Freezing Fog Event:  January 14, 2010

Angie Enyedi, NWS Jacksonville


An unusual freezing fog event happened this morning across portions of the Jacksonville County Warning Area (CWA).  Freezing fog is defined as a suspension of numerous minute ice crystals in the air, or water droplets at temperatures below 0 ° C, based at the Earth’s surface, which reduces horizontal visibility.  Freezing fog is also called ice fog.


This morning a ridge of high pressure was centered over coastal South Carolina and coastal Southeast Georgia. A light and shallow northeast flow filtered over much of the Jacksonville CWA around this ridge.  The moist and stable layer extended to about 400 feet above ground level (Figure 1, 12Z KJAX Sounding), then the airmass was significantly drier however strong subsidence remained in place.


Temperatures fell below freezing around midnight at the Jacksonville International Airport (JIA). The ambient temperature was around 32 ° F and dew point 31 ° F. Through 8 am local time (about 9 hours), the temperature at JIA remained below freezing with dew point depressions of only 1 ° F.  Calm winds and passing thin cirrus allowed almost ideal radiational cooling conditions to much of the CWA.


Freezing fog was reported from Alma, Georgia to Gainesville, Florida. Much of the observations were reported across northwest Duval County where moderate moisture advection combined with cold temperatures (Figure 2, MSAS surface analysis).


Sometimes freezing fog can settle on surfaces and create ice patches.  A special weather statement was issued early this morning to alert motorists of this potential hazard. is the U.S. government's official web portal to all federal, state and local government web resources and services.