Another Wintry Miss

I have been watching the forecast for tomorrow for a week now and it has actually been fairly consistent. When preparing a forecast each day, I look at nine different computer models that are in no relation to each other. It is good to look at many different suggestions to get a good idea about what may happen in the forecast. Because they are computers, there are biases. The GFS model is one and it is on the left. The NAM is another, which is on the right. You don't need to know what they mean, just that they are two completely different models. The GFS (left) has a bias to overdue precipitation amounts. So when it is showing precipitation, you know to knock it down a few notches. The GFS is also a long-range model, so it goes out 184 hours. The NAM (right) is a short-range model, which goes out 84 hours.

The GFS model has been predicting for the last week that the upper-level low pressure system headed our way will miss our area to the south. It was, however, still bringing in a lot of rain and snow for tomorrow morning. That would not be possible, since the best dynamics for rain/snow would be to our south. That shows the overdoing precipitation bias. However, the latest run this morning has gotten on board with the other eight models in keeping our area dry.

The NAM model is usually very bad when predicting precipitation for west Texas. It is not a good predictor, especially for severe weather season. However, this model has kept things consistently dry over the last few days for the forecast tomorrow. When the NAM is actually agreeing with other models, you know that things are lining up pretty well.

Computer models can be wrong, especially when it comes to winter weather in west Texas. However, with nine models all predicting dry weather, as a forecaster, you go with a dry forecast. Nearly all forecast models are available to all forecasters, as well as the general public. So every forecaster should be looking at the same thing, right? Well, some forecasters religiously rely on one, or two models, or will just go with a wet forecast because one, or two models are showing precipitation. So even though models can be showing one thing, or another, there is still a human element to the final product you see on tv, or online.

Now, with everything I wrote above about it being a dry forecast tomorrow, it does appear that some moisture will be able to make it into the southern counties. There will barely be enough for some light freezing drizzle, flurries, or very light snow. In all likelihood, there will be no accumulations in our area, even when a few see flurries. That is good news for driving on Thursday. However, even some light freezing drizzle can cause slick spots on the roads, so just be careful going to work and school tomorrow, as there will be some patchy icy spots few and far between.

The above photo is showing projected snow accumulation for Thursday by lunchtime. 90% of us will be dry tomorrow and will not see any precipitation at all. Everything I have written is the reason why I have 10% in the forecast for some very light freezing drizzle, flurries, or very light snow for tomorrow morning. All the activity will move east by lunch time tomorrow and we'll just see cloudy skies and much colder air.