SNOW!?!? Houston, TX and snow usually don't go in the same sentence, but they did yesterday. We had about 1.5 inches of snow at the house, enough to cover the grass, car, roof top, plants, and cover the deck. It started to snow about 5 or 6 pm and lasted till about 11 pm. There were a couple of times where we had a good burst of snow, but most of it was fairly light. Amber took quite a few pictures to document the event. We wish Emma was born so she could see the snow. It might be a while before she'll have another chance. Still, it seemed like the whole neighborhood was out looking at the snow and kids playing in it even at 9pm. Don't worry, school was not canceled but quite a few districts had a 2 hour delay. A lot of the snow had melted when I got up in the morning. The temperature overnight had stayed right around freezing or a degree or two warmer. The ground was still warm, so most of it had melted off the ground. The roads were mostly clear although there were quite a few overpasses iced up around Houston. There were plenty of wrecks to go around.
So what led to this early December snowfall along the coast in Texas? Well, let the meteorologist in me explain as it is not that simple. Usually, you need a cold airmass with freezing temperatures in place ahead of the storm system. Not only that, you need some moisture hanging around in the lower and middle parts of the atmosphere. Well, down here in the Houston area, we had a strong cold front come a day in advance of an upper level storm system. The airmass was colder than forecasted a few days in advance so it made the forecast quite challenging. We also had moisture in the atmosphere from the surface up to about 18000 feet. This allows for snow to develop in the clouds and fall. Usually the snow will melt as it falls because it enters a part of the atmosphere above freezing. Sometimes it will melt and then fall through another layer of air below freezing. If this layer is deep enough, sleet will result which is just the re-freezing of melted snow. Sometimes a warm layer of air is just above the surface. This melts the snow and rain results. But since the surface is below freezing, the rain freezes and you get freezing rain. If the whole column of air is below freezing, you get snow falling. In our case, we actually had a airmass below freezing but not right at the surface. So, this is how you can have snow and the temperature be just above freezing. The snow will typically be a wet snow. One of the main reasons why this temperature profile set up for snow is because of the strong lift in the atmosphere due to the upper level storm system. This storm system helped cool the air above the surface, and when combined with the moisture, we were able to get snow on the ground. Usually with time, the surface temperature will gradually drop to freezing. After the storm system passes, the surface may actually warm a little above freezing, as was the case last night. This allowed the snow to melt enough though it was night time when the coldest temperatures typically occur.
This is actually pretty cool stuff, and why I like enough my job. It is challenge to forecast because so many parameters have to come together at an exact time and place. In Texas, those parameters may not come together until the very last moment and the next thing you know, you have snow and you busted your forecast. Those parameters usually do not all come together in Houston, TX, so forecasting snow is often missed unless it becomes obvious the day before (i.e. forecast models agree on what will happen). It is weather like this that puts us forecasters in place because we are forced to realize there is a God, and we are not Him. Sorry for the long explanation, but if you were to ask me why it snowed, this is what you would get.
