Storm Forecast

Storm Forecast
Valid: Fri 28 Oct 2016 06:00 to Sat 29 Oct 2016 06:00 UTC
Issued: Thu 27 Oct 2016 21:07
Forecaster: PISTOTNIK

A level 1 was issued for the Ionian Sea for severe convective wind gusts and excessive convective precipitation.


A NW-erly mid-level flow increases between a strong low-pressure system over N Scandinavia and a large anticyclone centered over Spain and France. High pressure at the surface extends all the way to the Black Sea and beyond, yielding quiescent conditions over much of Europe.
Further downstream, the remnants of an old, positively tilted upper-level trough are placed over the Balkans and the central Mediterranean. Its tip cuts off and ejects towards Tunisia. A warm-core cyclone has formed beneath it over the Ionian Sea.


... Ionian Sea ...

High-resolution models suggest several competing low-pressure cores which are highly dependent on the convective activity. Therefore the overall path of this cyclone may become partly erratic, but the model pool largely agrees on a gradual southbound motion.
Storms in vicinity of the cyclone, probably embedded, will likely bring plentiful rain and strong to severe wind gusts, but are expected to stay mostly offshore. There is only a slight risk that the eastern coasts of Calabria and Sicily will be affected as well (high-resolution models like the Italian WRF and MOLOCH predict 10-meter means winds up to 20 m/s offshore).
Due lapse rates barely steeper than moist-isentropic, CAPE will only be on the order of 500 J/kg despite abundant low-level moisture. Together with mostly weak vertical wind shear, storm organization is not expected, except for the very southern rim of our forecast domain where CAPE starts to rise towards 2000 J/kg. However, upscale growth into disorganized clusters is possibly anywhere and anytime near the cyclone's center.
Remaining uncertainties about the cyclone's motion preclude a level 2, though a confined area along its final path may see widespread severe wind gusts and rough seas.

... S Baltic Sea towards Belarus ...

A vorticity maximum races SE-ward on the cyclonic side of the mid-level jet streak, whose axis runs from Oslo towards Kiev. Its lift acts upon maritime air with neutral to marginally unstable stratification and eventually catches up with the cold front of the Scandinavian cyclone, as it starts to cross Latvia, Lithuania, Kaliningrad and Belarus after 15 UTC.
On the cyclonic side of the jet maximum, convection may be deep enough to produce a little thunder, but vertical wind shear will likely be too weak to allow storm organization. On the anticyclonic side, vertical wind shear increases substantially, but convection will likely stay too shallow to benefit from it. Hence no level 1 seems to be warranted. However, isolated severe wind gusts are not ruled out near the jet axis in case the "ingredients" overlap better than anticipated.

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