Month: January 2018

As temperatures have plunged across the Houston area during the last six hours, rain has turned into a wintry mix of sleet, freezing rain, and snow. (Yes, it has already snowed lightly at Bush Intercontinental Airport this morning, the first time that has happened three times in a winter season since 1973). Here’s a look at what happens next.

More precipitation is coming

Houston has seen some breaks in the rain and sleet this morning, but there are additional areas of precipitation to the west of the region that will move into the metro area today. Although accumulations are unlikely to be too significant, it doesn’t take much moisture on the surface of a road to make it slick. Forecast models have been pretty consistent in bringing additional rounds of sleet, freezing rain, and snow through the region until about 4pm to 6pm CT today. Snow is more likely than other precipitation types this afternoon.

Roads are starting to freeze

Houston Transtar is keeping a (steadily growing) list of roadways affected by ice in the metro area. So far, most of the problems have occurred to the north, in Montgomery County, and west of Houston. This is understandable, as those areas have experienced freezing conditions for a longer period of time. Most roadways within Houston itself are still covered with just water, because the ground is still “warm” from Monday, when highs reached into the upper 60s. But now that most of Houston is now at about 30 degrees, and likely to slip into the upper 20s this afternoon, wet roads will gradually become icy roads—especially bridges and overpasses. How much of an ice rink Houston becomes depends upon the amount of precipitation this afternoon. With enough wind and breaks in the precipitation, there is a chance for some evaporation and perhaps we will have dry roads by the time the hard freeze hits tonight. Perhaps. But probably not. Best to leave work early today, if possible, and stay home this evening.

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As expected, a very strong cold front has moved through Houston this morning, and we’re in for a potentially messy day as precipitation falls on and off the day until about sunset. As of 5:45am CT we are already seeing a wintry mix over northwestern Harris County and Montgomery County. More freezing rain and sleet will move into the area later this morning as the freezing line moves from north of Houston, through the city, and down to Galveston by around noon.

Essentially, as the air cools down, the region is likely to see a progression from rain, to freezing rain, to sleet, to snow. This is largely driven by the depth of the warm air, which will decrease throughout the day as cold air moves into the region from the north. Here’s a graphic showing under which conditions each type of wintry precipitation falls.

Our concern for today in Houston, and the reason why schools and some businesses closed, is because of the transition from rain to freezing rain, which has the potential to very quickly ice over roads. Now, let’s take a detailed look at what may transpire later today.

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Schools are closing for Tuesday, and given what we know about the forecast, that seems a sensible precaution. Already, the National Weather Service has issued a winter storm warning for the entire metro area along and north of Interstate 10, and this effectively means there is a significant potential for snow and ice accumulation.

Basically, a mess is coming. The cold front arriving between midnight and sunrise on Tuesday seems to be a little bit colder than advertised, and this means that a freezing line should move through Houston earlier than expected, perhaps within an hour or two of sunrise. And that means the potential for freezing rain—the worst of all kinds of winter precipitation because it makes roadways incredibly slippery even with slight accumulations—will move into Houston around the same time.

Road crews are treating freeways and other major arteries with a salt-based solution that lowers the freezing temperature of water and could help some, but under the present forecast we can still expect some bridges and overpasses to freeze, in addition to untreated roads. In short, if you don’t have to get up and drive to work on Tuesday morning, don’t. If you run a business, please consider giving your employees the day off. It is by no means certain that some or many Houston roadways will be icy Tuesday morning or midday, but at this point there’s a pretty good chance.

The precipitation, some of which may transition from freezing rain to sleet or snow later on Tuesday across Houston, should end by the afternoon or evening hours. But with temperatures remaining below freezing, and depending on how much rain falls, roads may not improve much after the precipitation stops during the evening and overnight hours.

We will have a comprehensive update by 6am CT on Tuesday.

Just wanted to provide an update on conditions for Tuesday, especially because it now appears as though any freezing precipitation may move into the city a little earlier than expected. I know there are a lot of people and organizations out there looking to make decisions, so as of about 12:30pm CT on Monday, here’s what we know: A cold front is still on track to move through Houston between midnight and sunrise on Tuesday. The key questions are how cold it will get, how soon, and the timing of the precipitation. Here’s a look at what may happen at certain times.

Midnight-6am Tuesday

In the map below we see a mix of sleet and freezing rainfall moving from the northwest into the Houston metro area. This forecast from the GFS model shows accumulations for the 6-hour period from midnight to 6am, and they are slight. However when it comes to freezing rain (shown in pink) it doesn’t take much to cause problems on roadways, especially bridges and roadways.

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