Earlier this morning, over on our companion site The Eyewall, Matt wrote about a series of winter storms that are going to affect the United States. Part of the post dealt with a topic that a lot of readers have been asking about, the stability of the polar vortex, and whether that means an outbreak of arctic air is likely to reach Texas later this month. The short answer is that yes, the second half of January does look colder. But how cold? That’s a forecast that’s impossible to make as of yet. Here’s Matt with the details.

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.

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.

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.

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.

Good morning. Temperatures have dropped into the upper 30s to lower 40s across most of the Houston metro area this morning, and this is the coldest we’re going to get until the middle of next week. We’re still looking at the likelihood of widespread showers on Friday before a mostly sunny and cool winter weekend.

Thursday

After the cool start, temperatures today should reach about 60 degrees under mostly sunny skies. Winds will continue from the east, and we may start to see some gusts this afternoon of 20 or even 25 mph. Clouds will start to build in this evening, but I think rain chances will hold off at least until midnight, and probably more likely until the hours just before sunset on Friday. Look for lows tonight to drop down to around 50 degrees in Houston.

Friday

A low pressure system will bring widespread rain chances on Friday, particularly during the morning hours. There’s no indication in the atmosphere or forecast models for anything extreme, both in terms of rain accumulations or severe thunderstorms. Most of the area probably will pick up between 0.5 and 1.5 inches, with the greater totals more likely south of Interstate 10, closer to the coast. In terms of timing, the showers should generally move in from the west and exit to the east of Houston by around noon, give or take a couple of hours. We should see some partially clearing skies by later Friday afternoon, with highs in the low- to mid-60s.

Saturday and Sunday

The weekend should see partly to mostly sunny skies, with dry air, and daytime highs generally in the low 60s. Friday and Saturday nights should be cool, but by Sunday evening we’ll see a resurgent onshore flow that will start to pump up atmospheric moisture levels and humidity. This will set the stage for another round of showers on Monday.

Monday and Tuesday

Monday could be a bit dynamic as a strong cold front approaches the area. This will bring showers, and potentially some strong thunderstorms during the daytime. We’ll try to have some better details on this for you in tomorrow’s update. The front will then bring some very strong northerly winds with it, with gusts up to 35 or 40 mph in Houston, and the potential for even stronger winds closer to the coast. These winds are likely to peak on Monday night and Tuesday morning, so that’s something to be aware of if you’re going to be out and about. This may be an issue for any tailgating associated with Monday evening’s College Football Playoff National Championship at NRG Stadium, depending on the timing of the front.

Tuesday should be sharply colder, with highs only in the 50s to go along with the strong winds. Lows on Tuesday night will probably drop at least into the upper 30s for Houston, with a light freeze possible for areas further inland—we’ll see.

Rest of next week

We’ll likely warm back up by Wednesday or Thursday before another front brings things back down for the weekend. My sense is that startline temperatures for the Houston Marathon on Sunday morning will be in the vicinity of 40 degrees, but there’s still a lot of time to go before that forecast is set in stone.

We start this morning with a quick celestial note: Earth reached perihelion at 6:38 pm CT on Tuesday night, meaning it reached the closest point to the Sun in its (slightly) elliptical orbit about our star. Ironically for northern hemisphere residents, though we are closer to the Sun during the winter by a few million miles, it is coldest time of the year. This is due, of course, to the tilt of the planet’s axis rather than proximity to the Sun. We’ll reach our furthest point from the Sun, aphelion, just after midnight on July 5 of this year.

Speaking of weather, rain showers on Tuesday evening and this morning overperformed a little, dropping 1 to 2 inches across most areas south of Interstate 10, with lesser amounts inland. We’ll now see a couple of drier days before rain showers return on Thursday night and Friday. All of this is working toward a gorgeous, winter-like weekend.

Wednesday

Skies will be mostly cloudy today, with highs pushing perhaps into the mid-50s. After some gusty conditions overnight as a coastal low pressure system passed by, winds will be lighter today, generally from the north, at 5 to 10 mph. Lows tonight will be fairly chilly, dropping into the low 40s in Houston, with cooler conditions further inland.

Thursday

This will be a mostly sunny day, probably, with highs in the upper 50s. Winds will be light, generally from the northeast. Another coastal low will be building offshore, but I think its associated rain showers will remain away from the Houston area during the daytime and evening hours. Lows on Thursday night will drop to around 50 degrees, with some light rain possible after midnight.

Friday

This looks to be a wet day, with most of the area picking up between 0.5 and 2.0 inches of rain between early Friday morning and the evening hours. Rain accumulations should be greatest closer to the coast, and the low pressure system. I think the worst of the weather, including stronger thunderstorms, will remain offshore. So I expect this to be a mostly mellow rain event, but it will definitely put a damper on any outdoor plans you have. Look for highs in the upper 50s, and lows Friday night dropping into the low to mid-40s.

Saturday and Sunday

The weekend looks fine and mostly sunny. Highs on Saturday will be around 60 degrees, with overnight lows in the mid-40s, and then a bit warmer on Sunday, in the low 60s. It should be a great winter weekend for outdoor activities. Enjoy!

Next week

A chance of rain showers returns on Monday before a stronger front moves through. This will set the stage for colder mid-week weather, with the temperature likely bottoming out on Wednesday morning. A light freeze looks possible for inland areas, but we’ll have to see as we get closer. Temperatures then warm up again before another front likely cools us down for next weekend. If you’re weather watching for the Houston marathon on January 14, the forecast still looks chilly and dry, but the details remain fuzzy. Nevertheless I’m cautiously optimistic about running conditions!

Before we get too far into the new year, let’s take a quick look back at 2023. December finished with an average temperature of 57.3 degrees, which was 1.9 degrees above normal for the month. The coldest temperature of the month came on Dec. 11, when the low reached 33 degrees. As I noted last week, Houston did not record a single freeze during the calendar year. It has now been 372 days without a freezing temperature, and counting. We do have a chance at a freeze during the middle of next week, but that remains far from certain.

Last year was the warmest one on record in Houston, where meteorological records go back nearly a century and a half. If we look at the continental United States, we can see that large swathes of Texas, and a few other southern states, had their warmest year on record, or at least one of the five warmest on record. With El Niño persisting at least into the spring of this year, I would expect 2024 to rank very highly in terms of temperatures as well for Texas. But with the weather one can never be sure, and so we’ll be here every step of the way.

Tuesday

Rain is coming, but it should hold off for much of today. Skies should be mostly cloudy, with highs only topping out in the mid-50s for most. Winds will come from the east, at about 10 mph. Starting this afternoon we should see a mass of showers congeal to the west of Houston in conjunction with a low pressure system, and this will move through late this afternoon, evening, and during the overnight hours. Accumulations through Tuesday night should be on the order of 0.25 to 1.0 inch for most. With temperatures dropping into the low- to mid-40s it will be a cold and rainy night, but I don’t anticipate any particularly severe weather.

Wednesday

These rains will most likely end during the pre-dawn hours. After a cloudy start we could see some partial clearing of our skies by Wednesday afternoon, with high temperatures likely peaking only in the mid- to upper-50s. Lows on Wednesday night will probably be the coldest of the week, dropping into the upper 30s for inland areas, and low 40s in the urban core of Houston and closer to the coast.

Thursday

This looks to be a fine, sunny winter day with highs in the upper 50s.

Friday

Round two of rainfall arrives on Friday, with another low pressure system driving increased rain chances. The most likely time for rain will be during the daytime, and we likely will also see some thunderstorms. Will they be severe? Right now the overall dynamics do not favor this so much, so perhaps not. But I’ll be keeping an eye on it. In any case, I’d expect accumulations of 0.5 to 2 inches for most areas, so it could be a bit of messay day on the roadways.

Saturday and Sunday

After Friday’s mess clears out, the weekend looks sunny and cool. We’re talking highs of around 60 degrees on Saturday, lows around 40 degrees on Saturday night, and temperatures a bit warmer on Sunday, perhaps in the low 60s. Enjoy.

Next week

The forecast turns a bit fuzzy next week, but the broad outlines are clear. We’re going to see a brief warm-up on Monday, with temperatures in the low-70s, before some rainfall and a front arrives. This should pretty sharply cool things down for Tuesday, and by Wednesday morning we should be quite cold, perhaps even flirting with a freeze.

If you’re running the Houston marathon, our first peek at weather for Sunday, January 14, is necessarily blurry. But the most likely scenario is that some sort of reinforcing front pushes through ahead of the weekend, leading to a cold Sunday, perhaps starting in the 40s, and rising to the 50s. Certainly I can’t rule out rain showers, but at this point there’s no strong signal for it. I like it cold and dry, so this is an ideal forecast for a slow-goer like me. Such a far-out prediction is, of course, very speculative.