In brief: Houston’s forecast appears mostly on track, with a definite trend toward the heaviest snow and sleet emerging south and east of Houston by Tuesday morning. Accumulations may be as high as several inches under the most persistent bands, with a general coating to few inches elsewhere. Winds will gust near the coast Tuesday morning as well, and a very cold night still looks on tap tomorrow night.

Happening now

Well, our much advertised winter storm is underway across the Houston area. We’ve seen reports of sleet, graupel, rain, and snow across the region. We seem to be settling down into a tiered setup now with snow and sleet north and west, sleet and graupel in the lighter precipitation, and sleet and rain near the coast.

That area of snow and some sleet occurring north and west of Houston is going to gradually fill in and drop south and east through the night. As it does so, we’ll pick up some accumulating snow. As it gets closer to the coast and the potential for banding gets underway, that’s when we may see locally heavy snow anywhere from I-10 southward to the coast.

Forecast for the night

So before 3 AM, look for this potpourri of precipitation types. Again, plain rain should be expected in spots near the coast especially. This is not a surprise and was anticipated ahead of time. After 3 AM, there will be a transition to all sleet and snow and eventually just snow. There is a good chance we will wake up to snow falling tomorrow, although how much on the ground is an open question with a few possibilities. Snow should end from northwest to southeast after 9 AM tomorrow.

Why have we been kind of cagey on snow accumulation numbers?

Those that read us closely can tell we’re throwing out various accumulation numbers based on model data and National Weather Service forecasts but we’re not exactly confident. Now, the event is underway so we should be highly confident, right? Not right. The SREF is a short-range ensemble model, meaning it’s run multiple times with varying snapshots at the beginning to produce a more realistic spread in outcomes. Basically, we want to see how bad or not bad it can get. As of the 3 PM run this afternoon, this model showed snow totals ranging from nada to as much as 7 inches at Hobby Airport.

Now, Hobby Airport almost certainly won’t get 7 inches of snow. It probably won’t get 0.0 inches either. The average on this particular model is around 2 inches, which is reasonable, but there is such a spread in options here that it doesn’t necessarily inspire much confidence. The trouble with this event is that we’re dealing with a wintry mix at the start, we don’t know where banding will establish, we’re in a place that rarely sees weather like this so it’s far outside of the bounds of the climatology (normal) these models use, and we have the Gulf of Mexico in our backyard. All that to say, this stuff is hard. If you want snow, hope for the best. If you do not want snow, hope for the best. May the odds be ever in our favor.

Sleet versus graupel

Here’s a true story. Back in my on-air broadcast days in Utica, NY, I once was describing a day where we had a bunch of graupel fall in Upstate New York and explained what it was. Immediately after the news, I received a call from an older gentleman who told me he had a dictionary in front of him, couldn’t find the word, and proceeded to lambaste me for making up words. I can assure you that it is a real word. So what is it, and how does it differ from sleet?

We’ve gotten reports of sleet and pictures of basically tiny “balls” of ice across the area. When you look at the pictures, however, they look more like Dippin’ Dots than ice pellets (sleet). That’s a tell-tale sign of graupel. The differences? Sleet is straightforward: A snowflake falls, hits a layer of milder air above freezing, melts, and then refreezes in colder air below that, falling as quite literally an ice pellet. Graupel happens when you get water droplets that are still liquid below 32°, (or what is called “supercooled”). The supercooled water droplets collide with and freeze on a snow crystal, a process called riming (which is a homonym of “rhyming”). They basically fall to the ground as snow pellets. They tend to be whiter (hence Dippin’ Dots-like!), whereas sleet is clearer. Sleet melts in your hand, whereas graupel may fall apart or crumble in your hand.

What many of you may have reported as sleet tonight was actually graupel. This is a weird storm because we have a pretty intense layer of dry air from the surface up to about 5,000 feet and from about 12,000 feet up to 30,000 feet. The region of the atmosphere where snowflakes will grow is up above 15,000 feet, so we’re seeing a bit of chaos ongoing above our heads. As the night goes on, this dry air will erode as the atmosphere cools, leading to more regular snow.

Eric will have the latest for you in the morning. Stay safe, stay off the roads tonight, and we’ll see where we are tomorrow!

In brief: We are fast approaching the arrival of a winter storm, which is likely to begin with freezing rain or sleet late on Monday, and transition to snowfall early on Tuesday morning. Although we still have some questions about the details, there is little question that large chunks of Houston are going to get frozen in on Tuesday due to icy roads.

The coast with the most

One of the emerging trends we’re seeing in higher resolution models today is a greater concentration of snow in coastal areas, including Brazoria, Galveston, and Chambers counties. Matt mentioned the possibility of blizzard conditions tomorrow on Galveston Island, and I think it’s distinctly possible. Winds are going to peak between midnight and noon on Tuesday, with gusts likely above 35 mph. When you add the likelihood of heavy snowfall, you have the potential for a once-in-a-lifetime winter storm on the upper Texas coast.

How much snow will I get?

Snowfall forecasts are really difficult. Why? Because 0.1 inch of precipitation in rainfall equates, roughly, to 1 inch of snow. So relatively small differences in total precipitation lead to rather significant differences in snow accumulation. With that in mind, it does look as though the majority of the Houston area is likely to at least see at least 1 to 2 inches on Tuesday between midnight and noon. But totals could run much higher.

There likely will be a band of heavier snow, perhaps up to 6 inches or even a little more. I think it’s more likely this banding effect sets up near the coast, or possibly even just offshore. However, it could also line up along Interstate 10. Areas further north, including The Woodlands and College Station, appear to be less likely to get multiple inches of snow on Tuesday.

How cold will it get?

One area in which the models are really struggling is how cold air temperatures will get on Tuesday night and Wednesday morning. There remains a wide variance, and most locations in Houston may get as cold as 15 degrees, or remain relatively warm, in the upper 20s. Some of this variance is due to how the models are handling snowfall totals. In any case, we will try to refine this forecast in coming updates.

When will we thaw out?

Most of the model data continues to indicate that high temperatures will reach about 40 degrees on Wednesday. This, along with ample sunshine, should help to melt and dry out our roadways. If moisture remains on Wednesday night, then it is likely to re-freeze on Thursday morning. However at this time my best guess is that roads are OK beginning Wednesday afternoon, and onward. But it’s something we’ll keep an eye on.

How historic is this?

I’ve been writing about weather in Houston for a quarter of a century, and I’ve never seen a winter storm setup like this. Parts of the region saw several inches of snow back in December 2004, but it was mostly a coastal event, with much of Houston seeing flurries at most. We probably have to go back to 1895 to find an winter storm event that exceeds what the region is likely to experience on Tuesday.

Update schedule

Our next update will come this evening, no later than 10 pm CT. Then we will have full coverage for you on Tuesday, starting before sunrise. Please be safe and warm!

In brief: Houston is less than a day away from the onset of a winter storm that is likely to cripple transportation around the region. We’re still expecting primarily snow, with impacts on roadways through Wednesday morning. Expect two additional updates today on Space City Weather as we share what we know, when we know it.

Cold update

As anticipated, temperatures this morning have fallen a couple of degrees below freezing across the metro area. Fortunately, you still have today to prepare for a winter storm that will very probably bring more snow into the Houston region than we have experienced in at least two decades. The city is likely going to shut down from this evening through Wednesday morning, and it really should do so because we are ill-equipped to handle this kind of winter storm.

Before jumping into the post, I also want to thank the organizers of the Houston Marathon, as well as all of the thousands of volunteers and tens of thousands of spectators who make this such a special event. Yes, it was cold on the course on Sunday, but honestly after a mile or two the colder air felt great. It also feels great to be able to set aside my running shoes for awhile.

Monday

It is MLK Day, which honors the legacy of the civil rights leader Martin Luther King Jr. For kids, it’s a day off of school which, in addition to ‘snow’ days on Tuesday and Wednesday, makes for a five-day weekend. Not bad. It’s almost enough for me to wish I was seven years old again. Almost.

Anyway, today will be a brisk day with increasing clouds and high temperatures of around 40 degrees. A gusty easterly wind will add to the misery. We’ll see a slight chance of showers by around sunset this evening, but for the most part this should be rain in the Houston metro area. Please do plan to be wherever you’re sheltering from the storm this evening by about 8 pm for northern areas such as The Woodlands, and midnight at the absolute latest for central and southern parts of the Houston area.

Monday night and Tuesday

By around midnight temperatures in the region will reach freezing for most of Houston, and light rain will begin to transition to snow, sleet, and possibly freezing rain. The intensity of these snow showers or sleet will pick up on Tuesday morning. Low temperatures will drop to between 25 and 30 degrees for most of the region.

So what will you wake up to? I anticipate that most of the area will see 1 to 4 inches of snow, with some sleet mixed in by mid-morning on Tuesday. We still have some serious questions about the amount of precipitation, and I agree with Matt that there is a decent chance that some parts of Houston receive up to 4 to 6 inches. (Currently the favored region for this is probably along and south of Interstate 10, but we shall see). In any case, this should be wintry setup for which Houston-area roads are not prepared for.

Temperature wise, Tuesday is going to be interesting. The precipitation will end by around noon, and I expect we’ll see clearing skies during the afternoon hours. Temperatures will probably briefly get above freezing during the afternoon hours, and this may cause some of the snow and ice on the roads to briefly melt. However this window will be brief, as temperatures drop to below freezing by around sunset again. It will be a very cold night with slick streets.

Wednesday

How cold will it get? That will depend on the extent of snow cover where you are. I think most of Houston will fall to around 15 to 25 degrees, so a hard freeze all around expect perhaps for the immediate coast, such as Galveston Island. Air temperatures will likely reach above freezing at some point on Wednesday around noon. Then, sunny skies and temperatures in the upper-30s, at least, should help to clear roadways during the afternoon hours. By this time it should be possible to resume somewhat normal activities around the region. But we’ll need to see how the mobility situation plays out.

Thursday and beyond

Lows on Wednesday night will drop into the mid-20s in Houston, so another cold night. However by Thursday afternoon we’ll be well into then 40s. A light freeze is possible again Thursday night. The weekend looks mild, with temperatures climbing back into the 60s. A chance of rain returns by around Sunday, or so.

Best sledding in Houston

It’s kind of insane, but we’ve reached the point where we can legitimately talk about sledding here. Now Houston is a pretty flat city, so there are not a lot of great hills. But there are a few, such as the hill at Miller Outdoor Theater in Hermann Park. However, when choosing a locale for sledding on Tuesday (and possibly Wednesday) it would be foolish to choose a spot you have to drive to. Since we’re not going to be driving around on Tuesday, are we? In reality the best place for you to sled in Houston the steepest hill you can walk to.

Which doesn’t lead down into a pond or a bayou.

Update schedule

We plan on having two additional updates today. One will come this afternoon, probably around 3 or 4 pm; and another later this evening when we should be able to provide real-time information on the developing winter storm.

In brief: There have been few changes to the overall forecast today, with higher resolution modeling now coming into range on this storm and essentially validating most of what we’ve seen to this point. A legitimate, rare winter storm, with primarily snow and sleet is likely to impact most of the Houston area tomorrow night and Tuesday, causing significant travel disruption through at least Wednesday morning.

What’s new?

A few minor notes this afternoon, none of which are significant changes in thinking from this morning.

First off, the NWS has upgraded us to a Winter Storm Warning and increased their snow total forecasts for the Houston area.

They have also increased the “realistic worst case scenario” snow forecast.

Why has this happened? Well for one, modeling has continued to lock in colder with this storm, showing a sharp transition overnight Monday into Tuesday morning from plain rain, freezing rain, and a mix of sleet and snow to just sleet and probably mostly snow across the region. Secondly, high resolution weather models that only run about 48 to 60 hours out in time are now in range of the storm, confirming both that precipitation-type outcome and the potential for “banding” that will exacerbate local snowfall totals.

Again, we have to note: The snow will not fall perfectly uniformly across the region. Depending on where this “banding” sets up, that will determine places that are at risk for 6 inches or more of snow. Quite frankly, that could be anywhere in our area; we simply don’t know at this time. Recent model runs have favored the Houston through Liberty County areas, as well as Brazoria County through Beaumont areas, but that could easily change. I’d say we’ll know more tomorrow, but realistically, we may not know it until it starts.

Again, just to underscore: As long as the forecast stays on track, travel is going to be nearly impossible Monday after midnight and all day Tuesday. You will almost certainly be stuck where you are until at least later Wednesday morning. The exception to this may be the far north now (like north of Highway 105), where snow may end up lighter, no ice occurs, and roads may clear off a bit after the snow stops Tuesday afternoon. But even that may be optimistic. More to come on this.

Historical context

Realistically, this is the most significant snow threat to the region since Christmas Eve 2004. The 1895 storm stands alone as the greatest on record in Texas and Louisiana, and this storm will not dethrone that one. However, with that in mind, this has the potential to set a modern official snowfall record in Houston, which currently sits at a mere 3 inches back in February 1960. January 1940 also sits at 3 inches. While a few storms since then, including Christmas Eve 2004 have produced higher amounts in parts of the area, from a record-keeping perspective, we have a chance to make some noise.

Could it be a blizzard?

This morning I noted how wind gusts of 40 to 50 mph were possible on Galveston Island Tuesday morning with this storm. That obviously begs the question of whether or not this could end up meeting blizzard criteria. That will be hard. The technical requirements are:

1.) Sustained wind or frequent gusts to 35 mph or higher. (This will be close)
2.) Heavy snowfall or blowing snow that reduces visibility under a quarter mile. (This will be tough)
3.) Three consecutive hours of these conditions. (This will be very tough)

I’m not saying it can’t happen, but given how rigorous these requirements are, I have doubts that we’ll officially get there. But at least now you know what an official blizzard is. That said, we almost certainly will see blizzard-like conditions on the island if those winds come to fruition and a full changeover from sleet to snow occurs.

Whatever the case, we are into some seriously rare winter weather for Houston in what may end up being a generational winter storm. We will have the latest for you in the morning with revised model data at our fingertips.