A diagnosis of tropospheric effects upon surface precipitation amount for a sample of east coast snowstorms

Upper-air variables have been correlated with near-simultaneous precipitati on observations from 35 winter storms that produced heavy snowfall in the e astern coastal region of the United States. Standard radiosonde observation s (raob's) were used to calculate upper-air variables at mandatory levels, while liquid-equivalent precipitation amounts were gathered from surface re ports at five stations within the region. This study seeks to identify thos e synoptic-scale variables, individually and in combination with other vari ables that may be useful to estimate short-term precipitation amount. Using both simple and multiple correlation analyses, the selected variables (e.g ., thermal and vorticity advections, wind speeds, moisture convergence and advection, divergence, etc.) were correlated with precipitation amounts occ urring over 1-, 3-, and 6-h periods near raob times. The best correlated upper-air variables (using the 6-h duration) are 850-mb temperature advection (0.48), 850-mb equivalent potential temperature adve ction (0.45), 250-mb temperature advection (0.43), and 300-mb vorticity adv ection (0.41). Adding a second Variable increased the explained variance by 7%, but only a very slight additional explained variance was obtained by a dding a third variable. The relative importance of upper-air dynamics to pr ecipitation amount also varies by storm stage. For instance. Vorticity adve ction is apparently more important at the beginning stage, while temperatur e advection at lower- and upper-tropospheric levels and upper-tropospheric divergence are better correlated near the conclusion of a storm.