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London Marathon a washout or staying dry this weekend?

A look at model uncertainty over a frontal wave threatening to bring a wash out to the London Marathon on Sunday.

London Marathon a washout or staying dry this weekend?
Blog by Nick Finnis
Issued: 30th September 2022 12:38
Updated: 30th September 2022 12:53

The models have handled, at range, today’s wet and windy weather sweeping southeast across the UK well. However, over the weekend, the models are exhibiting a great deal of uncertainty over a trailing frontal boundary lying upwind over the Atlantic. A wave is forecast to develop along the boundary which threatens to bring a spell of persistent and heavy rain eastwards towards southern UK for Sunday morning and perhaps into early afternoon, which could coincide with the London Marathon. But it’s how far north the rain gets that the models are chopping and changing over.

A turbo charged 200 mph+ jet streak racing across the Atlantic to end the week, which is helping thrust a rather active and vigorous frontal system southeast across Britain today, ahead of a rather deep depression swirling around near Iceland over the next few days.

Winds could gust to 70mph over the Western Isles and western Highlands of Scotland, with gales likely elsewhere for a time too as squally rain along a cold front moves through from the northwest. The band of heavy rain and squally winds across Scotland, N. Ireland, Wales and western areas of England this morning will reach SE England and East Anglia in the evening. Winds tending to moderate following the frontal passage. But remaining windy overnight in the northwest, closer to the deep low near Iceland, with gales continuing around coasts and over hills, but generally windy around western coasts.



Saturday will be a breezy day with sunny spells for many, but also blustery showers blowing in across western areas – heavy locally across the northwest. Some showers may also get through to eastern areas, but generally drier and sunnier here.

Then uncertainty towards the south, as we head into Saturday night. The cold front that clears the southeast later today will trail from northern France west out across the Atlantic. The jet stream will run parallel to this frontal boundary and  shortwaves or ripples in the jet stream will cause waves to develop along the frontal boundary over the Atlantic this weekend, with a wave that looks to run close to or across southern England and perhaps south Wales during Sunday morning,  threatening to bring a spell of persistent and heavy rain which could threaten a washout for the London Marathon.

However, the models diverge over how far north the wave and thus area of heavy rain will get. Of the 00z runs, GFS was furthest north, with rain threatening south of a line from north Wales coast to north Norfolk coast. ECWMF further south, with rain south of a line from Pembrokeshire to north Kent, missing central London. ICON very similar to ECMWF but a good 12 hours earlier with arrival of rain on Saturday evening. UKV had the rain grazing the south coast of England Sunday morning.

A look a the 00z GEFS ensemble postage stamps shows a range of different outcomes for placing the wave and rainfall Sunday lunchtime.

The latest 06z GFS operational run that has just come out suggests the swathe of rain further south than its previous 00z run, more in line with 00z ECWMF.

So, there’s some uncertainty for now on whether the London Marathon will be a wash out or not. Elsewhere, away from the south of England and south Wales - where it will likely be cloudy even if it doesn’t rain, there will be a few showers in the northwest, but otherwise dry and bright or sunny.

Tags: UK Weather  Sport

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