91Èȱ¬

Updates:

SUN. 19:30BST: So, here we go. The rain approaches....

The broad theme remains unchanged, bar some key differences since my last update. The rainfall totals are only slightly diminished - 70mm versus 80 for certain areas - but it's still a fair number of districts seeing 30-40mm between around 10pm tonight through to 3am tomorrow.ÌýSome parts of the SW will see these sorts of totals in only 3 hours - and that's likely to be bothersome.

My major concerns for very heavy rainÌýareÌýparts of Somerset (e.g., Crewkerne, Chard, Wincanton, up towards Frome) and much of Wiltshire. Localised flooding seems possible in the 'flashy' river catchments for these areas.

Bristol, Bath, N. Somerset and S. Glos. also likely to see the heaviest (short-term) rain totals experienced so far this year.

As for the winds, the sting jet potential is now expected further east, off the coast of the Netherlands especially and with highest English winds probably further south on the Norfolk coast, rather than through the Wash as previously expected. Either way, some nasty weather approaches; the M4 corridor will NOT be a good place to drive around midnight, for sure.

SUN. 08:45BST: The Met Office has now issued anÌý, with 80+mm of rain (and widely up to 30mm) expected to fall during just 3 hours in some areas within a swathe extendingÌýfrom the SW across parts of southern-central England. The latest high-resolution (MetO-UKpp) modelling for the period between 10pm to 1am BST has a strong signal for some very heavy rain, notably through districts of Cornwall, Devon,ÌýSomerset, N. Somerset, Wiltshire, Hampshire, Berkshire and Oxfordshire. A further concern comes a little later, as the rapidly-deepening low crosses East Anglia, where theÌýforecast modelling suggests a sting-jet development could bring strong wind gusts (over 50kts)Ìýto coastal areas of Lincolnshire and N. Norfolk by around mid-morning on Monday.

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Question:

What happens when you cross an upper trough moving eastwards,Ìýwith some inherently warm, moist air easing-up from the south?

Answer:

Rain. Lots.

Later on Sunday evening, all eyes (at least from the weather-watching community) will be trained on developments from the southwest.

We'll beÌýwatching theÌývery soggy - and possibly troublesome - consequencesÌýresulting from a plume ofÌýhigh (16-18C)Ìýwet bulb potential temperature (WBPT) airmass spreading at low level out of the Bay of Biscay, while an upper trough from the west interacts with it, as an area of low pressure crosses southern England.

The likely result rather varies, depending which numerical weather prediction (NWP) model you place utmost faith in.

In an Anglo-French agreementÌýupon someÌýhighly complex mathematics, the UK Met Office's NAE - and the French equivalent model, called Arpege -Ìýconcur on a very wet solution, spinning-up a deepening area of low pressure that crosses southern districts of England overnight Sunday-Monday. It could generate 50-60mm of rain in places and winds gusting over 50 knots. The NAE offers the wettest area (50mm rain) around Bristol and adjacent South Gloucestershire.

OhÌýyes - and it's still summer. Honest.

Conversely, the Met Office's Global Model sits broadly aligned with two other 'pre-eminent' forecast models - namely ECMWF (it's my favourite)Ìýand the US-GFS - in offering a somewhat less deep or 'flatter'Ìýlow, but nonethless bringing some eye-catching rainfall totals through the same overnight period.

Either way, if you adopt a consensual approach - as the Met Office experts inÌýExeterÌýhave done - it looks like some pretty nasty weather will affect much of SW / S / S-Central England and Wales into the early hours of Monday. The GFS, for example, stillÌýdelivers some 30mm of rain in 6hrs during Monday morning... and it's a less extreme solution.

With some 30 to 40% of the individual runs (members) of ECMWF's ensemble also agreeing with the rapidly deepening modelling generated from NAE and Arpege, it's no wonder the Met Office has .

So lucky me then, as I plan a crafty, brolly-armed strategy for running to my car at around 03:25hrs on Monday morning,Ìýwearing a suit, ahead of working our 91Èȱ¬ Breakfast shift from 0400hrs.

I'll keep you advised here of the forecast developments...Ìý

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