A snow squall developed off of Lake Ontario during the morning of 18 Dec 2019 ahead of a southward surging surface cold front and related upper trough digging into the northeast US (Fig 1). As has been noted, these localized bands of heavier snowfall can be diagnosed in the Day Cloud Phase Distinction (DCPD) RGB from ABI. This can be useful to forecasters as a supplement to radar, particularly for developing snow bands and over lakes, as well as when radar data are unavailable, for use in conjunction with surface observations and webcams.
In this case, the DCPD RGB highlighted the development of the band over Lake Ontario, and it’s evolution southeast into New York (Fig 2). The 1-min imagery allowed for real-time analysis of the band as it evolved. The bright green areas indicate the likely areas of heavier snow, resulting from the relatively high reflectance in the 0.64 um band and cooler brightness temperatures in 10.3 um band (taller/convective clouds), but low reflectance in 1.61 um band (ice at cloud top). Convective cloud elements are also detectable along the snow band in the DCPD RGB owing to the high (500 m) resolution from the 0.64 um band component. The initial snow squall warnings were issued at the end of this animation. The Rochester ob indicates heavy snowfall and significantly reduced visibility at the end of the loop as the snow band moved overhead. GOES-16 DMWs in the SFC-900 mb layer over the lake indicated low-level cloud motion of 25-30 knots, comparing well to winds observed at the surface. A meso-low is also apparent over the far eastern portion of the lake.
It should be noted that the default settings for this RGB were modified to better highlight the features of interest for this case given the relatively cool airmass and low light. The ranges used were (Red: -63.5, -2.5…Green: 60, 0…Blue: 45, 1), while the gamma’s all remained at 1.
For the final time-step in the above animation, a qualitative comparison between the DCPD RGB and MRMS composite refelctivity reveals a correlation between the bright green areas and highest reflectivity (Fig 3) across New York and Pennsylvania. Additional snow squall warnings were issued for the bands in northeast Pennsylvania.
The DCPD RGB and radar imagery are compared again in a two panel for the hour immediately following the animation in Figure 2 (Fig 4).
Figure 5 includes a long radar loop with the aforementioned NWS Snow Squall Warning polygon.
Ground truth from a Rochester webcam revealed rapidly deteriorating conditions associated with the snow squall (Fig 6).
Bill Line, NESDIS