Convective Outlook: Wed 19 Jul 2017
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Wed 19 Jul 2017 - 05:59 UTC Thu 20 Jul 2017

ISSUED 23:23 UTC Tue 18 Jul 2017

ISSUED BY: Dan

... MORNING ELEVATED THUNDERSTORMS ...
Scattered elevated thunderstorms may be ongoing at the beginning of this forecast period, mainly over northern England and a second cluster over the Celtic Sea. With regards to the former, through Wednesday morning these should continue to move northwards into southern Scotland by midday, but probably with a decaying trend since the main axis of instability by these latitudes will have shifted east to the North Sea. Nonetheless, some lightning will still be possible across Scotland, but probably not as active as areas farther south earlier in the morning. The second cluster will move across the Irish Sea and into parts of Wales, perhaps the Isle of Man, while then merging with surface-based developments during the afternoon - outlined below.

... AFTERNOON / EARLY EVENING SURFACE-BASED THUNDERSTORM POTENTIAL ...
Attention then turns to the warm sector where warm, moist low level airmass will reside and subject to strong heating should sufficient breaks develop in any cloud cover. Surface troughing and low-level wind convergence beneath the upper trough, combined with diurnal heating, may allow a few surface-based thunderstorms to develop, which would be capable of large hail and localised flash flooding. Current thinking is these may develop initially over northern half of Wales, perhaps in conjunction with increased forcing associated with approaching elevated thunderstorm cluster from the Irish Sea, these then migrating across the NW Midlands and NW England to Cen N and later E/NE England by evening.
In general, would prefer better shear as it tends to reduce with time, but nonetheless some locally large hail to 2.0cm in diameter and flash flooding will be possible - though very much dependent on if any surface-based convection can develop on Wednesday afternoon / early evening given probably large amounts of cloud. Borderline SVR issued for now. Isolated thunderstorms will also be possible farther south across the Midlands and West Country.

... REPUBLIC OF IRELAND / NORTHERN IRELAND ...
Eastern portions of the Republic of Ireland and into Northern Ireland could also see a few heavy showers and / or thunderstorms on Wednesday afternoon / early evening, ahead or along the eastwards-moving cold front - hence the SLGT has been expanded westwards to cover this potential.

... SE ENGLAND LATE EVENING ...
Low risk of a few elevated thunderstorms (or at least showery precipitation) close to SE England in the 22 - 02z timeframe, but given weakening instability lightning will probably not be too significant with this activity.