Storm Forecast
Valid: Wed 19 Sep 2012 06:00 to Thu 20 Sep 2012 06:00 UTC
Issued: Wed 19 Sep 2012 06:04
Forecaster: PUCIK

A level 1 was issued for Northern Italy and Northern Adriatics mainly for excessive precipitation and to the lesser degree for marginally large hail.

SYNOPSIS

The major macrosynoptic feature at mid and upper levels of troposphere will be a large trough, briskly amplifying and travelling towards southeast during much of Wednesday. Its axis will stretch across Eastern Germany towards Central Mediterranean by Thursday morning. This trough is forecast to integrate the short-wave that will affect Eastern Iberia during the day. Associated with the trough, a strong cold front will push southeastwards during the day, attaining wavy structure over N Adriatics as lee cyclogenesis is predicted behind the Alps. Center of the low is forecast over the Norwegian Sea, with a ridge quickly spreading eastwards behind the cold front. Another, shallow surface low, is simulated over Southern Iberia.

DISCUSSION

... Northern Italy, Northern Adriatics ...

As the cold front will push over the Alpine region, lee cyclogenesis behind the range will likely increase the southern component of low level flow towards the coastline. Strong upper level forcing from the trough and position in the right entrance region of the jet-stream will likely contribute to enhanced upward motion along the front. Albeit CAPE values should stay relatively meager due to the lack of steep lapse rates, strong convergence along the front, high values of PWAT and RH across the whole vertical profile and parallel upper level flow to the front point to the possibility of excessive rainfall even with weaker updrafts. Other severe threats will be probably limited due to rather weak instability maybe except for Northwestern Italy, where strong DLS and steeper lapse rates (as well as more isolated DMC mode) might prove more conducive for marginally large hail.

... Southeastern Iberia ...

Deepening surface low over Southern Iberia will induce easterly component of low level flow from the Mediterranean sea. On the other hand, mid to upper level flow will have southwesterly direction with steeper lapse rates, resulting in moderate latent instability close to the coastline, decreasing further inland. Moderate DLS with values over 15 m/s will also be present here, especially earlier in the period, decreasing in the afternoon hours.. Steep lapse rates and moderate shear point to the augmented threat of marginally large hail with better organised storms. As vectors of low and mid/upper level flow are almost opposite, slow storm motion might be the result as well as increased potential for excessive precip. Nevertheless, 00 UTC Murcia sounding shows very strong cap, perhaps too strong to be overcome during the day, so storms will likely stay in more elevated mode. This negative factor precludes issuance of Lvl 1.