As promised, here is a final weather update for Run Reigate Sunday 21 Sept.
Reigate avoided any heavy showers or thunderstorms today. These got stuck over N London, Essex and Suffolk where it really has been chucking it down for the past 24 hours.
The weather is turning out ideal for runners tomorrow as the weather has done a timely U-turn: a northerly breeze is replacing the unseasonably humid and (potentially) showery southerly /SE airflow of recent days. A weak cold front moving south through the UK will complete this transition overnight and into early tomorrow morning. As it passes over Reigate through the small hours it will possibly yield some light rain. So expect first thing to still be cloudy and a little damp and misty as the last of this cold front moves south across the Channel and into Europe. Temperatures for early arrivals could be around 13C in Priory Park which will obviously feel cooler than the humid temperatures and nights of late, especially in a gentle 11-15mph northerly breeze (hardly notable really but certainly cooler for thinly clad runners).
From the outset the day will improve steadily… low clouds should gradually break up from the north through the morning and, as there will be no mid or high level clouds, sunny spells should break through nicely and lift temperatures to 17C by midday. Humidity will fall from an early 90% RH to 55% later and, with a gentle drying NE breeze, this should be perfect for runners. How about the rest of the week?
The outlook for #Reigate this week (shown in charts above) is for dry weather dominating, pressure remaining mostly high in the south and temperatures being maintained above the 30 year average. The jet stream is kept well to the north and, as we continue to sit well to the south of the jet, we will continue to enjoy un-Autumn like conditions. The north of the UK will be swept by storms as Icelandic lows move NE and fronts brush across the North. Any fronts reaching the south will be weak and not amount to much on current models. The amount of rain expected in Reigate is minimal this week, a mere 1 or 2mm. So watering the garden will probably need to continue for gardeners. As nights are cooling off misty mornings are likely. The potential for any autumn storms reaching Reigate has been pushed way further back in these latest model runs and it seems Autumn is continually being held at bay by HIGH pressure dominating the south. Dry, pleasant conditions prevail. Enjoy!
As a final thought, IF Bardarbunga caldera in Iceland erupts explosively then the winds this week are mostly favourable for keeping ash away from European airspace. With LOW pressure over Iceland and HIGH over the south of the UK it is likely that upper atmospheric winds will be kept blowing strongly to the North / NW over Iceland for much of the week (i.e. S/SW winds prevailing). There are hints of occasional westerlies or SW and these might send any ash to Scandinavia. In any case, it is purely speculative and the caldera seems happy to continue its collapse right now without any imminent sign of explosive subglacial eruption. Worth watching though.