[paul cotter (OP)]

Today in Ireland we had extensive and very active thunderstorms. I understand the "summer thunderstorm" where convective activity supplies the energy. I doubt there was sufficient convection today. I have heard the term "frontal" storm activity but I am not sure if this is applicable.

[Bored chemist]

There's a lot of energy in the Atlantic. It has been warming up all Summer.

[Halc]

Any temperature difference can supply energy.  Cold air against an even colder front coming in can produce significant storms.  I do get the occasional thunder-blizzard around me, but most of the big snow storms are all wind and precipitation and not so much lightning.
Gotta admit never seeing a tornadsnow.

[evan_au]

There's a lot of energy in the Atlantic.

The Gulf Stream carries an enormous amount of heat from the Caribbean up to the UK+Eire, warming the UK considerably compared to the same latitude in Canada.

There are concerns that the melting of the Greenland ice shelf could halt this marine heater, dropping the temperatures in UK+Eire by several degrees.

[paul cotter (OP)]

Perhaps I should have phrased the question in a different manner. Yes the atlantic will build vast amounts of energy, especially during summer months. To produce a thunderhead, to the best of my knowledge( which isn't great ), there is a need for rapid convective updraughts to the tropopause. It is the mechanism for this to happen in cold weather that I seek to understand.

[Origin]

To produce a thunderhead, to the best of my knowledge( which isn't great ), there is a need for rapid convective updraughts to the tropopause.

That is not necessary.  In the summer convection to very high altitudes is needed for the formation of ice and snow.  In the winter the snow and ice are near the earths surface, all that is needed is a strong enough convection to separate the charges.  There is not usually enough convection in snow storms for there to be lightning, but of course sometimes there is.
The energy for the convection usually comes from a very 'deep' low pressure system or from a difference in temperature such as lake effect snow.

[alancalverd]

What has beset these islands for the last couple of days were occluded fronts.

I'm rarely happy when my little Cessna is grounded with a suspected ignition fault, but this morning, instead of taking myself to work in Glasgow I had the pleasure instead of visiting the flight deck of an Airbus 320 sat on the tarmac for an unscheduled hour whilst half of the pilots in British airspace were groping for a gap between the storms, and the others were exercising professional discretion and staying on the ground. All thanks to occluded fronts.

Difficult to describe without lots of diagrams, but imagine a tongue of warm air moving northwards from the equator into a region of cold air. As the equatorial air is also moving rapidly eastwards compared with the polar air, it forms a rotating wedge. The leading edge of the wedge rises over the cold air and produces gradually lowering  stratus clouds as seem from the ground - this is the warm front (not very well defined) and the warm sector (cloudy, drizzly) of a depression.

The trailing edge tends to be a more sharply defined cold front where the polar air shoves the war, damp air rapidly upwards, forming towering but avoidable cumulus or cumulonimbus clouds in otherwise fair weather.

Problems arise when the cold front advances  faster than the warm, and "squeezes" the warm sector. Since the wind at altitude is always stronger than the surface, you can get polar air overlying parts of the equatorial "tongue", so convection becomes very rapid  (forming cumulonimbus - thunder clouds) embedded in a thick layer of rainy, foggy stratus - characteristic occluded frontal weather and very unpleasant flying conditions with negligible visibility from the ground to 20,000 ft, pockets of violent turbulence, and every form of water moving in every direction, accompanied by  flashes of lightning from clouds you can't see!

[paul cotter (OP)]

Thank you, alancalverd, that was an excellent and thoroughly comprehensible explanation.