[Tony Gilbert]

Slight Risk of Isolated Post Frontal Thundery Showers with Hail 10Z-18Z Ireland, central and southern UK regions Sat 17th March 12

A low risk outlook added as an item of interest.

Toward the lee of the early day cold front we can expect a more unstable environment to develop through the afternoon. Whilst models currently forecast CAPE advecting in from the western sea region, I would more likely expect CAPE to develop slightly inland from the coast where stronger insolation can take place. Whilst we might only see around 10 deg C surface temps the upward influence of the cold pool aloft should rapidly generate steep height falls. The results might see a wave of isolated cunimbs capable of developing sharp showers with hail. Some of which may in fact turn thundery if surface temps can be sustained for long enough.

Much will depend on clearings between a general cloudy sky. Though mid level flow looks to push this clutter progressively eastward. Vertical shear profiles look weak though some surface convergence looks possible NW Wales and NW Ireland where the odd early season funnel could develop.



If you would like to comment or add further discussion Nigel B has started a chat thread here http://www.ukweather...8th-march-2012/

This post has been edited by Tony Gilbert: 16 March 2012 - 11:06

[Tony Gilbert]

UPDATE 7.30pm Fri

Remains low level risk

As per earlier forecast with risk box expanded further across SW UK and period shifted forward to 12 noon till 18Z as per map below.

GFS model now shows the potential for some overlay of stronger 500mb winds to forecast post frontal troughing for Devon, Dorset and Somerset during the afternoon. Some interesting features could be in play here regarding the odd isolated stronger convective cell developing where any updraft can reach 500mb. At present models suggest a slow increase in vertical shear to mid levels then an abrupt increase in speed shear and directional shear could take place upwards from this layer
!. This potential via the GFS is also reflected within the sudden increase in PVA just behind the subsidence left in place from the earlier cold front.

All in all ATM there would be some potential for one or two isolated convective cells to develop in the 'said region' with stronger potential. Though as always such predictions can only be based on the reliability of the models available . In addition to this we have the usual early season restrictions such as cold SST influencing any outcome!

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This post has been edited by Tony Gilbert: 16 March 2012 - 19:56