Convective/Thunderstorm Discussion : Spring/Summer 2020

Cold air spreading aloft tonight after the cold front into tomorrow and the passage of troughs giving instability along with diurnal heating tomorrow afternoon will give some heavy showers and some might contain hail and a few sporadic showers may become electrified although there is low shear and lapse rates available. Pulse type brief thunder storms if any. Later Sunday evening the NW/ N might see some heavy showers and again some might have hail and become electrified.

Getting some sferics in Northern counties. looks like some heavy rain going through.

ZX7R wrote: »

Definitely a feel of thunder in the air

I see a nice bit of heat recorded today, creating some instability.

Just a few drops here earlier from high elevated blanket cloud, feels humid.

Trough approaching the S /SE tomorrow evening might have a slight chance of producing some weak thunderstorms, maybe off or along the coast. Relatively warm moist air over relatively cold sea with cold uppers.

The cells exploding in NW France.

Not much rain showing up so far, gone very dull here near Tralee, heavy cloud overhead and hazy below it, got up to 17.3C but temp has dropped down now to 12.8C. Satellite showing convection with growing cloud heights but rain staying up there for the most part for now.

A lot of interesting detail in Convective Weathers forecast. Been an age since there has been a modest to decent bit of potential for convection and lightning if somewhat sparse. From a weather watchers perspective an interesting spell of weather over the next few days after the extended calm spell.






Day 2 Convective Outlook
VALID 06:00 UTC Wed 29 Apr 2020 - 05:59 UTC Thu 30 Apr 2020

ISSUED 20:26 UTC Tue 28 Apr 2020

ISSUED BY: Dan

A broad LOW threat level has been issued to cater for the very low risk of isolated lightning strikes that may occur with various weather features during this 24 hour forecast period. However, for most places the risk is considered very low, and hence the vast majority of the large LOW threat area will remain void of any lightning.

At least two organised occlusions, and associated bands of rain, will sweep northwards and eastwards across the British Isles during this period, one during Wednesday daytime, and a second primarily during the evening and night. In both cases, these features will initially be quite active given strong forcing aloft, with heavy bursts of rain and embedded deep convection likely as they approach southern Ireland and southwest England, but as the forcing aloft shears away to the northwest, the bands of rain are expected to gradually weaken as they track farther northeast, eventually stalling somewhat over Scotland while decaying. In general, the risk of lightning will be greatest with these features as they approach southern Ireland/southwest Britain (20-25%), the risk then reducing as they push farther north and east (5-10%). CAM guidance suggests meso-vortices may develop along the rear edge, especially located near the most intense convection, and this may aid the potential for damaging gusts of wind (50-60mph possible over open waters and exposed Celtic Sea coasts). Multi-model guidance suggests Pembrokeshire and along the coast of Cardigan Bay could see some strong gusts of wind during Wednesday morning, for example.

In-between these two occlusions there will likely be a window of cloud clearance coinciding with peak diurnal heating, particularly in a swathe from central Ireland across Wales and central southern England. With the mid-levels having cooled considerably by this stage, this may yield a couple hundred J/kg CAPE - more especially over Ireland, with greater proximity to the upper cold pool. As a result, some convection and a few showers could develop, although the pronounced mid-level dry layer will act as a lid, restricting the depth of convection and hence limiting the overall lightning risk. Nonetheless, a 10-15% risk of lightning may exist over Ireland during the afternoon hours, although the second occlusion will already be arriving in southern Ireland by mid/late afternoon.

Behind the second occlusion, a pronounced shortwave will approach the Celtic Sea and SW England on Wednesday night, driving deep convection and numerous showers which may evolve into a comma-type feature by the end of the night. Given some reasonable speed and directional shear, strong forcing aloft and 300-500 J/kg CAPE, some sporadic lightning seems possible. A low-end SLGT (30%) has been issued to cater for this risk. Once again, some damaging gusts of wind could occur near exposed coasts and some hail is also likely in the most intense cells. Ironically, this type of setup is more akin to autumn/winter rather than mid/late spring!