Fog in late Spring, Summer and Fall

During late spring, summer and early fall, fog of any type does not create a problem except for brief periods near sunrise when the visibility is reduced to less than 4 miles. The following are scenarios that have been researched to identify the onset and dissipation of summertime fog regimes.

1) When high pressure sets up over east central AL/GA with northeast to easterly flow from 500 mb to the surface, fog will form after 06Z/01 local and dissipate about 12Z/07 local. Visibility can be reduced to 4 nm.

2) When the Bermuda High ridges at the surface from the western Atlantic over FL/AL/MS, and the 850 mb high is located over central AL, and the 500 mb high is located over southern AL/FL border, (east of NAS Whiting Field), expect fog in the early morning and haze late morning into the late evening. Fog and haze will persist for 24 to 36 hours or longer as long as the SE wind component persists at the lower levels. Approximate sky conditions: 020 Scattered to Broken and 250 Broken. Visibility will decrease to 4-6 nm in haze, and 3-5 nm in fog. Fog will begin to develop by 07Z/02 local.

3) When a surface and and 850 mb ridge/high moves or develops to the NW of NPA, from LA through AL, and the surface and upper level winds are northwesterly, a drying condition will exist and fog and haze will not form. Sky condition: Scattered Cirrus. When the high pressure system moves eastward and a southeasterly flow develops at the surface as well as the 850 mb, expect fog to develop after 06Z/01 local and haze to develop after 11Z/06 local reducing visibility to 4-6 nm in haze, 3-5 nm in fog.

4) When a surface high develops or moves over central GA and the 850 mb high develops or moves over the east coast of FL (JAX, ORL area) or southern GA, expect the onset of fog to develop after 06Z/01 local and continue for two to four hours. Expect light SSE-SSW surface winds, <8 knots, sky condition: 015-020 Scattered, Scattered Cirrus, visibility: 4-6 nm in fog.

5) When the 850, 700, 500 and 300 mb upper level high and/or ridge is stacked or nearly stacked over central TX, expect visibility to lower to 5-6 nm in fog. Predominant winds are a SE flow at all levels. If this condition persists for 36 hours or more (NPA on the strong side of the high), expect haze to develop by the 2nd day and reduce visibility to 4-5 nm and fog to develop after 03Z/22 local reducing visibility to 2-3 nm in fog. Expect daytime surface winds from 120-150, at 10-12 knots, decreasing to less than 8 knots after sunset. Expect haze to dissipate as the high moves eastward to the NW of NPA as per para 3.

6) Occasionally a quasi-stationary front will extend north of NPA across the N FL/ Southern AL/GA border. The weak surface high will usually set up over the eastern Gulf of Mexico, Central Florida, or the Western Atlantic. With the frontal boundary just to the north, fog and haze formation is rare due to the northwest-northeasterly component at 850 to 300 mbs. If the frontal system is located more to the north across Central AL/GA and the surface high pressure center is located over the northeast Gulf of Mexico, Central FL, expect fog to form after 06Z/00 local decreasing the visibility to 4-6 nm then dissipate after 10Z/05 local. If the front moves to the south of NPA and there is a surface high located over NC/VA look for fog to develop north of the field and inland, but not at the station.

d. True frontal fogs are a rarity, but slow moving and quasi-stationary frontal systems in combination with advection fog produce widespread fog and low stratus that can persist for days.
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