Quick update for the weekend:
Reigate and Southern UK is likely to see heavy showers and possible spells of persistent rain this weekend as a slow moving LOW out west brings mild humid southerly and south westerly winds into the south. Whilst Tmax could hit the high teens in sunny intervals the main feature of this relatively warm unstable air mass is that it will build heavy showers and create possible thundery rain at times over southern coastal regions and these will move inland. One reason for this is that the brisk surface southerly airstream is arriving on the south coast quicker than it is leaving. This situation is called convergence. Convergence means that air “piles up” as it slows down (like lorries going uphill) and so the air has nowhere to go except UP! Rising air creates showers and rain, possible heavy. Couple this with some frontal rain and the weekend has all the ingredients for a wet one: humid moist airstream, convergence and frontal uplift.
It is also worth noting that the Atlantic is currently warmer than it usually is at this time of year, so air from the Atlantic (west or southwest) is likely to be laden with moisture and energy, perhaps more than usual. More on the potential thunder risk later but some interesting weather for the weekend.