Correlating satellite infrared trends, total lightning flash rates, and rainfall to convective initiation, development and evolution

Accurately forecasting the initiation, temporal and spatial scales, and the immediate impacts of thunderstorms remains a significant problem in various aspects of meteorology. This presentation will highlight several satellite-based methods that improve upon our ability to nowcast (0-6 hour forecast) convection initiation (CI) and assess the early trends in thunderstorm intensity. Our current CI nowcasting methods rely on the use of infrared (IR) and visible (VIS) satellite data from GOES only, and cloud-motion winds for tracking cumulus clouds. These techniques relate the VIS and IR data to cumulus cloud phase (e.g., first time glaciation of cumulus cloud tops), cloud growth and deepening, and are built to include several existing methods in the literature. Current work shows that 30-45 minute CI nowcasts can be provided over large geographical regions in realtime, with accuracies on the 1 km scale of about 60-70%.

New work is underway at the University of Alabama in Huntsville (UAH) and the University of Wisconsin Cooperative Institute of Meteorological Satellite Studies (UW-CIMSS) towards enhancing our GOES-based CI processing with lightning information, as well as data from the MODerate resolution Infrared Spectrometer (MODIS). Improved means of correlating VIS and up to 20 IR fields from GOES and MODIS with rainfall (i.e. radar reflectivities greater than 25) are being undertaken toward improving CI nowcasting. Other aspects of satellite-based CI work now underway include: a) correlating radar echoes, satellite IR and total lightning flash rate data as a way of predicting convective cloud expansion and growth, b) determining the relative importance of the various IR signals (e.g., the time trends in 6.7-10.7 um temperature differences for moving clouds), and c) the forecasting of lightning flash trends as related to satellite IR information. The evaluation of patterns (lines and clusters) within realtime satellite imagery is yet another area of concentrated research in that pattern analysis of clouds can lead to an improved ability to deduce where and when storms will initiate. Capitalizing the IR-based processing toward nighttime CI nowcasting, when VIS data are unavailable, is another long-term goal of this work. The procedures that allow for the validation of our techniques are engrained in our data processing.

This project's goals coincide with those of the FAA Aviation Weather Research Program (AWRP) efforts at the National Center for Atmospheric Research (NCAR) to nowcast CI for the purpose of enhancing aviation safety over land and oceanic regions. As proven techniques are developed, they will be transferred into the forecast systems supported by the FAA for nowcasting convection.