Advances in Downburst Monitoring and Prediction with GOES-16

The launch of Geostationary Operational Environmental Satellite (GOES)-16 in November 2016 and subsequent activation of the Advanced Baseline Imager (ABI) in January 2017 has resulted in the increased accessibility to high spatial and temporal satellite image datasets for convective storm monitoring and nowcasting. The existing suite of GOES downburst prediction algorithms employs the GOES imager and sounder to calculate potential of occurrence based on conceptual models of favorable environmental thermodynamic profiles for downburst generation. Traditional meteorological satellite techniques for deep convective storm monitoring, including the water vapor – longwave infrared (WV – IR) brightness temperature difference (BTD), have recently been extended by multichannel techniques for diagnosing attributes of a favorable downburst environment. The WV-IR BTD has demonstrated the ability to infer convective storm structure signatures that signify the occurrence of hazardous conditions that entail large hail and severe and potentially damaging straight-line winds resulting from downbursts, and, with 2-km resolution GOES-16 ABI data, the BTD product is able to detect fine detail signatures more effectively when compared to 4-km resolution GOES-13-15 imagery. Accordingly, a three-channel BTD algorithm incorporating split window IR channels (11μm, 12μm) and a WV channel (6.7 μm) produces an output BTD that is proportional to downburst potential and supplements the sounder-derived Microburst Windspeed Potential Index (MWPI) that is designed to diagnose attributes of a favorable downburst environment: 1) the presence of convective available potential energy (CAPE), and 2) the presence of a deep surface-based or elevated mixed layer with a large temperature lapse rate. This paper presents an updated assessment of the imager and sounder-derived algorithms applied to GOES-16 ABI data featuring case studies that demonstrate effective compositing of cloud and moisture imagery with 3-km High-Resolution Rapid Refresh (HRRR) model data to simulate advanced sounder-derived products. An early example of the application of GOES-16 imagery is a winter severe thunderstorm outbreak over the southeastern United States on 22 January 2017. During the late morning of 22 January, a line of strong thunderstorms developed over the northern Gulf of Mexico and southern Alabama coast ahead of a cold front, and then tracked eastward and intensified over the Florida Panhandle during the afternoon. The first severe thunderstorm wind event, associated with a downburst, was recorded at Tyndall Air Force Base (AFB), Panama City, Florida, near 1900 UTC. A comparison of GOES-13 imager WV (channel 3) – IR (channel 4) BTD to the GOES-16 ABI upper level WV (channel 8) – IR (channel 14) BTD for this severe thunderstorm event revealed much higher detail apparent in convective storm cloud structure, especially cold cloud tops and dry-air filaments on the rear-flank of the squall line. Although larger dry-air notches were apparent in GOES-13 BTD imagery, the fine detail of the cloud structure was absent. The prominent dry air filaments most likely indicate the occurrence of local-scale mid-tropospheric dry-air entrainment and intrusion into the convective storms, promoting downdraft development and subsequent downburst generation. In addition, a local maximum in convective wind gust potential (> 40 knots) derived from the MWPI product and generated from the HRRR model was apparent immediately downstream of the squall line as it tracked through the central Florida Panhandle and northeastern Gulf of Mexico. Downburst-related wind gusts of 52 knots were recorded at Tyndall AFB at 1903 UTC and at Tyndall AFB Tower C at 2016 UTC, respectively, exceeding severe thunderstorm warning criteria.