Convective/Thunderstorm Discussion: Autumn2022
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01-09-2022 8:36pm#1
Over the weekend into the early days of next week conditions look like giving potential for thunderstorms at times.
Saturday behind the cold front the atmosphere should be quite unstable over the Western half of the country and more so towards coastal counties with very cold air aloft over warm SST's giving rise to convection with heavy showers and could well see some thunderstorms and wouldn't be surprised to hear of hail falling locally. Temperatures looking very low along Atlantic coastal counties so a lot of the instability coming from the sea temperatures I would think. Could get some good pictures of Anvils in the afternoon and towards evening
Post edited by DOCARCH on4
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Some nice convection visible off the Kerry coast, quite cloudy in general but bright with pockets of blue sky. Will see what enfolds today, might get some thunderstorm overland in Kerry today and up along western coastal counties, convective weather has shown a fairly wide area with potential interest and interesting what might develop later tonight early Sun morning in the SE, E.
Day 1 Convective Outlook
VALID 06:00 UTC Sat 03 Sep 2022 - 05:59 UTC Sun 04 Sep 2022
ISSUED 06:49 UTC Sat 03 Sep 2022
ISSUED BY: Dan
A sharp prefrontal trough will migrate gradually northwards across England into southern Scotland on Saturday. The low-level wind convergence along the trough axis, combined with modest heating of a moist low-level airmass (dewpoints 14-17C) yielding around 500 J/kg CAPE, will provide an environment increasingly favourable for scattered heavy showers and perhaps a few thunderstorms, especially with time (meaning northern England/southern Scotland at greatest risk, towards late afternoon and into the evening hours). There will likely be issues with mid-level capping restricting the depth of convection in places - and so lightning activity is questionable - but this should be less of an issue towards far northern England and southern Scotland. Here, reasonable speed shear and subtle veering with height may create an environment with around 30kts DLS, which may aid cell organisation for a time. Greatest threat for local surface water flooding is SW Scotland where multiple cells may train over similar areas. Eventual upscale growth into a band of rain is anticipated through the evening and night hours, and so lightning activity will likely wane. However, an uptick in elevated convection is possible in E / SE Scotland during the early hours of Sunday, spreading inland from the North Sea. Confidence is not overly high on much in the way of lightning occurring, but tentatively introduced a SLGT here.
In the post-frontal environment, scattered showers are likely in C / W / S Ireland in a strongly-sheared environment. Limited CAPE and the potential for clusters of showers to morph into areas of showery rain casts some uncertainty over how much lightning activity may actually occur. By the overnight period model guidance diverges substantially as a pronounced dry intrusion engages with the trailing cold front over the Celtic Sea, inducing a wave or even a developing surface low. Strong forcing could result in a few active thunderstorms somewhere over the Celtic Sea, which could impact SE Ireland and/or SW Wales/SW England, but there is a lot of uncertainty over whether this will even occur let alone areas potentially affected. ECMWF and derived products have been consistent in a more active feature/greater pressure falls, and therefore favour a track further to the west into Ireland, whereas other model guidance is less-developed and further east (into more of Wales/SW England). Given strong low-level shear and backed winds in the vicinity of the cold front, there is a threat for both SLW and isolated tornadoes - and a SVR has been introduced for this risk. Some local surface water flooding may also be possible with pockets of more intense convection, especially where this trains over similar areas.
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Rare Estofex for Ireland
Ireland and Ulster, W coasts of England, Wales and Scotland ...
Close to the active Atlantic cyclone, two pronounced synoptic features cross Ireland and Ulster from SW to NE in this forecast period, which can be interpreted either as commas or as quickly occluding frontal systems. Intense lift from accompanying mid-level troughs will likely create two forced convective rainbands in an environment that is favorable for severe wind gusts as well as tornadoes.
The first system crosses Ireland and Ulster already Saturday night and leaves it shortly after the beginning of this forecast period at Sun 06 UTC. While the kinematic conditions are most impressive (e.g., shear up to 20 m/s and storm-relative helicity up to 300 m^2/s^2 across the 0-3 km layer), a lack of CAPE could be an issue, and it is not clear if the first rainband will grow deep enough to produce lightning.
The second system follows in the 18 to 03 UTC time frame and features slightly weaker kinematics, but more robust CAPE, probably on the order of 500 J/kg.
All in all, the combined threat by both systems appears high enough for a level 2. The assessment of the main hazard (straight-line winds or tornadoes) depends on the mesoscale structure of the rainbands and needs to be left to the nowcasting time frame. In case mesoscale vortices develop, the expected very low cloud bases (just a few hundred meters above sea level) could even support an outbreak of several tornadoes.
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Some squall line heading up but looks like it will be out to sea if it holds
Thats heading towards the uk. There's looks like another to the south of ireland. can just see it on the edge of the radar straight down from limerick
Post edited by spookwoman on1 -
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