|Snowfall accumulation (in inches) for the March 13-14, 1993 major snowstorm. This event was dubbed the Storm of the Century and the Blizzard of '93, which dumped very heavy snow amounts along the Appalachian mountains from northern Georgia to Pennsylvania and New York. Isolated amounts up to 2 feet fell across eastern Kentucky. Only light snow fell across central Kentucky on the western fringe of the storm. Eastern Kentucky is proned to East Coast storms, while the rest of the state and southern Indiana usually are too far west for major snow accumulation.|
TOP ROW: Composite synoptic charts at 1200 UTC 3/13/93 (top left) and 0000 UTC 3/14/93 (top right). On these charts, surface fronts are shown, including a cold front in solid blue color and a warm front in red. In addition, a surface low is indicated by a red L and labeled with minimum pressure (e.g., 960 mb at 0000 UTC 3/14/93). Also shown are 1) 850 mb temperatures every 5 deg C from +10 to -10 deg C (dashed red lines with 0 deg isotherm in sold red), 2) the axis of the low-level (850 mb) jet (bold black line with arrowhead) with wind speeds in knots indicated along the jet, 3) 500 mb heights in meters every 120 m (thin black lines), 4) 300 mb isotachs (lines of equal wind speed) in knots (green lines), and 5) 300 mb jet core (bold green line with arrowhead).
BOTTOM ROW: Contours of frontogenesis at 850 mb (blue) and 700 mb (red), and 850 mb positive equivalent potential temperature (theta-e) advection (dashed green) at 1200 UTC 3/13/93 (bottom left). Values of frontogenesis are in deg Kelvin per 100 km per 3 hours (K/100 km x 3 hr). Strongest frontogenetical forcing for lift usually occurs within and just south/east of the axis of strongest frontogenesis, with frontogenetical forcing tilted with height toward cold air. Values of theta-e advection are in 10 to the minus 1 power deg Kelvin per hour (10 e-1 K/hr). At bottom right, the axis of the maximum 850 mb (blue) and 700 mb (red) frontogenesis is displayed at 0000 UTC 3/14/93 (note the tilted frontogenetical zone with height toward cold air). Also shown are 300 mb isotachs (green), the 300 mb jet core (bold green line with arrowhead), and the surface low (blue L) position 24 hours earlier at 0000 UTC 3/13/93 (i.e., as the storm was beginning its rapid intensification phase). The main frontogenetical forcing at 0000 UTC 3/13/93 (not shown) was across the southeastern United States.
Summary of Event
Surface: This event, named the "Blizzard of 93" and the "Storm of the Century," blasted the eastern U.S. with very heavy precipitation, record snows, and strong winds, with tornadoes in Florida. At the surface, a low pressure center across the northern Gulf of Mexico (approximately 993 mb) at 0000 UTC 3/13 showed explosive development as it moved to eastern Georgia by 1200 UTC 3/13 (980 mb), and to the Delmarva area by 0000 UTC 3/14 (960 mb). The low weakened slightly thereafter as it moved into Maine by 1200 UTC 3/14 (964 mb). Intensification resulted from substantial low-level convergence along a strong baroclinic zone, strong upper-level divergence, significant diabatic heating, and a tropospheric undulation of warm stratospheric air aloft overtop the baroclinic zone. Eastern Kentucky remained in cold northerly flow west of the low center during the event.
850 mb/700 mb: Similar to the surface low, the 850 and 700 mb lows intensified rapidly as they moved from the north-central Gulf at 0000 UTC 3/13 to the Delmarva region by 0000 UTC 3/14. The low-level jet increased dramatically (60-75 kts) in response to the rapid deepening, which caused strong warm advection, isentropic lift, and east-to-west moisture transport along and east of the Appalachian mountains to the north of the low center. Significant forcing extended westward into eastern Kentucky. Strong low-level moisture convergence and theta-e advection were noted along and especially east of the mountains. Pronounced frontogenetical forcing occurred at 850 and 700 mb across the southeastern U.S. at 0000 UTC 3/13, then along the spine of the Appalachians from northern Georgia to Pennsylvania, including eastern Kentucky, at 1200 UTC 3/13. The strongest forcing moved northeastward by 0000 UTC 3/14.
500 mb: A strong shortwave across the central Gulf of Mexico and a second shortwave digging southeastward across Oklahoma at 0000 UTC 3/13 began to phase by 1200 UTC 3/13 across the southeastern U.S. accompanied by very large height falls (250 m in 12 hours). This caused the southern portion of a 500 mb meridional height trough axis to become negatively tilted with a downwind shortwave ridge induced across the middle Atlantic states. The shortening wavelength between the deep trough axis in the Southeast and the downstream ridge promoted a dramatic increase in vertical motion along and east of the Appalachians. Additional height falls occurred as the system closed off and reached the central Appalachian mountains by 0000 UTC 3/14. The low lifted quickly to New England by 1200 UTC 3/14.
300 mb: A high-speed anticyclonically-curved jet stream (maximum winds above 150 kts) was located from the lower Mississippi Valley northward across the Ohio Valley to New England at 0000 UTC 3/13. Strong along-stream variation was noted within the jet's entrance region (e.g., 55 kt winds at Lake Charles, LA increasing to 115 kts at Little Rock). As a result, ageostrophic wind vectors revealed strong upper divergence over the Gulf and southeastern U.S. along the low-level baroclinic zone, a key in rapid surface intensification. A secondary jet streak was digging southeastward across the high Plains at 0000 UTC 3/13. By 1200 UTC 3/13, the anticyclonic jet lifted northward with continued entrance region along-stream variation across the Ohio and Tennessee Valleys. At the same time, the secondary jet became cyclonically-curved as it translated/reformed through the base of the trough across the southeastern U.S. and southern Appalachians. As a result, a coupled jet structure was evident across the central Appalachians, which enhanced upper divergence and lift toward the divergence maximum. Satellite imagery revealed a large comma-shaped cloud pattern across the Appalachians (including eastern Kentucky) associated with the jet dynamics and period of maximum lift. Similar to other studied events, the presence of a pronounced anticyclonically-curved jet streak entrance region provided an enhanced region of divergence. The low-level ageostrophic flow within the entrance region's direct thermal circulation promoted low-level cold advection and convergence, thereby enhancing frontogenetical forcing and lift. The resulting adiabatic cooling combined with the ageostrophic flow played a key role in keeping cold air in place across inland areas of the middle Atlantic states and Appalachian mountains, despite strong low-level warm advection. By 1200 UTC 3/14, the strongest jet dynamics pushed well to the northeast of eastern Kentucky.