Severe thunderstorms are in the forecast for the Deep South this week, however the system will diminish in intensity as it moves east towards the state of Georgia.
The reason for the stronger threat of severe storms in the Mississippi and west Alabama areas are due to the stronger wind dynamics as well as greater values of convective available potential energy (CAPE) in those regions verses in the state of Georgia.
More rapidly rising air, known as CAPE, is available in the Mississippi River Delta area, however this CAPE diminishes as the system moves east.
With less rising air available over North Georgia, the storms will lose intensity, though heavy rain will still be an issue between Midnight at 8am Thursday.
But the severe storm threat is also better supported by the upper level jet, which has maximum diffluence over the Mississippi River Valley.
In the upper level atmosphere, approximately 5 to 6 miles above the ground, the air is diffluent over Louisiana and Mississippi. Diffluence is a wind flow in which air flows outward, or away -- it “fans out”, causing rapidly rising air to occur in the air layers down below. The black box below denotes the area of diffluence on the 300 millibar map (the layer of atmosphere approximately 5 to 6 miles above the ground).
However, once the system moves east, that diffluence becomes more lacking, and the stronger winds within the jet stream are located further north of the state of Georgia.
The low level jet (located about a mile above the ground) will still be strong over the state of Georgia, but it will be in the same direction as the upper level jet. As a result, the wind will flow parallel from the surface of the ground compared to 5-6 miles above, which tends to produce a linear squall line at the ground. Still, with a low level jet in the 60-70 knot range, a few damaging wind gusts cannot be ruled out for Thursday morning.
The squall line will approach north Georgia just before midnight, and it will move into the Northwest Metro Atlanta area through 5am. The line of heavy rain and thunderstorms will move over Downtown Atlanta through 8am, and the entire Metro Atlanta region will dry out by 10am.
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