• MAP Weather Report (MOC Forecasters)

Shallow Föhn event over Wipptal
 

Synoptic Pressure and Temperature fields of ECMWF forecast

The pressure field at 12UTC shows a typical Föhn pressure nose, with a pressure drop of about 6hPa over the target area.
Additionally, a warming north of the Alps was forecast, yielding a temperature difference of about 5^oC.
Persistent southerly flow was expected over the Wipptal for that day.

MSLP (ECMWF) and T@850hPa (SM)

 

MC2 cross-sections of Föhn winds over the target areas

MC2 predicted shallow Föhn over the Wipptal which deepened through the course of the day as the southerlies increased in strength.
This resulted in downslope winds on the northern side of the Brenner Pass with wind speeds up to 30m/s.
The Föhn in the Rhine Valley started earlier and was somewhat stronger, with predicted wind speeds increasing 40m/s.
 

Velocity along the Wipptal  and Potential Temperature based on MC2 forecast 991019_21

Velocity along the Rheintal  and Potential Temperature based on MC2 forecast 991019_21

for full size click on figure

MC2 horizontal fields

The 500m wind evolution illustrates how the southerly flow to the north of the Alps pics up during the event
as the air from higher levels decends over the ridge, while the easterlies in the Po Valley prevailed throughout the entire day.
Maximum wind speeds 500m above the crest are about 30m/s.
In connection with that, the cloud cover and relative humidity distribution predicted by MC2 shows how the Föhn wall south of the ridge built up during the day.
 

500m winds based on MC2 forecast 991019_21

Low level cloud cover based on MC2 forecast 991019_21

Relative humidity cross section, 15UTC based on MC2 forecast 991019_21

for full size click on figure

Inversions observed in Radiosoundings

The cold and humid air pool present in the Innsbruck region before it gets swept away by the Föhn onset is captured by MC2's pseudo skew-T plot.


 

Wind speeds observed at Patscherkofel

Photos from the flight