Valid: Fri 24 Jan 2014 06:00 to Sat 25 Jan 2014 06:00 UTC
Issued: Thu 23 Jan 2014 18:42
A level 1 was issued for parts of the C/E Mediterranean mainly for excessive rain, isolated large hail, severe wind gust events and numerous waterspouts (not necessarily bound to supercells) and isolated (supercell) tornado events.
A pronounced impulse drips off the westerlies and evolves into a closed upper low over the C-Mediterranean. A ridge over the Azores builds east with stable conditions regarding DMC probabilities. Same over NE Europe as high pressure with chilly air remains in place. The most widespread thunderstorm activity occurs over the C/E Mediterranean.
Weakly electrified maritime convection aproaches N-Scotland during the end of the forecast. Despite sporadic lightning activity, no area was added for now.
... C Mediterranean ...
This event will be a messy one as a surface low fortifies during the forecast. Various foci for some kind of severe exist:
a) Albania to SW-Greece :
Surface pressure decreases over the Ionian Sea to the S-Adriatic Sea with intensifying winds at 1-2 km AGL ahead (to the east). Influx of moist and unstable air with abundant forcing result in scattered to widespread activity. Northern most part (here: Albania) might see an early cut off of favorable inflow air due the cold front's passage, but timing of that front remains a bit uncertain (depending on strength of the surface trough over the Ionian Sea). QPF maxima show amounts up to 100 mm/24 h over N-Albania and we won't argue with that. Further south (W-Greece), conditions become favorable for an organized MCS event, which gradually builds south along eastbound moving cold front. Heavy to excessive rain will be the main hazard, but any more discrete storm (e.g. tail-end storm) could become supercellular with an isolated tornado, strong to severe wind gust and large hail risk.
Between 21-00Z, a lull in activity is expected before the main surface / upper low approaches from the west. LLJ now from the west advects less BL moisture towards W-Greece, but colder mid-levels still create enough instability. Once again, heavy rain, strong to severe wind gusts, marginal hail and an isolated tornado event are possible. We would not be surprised about a W-E aligned and training MCS along the W-coast of Greece between 3-6 Z. Same for SE-Italy with quasi-stationary /back-building convection
b) Tyrrhenian Sea, Adriatic Sea:
Weak shear beneath the strengthening low favors rather disorganized cells. Widespread CI however is forecast and repeatedly onshore moving storms could produce a few flash flood events (e.g. E-coast of C-Italy and SW-Italy). In addition, conditions for numerous waterspout events are quite good with widespread LLCAPE in excess of 100 J/kg and numerous convergence zones in place.
a) and b) were combined in a large level 1 area.
... Aegean Sea and adjacent areas between 00-06 Z ...
Eastbound moving cold front approaches the area of interest from the west around midnight. Sufficient prefrontal moisture advection and steepening mid-layer lapse rates result in widespread 400-800 J/kg SBCAPE. Winds at 1-2 km AGL intensify and training convection along the N-coast of the Aegean Sea and the W/SW coasts of Turkey with heavy to excessive rain are forecast. Despite short time frame and progressive nature of that front, we don't want to rule out very havy rain beneath slow moving MCSes and hence a level 1 was added. In addition, 0-6 km bulk shear oscillates around 15 m/s, which could support a few organized multicells with large hail and gusty winds the main hazard. SRH-1 in excess of 200 m^2/s^2 also indicates an isolated tornado risk...especially with more discrete convection (e.g. tail-end storms).
Crete experiences stronger shear with less forcing. Still, well organized DMC with large hail, severe wind gusts, heavy rain and an isolated tornado event are possible. The level area was expanded south to inlcude Crete.