high shear, very low cape

In the early evening of Friday, august 27th 2010, nice altocumulus lenticularis forms were observed:


Here, these clouds are often indicative that a coldfront is approaching.










On Saturday there were minor chances for thunderstorms. But if they developed, they could be supercells, i.e. storms with a rotating updraft.
Chances were low, because the dry air in the lowest layers and high temperatures aloft, created a thermodynamic profile with almost no CAPE (a measure of instability). This can be seen in the prog-sounding for my location. The vertical windshear is strong with a windspeed 58 kt at 500 hPa.




















This situation was also well forecast by ESTOFEX:

...Romania, Ukraine...
Large wind shear and curved hodographs are favorable for supercells with large hail, but it is unlikely that with such low instability as indicated (<200 J/kg) something can develop.


Nonetheless, late in the afternoon I observed an interesting cloud-structure:



Same photograph as above. An inflow-band (orange arrow) is feeding this "wannabe storm" from the north. As often the low-level wind was modulated by the river Mures valley and not from the northwest as indicated by the gfs-model. In light blue the cloud movement at the lower mid-levels. In dark blue the cloud movement at "anvil" level.


It was a light shower by then and I felt a few raindrops falling out of the cloudband. Thunder was not observed.


The shower struggled and struggled, but due to the low instability it didn't succeed in developing into a storm. Finally it collapsed due to the strong windshear and entrainment.







On radar I saw that about the same time, behind the eastern Carpathian Mountains near Bacau, one storm succeeded in becoming a strong cell. Perhaps this one caused severe weather over there?