On Saturday October 1st the remnants of Hurricane Ian were moving northward through the Mid-Atlantic region, after making a second U.S. landfall the previous day in South Carolina. Overnight, the SPC was monitoring the final stages of Ian’s extra-tropical transition with a marginal threat for severe weather in the coastal North Carolina/Virginia region.
One forecaster on shift that night was monitoring the remnants from the perspective of GOES-16, and noted how various ABI products could be used to examine cloud layers and types in this dynamic environment.
CH7 shortwave and CH13/15 longwave IR shows mainly the cooler cloud tops associated with high-level clouds. Low-level clouds can be inferred by the warmer temps (CH7) or weaker grey features in CH13/15. However, the NtM [Nighttime Microphysics] RGB composite satellite data neatly contrasts colder, high-level clouds (western PA westward and in a warm conveyer belt over the Atlantic) from the lower but cool clouds (North Carolina into Virginia) and the very low, warm clouds (southeast Pennsylvania into New Jersey and Delaware). Though buoyancy is scant and severe is not expected in this area, the NtM RGB composite’s ability to contrast cloud types in this event demonstrates potential to identify important cloud features related to severe weather.SPC Forecaster Comment
When overlaid with the RAP mesoanalysis field at 500 mb, the Channel-13 (Clean Longwave IR) and Channel-7 (Shortwave IR) bands from the ABI reveal the higher, cooler cloud tops north of the low into Pennsylvania. The warm conveyor belt over the Atlantic coast can be seen in the 500 mb RAP mesoanalysis with enhanced southerly winds east of low, and from the ABI infrared imagery with a lack of high clouds due to upper level subsidence.
While these bands individually can be used to point out these features, the forecaster notes that the Nighttime Microphysics RGB allows them to more readily identify and monitor these cloud features from the tropical cyclone remnants at night. This is driven by the RGB’s ability to combine information from multiple ABI bands (7, 13, and 15) to provide qualitative information for forecasters regarding cloud types and heights.