Hot and mostly dry pattern to continue

Published 7:00 am Tuesday, July 14, 2015

The central Gulf Coast is stuck in a hot and dry weather pattern, and it will likely continue until at least the early part of next week.
Every day the hot July sun is heating up the air near the surface of the earth. Due to our proximity to the Gulf of Mexico, there’s plenty of water vapor in the air. Hot air at the surface usually rises, and in combination with the moisture, usually leads to afternoon summer thunderstorms.
But since late last week, warm and dry air aloft has put a lid on those bubbles of air as they rise from the surface. Most of the puffy cumulus clouds that have formed simply can’t punch through the warm temperature cap, also called an inversion, that exists about one mile above the surface.
The reason for that cap is that at even higher altitudes, several miles above the surface, a warm ridge of high pressure is in place, and, in fact, is growing stronger. Friday and Saturday it was centered over us. The center of the high has since shifted to the west over Texas, but it still extends eastward into our area. The sinking air associated with the high is called subsidence and is the cause of the warmer and drier-than-average air aloft.
Until the upper high moves or weakens, we will stay very hot, with highs in the mid 90s, with only very isolated showers in south Mississippi and Louisiana.
Even though it is drier than average at upper levels, the atmosphere down where we live still has plenty of water vapor. Dew points have been running from about 72 to 77 degrees. As I explained in a column in May, anytime the dew point rises above about 70 degrees our perspiration becomes much less efficient at cooling us off, and most of us are going to feel sticky and uncomfortable.
The effect of the humidity is accounted for and combined with the air temperature to compute the “heat index.” The heat index is a measure of how hot it feels to us humans. The heat index in the afternoon the last few days has been from 105 to 110 in Pearl River County and across most of south Mississippi and Louisiana. That is likely to continue as long as the current pattern holds.
The heat index applies to the shade not the sun. If you are out in the sun, especially in the middle part of the day when the sun’s rays are the most direct, the apparent or “felt” temperature affecting your body is going to be even higher.
That’s why it is so important, if you must be outside during weather such as we are having right now, to drink plenty of fluids, limit your physical activity, and try to stay out of the direct sun.
In other words, business as usual for the peak of July heat in the Deep South.
A little ray of hope, or more accurately more widespread afternoon showers to cool us down a little, appears in the numerical weather model runs for early next week. The models predict that the upper high will break down as a trough of lower pressure moves from west to east across the northern states of the U.S.

By Skip Rigney

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