Quick update Tuesday: Friday sees upper trough sinking over Ireland with dramatic loop in jetstream rapidly developing a surface low East England tracking NW taking rain with it. Worst of rain set for NW. Looks wetter for Reigate on Friday but potentially reasonable for rest of weekend, even temps recover somewhat during day. Changeable and interesting, check back.
The late summer mini-heat wave currently building nicely mid-week with temperatures up to 28ºC possible for Reigate looks likely to end with rain on Friday and then some heavy thundery showers developing through the weekend and possibly into early next week. A cold front is moving south bringing cooler surface air on Friday and this will interact with a warm plume of upper air coming the opposite direction from Spain at the weekend.
The result could be heavy thunderstorms. Whilst convective showers are typically hit and miss, it is probably safe to assume it will be a wet weekend at times in some places in the south. Total rainfall for Friday through to Monday for Reigate could potentially exceed 20mm.
So, periods of heavy rain and possible thunderstorms are looking more likely for Reigate and parts of Southern England from Friday through the weekend (especially Sunday / Monday) as the cut-off LOW over the Bay of Biscay winds up and pushes a warm upper air flow across the south which will interact with a cold front moving across the region on Friday. Indicators like CAPE and Lifted Index which measure instability (the propensity for buoyant air to LIFT / convect upwards, condensing and forming cumulonimbus clouds) are all set for some potentially perky convective thundery activity at points anytime from Friday through to Monday. Heavy thundery showery rain is possible during this period. Nevertheless, such activity is prone to miss places entirely and drift off at the last minute so… check back for updates!