Issued 2018-10-11 10:24:16
Valid: 11/10/2018 0600 - 12/10/2018 0600
A large-scale upper trough and surface low pressure system over the N Atlantic will increasingly influence the weather across the British Isles over the coming days. A cold front will move east ahead of a deepening low moving NE to the west of Ireland later today, bringing a band of intense convective rainfall with isolated thunder. Tonight, deep low Storm Callum moving NE to west of Ireland may interact with warm moist air wrapping into it to produce some intense convection, perhaps severe, towards western Ireland.
… ENGLAND, WALES, SCOTLAND …
A cold front will advance eastwards across the UK today ahead of deepening low to west of Ireland, warm moist airmass advecting north ahead of this front will become weakly unstable with weak CAPE in places. Some intense convective downpours are expected to develop along the front as it moves east, strong deep layer shear (40-70 knots) and strong southerly flow aloft parallel to the front will favour organised line segments capable of producing a brief spell of strong wind gusts of 40-50 mph, locally 50-60 mph in the north, as they pass through. The convective rainfall along the cold front may produce some localised flooding and accompanied by isolated lightning/thunder.
… IRELAND tonight …
A deepening depression (Storm Callum) moving NE to the west of Ireland tonight will wrap in a tongue of warm moist air from the SE which will be unstable as strong lift along with colder and drier air from aloft wraps around the low above – generates sufficient instability / CAPE for some intense squally convective rainfall and possibly thunderstorms. Convection/storms will be in an environment of very strong deep layer shear (50-70 knots) and strong low-level shear which will favour bowing line segments and mesocyclones capable of bringing damaging convective wind gusts (60-70 mph) and perhaps one or two tornadoes.
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.