of snow, mixing with and changing to rain, then perhaps ending as snow for DC, Philly, and New York. For New England, it’s a lot more complex. The current “mean” storm track is definitely favorable for snow there, but a track on the other side of the Benchmark would probably put severe pressure on meager cold air and increase mixing chances.

The bottom line: I worry about the finer details here, but in general it looks like a winter storm is coming for someone. But if I lived from NYC to DC, I’d keep my expectations in check. This has the feel of a “north and west” event. I’d feel better about snow in New England.

What’s next?

Beyond this storm, there appears that another, potentially bigger storm will arrive around Tuesday or Wednesday of next week. This one looks likely to be an inland cutter, meaning it will track across the Great Lakes or up the Appalachian spine. But this has potential to be a significant snowstorm or mixed precip event in the Midwest next week.

A significant storm is going to bring heavy rain and heavy snow to the Eastern US next week. (NOAA)

Folks in the Midwest and East should watch this one closely for both heavy snow and heavy rain. A continued active pattern seems likely in the coming weeks. Stay tuned!

Holiday travel has been worse before, but 2023 will bring its own set of headaches

One-sentence summary

While we’ve had worse travel outlooks for Christmases in the past, this year doesn’t look spectacular, with a few areas likely to experience weather impacts through next week.

Christmas weekend outlook: Rough in spots; not bad in others

After a rollicking couple of days on the Eastern Seaboard with record flooding in Charleston, nasty weather in Florida, and powerful winds knocking out electricity to hundreds of thousands in the Northeast, we will mercifully get a couple days of a break in the East. Meanwhile, the West is just getting started with another storm aiming to bring rain to California today and tomorrow.

Rainfall over the next few days will be significant in California with a flooding threat developing in portions of SoCal on Wednesday and Thursday. (Pivotal Weather)

As all of that mess starts to exit the West later this week, it promises to setup some impacts on travel days heading right through early next week. It doesn’t look horrific on any given day right now, but a series of systems will probably keep some travel headaches going into next week. Let’s walk you through what and where to watch as it stands right now across the country.

Wednesday: Focus on California

The main headaches on Wednesday are likely to be in California, with heavy rain expected as a cold front pushes down the West Coast tied to a storm system offshore. The highest risk for any flooding will probably be in the LA Basin and Ventura County into Santa Barbara in SoCal. About 1 to 3 inches of rain is expected from this storm on Wednesday which may be enough to cause some flooding and certainly impede travel a bit between LA and San Francisco.

Thursday: More rain, flooding in California

That storm system is expected to kind of slow down offshore of California, keeping a wet forecast going, especially in SoCal on Thursday. Another inch or two will be possible there, with flooding a definite concern. The Weather Prediction Center has placed the western portion of the LA Basin into Ventura and Santa Barbara under a level 3 of 4 moderate risk for excessive rainfall.

A moderate risk of flooding is in place in coastal SoCal from Santa Barbara through LA on Thursday. A slight risk is in place north of there and down the coast to San Diego. (NOAA)

Farther to the east, showers will begin to become a possibility in the Plains, but no real serious travel headaches are expected in the eastern half of the country.

Friday: Weather shifts east

I don’t foresee any real serious issues on Friday, but there will be a couple areas to watch. Rain in California will finally start to push east, more into Arizona, where heavy rain may fall in parts of the state, including Phoenix.

Forecast rainfall on Friday in Arizona is considerable, with some travel impacts and localized flooding possible in the Phoenix and/or Tucson areas. (Pivotal Weather)

Meanwhile, rain and/or thunderstorms may push across Texas into Louisiana Friday afternoon, perhaps causing a few modest delays in the Houston area.

Saturday: Calm before the storm

Nationally, Saturday may be the best travel day overall with only some minor issues in parts of the Rockies, Southern Plains, or Southeast. No major problems are currently foreseen.

Christmas Eve: Rockies, Plains, and Mississippi Valley see stormy weather

As everything slides east, we’ll get low pressure developing in the lee of the Rockies, probably between the Texas Panhandle and Kansas. This will lead to rain and thunderstorms in the Plains through Texas, expanding east to the Mississippi Valley as the day wears on. Some of these storms could be on the stronger side.

Snowfall/winter storm information that is known as of this morning for the Rockies. (NWS Boulder/Denver)

Meanwhile, snow should break out in the Rockies, with Colorado and Wyoming the most likely areas to see accumulation and potential travel headaches.

Christmas Day: Wet Southeast

The forecast confidence begins to fade rather aggressively here, as we end up with a storm system over the Midwest and a wet Southeast and perhaps Mid-Atlantic. Travel doesn’t look particularly awful here, but there will probably be some wet roads for the East in spots. Snow or a mix should continue on the backside of the storm from Wyoming into perhaps parts of Nebraska and South Dakota.

Beyond Christmas Day: East Coast Storm? Still wet in the West

Uncertainty plunges later next week. If you look at this map showing the forecast interquartile range for next Wednesday afternoon from the European ensemble, you can see ample uncertainty.

There is significant uncertainty on exactly how next week’s weather plays out. A major storm is possible in the Eastern U.S., but details are very much lacking at this time on timing and intensity. (Tomer Burg/Polar Wx)

The IQR shows the difference between the 75th minus the 25th percentile of ensemble sea level pressure. The higher the values, the greater the potential uncertainty with placement and intensity of low pressure (or high pressure). In this case, we see a strong signal for a storm in the Eastern U.S. What we do not see is any confidence within the ensemble members regarding location or intensity. So we know something is probably going to happen that could be a travel headache in the Eastern U.S. after Christmas, but we aren’t exactly sure what, when, or where.

Temperatures next week are likely to be warmer than normal in the Northeast, so this probably precludes snow risk for the major cities, but interior areas could be prone to some snow in the right (wrong?) scenario.

Temperatures are likely to be above to well above normal next week in the Northeast and Midwest, probably minimizing snow chances a bit with any storm system. (NOAA)

Meanwhile, the West looks mild too, with continued rain and mountain snow lashing the West Coast. This is pretty clearly an El Niño flavored pattern across the U.S. to close out 2023.

Let’s talk about the concept of blowing up a tornado

One-sentence summary

Today we assess some of the commentary around a viral tornado video from the weekend to discuss if it would be possible to “blow up” a tornado.

Can you actually blow up a tornado?

That’s a provocative subheading above, but it’s taken on a little more curiosity after video emerged from this past weekend’s tragic tornado outbreak in the Deep South and Tennessee Valley.

Click to enlarge severe weather reports from Saturday across Tennessee and Kentucky. Note the cluster of tornado reports north of Nashville. (NOAA)

The tornadoes killed six and injured over 80 in Middle Tennessee on Saturday. Clarksville was hit with an EF-3 tornado. This area has seen more than their fair share of significant weather in recent years.

A video from one of the tornadoes is what seems to have grabbed everyone’s attention, and justifiably so.

This one occurred between Madison and Goodlettsville, just north of Nashville, east of I-65. What you essentially see is the tornado striking a power substation, followed by an explosion. The power substation was Nashville Electric Service’s, which just released video from the site on Monday showing the strike and explosion.

But what’s notable about this whole thing: In the original video, it appears that, if only for a fleeting moment, the condensation funnel (what you are visually seeing as the tornado) disappears. Naturally, that started some interesting conversations on various social media platforms. The underlying question you would expect humans, especially on social media to ask was: Can you actually, like, blow up a tornado?

Before we go on: No. We cannot “blow up” tornadoes, just as we cannot “nuke” hurricanes. It’s too complex, not to mention the likelihood of collateral damage. So, let’s just get that out of the way.

But in a theoretical world without risk to lives or property, could you do it? I still don’t think so. Noted storm chaser Reed Timmer posted on X, formerly Twitter over the weekend that the “explosion changed the thermodynamic gradients dramatically within the vortex and blew up the Clausius-Clapeyron equation.” I’m not going to lose our audience here with a math lesson, but the C-C equation relates saturation vapor pressure to temperature. What is saturation vapor pressure? Vapor pressure is basically exactly that: What is the pressure of the water vapor in the air. But at a given temperature, there’s a maximum amount of moisture that the air can hold. That would give you the saturation vapor pressure. Using C-C, we can determine that as temperature increases, the saturation vapor pressure of the air increases exponentially. In other words: Warm air can hold a lot more moisture than cold air, and the relationship is exponential.

What does this all mean? Theoretically (very theoretically), the heat released from an explosion within the condensation funnel of a tornado would lead to a dramatic increase in saturation vapor pressure, thus decreasing the humidity in the vicinity of the funnel. You’re not adding more moisture to the equation, so all you’re doing is increasing temperature and increasing the air’s capacity to hold water — exponentially. All else equal, you’ve decreased humidity, and because the air is no longer saturated, the condensation funnel (which you see when the air is saturated) visually disappears.

If the condensation funnel is our visual cue of a tornado and it disappears, then to the human mind the tornado itself has disappeared. So you can actually blow up a tornado, right? Not quite. Other videos from other angles that I’ve seen seem to show the condensation funnel picking back up a little after the viral video ends. Meaning the tornado was only briefly visually disrupted, not destroyed. Were the winds disrupted or just our visual cues? I’m not sure. Thunderstorms are big, and the forces producing tornadoes are also significant. To truly destroy a tornado, you’d likely have to go after the supercell thunderstorm itself, which is producing the tornado, in theory perhaps something that could be done but in practice probably next to impossible.

While it’s certainly a fun thought exercise, also keep in mind that we’re all taking some liberties here to make assumptions about this using the science that we know. There could be another explanation for what’s happening here, but the one suggested by Reed and others seems to be the most reasonable that I’ve seen. But the bigger point still stands: Blowing up a tornado is not a practical alternative to preparedness, structure hardening, shelter availability, and awareness on severe weather days.