Convective/Thunderstorm Discussion : Summer/Autumn 2021

Met Éireann just included Galway now in the warning.

Great capture Rikand

👍️

Some thunderstorms possible in the NW, N today in the afternoon during peak diurnal heating, Cold air aloft giving modest CAPE over the sea and moving over land , LLS and DLS giving decent Lapse Rates, good parameters for funnels with a touchdown possible.

Less potential with lower CAPE for tomorrow since earlier runs, if lightning occurs it could stay over the sea off the SW or along the coast but looks low enough risk.

There was some sferics picked tonight out to sea perhaps around 200km/h from W Cork. Seeing Flashes but hearing no thunder would often indicate elevated storms ie. they are so high you can see the flashes from long distances away, especially if you are on some high ground yourself. Some of the posters here have reported seeing lightning from great distances in the past , I would think 100 km + . Not too aware of the term heat lightning, googled it and came up with a good explanation below

https://www.weather.gov/safety/lightning-heat

Interesting day ahead Pad especially for your neck of the woods, Thunderstorm Alley !

Could see thunderstorms outside of the warning area also , /ECM showing loads of CAPE in Munster also from early but storms and heavy rain will probably peak in the afternoon during peak diurnal heating in the warning areas, wouldn't be surprised to see parts of Munster added to the warning. Looks like a negatively tilted trough passing over the country so giving it a bit more umph

From Dan Holley of Convective Weather :

Day 2 Convective Outlook

VALID 06:00 UTC Sat 21 Aug 2021 - 05:59 UTC Sun 22 Aug 2021

ISSUED 21:08 UTC Fri 20 Aug 2021

ISSUED BY: Dan

Trough disruption will occur over the North Atlantic on Saturday, with a resultant cut-off upper low drifting gradually eastwards across southern Ireland during the day, and then southern Britain during the evening/night hours. Outbreaks of rain will affect many parts of the UK and Ireland at some stage during Saturday, lifting erratically northeastwards. Forecast profiles suggest some weak elevated convection is possible embedded with this frontal rain, particularly in the 600-850mb layer, but given rather moist profiles the risk of lightning is relatively low in any one location - but a few sporadic lightning strikes may be possible. In particular, the southern North Sea could exhibit some active thunderstorm activity during the late afternoon/evening hours as unstable air advects northwards from the Low Countries ahead of this front. 

The main focus for lightning, however, will be associated with the post-frontal environment as cool air aloft overspreads a moist low-level airmass with dewpoints typically 15-17C widely. The coldest mid-level air will be associated with the upper low, over Ireland during the day, and swinging across southern Britain during the evening/night. Modest surface heating is likely to yield 500-900 J/kg CAPE, with the potential for scattered showers and a few thunderstorms to develop - especially aided by low-level convergence and orographic forcing, but also PVA lobes within the base/forward side of the upper low. Speed shear is a little weak below 500mb, but some increasingly strong flow aloft will yield reasonable cloud-layer shear, especially when coupled with backed low-level winds. Overall, the environment may be conducive for some cell organisation and hence longevity, and there may be scope for an isolated supercell in the West Country in particular (e.g. Somerset / Dorset / Wiltshire). If an organised thunderstorm can develop it could pose the risk of some marginally-severe hail and perhaps an isolated tornado. Otherwise, the main hazard, aside from lightning, is the risk of local surface water flooding.

The forecast evolution in Northern Ireland is less clear, with the potential for frontal rain to potentially linger and limit instability. However this will be monitored and an additional SLGT could be issued if confidence increases. Elsewhere, while instability will gradually reduce during the mid/late evening onwards due to nocturnal cooling of the boundary layer, forcing aloft and residual humid airmass will still pose the risk of some showers and the odd thunderstorm overnight as the main upper low shifts eastwards across southern Britain.

Looks a bit out of the firing line tomorrow, if there was some activity maybe East Galway with the best chance i reckon , where is showing up as maybe being fairly active on latest AROME run is the SE and up to to around mid Leinster but as ever can be notoriously difficult to pinpoint Lightning especially Ireland. Spot flooding possible under some of the bigger convection and would imagine some tricky road conditions in the warning counties.