Some results from a sounding enhanced observing period focusing on low ceiling and visibility conditions in the northeastern United States

The NCAR mobile GPS LORAN Atmospheric Sounding System (GLASS) was deployed at the FAA C&V field site in Brookhaven NY during the month of May 2005 to enhance the observing capabilities for the study of low clouds and fog. Complementing the regular NWS soundings performed at the nearby Upton NY weather office, additional radiosondes were released to sample the vertical structure of the lower atmosphere during evolving low ceiling and visibility conditions. The data from GLASS soundings were collected and analyzed to identify important influences on the evolution of low stratiform cloud ceilings over eastern Long Island NY. A case study analysis of an intrusion of a marine stratus cloud layer is reported in this paper, as well as distinct features observed during the dissipation phase of two other low cloud ceiling events. Results indicate that the evolution of low clouds is greatly influenced by advective processes associated with mesoscale circulations and variability of temperature and moisture in the coastal lower atmosphere.