Convective Outlook: Thu 18 Jul 2019 |
|
What do these risk levels mean? |
Convective Outlook
VALID 06:00 UTC Thu 18 Jul 2019 - 05:59 UTC Fri 19 Jul 2019
ISSUED 21:09 UTC Wed 17 Jul 2019
br> br>ISSUED BY: Dan
... SCOTLAND / NORTHERN IRELAND / REPUBLIC OF IRELAND ...
An upper trough will extend across the British Isles on Thursday, with a couple of shortwaves rotating northeastwards around its base. The associated cool air aloft will steepen mid-level lapse rates, and help yield 500-900 J/kg CAPE in conjunction with diurnal heating. Scattered showers will affect many parts of Scotland, Northern Ireland and portions of the Republic of Ireland - the best instability will be located in northern and eastern Scotland (where the deepest convection is most likely, and hence greatest potential for a few sporadic lightning strikes), while the more-sheared environment will exist over Ireland and across northern England (but cloud depth severely stunted by a nose at 550-600mb).Consequently there is a lack of an overlap between best CAPE and shear, though one area of focus could be the SE Scottish Borders late afternoon / early evening. Scattered showers / storms will tend to gradually decay overnight, becoming mainly confined to exposed western coasts.
... EAST ANGLIA / SE ENGLAND ...
A cold front (and associated cloud / patchy rain) will clear eastwards from these areas during Thursday morning, leaving residual low-level moisture (dewpoints 13-16C) to be subject to some surface heating by the afternoon hours. This combined with low-level wind convergence may allow a few isolated heavy showers to develop, cloud depth perhaps limited somewhat in height but a few isolated lightning strikes cannot be ruled out. Any showers here will decay / move offshore by mid-evening.
... S IRELAND / CELTIC SEA / SW ENGLAND / SW WALES: OVERNIGHT ...
On Thursday night, an Atlantic frontal system will approach, bringing initially a period of dynamic rain associated with the leading edge of the warm front, but also advecting a very warm, moist low-level airmass. Increased forcing on the forward side of the approaching sharpening upper trough may encourage the development of elevated convection, and so the potential for a few elevated thunderstorms exists over these areas late in the night and into Friday morning. The exact coverage, timing and placement is quite uncertain, and so for now have refrained from introducing a SLGT - but trends will be monitored and one may be introduced if confidence improves.