[Tony Gilbert]

Posted Sun 7.40pm

Slight Risk of Thundery Showers Central/ SW UK & Ireland 12Z-18Z

UKMO fax chart shows a develop surface wave feature across the UK and Occlusion for Ireland. Long wave upper trough spreads eastward increasing lapse rates. A relatively moist surface flow looks possible with dew point around 12 deg C. For the UK both GFS and NMM suggest that the wave will be primarily non convective but there looks to be some scope for a narrow prefrontal trough. Models are currently holding the strongest instability for the UK within this zone. Moderate upper jet stream increases vertical shear to a level which should allow some longer lived multi cell clusters to exist for a time with a risk of lightning and small hail. Some restrictions may exist regarding weak PV aloft and winds look fairly straight lined at all levels ATM.

Ireland continues to show the strongest developing CAPE and looks to have the higher risk of sferic activity. Some basic shear in place with multi cell activity the likely result.

The outlook whilst currently looking rather low risk ATM nevertheless has the potential to be upgraded based on the forward projection of the front left exit region of the jet stream and increased PVA aloft. Certainly one to keep an eye on!

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This post has been edited by Tony Gilbert: 06 May 2012 - 18:55

[Tony Gilbert]

10am Mon UPDATE

As per earlier forecast with changes as below;-

Upper cold pool at 500 mb is now 2 deg C less than earlier prediction within the convective zones. This combined with a saturated mid level will likely restrict convection spatially today. The best instability remains to the SE of the wave feature as per yellow enhanced box for the UK. Though it is noted that a decrease of mid level winds and an increase in 850mb winds will likely result in less organised cell development. This has nevertheless increased low level shear somewhat and cannot rule out an isolate brief tornado event close to the enhanced zone after 15Z. Though prime risk today looks to be small hail, gusty winds (non severe) and some isolated sferic activity ( UK specifically)

Lightning is not guaranteed for the UK!

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This post has been edited by Tony Gilbert: 07 May 2012 - 09:16

[PaulKn]

TORRO TORNADO WATCH 2012/002

A TORRO TORNADO WATCH has been issued at 1445GMT on Monday 7th May 2012

Valid from/until: 14:45- 21:00GMT on Monday 7th May 2012 for the following regions

Parts of (see map)

SW England

SE Wales

Midlands

E England

THREATS

Tornadoes; wind gusts to 60mph; hail 10-15mm diamter; CG lightning; torrential rain

DISCUSSION

Cold front moving in from the west is being held up by a developing frontal wave as an upper trough moves in. Sunshine ahead of this has allowed scattered thunderstorms to develop in a region of favourable vertical wind shear for organised thunderstorms, with low-level veering profiles suggestive of low-level rotation and possible tornadoes.

Further convection is approaching SW England and may contain strong wind gusts although a more veered surface flow here suggests a somewhat lower tornado threat. Convection may continue overnight as the cold front drifts eastwards with strong shear suggesting a mainly straight-line wind threat. A further forecast may be required later.

Forecaster: RPK.

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[PaulKn]

Made a small addition to the watch area to include a bit more of E Anglia - see the TORRO forecast page.