A vigorous shortwave trough dug southeast out of Canada starting the evening of 19 Jan, continued across the middle of the US from the 20th to 21st, and across and east of Florida from the 21st to the 22nd. A long loop of GOES-East upper level water vapor imagery highlights the evolution and the shortwave as it dives southeast, with sinking and drying air (warm colors) on it’s western periphery, and rising and moistening air (white to green colors) to it’s east (Fig 1).

Zooming in to the southeast US as the storm moved offshore during the night of the 21st to the morning of the 22nd, significant strengthening of the shortwave is observed as thunderstorms in the ascending region and drying in the descending region both become more pronounced (Fig 2). Relevant large scale features are highlighted at the end of the period.

An alternative view of the strengthening is provided in the Airmass RGB imagery from GOES-16. The shades of red becoming more apparent on the western side of the storm represents sinking/drying/higher PV air into the upper troposphere (Fig 3).

The upper trough was accompanied by anomalously dry air and cold temperatures for the southeast US. Cooling temperatures can be visualized by the GOES-16 Land Surface Skin Temperature product, with skin temperatures across south Florida falling from the 70s during the day of the 21st to 30s during the evening (Fig 4).

The dry air is simialrly captured in the GOES-16 TPW product, with values across much of south Florida dropping to near or below 0.3″ (Fig 5).

This drying was also captured in radiosonde data, with the 12Z sounding from Key West measuring 0.3″ of TPW (Fig 6), which is well below average (1.2″) and actually is a new daily min for that location (Fig 7).

A surface low and intense and nearly stationary convection associated with the shortwave was captured in GOES-16 visible imagery and GLM Flash Extend Density data during the day on the 22nd (Fig 8).

Bill Line, NESDIS/CIRA