Hard Freeze Tonight, But How Cold?

One of the hardest part about being a meteorologist is using computer information as guidance. A fair amount of the time, they are great guidelines, but not to be used verbatim. One way we can tell if a model will steer us in the right direction is if it initializes well. In other words, if the model predicted the current weather well, then its future forecast will do well. However, if there is a drastic difference between the model and what is really going on outside, a meteorologist needs to dig much deeper to find a solution for the forecast.

Toady's dilemma has to do with the overnight temperatures. In order to get a frigid night there are three main ingredients; a clear sky, dry air, and light winds. Despite very high winds this morning, high pressure will crest in central Texas tonight and calm the wind. We are all go for a light wind. Also, there are high thin clouds that will float overhead. Therefore the sky will not be completely clear, but a fair amount of the solar radiation from this afternoon will escape into the atmosphere. The big question is with the dry air.

Computer models predicted that dew points will be in the mid to upper teens this afternoon. Actually, the dew points were near 10° if not in the single digits. Since the air was much drier than predicted, this leads me to believe that the temperature will be lower than the actual computer forecast.

Note: The drier the air, the less energy air needs to cool and warm. At night, after the sun goes down, a dry air mass will cool rapidly, as opposed to one that is moist (more humid).

Overall, the air is much direr than predicted, and from what I learned in the classroom, the temperature should drop lower than what the computers illustrate.

Here is an example of our in house computer model of the low temperatures tonight:

The above image shows temperatures in the 30s and upper 20s. Based on how the atmosphere is set up right now and where it will be tonight, I very much disagree with these numbers. Dew points will be in the single numbers and lower teens tonight. This means that the temperature could fall at most to these values. With a few clouds overhead, the air will not cool as efficiently. In other words, temperatures will likely be a bit above the dew point.

What I am trying to spell out here is that tonight's forecast is a tough one. Computers have been way off, and my personal predictions may not shape up, but its an educational guess based on many parameters.

The following image displays my current forecast for tonight, which is much different than the model forecast.

This is the toughest part of meteorology when your forecast is drastically different than the guidance. Its all a learning game. If I am way off tonight, then this will be a learning experience.

Make sure to wrap the pipes tonight, get the plants and the pets in too. Warm up with a hot cup of tea.