Frightful weather for Christmas? Remains to be seen

HOUSTON - Oh the weather outside is frightful -- or at least it certainly could be. We've had lots of questions regarding a possible winter storm in Texas in the days leading up to Christmas. While some of it is hype, there are nuggets of truth. Let me try and sort it out for you.

What we know:

Not much. One thing is for sure: it's going to get very cold beginning next Friday and lasting all the way through Christmas Day. Last year's high temperature of 80° on Christmas Day will be nothing but a bad dream for cold weather lovers. 

It's also looking more and more likely that there will be widespread precipitation leading into Friday, Saturday, Christmas Eve and Christmas Day.

That's what we *know.*

Cold Rain or...?

So we'll have the cold and the precipitation. Isn't that all that's required for winter weather? Yes and no. So much of what happens at the surface depends on what happens above our heads. Picture the atmosphere as a tall column. If the entire column is below freezing, it snows. That's what we consider a "deep, cold column." If any part of that column is above freezing, the snowflakes above our heads melt and fall as rain. If the air at the surface is cold enough, that rain drop can refreeze into freezing rain and sleet.

Unlike last week where we had a deep column of below freezing air that allowed for widespread snow, the arctic airmass coming for Christmas will be very shallow -- meaning that our column is infiltrated with lots of warm air above our heads that will melt the snowflakes. The question becomes, will our surface temperatures be cold enough to support ice.

Here's a look at a chart we call a "Skew-T diagram" for Christmas Eve morning:

All that's important in the image above is the yellow line and where the red and green lines cross it. The yellow line is the freeze line as you ascend into the atmosphere. The green line is the dewpoint with height and the red is the temperature with height. The red and green lines cross the yellow line around 10,000 feet up into the atmosphere. That means that the lower portion of the atmoshere where we live is above freezing -- the warmer air is far too thick to allow anything frozen to survive the journey to the surface.

Ergo, based on that one model run alone, it appears as though we'll have a very cold rain leading into the Friday, Saturday, Christmas Eve and Christmas Day as the atmosphere looks identical to the image above on all those days.

If you wanted it to snow, like it did last week, you'd want to see the red and green lines almost completely on the left side of the yellow line in the below freezing air. Clearly that is not the case this time around.

If the models do begin to show a more serious winter weather threat here, it would NOT be snow. It would strictly be an ice event (freezing rain/sleet). It's a low possibility but one that could happen if models begin trending colder. It definitely bears watching.

Headed to Dallas or Austin?

If your travel plans take you further north or northwest of Houston, you won't have to travel far to run into big problems with ice and snow. Austin may be in for freezing rain while Dallas would be in for more of an ice/snow mix. Either way, whether it's just cold rain, ice or snow or all three, travel conditions leading up to Christmas across Texas don't look good at this time.

The Uncertainty is Extremely High

I can not stress enough how uncertain the forecast is at this time. The only thing we know is that its going to get much colder heading into Christmas. Outside of that, everything else is up for debate and fluctuations. There are three possibilities here: 1). it's cold and dry. 2). it's icy/snowy for central and north Texas and 3). the front is stronger than forecast and the wintry weather makes it deeper into southeast Texas. 

It's hard to ignore the GFS (American) model. For 20-something runs in a row now (have lost count its been so many), the GFS has consistently been advertising a winter storm for Texas, a very unusual consistency for being so far out into time. That's why this bears watching.

While I currently favor option 2 above, anecdotally speaking, winter storms almost always offer one or two surprises -- like the 1 to 3 inches of snow we got last week after the forecast only called for a dusting at best. 

There are many, many questions we don't know the answer to yet so stay tuned to Channel 11 and we'll keep you updated as we know more. 

 

 

 

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