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Convective/Thunderstorm Discussion : 2019 and Winter 2020
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Convective Weather
Day 2 Convective Outlook
VALID 06:00 UTC Wed 10 Jul 2019 - 05:59 UTC Thu 11 Jul 2019
ISSUED 20:51 UTC Tue 09 Jul 2019
ISSUED BY: Dan
Upper ridge initially over the British Isles on Wednesday will gradually retreat to the southeast, allowing an upper trough to approach from the Atlantic and ultimately allowing the flow aloft to gradually flatten. The surface pattern is rather messy, with fairly extensive cloud layers courtesy of a broad warm sector - surface dewpoints will widely be between 13-15C, but 16-17C widely over Ireland behind a second warm front which will move eastwards across the island during Wednesday morning / early afternoon.
In general, cloud cover could be a major inhibiting factor for deep convection - however, guidance favours some clearance over eastern Scotland and portions of Ireland during the afternoon and evening hours. Provided sufficient heating of this rather moist low-level airmass occurs, scattered heavy showers may develop.
Over Scotland cloud depth may be somewhat limited, which combined with very weak shear suggests that there may not be much in the way of lightning activity, despite the potential for heavy, slow-moving "pulse type" showers. We have tentatively included a low-end SLGT to highlight the main area of interest, and it could be the case that most activity occurs quite late in the day (i.e. in the evening hours). Localised surface water flooding is the main concern given slow movement of showers.
A low-end SLGT has also been issued for parts of Northern Ireland / Republic of Ireland, where a slightly better environment will exist for lightning potential. It seems plausible that scattered showers and a few thunderstorms could develop during the afternoon through the central areas, drifting to the NE with time - with most activity then weakening and/or clearing to the Irish Sea by mid-evening. A few isolated strikes from elevated convection is also not out of the question along northwest Atlantic coasts, running NE into W Scotland during the evening/night hours, though confidence is not particularly high given a lack of widespread NWP support.
Met Eireann also mentioning: 'Some dry spells in eastern areas at first. But the rain in western and northern areas will become fairly widespread by early afternoon. Some heavy bursts are likely later too, with a risk of thunder.'0 -
The models showing the possibility of some heavy showers in places tomorrow and increasingly so in the afternoon and evening in the Eastern half of the country. It remains to be seen if convection gets established enough to become electrified. The main models showing some possibility of lightning.
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Off or just along the SW coast looks like an area with the parameters for Convection and some thunderstorms early tomorrow morning with good model agreement.
Thurs in Northern counties would be an area most favorable for some sporadic lightning perhaps. Thurs night into Fri looks favorable for sporadic thunderstorms, initially in the SW or W early Fri morning and later for that afternoon the models have been showing Fri as heaving a lot of potential for fairly widespread thunderstorms but too early to know for sure yet . Been a couple of busts recently even with what looked like having the parameters in place , but interesting to study nonetheless.
Fri early look at some of the parameters. Strong jet over Ireland , Lot of moisture in the atmosphere, probably good LLS and DLS, areas of convergence, upper low, good surface heating up into the low 20's, DP's 16 to 18C. Been showing this for a number of runs now. Should be a fair amount of instability in the atmosphere.
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Fri looking like it could be an eventful day. ECM has been very consistent showing big potential for heavy convective rain and has been showing potential for widespread thunderstorms. On tonight's 12Z run it is showing increased rainfall amounts, possibly to warning level. Currently looking like rain arriving late Thurs night as a slow moving complex LP migrates across Ireland with it's associated warm and cold fronts and embedded troughs.
ECM has been showing high CAPE readings and areas of convergence, good to reasonable shear , high Theta -E readings , plenty of instability in the atmosphere.
Sunshine levels will be quite low if any for many places, S and SE atm looks the best and this will lead to the highest CAPE readings towards the afternoon with the winds from the SSW bringing convection and possible thunderstorms towards Midlands and Leinster in particular . Will need to look closer at this tomorrow evening.
Probably talking about elevated thunderstorms for the most if they materialize. Similar type set ups recently did not bear any thunderstorms . Not sure if this will be different as yet but thinking there is better potential this Fri due to frontal forcing and the proximity of the upper low and more shear this time.
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Day 2 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
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.0 -
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