Nowcasting Storm Initiation and Growth UsingGOES-8and WSR-88D Data

Abstract

The evolution of cumulus clouds over a variety of radar-detected, boundary layer convergence features in eastern Colorado has been examined using Geostationary Operational Environmental Satellite (GOES) imagery and Weather Surveillance Radar-1988 Doppler (WSR-88D) data. While convective storms formed above horizontal rolls in the absence of any additional surface forcing, the most intense storms initiated in regions above: gust fronts, gust front interaction with horizontal rolls, and terrain-induced stationary convergence zones. The onset of vigorous cloud growth leading to storm development was characterized by cloud tops that reached subfreezing temperatures and exhibited large cooling rates at cloud top 15 min prior to the first detection of 10-dBZ radar echoes aloft and 30 min before 35 dBZ. The rate of cloud-top temperature change was found to be important for discriminating between weakly precipitating storms (Ͻ35 dBZ) and vigorous convective storms (Ͼ35 dBZ). Results from this study have been used to increase the lead time of thunderstorm initiation nowcasts with the NCAR automated, convective storm nowcasting system. This improvement is demonstrated at two operational forecast offices in Virginia and New Mexico.

Radar climatology of the COPS region

“…This reflectivity interval was chosen as the threshold based on previous work defining CI when radar reflectivity values exceeded 35 dBZ (e.g. Wilson and Schreiber, 1986;Mecikalski and Bedka, 2006) since that value correlates well with the development of mature cumulonimbus clouds (Roberts and Rutledge, 2003). If there was adjacent existing convection, identification of CI was not made.…”

Detection of deterministic and probabilistic convection initiation using Himawari-8 Advanced Himawari Imager data

“…Therefore, the threshold of ≥35 dBZ precipitation intensity has been widely used as the definition of convective events (Mecikalski and Bedka, 2006;Mecikalski et al, 2008Mecikalski et al, , 2010Roberts and Rutledge, 2003;Walker et al, 2012). In this study, the first occurrence of rainfall with ≥ 35 dBZ precipitation intensity was defined as CI.…”

“…The existing literature on nowcasting CI has commonly used deterministic approaches which classify clouds as CI and non-CI using the criteria of several interest fields based on simple thresholding approaches (Mecikalski and Bedka, 2006;Mecikalski et al, 2008Mecikalski et al, , 2010Morel and Senesi, 2002;Sieglaff et al, 2011;Roberts and Rutledge, 2003;Sobajima, 2012). Such deterministic approaches might provide incorrect classification results for unsampled pixels (or objects), especially around the boundaries of CI, increasing the FAR of predictions.…”

Observation of convection initiation processes with a suite of state‐of‐the‐art research instruments during COPS IOP 8b

“…It is interesting to note that the temperature change rate found with the 5-minute satellite data is twice the value compared to −2.0 K/minute which is found if only 15-minute data are analysed. These are much larger values than the ones reported by Roberts and Rutledge (2003). They found temperature change rates of up to −1 K/minute but for the median of a certain area and with a temporal resolution of the satellite data of 15 minutes.…”