[John Mason]

Just a quick run-through: tomorrow has a few features of interest in a generally showery regime. From late morning onwards marked lowlevel convergence seems likely from SW Wales up towards Humberside, the strongest convergence transferring ENE through the day. Some impressive CAPE values realised by the afternoon especially over E Anglia coincide with strongish deep-layer shear in excess of 40kts. Combine these factors of low-level directional shear, a buoyant atmosphere and good venting aloft and I'd say a rotator or two couldn't be ruled out tomorrow, CS England-S Midlands over towards Norfolk/Lincs, with attendant slight tornado risk. Also potential for funnels across S wales in towards this area as convection develops late morning. All in all looks one of the more interesting convective setups of the year so far.

Elsewhere heavy downpours, possibly thundery, will be on the cards.

Cheers - John

[Tony Gilbert]

8.55pm Tues

Moderate Risk of Scattered Thundery Showers Ireland & UK 09Z-21Z

Stronger Organised Convection Possible (as per yellow box)

Irregularities between models now much less obvious. GFS, NMM and WRF now pretty firm on the potential for a widespread thundery regime through Weds, Hence a Moderate Risk level is more appropriate!
An unstable environment builds within the post frontal sector. A number of surface troughs expected to develop from quite early on Weds morning. Relatively weak upper trough nudges eastward increasing lift with a number of moderate strength PVA Max's looking to further increase lift along the northern periphery of the upper jet stream. Some marginal overlay of vertical shear to instability looks to take place for southern UK as per yellow box. Though based on the forecast vertical wind profiles I do not ATM see this support developing supercell characteristics on any storm building in this sector (though this could change)! Whilst Deep Layer Shear would appear strong, the vertical velocities are not showing cloud tops reaching this level. This will means that any building storm cell will be unlikely to tap into this strong upper motion. Lack of convergence right across the board and the low level shear looks rather weak ATM with fairly straight lined winds at all levels. So not ready to suggest any risk of tornado development. Though this cannot be entirely ruled out.

Prime regions where lightning could be more prolific might be around W.Midlands later in the day. Also likely to be a risk of strong gusts (non severe). Confidence is fairly good for results ATM. Certainly worth a heads up and requires careful monitoring.

It would only take some minor changes within the models to increase the severe aspect of this outlook.

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This post has been edited by Tony Gilbert: 05 June 2012 - 20:19

[Tony Gilbert]

8.40am Weds UPDATE

As per earlier forecast with yellow box signifying the risk of 'stronger convection', now removed. Whilst based on this mornings model update it would seem wise to maintain a moderate risk for thundery activity today, there have been some subtle changes noted;
Mid level jet stream now likely to remain primarily over the continent with even less overlay to instability across the UK than of yesterday. This combined with a reduced SEsterly momentum for the upper trough will likely have the net effect of lessening thunderstorm potential across the southern sector of the convective box. However the best potential for scattered thundery activity remains across the Midlands through to Humber by mid afternoon. Ireland will also see scattered thundery activity today though within a very weakly sheared environment.

This post has been edited by Tony Gilbert: 06 June 2012 - 07:58