Evaluation of NCAR’s AutoNowCaster for Operational Application within the National Weather Service

NCAR’s AutoNowCaster (ANC) was modified to run over a large domain which encompasses Chicago’s, New York City’s and Atlanta’s Air Traffic Management hubs. ANC produces nowcasts of Convective Likelihood (CL), with higher values delineating areas where storms are likely to form and be sustained, and vice-versa. This paper presents the results of verifying ANC’s 60-minute nowcasts of CL over the study area using data collected from June 11 to September 30, 2012. To reduce the high sensitivity of statistical scores to small errors in location and timing, spatial and temporal relaxation techniques were explored. The results show that, at a spatial scale of roughly 50 km and with no temporal relaxation, a CL value of 0.6 is an optimum threshold for nowcasting the general areas both where new storms may initiate and where existing storms will be sustained. Moreover, at that same spatial scale and with temporal relaxation (45 to 90 minutes from the nowcast issuance time), a CL value of 0.7 is a good threshold for nowcasting convective initiation alone.