Archives For run reigate

2015-09-18_19-00-43

run reigate weekend wins out for a great day

The second annual Run Reigate half marathon and 10km race on Sunday is a major event for the town.  Happily the weather looks PERFECT for both runners and spectators!

A ridge of HIGH pressure is building in as the trough which brought a few sharp showers this afternoon moves off NE. So we expect no rain at all this weekend.

A beautifully settled early autumn weekend is expected.  Cool nights at Tmin 10C with some autumnal mist early morning are likely.  Days will brighten up in sunshine to reach possibly Tmax 20C in the afternoon.

Light winds and little cloud will be appreciated by runners and spectators. The outlook is for unsettled cooler than average conditions to gradually return on Monday and into next week with rain at times as Atlantic fronts progress across the country with low pressure. Further ahead there is a chance of a warmer and drier end to September as a Scandinavian high builds to the east.

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outlook shows a fortunately settled weekend for Run Reigate

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.

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Things have changed a bit since the previous post so a quick update is needed for race day.  Expect a final update Saturday night!

The unseasonable humidity and thundery showers for the end of the week and Saturday are set to be “blown away” on Sunday and replaced by ideal weather conditions for runners.  The charts below show a big difference in Tmax temps between 26C 22C (updated) for parts of the SE on Saturday (itself depending on cloud cover and showers) and a cooler 16C on Sunday.  The reason for this marked fall in temperature is a re-building HIGH pressure to the north which is introducing cooler air from a northerly direction to replace the humid continental air flow of the previous week. This change was expected but has arrived a day earlier than modeled previously.  So Sunday is drying up and cooling down, perfect weather for the day! More details below:

Race day is likely to start with lingering cloud but it will brighten up slowly, albeit remaining cloudy through the morning.  Some models keep light rain for a while but any remaining lingering showers should move away early.  Humidity will also fall, from 90% RH at race start to around 70% RH by midday,as a drier cooler clearer northerly air mass quickly replaces the humid continental air of previous days. The fresher upper air will be wrapping around the HIGH pressure building to the north and arriving in Reigate as a Northeasterly breeze.

Early on, temperatures of 13C will make for a fresher start for runners.  Sedentary early-bird spectators might begin to feel a little cool at the start after the relative heat of the previous days, especially in places open to the light NE breeze.  An extra layer might be a good idea for spectators. The day is set to warm up steadily to a pleasant Tmax 16-17C, ideal running conditions.

Though never a real nuisance inland, a gentle breeze is set to pick up to 11-12mph from the NE by mid-morning and there might be low “gusts” reaching 15-20mph for open parts of the route away from trees and exposed to the NE.  Reigate is sheltered from northerly / NE winds by the North Downs and any drying breeze is more likely to be welcome by sweaty runners! Another benefit is the air quality will be excellent compared with previous days of high pollution before the northerly moved in.  So a healthy run too!

Overall, the day is set to be great weather conditions for runners: a cool start, cloudy but drying out and warming up pleasantly with a drying breeze.

A great way of illustrating the air mass change this weekend is to look at Theta e and CAPE graphs below.  Theta E basically measures air mass instability (the higher the temp value the more “unstable” showery the air mass can be, similar with CAPE (convective potential energy)… spot how these two dramatically change on Sunday: from relatively unstable, energetic and showery conditions, to much more stable cooler air mass in a short space of time.

2014-09-17_21-17-30