The La Mancha Index (LMI): Correlating Eastern Pacific Sea Surface Temperature Anomalies to California Precipitation Variabili
Miles Muzio, KBAK-TV, Bakersfield, CA
Sheldon Kusselson, Retired NESDIS
Jan Null, Retired- MIC San Francisco
Kahtia Hall, KBAK-TV

An ongoing 5-year drought in California came to sudden and unexpected end during the winter of 2016-17. NOAA’s seasonal forecast from the previous autumn had been pessimistic for any substantial relief. In central California, the Drought Monitor improved from “Exceptional Drought” to no drought in 6 weeks. The Sierra snowpack reached a 22-year peak. A conspicuous region of cold SST anomaly was present near 40°N and 140°W, nearly 2000 miles WSW of Seattle. This same feature was present during two previous periods of extreme rainfall in California (December 2010 and the 1997-98 El Nino).

An investigation has been undertaken to define the region (tentatively named “La Mancha”) and its relationship to other atmospheric entities which have together produced heavy rain in California. How does this promote or enhance atmospheric rivers? What role does La Mancha play with precipitable water plumes? Does it work in concert with ENSO or other teleconnections? When in a warm phase, does this feature help produce or exacerbate drought conditions? Is there a reciprocal downstream enhancement of cold weather in the eastern US during the warm phase of La Mancha?

This study attempts to answers those questions. New methodology is introduced using standard deviation of both SST anomaly and total precipitable water to compare regions in the eastern Pacific. Water vapor data dates back to 1987 and SST data to 1950. The expectation is to discover a statistical correlation that may be applied to future medium and long range precipitation forecasts in California and the western US.