It's not often that I might start a thread about the potential for sleet/snow here in southeast Texas. Usually, I'm trying to explain why it won't sleet or snow here. However, I do think that it is looking more possible that we could actually see the "S" word here in Houston Sunday/Monday. That is, if the ECMWF is even close to correct. Take a gander at the 12Z (6am CST) ECMWF forecast. Mouse over the times in the upper left to advance the map from day 1 through day 7:
http://www.meteo.psu.edu/~gadomski/ECMW ... floop.html
In particular, look at the map for 6am Monday:
http://www.meteo.psu.edu/~gadomski/ECMWF_12z/f168.gif
Note the red dashed line in the map on the upper left. That's the 5400 meter sfc-500mb thickness line. You don't need to know what that means, technically, but generally the snow line is well south of that red dashed line. A good rule of thumb for us is that the rain/snow line is one line out ahead of that red dashed line, the 5460 meter thickness line. So that shows the air is cold enough for snow all the way down to Victoria on Monday morning.
Now look at the map in the upper left, the 500 mb (18,000ft) contour map. Note the axis of low pressure is well to our northwest and a disturbance is rotating around the bottom of the trof. That's a sign that another wave will be developing along the cold front on Monday morning (translation - precipitation likely here) with temperatures cold enough for snow here.
Now look at the lower 2 maps indicating relative humidity (moisture) in the lower to mid parts of the atmosphere. Plenty of moisture available.
So we have air cold enough for snow, a disturbance moving across the cold air to produce lifting, and plenty of moisture to squeeze out precipitation. All this points to frozen precipitaion possible in Houston on Sunday/Monday.
The ECMWF has been consistent in this forecast (the general idea) for 2-3 days now, though it wasn't as bullish on frozen precip chances until the last few runs. The American model, on the other hand, is completely lost. And that's the model that the NWS and Weather Channel are following with their temperature forecasts. The GFS did absolutely terribly with the last event, as it just can't handle Arctic air. It's clearly out to lunch with the coming weekend's Arctic air. The NWS is forecasting a high in the 50-52 range here Sunday/Monday, when it could be as cold as 34-36 for the highs, maybe even colder.
Bottom line -- it's by no means a certainty, but I think that we may have a reasonable chance of seeing frozen precipitation here in Houston on Sunday/Monday. It certainly looks very cold, regardless. Let's see if the ECMWF continues the current trend over the next 2-3 runs (every 12 hours), and if the GFS ever gets a clue in the coming days.