[Tony Gilbert]

8pm Tues

Moderate Risk of Scattered Thundery Showers central and central Southern UK 12Z-19Z

Slight Risk of Funnel Cloud Development as per region above

Almost stationary low central UK acts as fulcrum to wrapped occlusion allowing for another round of thundery showers to develop through Weds afternoon within a cyclonic circulation. GFS and NMM are currently bolstering CAPE above 500 j/kg by mid day based primarily on almost 100% humidity at surface. Surface temps and dew point almost run parallel within the the marked zone by early afternoon suggesting very low cloud bases possible. This combined with strong vorticity at all levels would suggest a defined risk of FC's possible.

Opinion; concerns are raised as to whether the 500mb upward CAPE values will actually be achieved based on cloud cover reducing heating somewhat and a saturated atmosphere in place up to the tropopause slowing the cooling of cloud tops? Based on the current model output it is quite possible that due to a rapid increase in cold pooling at surface once the first lot of showers occur that instability could rapidly diminish by mid afternoon. We can nevertheless expect to see some photogenic hard mid level inversions spread to many parts during this process.

There is a small risk of thundery showers for central Ireland and Scotland. This will need to be addressed using the morings model ouput.

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This post has been edited by Tony Gilbert: 17 April 2012 - 19:22

[Tony Gilbert]

UPDATE 8.17am

As per earlier forecast.

A closer look at the models might suggest that any thundery activity today will in fact be associated with a small surface trough central to the low pressure and not the outer circulating occlusion which looks to remain primarily non convective!

[PaulKn]

TORRO CONVECTIVE DISCUSSION 2012/002

A TORRO CONVECTIVE DISCUSSION has been issued at 0940GMT on Wednesday 18th April 2012

Valid from/until: 0940GMT – 1800GMT on Wednesday 18th April 2012 for the following regions of the United Kingdom & Eire:

Much of Scotland

THREATS

Isolated tornadoes; heavy hail to 10-15mm; CG lightning; heavy rain; gusty winds

SYNOPSIS

Major upper and surface lows across southern Britain will be slow-moving today. A shortwave trough is rotating westwards into Scotland this morning and will provide lift for ascent which, when combined with diurnal heating, is expected to allow numerous showers and a few thunderstorms to develop. With fairly cold upper air and reasonable instability, hail to 10-15mm is possible, and given the slow-moving nature of the showers/storms, this could lead to reasonably accumulations in places. Gusty winds and CG lightning are also likely. With a slack surface flow, complex topography could allow local pockets of vertical vorticity to develop, and if ingested by a passing updraught, one or two weak tornadoes may develop.

Forecaster: RPK.

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[Tony Gilbert]

Tony Gilbert, on 17 April 2012 - 19:19, said:

Opinion; concerns are raised as to whether the 500mb upward CAPE values will actually be achieved based on cloud cover reducing heating somewhat and a saturated atmosphere in place up to the tropopause slowing the cooling of cloud tops? Based on the current model output it is quite possible that due to a rapid increase in cold pooling at surface once the first lot of showers occur that instability could rapidly diminish by mid afternoon. We can nevertheless expect to see some photogenic hard mid level inversions spread to many parts during this process.

There is a small risk of thundery showers for central Ireland and Scotland. This will need to be addressed using the morings model ouput.

Regarding my earlier comment as per above; This looks to be the primary result for today!