Issued 2018-04-21 21:54:57
Valid: 22/04/2018 0600z - 23/04/2018 0600z
During Sunday, occluding cold front moving east ahead of low moving NE between Iceland and Scotland will bring a band of cloud and rain across country with cooler and more stable conditions of Atlantic origin following. However, warm, humid and unstable airmass will hang on across SE England and E Anglia into the afternoon, - which may trigger isolated thunderstorms with surface heating.
DAY 1 THUNDERSTORM OUTLOOK
VALID: 22/0600Z - 23/0600Z
... SE ENGLAND and E ANGLIA ...
*Risk of ...
Hail (isolated large), flash-flooding, gusty winds and frequent lightning
Warm and humid airmass ahead of cold front moving in from the west will become unstable with surface heating in sunny spells aided by continued cooling aloft steepening lapse rates, surface breeze convergence ahead of approaching front the west combined with large scale ascent of approaching upper trough may support the development of a few thunderstorms with peak heating in the afternoon, provided there is some sunshine. 30-40 knots of deep layer shear, strong SWLy flow aloft and 300-600 j/kg CAPE may allow storms to organise, perhaps strong enough to bring some isolated large hail, localised flash flooding, gusty winds and with LCLs lower than today, a brief funnel or weak tornado can't be ruled with storms forming or crossing along wind shift.
Issued by: Nick Finnis
Issued by the Netweather forecast team whenever there is a risk of storms or severe convective weather, these discussion based and in depth forecasts will highlight the areas at risk and give an in depth description of the risk and the factors surrounding it.
Thunderstorms - Severe thunderstorms unlikely to occur, slight risk of hail, gusting winds and localised flooding.
Slight Risk - A slight risk of severe convective weather exists. Hail >2.0cm diameter, wind gusts exceeding 50mph or 5-10% risk of a tornado within 50 miles of a point, or > 30% risk of localised flooding.
Moderate Risk - A moderate risk of severe convective weather exists. Hail 4-5cm in diameter, or wind gusts of 60-70mph, or a 10-15% chance of a tornado within 50 miles of a point, or >50% risk of localised flooding.
High Risk - A high risk of severe convective weather exists. Rarely, if ever used on the UK. Hail >5cm, or wind gusts in excess of 80mph, or >20% risk of a tornado within 50 miles of a point, or >70% risk of localised flooding.