Met-11 WV (Aspot)

Signatures of foehn & bora in water vapour images

14 April 2020 05:00-18:00 UTC

Met-11 WV (Aspot)
Met-11 WV (Aspot)

Investigating the foehn situation on 14 April 2020 and on how it is seen in water vapour imagery.

Last Updated

06 May 2022

Published on

09 February 2021

By Jochen Kerkmann (EUMETSAT), HansPeter Roesli (Switzerland) and Ivan Smiljanic (CGI)

In the case study Retour d’est or extended Bora flow along Po Valley, the 'Retour d’est' or extended Bora flow along the Po Valley is discussed using visible, infrared and near-infrared satellite imagery.  The synoptic situation is a typical north-foehn situation over the alpine southside and the Po Valley. Figures 2 and 5 of the case study show the two main foehn corridors in northern Italy/southern Switzerland, the foehn which is later consumed by the Retour d'est.

This case study concentrates on the foehn situation on 14 April 2020 and on how it is seen in WV7.3 (and WV6.2) imagery. Figure 1 shows the WV7.3 image corresponding to the Airmass RGB image of the Retour d'est case study (Figure 2 in that case). One can see distinct warm (dark) stripes extending from the main crest of the Alps southward into the Po Valley. Our interpretation of these stripes is that these swaths represent the main foehn corridors on the alpine southside, very dry air at mid and low levels that replaces the moist air in the Po Valley. The broadest foehn swath is the one over Ticino, further to the east the swaths are smaller and less pronounced.

Meteosat-11 Water Vapour 7.3 imagery

Annotated Meteosat-11 WV7.3 compare1

Figure 1: Meteosat-11 WV7.3 image from 14 April 2020, 10:45 UTC.

Suomi-NPP True Color imagery

Annotated Suomi NPP True Color RGB compare1

Figure 10: Suomi NPP, VIIRS, True Color RGB, 23 February 2019 (Credit: NASA).