Storm Forecast
Valid: Thu 25 Feb 2016 06:00 to Fri 26 Feb 2016 06:00 UTC
Issued: Wed 24 Feb 2016 23:51
Forecaster: GATZEN

SYNOPSIS and DISCUSSION

A broad long-wave trough is centred across northern Europe, and a few isolated storms may form over Denmark and surroundings. The polar jet stream curves around its periphery from the Iberian Peninsula to the south-western Mediterranean and further into the Black Sea region. A well-developed short-wave trough embedded in the flow will travel from Iberia across the west Mediterranean and is expected over Italy and the Adriatic at the end of the period. At lower levels, rather rich low-level moisture is situated across the Mediterranean and the Bay of Biscay, whereas drier air dominates northern and central Europe. Steep lapse rates can be observed over Scandinavia, the Baltic Sea region, and surroundings as well as together with the short-wave trough moving over the Mediterranean, where lapse rates will overlap with rich low-level moisture.

Best potential for thunderstorms will be in the wake of a cold front moving eastward across the western Mediterranean and crossing Italy during the period. Steep lapse rates within the base of the trough and only slowly decreasing low-level moisture in the wake of the cold front allows for some CAPE. Although low-level convergence is rather weak, DCVA ahead of the trough axis is expected to support initiation of convective storms that spread across the west Mediterranean and the Adriatic Sea. Vertical wind shear is weak initially but can increase later in the period from southern Italy to the Adriatic Sea. Some better organized multicells may produce some hail and severe gusts, and tornadoes may also be possible, most likely over the northern Adriatic with strongest low-level vertical wind shear. Overall threat is expected to be too low for a categorical risk.

Along the cold front, deep moist convection becomes increasingly likely late in the period as the cold front slows down over the southern Adriatic. The advancing upper-level front promoted stretching of the moist low-level air mass and models indicate decreasing equilibrium level temperatures. Rich low-level moisture, moisture flux convergence along the cold front, upslope flow along the Balkan coasts, and slow cold front movement support quite intense precipitation. The potential is expected to be too low for a level 1, though.

Late in the period, another trough digs west of Europe, associated with a mid-level vort-max moving into the Bay of Biscay. Steep lapse rates will evolve in response and overlap with rich low-level moisture. Low-level convergence will evolve near the coasts of western Iberia and storms are forecast. Strong low-level vertical wind shear is forecast by latest GFS and linear segments along the cold front may be associated with mesovortices capable of producing tornadoes. Overall threat is rather limited, and a level 1 is not issued.