Day 3 maximum temperature outlook

Day 3 maximum temperature outlook

The other day, as my wife applied some lotion to her hands, she asked what the humidity level was. When I told her that the relative humidity was then 80 percent, she was surprised and wondered how it could feel so dry with humidity at that level.

I then explained to her the difference between “relative humidity” and “absolute humidity” and she suggested that I share this information with readers. So here goes:

Relative humidity describes the amount of total moisture (water vapor) in the air as a percentage of the total amount that can be held at a given temperature. Since warm air can hold far more moisture than cold air (up to six times as much by volume), the relative humidity of cold air will be higher than warm air at the same temperature, even though the absolute humidity might be the same. Expressing this another way, 80 percent relative humidity at 78 degrees would feel like a virtual steam bath, while 80 percent at 50 degrees might not.

As such, the relative humidity tends to be high in the morning and lower in the afternoon when the atmosphere warms. For example, the relative humidity in Galveston at 5:45 a.m. Wednesday was 90 percent (with a temperature of 45 degrees), while it was only 37 percent at 5 p.m. Tuesday, with a temperature of 62 degrees.

Looking at the weather quickly, clouds and rain chances will be increasing as we finish the week and move through the weekend. An upper-level trough and disturbance moving slowly east and a cold front expected to move off the coast and slow-down or stall, will be the primary ingredients promoting this change.

As it looks now, I would not be surprised if Friday is quite cool here, with breezy conditions and high temperatures in the 50s.

7 day precipitation outlook

Wednesday through Friday forecast map loop

Finally, moving into the range of speculation, several of the forecast models are suggesting an outbreak of Arctic air around Christmas, combined with wet conditions. While this is too far out for any certainty, it will be something to watch as we head for the holiday. Could parts of Texas see a white Christmas?

Stan Blazyk is a life-long weather enthusiast, long-time Galveston resident and author of "A Century of Galveston Weather." He has written the weather blog for the Galveston County Daily News for more than a decade.

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