Synoptic-Scale Conditions Leading to Flooding in South Carolina: A Case
Study of October 22-23, 1990(www.treehugger.com)
Erik D. Kabela Joanne Stevenson
Mini Tech 2009
Objectives• Illustrate the effects on society (public/private property
damage, evacuations, loss of life, etc) of this event.
• Link Maddox's (1979)* definition of a synoptic flash flooding event with October 22-23, 1990 event– Determine which of the 5 heavy rain event set-ups
identified by Konrad (1997)** fits with this event
• Enhance the understanding and application of pattern recognition in heavy rain and flood forecasting
*Maddox, R. A., Chappell, C. F. and L. R. Hoxit, 1979. Synoptic and Meso-α Scale Aspects of Flash Flood Events. Bull. of the Amer. Meteor. Soc. , 60 (2), 115-123.
**Konrad II, C. E., 1997. Synoptic-Scale Features Associated with Warm Season Heavy Rainfall over the Interior Southeastern United States. Wea. Forcasting, 12, 557-571.
Methods•Archives
• The State, Greenville News, Aiken County Standard, The New York Times
• SHELDUS
•Web interfaces: • NCDC - NOMADS• Plymouth State University -Plot
generation interface• NOAA - National Severe
Storms Laboratory
•NOAA – Daily Weather Maps•USGS – Water Resources Data
(Maddox et al., 1979)
Flooding Impacts•SC hit by disintegrating Hurricane Klaus and Tropical Storm Marco (Oct. 8-14)
•Up to 15” of rain•Damage of $3-8 million, several thousand evacuations, 120 dam failures, 5 deaths
•Cold front moved through (Oct.22)•Day and a half of nearly continuous rainfall on already stressed hydro system•11 counties receive Presidential Disaster Declarations (PDDs)
• >1,400 registrations for temporary housing, recovery of lost property, or repairs
• >$10 m of aid administered by federal government
(NOAA,http://www.hpc.ncep.noaa.gov/tropical/rain/marcoklaus1990.html)
Pre-Exisiting Conditions
Flood Stage
Heavy Rain/Flood Definition
• According to Konrad (1997)– At least 2 inches in a 6 hour period
• Break in between hourly precipitation could not exceed 2 hours
36-Hour Total Precipitation
Components of a Maddox Synoptic-Type Flood Event
• Quasi-stationary or slow moving weak cold front
• Ample low-level moisture– Usually greater than 60°F surface dew point
• 500mb strong short-wave trough• Ample mid-level moisture
– Dew point depression of <= 6°C
Surface Map – Oct. 22, 1990
500mb – Oct. 22, 1990
Maddox Ideal vs. Oct 23 00Z Surface Map
Td = 70
Td = 70
Maddox Ideal vs. Oct 23 00Z 500mb Map
Comparison to Konrad – Type 2Key Contributions Include:• Slow moving cold front
– Type 2 typically occurs during the transition season
• Ample low- and mid-level moisture• Low-level convergence
– Located NW of heavy rain• Upper-level divergence• Strong 500mb Vorticity Max• Strong mean 850-200mb winds (>21 m/s)
from the SW
• Strong instability using the K-Index• 850mb warm-air advection• Rain cells develop in “echo train” pattern
Ample Mid and Low-Level Moisture
700Mb mixing ratio of greater than 7 g/kg
Surface precipitable water of greater than 1.5 inches (38.1 mm)
Low-level Convergence
• Low-level convergence max to the NW of the heavy precipitation
200mb Divergence
• Upper-level divergence promotes upward motion
• Heavy Rain area located over the left exit region of jet
500mb Vorticity Maximum
• Heavy rain located to the right of vorticity max
850 – 200mb Winds
• Mean 850 to 200mb winds blowing parallel to surface boundary
• Mean 850 to 200mb wind speed ≈24m/s
Instability with the K-Index
• K-Index between 28 and 32– Corresponds to roughly 40-
60% chance of showers and thunderstorms
850mb Warm-Air Advection
• 850mb WWA promotes low-level rising motion
Conclusions• Pre-existing stream conditions lead to
increased potential for flooding on Oct 22-23• Flooding event of Oct. 22-23, 1990 fits
classification of Maddox synoptic-type flood• Flooding event further broken down into a
Konrad Pattern 2 heavy rain event• Provides a basis for using climatological
studies for use in everyday forecasting• Can prove useful for operational forecasters
as well as emergency managers
Top Related