Convective/Thunderstorm Discussion - Summer 2023
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03-06-2023 8:21pm#1
A bit of convection over the south Irish Sea, will it spark?
Post edited by Meteorite58 on1
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A lot of heat and moisture in the atmosphere on Saturday. MUCAPE readings fairly high especially in the Northern half of the country later in the evening or night, high Dp's, high Theta E, lower convergence, some upper shear especially in the Northern half and a trough giving instability. Some charts showing as high as 27C in central counties on Sat so plenty of fuel. Very muggy especially where there is rain.
Will see also if some activity in the Southern half earlier in the day especially the SW as it gets clipped by the occluded front although a lot of the activity could be over the sea or near the coast. Bit early yet but signs of some thunderstorms possible.
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VALID 06:00 UTC Fri 09 Jun 2023 - 05:59 UTC Sat 10 Jun 2023
ISSUED 07:48 UTC Fri 09 Jun 2023
ISSUED BY: Dan
A similar evolution is anticipated on Friday to that of Thursday, with a broad upper low residing to the southwest of the British Isles and slow advection of high Theta-W plume (>16C at 850hPa) progressively northeastwards. The main interest will be in the vicinity of an occlusion straddling NW France, western English Channel, SW England and into Ireland, where pulses of showery rain will continue to develop at various times through Friday and Friday night, with an ongoing chance of a few elevated thunderstorms - more especially from late afternoon and through the evening/night hours, although confidence on lightning coverage is rather low. Tentatively introduced a fairly broad SLGT risk although many areas may remain void of lightning.
Elsewhere, while substantial CAPE may build across central and southern Britain on Friday afternoon (this then advecting across the Irish/Celtic Sea to SE Ireland overnight atop the mixed layer), forecast soundings reveal very dry profiles with capping at several levels and therefore for the most part it is unlikely any substantial surface-based deep convection will occur. That said, additional orographic forcing over Exmoor and higher terrain in Wales may be sufficient to develop a few isolated heavy showers/thunderstorms, drifting offshore and towards SE Ireland where they could potentially grow upscale into a small cluster as vorticity associated with the remnant MCV over the Brest peninsular this morning arrives from the SE (this already not handled very well in CAM guidance this morning) - this aspect is rather uncertain, but a low-end SLGT has been introduced.
Also, there have been subtle hints on Friday night of odd elevated showers developing within the broader Theta-W plume across central/eastern England emanating from the Low Countries during the evening and migrating northwestwards with time. However, current thinking is the chance of lightning is too low to warrant any extensions/additions to existing highlighted areas.
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WRF and ECM suggesting that there could be some activity moving onto the S coasts later tonight/ early Sat morning, Cork area in general being currently highlighted for possible thunderstorms moving on to the coast overnight.
AROME showing potential for heavy convective rain moving through the SW early evening and later tonight / early Sat morning in southern counties. Not huge MUCAPE showing up but with all that warm moist air advecting up over Ireland at height over converging winds down at low level and add in lift due to topography bound to provide instability. The convection /heavy rainfall shown by AROME for early evening if it materializes might give an indication of how active it might be later in the night/ early morning and another active day possible in parts during Sat.
Showing spot flooding potential tonight/ early Sat morning but as always very hard to pinpoint, but in the main coastal areas in Cork/ Waterford shows up on the models, new weather set ups beginning, some active or very active days possible next week. Getting into the type of weather where warnings for heavy rain/ thunderstorms might be issued at short notice.
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Met Eireann not going for much rain tonight, mentions more towards dawn a band of showers possibly with heavy falls. The radar this evening showing convection growing as it approaches Ireland, still a bit away but this would correspond with the ECM showing rainfall and heavy in places later tonight moving into the S, SW and SE and moving up the country towards the W, NW
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The W being highlighted tomorrow as an area of interest with fair potential in the afternoon as convection matures crossing the country coinciding with peak heating, high Dp's . Looks very active over in the UK tomorrow. Will see if the NE gets some some storms later in the night into Sun morning.
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From the National Weather Service: MUCAPE (Most Unstable Convective Available Potential Energy) is a measure of instability in the troposphere. This value represents the total amount of potential energy available to the most unstable parcel of air found within the lowest 300-mb of the atmosphere while being lifted to its level of free convection (LFC).
MUCAPE: This measurement finds the most unstable parcel of air possible within a sounding and records that value. Typically, this is most useful when there is a strong surface inversion and thus, storms are likely to be elevated.
Only an amateur but find MUCAPE potential a good guide when dealing with warm moist elevated airmass. Surface CAPE will also be important but a lot of the instability tomorrow is more elevated I reckon. Surface based soundings may not tell all the picture with set ups like this.
CAPE readings quite good for near Galway city tomorrow, a lot of water available in the atmosphere, could produce very heavy showers. The KO reading a good guide also as showing fair potential for thunderstorms, decent enough shear.
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