NUCAPS Soundings ahead of and behind Cold Front

The NUCAPS soundings available in AWIPS-II are generated from the CrIS and ATMS instruments aboard the Suomi NPP polar-orbiting satellite. A swath of soundings are available over generally the same locations at roughly the same times each day. On Tuesday, the swath over the east coast with a timestamp of 1815Z was available in AWIPS-II around 1930Z. This is great timing, as it falls between the 12Z and 00Z RAOB launches, providing an update on the thermodynamic environment.

Today, one group was operating in the Sterling CWA where the threat for severe weather was quite low, but a cold front was quickly making its way through the region. The 1815Z NUCAPS pass was timely as participants were able to view atmospheric profiles on both sides of the front (Fig 1).

Fig 1: NUCAPS sounding points with surface obs and visible satellite imagery overlayed. Centered over Sterling CWA.

Selecting a sounding ahead of the front, the surface conditions (temperature and DP) needed to be adjusted to match actual surface conditions (Fig. 2). Additionally, the bottom few points of the sounding were smoothed out to make a more realistic profile LL profile. Upon making these changes, instability was still present ahead of the front given decent MUCAPE and SBCAPE. However, MLCAPE was virtually nonexistent, and a possible inversion was apparent between 700 and 850 mb, perhaps the reason for a lack of robust convective activity.

Fig 2: Modified NUCAPS sounding ahead of CF.

Selecting a profile behind the front and making the necessary changes to the lowest parts, one can certainly tell that the front had passed through the area (Fig 3). With significantly cooler and drier air aloft (in addition to at the surface) the atmosphere is now completely stable.


Fig 3: Modified NUCAPS sounding behind CF

This was a good example of how a forecaster can use the timely NUCAPS soundings to identify the existence and locations of boundaries, especially those that are not as obvious from other guidance.

– Bill Line, SPC/HWT Satellite Liaison