CONVECTIVE FORECAST
VALID 06Z THU 26/06 - 06Z FRI 27/06 2003
ISSUED: 25/06 19:51Z
FORECASTER: HUGO

There is a slight risk of severe thunderstorms forecast across Northern Italy, Switzerland, E=ern France, W=ern Austria & SW=ern Germany

General thunderstorms are forecast across S=ern Sweden & Finland

General thunderstorms are forecast across Maldova, Ukraine, Belarus & parts of W=ern Russia

General thunderstorms are forecast across A large area of the Central & S=ern Med (Excluding SLGT risk region)

SYNOPSIS

A developing closed mid to upper level blocking anticylonic feature over NW Europe in association with a Northward moving surface high pressure from the UK into parts of Scandinavia allowing for a sharpening mid-level trough to move into far W=ern regions of the UK during the forecast period...The mid to upper level blocking antiyclonic feature will slowly decay and fill towards the latter stages of the forecast period...A large section of E=ern and NE=ern Europe will be dominated by a quasi-stationary mid to upper level cyclonic closed low feature in association with 2 areas of weak surface low pressure...The central & S=ern Med will be dominated by a slack mid to upper level flow along with a slack surface pressure gradient...A degragmenting embedded low pressure over France will be present throughout the forecast period with warm and cold front features effecting a swathe of central parts of Europe.

DISCUSSION

...Northern Italy, Switzerland, E=ern France, W=ern Austria & SW=ern Germany...
Convection is expected to initiate within the warm sector region of the defragmenting surface low pressure over France into the early to mid afternoon and then throughout the evening in conjunction with diurnal heating...Forecast ascents for the region show a highly unstable mid to upper level atmosphere but a conditionally unstable (low CIN values <-50j/kg) lower layer which could create a 'loaded gun' situation as the heat of the day builds...Lowest 30hPa MLCAPE values throughout the above mentioned regions are expected to be between 1300 and 1800j/kg with LI values of between -4 and -6 possible...As long as the low level stability is overcome, in which forecast CAP values of between 1.5C and 3.0C are expected there is a SLGT risk of severe thunderstorm development...There is some limited deep layer shear (0-6KM) over the SLGT risk region in association with a weak upper level jet in association with the defragmenting low pressure over France and values of between 25 to 35KT are possible...This could bring the risk of multicell development and possible MCS development depending on the amount of activity tomorrow evening...There is also scope for a low risk of supercell development in association with some limited (0-3km s-rh 100-150m2/s2) helicity values over parts of SE=ern France and some regions of N=ern Italy this risk being aided by the deep layer shear, however there is expected to be little or no low level shear (0-1KM - 5-10KT)...A forecast STP (Significant Tornado Param.) value of around 1 in association with the above factors is possible over parts of W=ern N=ern Italy and into SE=ern regions of France...All areas of the SLGT risk could see torrential rainfall and with reasonable WBZ heights (7000-8000ft) there could well be some moderate sized hail...Forecast T2GUST max windspeeds within the SLGT risk region could reach 40 to 50mph so some moderate to strong convective gusts are possible...One or two funnels/tornadoes within the SLGT risk region cannot be ruled especially over SE=ern regions of France and into parts of W=ern N=ern Italy as these regions are expected to see the lowest LCL and LFC heights and also inconjunction with the above favoured criteria...Convection will persist through a large part of the evening and into the overnight period depending on the amount of organisation that has occurred by that time frame.

...S=ern Sweden & Finland...
Scattered TSTSM activity over parts of Southern Sweden & Finland is possible during the course of the afternoon and evening on the 26th...An embedded weak surface low pressure (1018mb)and an associated surface trough will provide a limited amount of mid to upper level PV...Forecast ascents for the region tomorrow show a reasonably unstable atmosphere with a lowest 30hPa MLCAPE values between 400 and 700j/kg and with LI values of between -2 and -3...Convection will be solar reliant as there will be little or no deep layer or low level shear (0-6KM < 10KT)...Convection will reach peak intensity just before the convective maturing stage is reached and some reasonable sized hail is possible in association with highly favourable WBZ heights of between 7000 and 7500ft...Due to the lack of deep layer shear any convective activity will be short lived as any updraughts are surpressed by convective downdraughts and will soon decay towards evening.

...Maldova, Ukraine, Belarus & parts of W=ern Russia...
A weak area of surface low pressure (1001-1003mb) will dominate the above regions in association with the closed mid to upper level cyclonic pattern...Convection will again be solar reliant during the course of the day as deep layer shear will be low (0-6KM <5KT) but there will be some limited low level shear (0-1KM >15KT) in parts...Forecast ascents for the region are only marginally unstable however to around 400mb with quite a stable layer within the boundary layer (920mb)...TSTSM activity is expected on a scattered level with no severe weather expected from the activity with only favourable WBZ heights (5500ft to 6500ft) any hail will be relatively small and forecast max wind gusts aren't expected to exceed 25KT...Convection will slowly decay later in the day.

...A large area of the Central & S=ern Med (Excluding SLGT risk region)...
A large section of Central & S=ern Europe (excluding the SLGT risk region) will see a GEN risk of the usual 'Summer' afternoon diurnal related thunderstorms...Forecast ascents within the GEN risk region all show scope for some limited active TSTSM activity as convection reaches the maturing stage, but with a general lack of deep layer shear throughout the GEN risk region no major severe activity is expected...However some limited (100-150m2/s2) 0-3KM helicity over parts of S=ern & SW=ern France could bring the risk of something more organised within this region for a time, but with unfavourable LFC and LCL heights along with only marginally favourable WBZ heights the risk of significant hail is low as is the risk of tornadic activity...Convection will slowly decay as the solar input reduces later in the day...Regions directly surrounding the SLGT risk region however will be at a slightly higher risk of seeing a more convective severe weather event especially as any convective activity slowly moves towards the East during the course of Thursday evening and night.

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