by Angie Enyedi, NWS Jacksonville
The Honey Prairie wildfire continued to burn across the Okefenokee Swamp the evening of May 8th. The plume from the fire was very thick and, around 5 pm, extended generally east of the fire. Visibilities as low a 1 mile were reported in Kingsland, Georgia, about 40 miles ENE of the ground fire. Prevailing surface winds at the Jacksonville International Airport (JAX), were expected to remain WSW through the evening, which would keep the smoke north of the airport terminal. However, between 5:30 pm and 6 pm local time, winds shifted to the NNE at JAX and the smoke plume invaded the terminal's skies. What caused the wind shift?
At 5 pm, the JAX observation reported surface winds from the NW. The visible satellite image from 5:15 pm EDT showed the southern edge of the smoke plume north of JAX, and the observation reported P6SM visibility (greater than 6 statute miles for surface visibility). A quick glance at the 0.5 degree elevation slice from the NWS Jacksonville 88-D Radar showed the east coast sea breeze front making slow progress inland (prevailing WSW flow today), but also an interesting boundary moving slowly SSE north of JAX. This boundary looked like it coincided with the southern fringe of the smoke plume. At this time, it is believed that this boundary developed due to the thermal gradient between the cooler air under the thick smoke plume and the warmer air just outside of the plume, where JAX was reporting 90 degrees at 5 pm. This boundary was slowly moving SSE as the coast sea breeze approached from the east, both headed toward JAX. Please refer to Image 1, satellite and radar data from just before 5 pm through about 5:15 pm.
By 6 pm, the two boundaries merged just north of JAX, then the hybrid boundary moved south-southwest and crossed JAX by 6 pm. The observation from JAX at 6 pm reported a temperature drop to 84 degrees and wind shift to the northeast. Visibility was 4SM due to smoke. Please refer to Image 2 for satellite and radar data between 5:31 pm and 6 pm.
It is amazing how microscale meteorology can alter the weather so quickly and create drastic changes!