Reigate should see 30ºC Tmax for the first day of August and high 20’s on Friday. The cause is a warm tropical plume of air flooding over the south of the UK from Iberia (Spain) and Africa brought in as the jetstream moves north and a LOW to our west and HIGH to the east builds a brisk Southerly airstream. Thursday will be dry and bright and the night will feel very muggy with high dew points and lows of over 20ºC at midnight: warm and damp, the air will feel close! Friday will be warm too but slightly less so for Reigate, dawning bright but with cloud spilling in associated with a weakening cold front pushing east across the country. Little frontal rain is expected but the cooler upper temps could release the huge heat energy built up in the lower atmosphere and kick off heavy / thundery showers for a while, especially Friday morning. Confidence is low currently but this might occur, the potential is there with all that heat.
Every thunderstorm indicator is giving green lights to thunderstorms in the SE sometime in the next few days BUT the airstream is capped with warm uppers: this appears to be the only factor stopping convective action. This means heat building in the lower atmosphere will stay put until forced to rise into the unstable layers above (see sounding graph above). The approaching cold front might be sufficient to produce something of convective interest on Friday, morning especially… before the warm Euro air retreats back to east. So far Reigate has seen little of the impressive thundery activity elsewhere in the UK this summer. You might be forgiven for thinking it must be our turn soon! It’s unlikely to be in the next few days as the risk is small for any major thundery outbreak.
The synoptic situation remains similar over the next few days with HIGH pressure over the continent and LOWS edging close to the NW of the UK bringing rain and wind to the NW. The SE should escape with any trailing fronts weakening and Reigate should remain largely dry but for any threat of isolated thunderstorms in building heat.