Orographically induced cirrus clouds east of the Southern Appalachian Mountains

The development of orographically induced cirrus clouds east of the southern Appalachian Mountain chain can result in areas of unanticipated cloudiness downstream from the higher terrain across the Carolinas and Virginia. Both the degree of cloudiness and its impact on surface temperatures can have an adverse impact on forecast accuracy. The general environmental conditions favorable for orographic cirrus development are known and have been qualitatively documented, but to this point have not been extensively quantified. This study will attempt to quantify the conditions necessary for orographic cirrus development across the southern Appalachian Mountains.

Data for this project spans one year from February 2009 through February 2010. Forty unique cases in which orographic cirrus was observed on GOES infrared satellite imagery near regional upper-air observations were identified and will be evaluated. Regional radiosonde observations from Atlanta, GA., Greensboro, NC., Roanoke, VA., Sterling, VA., and Pittsburgh, PA. were included in the study. Frequency graphs that evaluate the month of occurrence, duration of the event, as well as the inversion height, depth and strength associated with each orographic cirrus case will be shown. Wind roses will be constructed to show winds at the top of the inversion as well as at the tropopause. A composite sounding will be developed to depict ideal conditions for orographic cirrus development.

NCAR/NCEP reanalysis data is used to evaluate the regional synoptic environment prior to and during the orographic cirrus outbreak. A composite synoptic analysis will be created to show an ideal pattern favorable for cirrus development.