Mean Recurrence Intervals and Annual Probabilities
A Winter Weather Climatology for the Southeastern United States
Christopher Fuhrmann and Charles E. Konrad, II
Department of Geography
The University of North Carolina at Chapel Hill
Freezing Rain
Freezing rain events (0.25 inches and greater) show the shortest recurrence intervals (1 per year) across the western Piedmont
of Virginia and North Carolina . Recurrence intervals of one event every two to three years are found over a broader area stretching from northern
Georgia northeastward to Virginia and the eastern half of West Virginia . Extreme northeast Tennessee and southwest Virginia display the longest
intervals (one event every eight years) where adiabatic warming and cold wedge erosion are quite common. Moderate icing events display similar patterns
of frequency with a maximum of one event every five years observed from portions of northeast Georgia, northwest South Carolina northeastward through
the Piedmont of North Carolina, central Virginia, and eastern portions of West Virginia. The recurrence intervals for the heaviest events (1.0 inches
and greater) show less regional continuity as multiple occurrences over each station's period of record are restricted to a few locations (e.g. Atlanta,
GA; Raleigh, NC; Greensboro, NC; Roanoke, VA; Beckley, WV). The heaviest freezing rain events occurred across portions of the Piedmont of North Carolina,
the plateaus of southern West Virginia , and along the Appalachian escarpment in southwestern Virginia. These include the December 2002 event (1.42
inches at Raleigh, NC ), the early season event at Beckley, WV (1.68 inches in mid-November 1991), and the February 1994 events at Roanoke, VA (1.87 inches).
Click here to view a table of station by station freezing rain MRI and annual probabilities.
Sleet
Given the rarity of sleet dominant events across the Southeast, recurrence intervals are much longer than those associated with
other frozen precipitation types. Sleet events (0.12 inches and greater) are relatively more common (once every 15 years) over the southeastern three-quarters
of the study area with the highest frequencies (one event every five years) found over portions of North Carolina, extreme northeastern Tennessee and
southern Virginia. Heavier icing events (0.25 inches and greater) are most frequent (one event every 10 years) in the Piedmont of North Carolina, extreme
southern Virginia, and northern South Carolina . One-third of the stations in the study, especially those across the western portions of the Appalachian
Mountains, did not experience a single sleet dominant event of this magnitude over their period of record. The heaviest sleet events (0.75 inches and greater) were
confined to the southern part of the region and the extreme eastern Piedmont of North Carolina with recurrence intervals ranging from one event every 27 years at
Raleigh, NC to one event every 46 years at both Columbia, SC and Athens, GA. The heaviest sleet event was recorded at Columbia, SC over the period February 17-18,
1979 where 1.38 inches (liquid equivalent) was measured.
Click here to view a table of station by station sleet MRI and annual probabilities.
Snow*
The annual recurrence of various snowfall intensities shows great latitudinal variability, with some coastal influence. This pattern
remains fairly consistent up to snowfall totals of 15 inches and greater, in which case the shortest intervals occur in the northwest part of the region in
the Appalachians (one event every 15 years), with one 15-inch-plus event occurring along the North Carolina coast. Snowfall totals of 20 inches and greater
are generally confined to the mountains, although a "surprise" yet rare winter storm in January 2000 dumped over 22 inches of snow in Raleigh, NC.
Click here to view a table of station by station snow MRI and annual probabilities.
*As measured at cooperative observer stations, see Data and Methods
