Sea fog has returned to the area with a vengeance eating the buildings in Galveston!
Check out this 7:45 a.m. shot in Galveston from my friend, Patrick Bean. There is supposed to be that big white, 26-story ANICO building in the background:
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Just so you know where the ANICO building normally is seen, I asked Patrick for a picture a couple of hours later when the fog lifted a bit:
Understanding the fog and what causes it is really pretty simple. Here’s the National Weather Service Explainer which I’ll go into a bit more:
Here is the simple part. The water right now is averaging 58° and the air streaming over it is in the low 60s. That cool water cools the air and when air cools, it condenses. What’s that? The air molecules move closer together causing them to release moisture. You see this with clouds all the time -- the warm air from the ground rises up into the air where it cools, condenses and forms clouds (or rain).
You’ve also seen “sweat” on a glass of iced tea or cold soda can. That cold can cools the warm air around it and that cooling results in condensation, or water droplets.
Easy enough. The graphic from the NWS gets confusing when we get to the dew point temperature because no one seems to quite get that.
So what is dew point temperature?
It’s easier than you think. If we are going to cool down the warm air to make it condense, then we need to know the temperature we need it to cool down to! And that number is the dew point. But it can change and that’s what is confusing. The actual temperature might be 80° and it’s already so full of moisture it only needs to cool to 75° to produce condensation. Or if the air is really dry, we might need to cool it down all the way to 50°. The dew point temperature depends on just how much moisture is already in the air and, as you know, that air can be really humid or really dry depending on the day!
So what about the fog?
Here’s a rule of thumb about fog that I use: if at 10 p.m. I see the difference between the actual temperature and the dew point temperature is 2° to 5°, then fog development is possible by morning, especially if the winds are light. That’s why I show the dew point temperatures -- they are a great measure of just how low the current temperatures have to drop to get some kind of condensation, whether it is fog, frost, dew, clouds or rain.
Here’s this morning in Pearland and you’ll notice the actual temperatures and dew point temperatures are only 2° apart (61 and 59), the humidity is super high and the winds are only 3mph -- a perfect fog set up:
The result is some kind of precip and in this case, fog and mist which resulted in low visibility. This looks like the forecast for the next couple of mornings, so get used to hearing about the dew point!
Frank