Typical mild, dry air returns by Thursday

Published 7:00 am Tuesday, September 29, 2015

Low pressure in the middle and upper atmosphere and a surface low in the Gulf of Mexico combined to bring a surge of moisture, clouds, and rain out of the Gulf and into our area on Sunday.
Most of the county received about two-thirds of an inch of rain Sunday.
Much heavier amounts fell just to our east along the Gulf Coast. Areas near Pascagoula and Mobile received over seven inches of rain Sunday through early Monday morning.
These low pressure systems are expected to hang around through Tuesday and part of Wednesday giving us high humidities and a chance of showers each day.
What will get us out of the humid, showery air from the Gulf? An upper level wave of low pressure, three to seven miles up in the atmosphere is riding to our rescue on the northern jet stream. Diving south out of the Canadian plains, this trough is likely to extend from the Great Lakes all the way down into the Gulf of Mexico by Wednesday night.
The upper trough will also push through an associated surface cool front. All of which means that our winds through the lowest seven or so miles of the atmosphere will switch from southerly to northwesterly.
Those winds will bring dry air and mostly fair skies for Thursday, Friday, and Saturday. The air mass behind Wednesday’s front will be very seasonable. High and low temperatures will be near our averages for the first few days of October, about 84 and 60 degrees, respectively.
What can we expect in the longer term?
Every six hours, the National Weather Service’s Center for Environmental Prediction, NCEP, runs their global computer-based numerical weather model, known as the Global Forecast System or GFS, out to 16 days. As I’ve discussed in this column before, the skill of the model in depicting the largest, most significant weather systems is usually pretty good out to five to seven days from the time that it is run on NCEP’s supercomputers. In fact, that’s the main reason that I am able to write this column on Monday morning and discuss the upcoming week’s weather with some confidence that I won’t routinely be embarrassed.
For a whole host of reasons, and in keeping with what common sense would tell you, model skill of the GFS — and all other computer models — gets poorer the longer the forecast period is from the time that the model is run.
Still, these models can give us some information about the general trends in our weather over the next two weeks. Monday morning’s GFS model run is indicating that this Wednesday’s predicted high of 87 will be our warmest temperature for the next two weeks.
In other words, it looks like the seasonal shift from late summer to early fall is about complete.
You probably didn’t need the GFS supercomputer-based weather model to tell you that. Those leaves in your yard that need raking were already a pretty good indication.

By Skip Rigney

Sign up for our daily email newsletter

Get the latest news sent to your inbox