FOEHN - KEY PARAMETERS

by ZAMG

Height contours at 1000 and 500 hPa:
Well developed low to the W to NW (in the case of south Foehn) of the mountain range; closed low at all layers and with vertical axis;
Equivalent thickness:
The corresponding frontal cloud band is associated with a zone of high gradient of thickness; as the mesoscale features linked to the Foehn process appear in the leading part of the frontal cloud, the modifications often appear already in the thickness ridge;
Thermal front parameter (TFP):
The corresponding frontal cloud band is accompanied by a TFP; the location of the TFP, in relation to the frontal cloud band, is dependant upon the synoptic situation; as the mesoscale features linked to Foehn appear in the leading part of the frontal cloud the modifications appear either within or in front of the TFP
Wind direction at 850 - 500 hPa:
There is a strong stream over a thick layer perpendicular to the mountain chain;
Radiosoundings: humidity + temperature:
Radiosoundings on the windward side show a thick wet layer reaching nearly up to the tops of the mountains; to the lee side of the mountain chain they show a dry layer from the surface up to middle levels and a wet layer in middle to high layers; the latter represents the high Lee Cloud.

Height contours at 1000 and 500 hPa

	06 November 2000/12.00 UTC - Meteosat IR image; magenta: height contours 1000 hPa, cyan: height contours 500 hPa

	06 November 2000/12.00 UTC - Meteosat IR image; green: equivalent thickness, blue: thermal front parameter

	06 November 2000/12.00 UTC - Meteosat IR image; green: wind direction 850 hPa, red: wind direction 500 hPa, yellow: wind direction 300 hPa



Stau side: 06 November 2000/12.00 UTC - Radiosounding Udine; black solid: temperature, black dashed: dewpoint temperature	Lee side: 06 November 2000/12.00 UTC - Radiosounding Munich; black solid: temperature, black dashed: dewpoint temperature