Hottest Weather Of Season In Forecast
Upper air high pressure returned to the area on Friday, raising temperatures, suppressing showers, and promising the hottest weather of the season thus far for the weekend and early next week.
The ridge was oriented from New Mexico across North Texas and into the Mississippi River Valley. It should hold roughly that position through Tuesday, with a slow westward retreat afterwards. At the surface, high pressure was to the southeast of the region and low pressure to the west. This caused a southwesterly wind at 5-15 mph, which may increase in velocity slightly.
Also, temperatures at the top of the “boundary layer” the bottom few thousand feet of the atmosphere—are forecast to warm to near 80. In addition, the boundary layer is unusually thick, running near 4,800 feet. The top of the boundary layer is determined by the altitude at which the barometric pressure falls to 850 mbs., about 25.5 inches of mercury.
These together translate to hot temperatures. The upper air high brings subsiding air flow; the southwest winds bring air down terrain. As air moves downward through the atmosphere, it warms and dries.
The thick boundary layer and high temperatures at its top mean that vertical air mixing results in cooler air above its top being shut out, and warm air mixing down.
There will be a shallow layer of rather moist air trapped at the surface. This will result in high relative humidities.
As a consequence, a heat advisory may be needed for the region beginning Sunday.
The ridge should begin a westward shift at mid-week. This will take some of the pressure off afternoon temperatures, and might even permit some showers late next week.
The salutary effects of the late-June rains are gone. Thus, moist soils and lush vegetation will no longer act as a brake on the heat as occurred earlier this month.
The rains associated with Dolly were too light and scattered this far north to reinforce the damper. Over the southern and southeastern counties, the heat should not be as intense because rains of one to three inches were general below a Center-Livingston line.
Another effect of subsiding air can be the accumulation of atmospheric pollutants, particularly ozone. This should bring a haze layer, which will likely hold visibilities at around 5 miles during the daylight hours.
Friday saw temperatures rise a couple of degrees above Thursday’s levels, and run about 2 degrees above normal. Saturday’s temperatures should climb another couple of degrees, with an additional 2 degrees forecast for Sunday before averages plateau.
Low readings Friday morning were in the 70s, and were higher than on Thursday.
Low temperatures Saturday through Monday should also be in the 70s.
Afternoon highs Saturday were from the lower to middle 90s, also higher than on Thursday.
High temperatures Saturday should run from the middle to high 90s, with high 90s to around 102 likely Sunday through Tuesday.
A low overcast developed around dawn, but had burned off from most stations by mid-morning.
Tyler’s highest sustaining wind Friday was southerly at 15 mph with a peak gust of 18 mph, and an average velocity of 8.9 mph. Thursday’s average wind velocity was 8.6 mph.
Friday’s average relative humidity was 61 percent, with lower values likely Saturday through Monday. Thursday’s average was 66 percent.
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