Convective outlook - Friday July 13th 2012
Posted 12 July 2012 - 15:16
Posted 13 July 2012 - 08:06
Moderate Risk of Scattered Thundery Showers 12Z-21Z all central and Southern UK regions
Prime Risk CG's and Slight Risk of Funnel Cloud/ Weak Tornado Development.
Following on from Paul's forecast and in agreement.
Confidence Level; Medium
Low pressure moves slowly eastward with deep upper trough gradually overspreading region through the afternoon and evening. Occluded front and surface trough to the south expected to initiate rain and convective showers across many parts within the white box zone today.
A weakly sheared environment right across the board today though with a line of strong convergence marked yellow box running from N.Wales through to Essex expected to initiate lift and low level vorticity with the chance of one or two FC events possible. GFS now predict dry mid level incursion across central region. This may increase buoyancy of any lifted parcel later today around N.Hants and Cambs region. Though some concerns today regarding solar heating as according to WRF a thick layer of elevated cloud expected to move north from the continent reducing surface temps.
All in all this outlook has some specific detail which could undermine the results and my posting is only now added due to the forecast dry incursion which was not there last night. Additional concerns regarding how much instability will develop along the expected line of convergence today. Though, it should be noted that the forecast convergence vector looks optimised to create the best chance for close nit circulations! Some scope for continued storms Southern coast up until mid night as further convection possible along English Channel.
This post has been edited by Tony Gilbert: 13 July 2012 - 08:08
Posted 13 July 2012 - 09:57
A TORRO CONVECTIVE DISCUSSION has been issued at 0950GMT on Friday 13th July 2012
Valid from/until: 0950GMT – 2300GMT on Friday 13th July 2012 for the following regions of the United Kingdom & Eire:
Portions of Wales
The Midlands and E Anglia
Isolated, weak tornadoes; heavy rain; CG lightning; hail
A large upper cold pool covers much of the British Isles and western Scandinavia. A trough will move eastwards across France with a sliver of vorticity pushing into southern and central England. This, along with diurnal heating and a well-marked convergence zone is likely to produce showers and thunderstorms, although coverage will vary due to a fair amount of cloud cover, which may limit the heating in places.
Any showers and thunderstorms developing in the vicinity of the above-mentioned surface convergence zone, and also along a potential sea breeze front across west Wales, may ingest and stretch vertical vorticity enough to produce funnel clouds and weak tornadoes. This convergence zone will move slowly southwards through today and this evening. Showers and thunderstorms may continue well into this evening.
Heavy rain is possible in places too due to the slow-moving nature of the storms, along with hail and CG lightning.