Storm Forecast
Valid: Fri 19 Jun 2015 06:00 to Sat 20 Jun 2015 06:00 UTC
Issued: Thu 18 Jun 2015 19:01
Forecaster: TUSCHY
A level 2 was issued for the N-Adriatic Sea and surrounding areas mainly for large hail and severe wind gusts. An isolated tornado event is possible along the coasts.
A level 1 was issued for N/CNTRL Italy mainly for large hail and severe wind gusts.
A level 1 was issued for NW Algeria mainly for large hail and severe wind gusts. Excessive rain is possible.
... SYNOPSIS...
Slightly positive tilted trough over Sweden steers a moist and cool air mass towards CNTRL Europe. Elongated fetch over the North Sea sustains moist low-tropospheric air mass with widespread precipitation forecast over most parts of CNTRL Europe. CAA north of the Alps ensures rising hights with falling pressure over NW Italy and the Gulf of Genoa. This evolving low combined with the Alps assists in a slow-down of the southbound moving synoptic front/occlusion. Less disturbed CAA in the mid-troposphere overspreads warm/moist BL air mass over N-Italy which results in moderate MLCAPE. This region will be the focus for the most organized DMC activity!
A lifting trough over SE Europe overspreads a seasonable moist low-tropospheric air mass with widespread thunderstorm activity.
... DISCUSSION ...
... N-Italy ...
The stage is set for numerous well organized thunderstorms over N-Italy. IPV maps show SSE-ward digging upper trough (its tilt becoming more neutral during the forecast) over NE Italy during the afternoon hours. It's not of surprise to see unanimously strong signals for upward motion in the Q-vector fields, which spread rapidly S over NE Italy and the N Adriatic Sea. Further west, evolving but weak/diffuse lee cyclogenesis acts to keep conditions for enhanced upward motion in place until the overnight hours. Local models show a complex thetae/frontal pattern over N-Italy but in general thunderstorm probabilities should end until sunset from N to S over NE Italy with ongoing convection further west.
Forecast soundings reveal rather thick mid-level CAPE profiles due to marginal mid-level lapse rates overspreading 15-17 °C surface dewpoints. Up to 1 kJ/kg MLCAPE is forecast. Some uncertainties remain, where mid-level jet maximum will cross N-Italy although more models tend to point to NE Italy. DLS increases to 20-25 m/s with enhanced storm relative (inflow) winds over the N-Adriatic Sea and surroundings. Either expect early CI or ongoing storms to increase in coverage/strength as they move to the SE, entering a more moist/warm air mass,
where LCL height drops to less than 1000 m. Numerous well organized multicells/isolated supercells are forecast over NE Italy to race towards the Adriatic Sea until 18Z, also affecting W-Slovenia and parts of NW Croatia. Large hail (an isolated very large hail event possible) and severe wind gusts are forecast. As LCL height decreases towards the coast (in addition to a diurnal decrease during the evening hours), an isolated tornado risk may arise over the N/NE Adriatic Sea and surroundings. In case storms are capable of producing a strong cold pool, a line of DMC may result in a more widespread severe wind gust risk over the NE Adriatic Sea. We therefore expanded the level 1 far south over the Adriatic Sea.
Further west, over W/N-CNTRL and CNTRL Italy DLS could be a tad weaker, but remains aoa 20 m/s. Forecast soundings
would favor a large hail and isoalted severe wind gust risk. Thunderstorms (onshore) weaken after sunset with loss of diabatic heating/CAPE, whereas offshore storms may continue all night long. Marginal hail and heavy rain will be the main hazard during the night as DLS abates a bit.
... W-/CNTRL Turkey ...
Leisurely eastward moving synoptic (cold) front inserts early and widespread CI over the area of interest. Weakly capped air mass with eastbound moving forcing increases confidence in this scenario. Weak winds in the mid/upper troposphere preclude organized DMC, although clustering and slow moving storms may pose a localized excessive rainfall risk. Initiating storms may add an isolated large hail risk during the first few hours. The activity gradually diminishes from W to E.
...W-Tell Atlas mountains ...
Eastbound travelling trough and temporarily falling surface pressure induce an onshore flow, which advect rich W-Mediterranean air towards NW Algeria. With steep mid-level lapse rates aloft, MLCAPE of 1 kJ/kg seems reasonable. 20 m/s DLS affects that region and organized multicells/isolated supercells may bring large hail and severe wind gusts. In addition, given arid nature of this area, clustering and slow moving storms may also pose an excessive rainfall and flash flood risk. Betimes the activity moves to the SE and out of our forecast area.
...General thunderstorm areas ....
Elsewhere, no organized DMC activity is anticipated as either shear or CAPE or both remain limited. Graupel and
gusty winds remain the main hazard. Thunderstorms over the far W Baltic Sea may bring heavy rain to Denmark and the NE coast of Germany due to signals of better organized and longer lived convergence zones in this NW-erly flow regime.
