The drier air that’s outflowing from the large anticyclone that’s sat across southern Germany and Austria, is migrating its way slowly northwestward from France and across the English Channel today (fig 1). Unfortunately it looks like it will be a little too late to bring sunny skies for here in mid-Devon, but it does herald a much sunnier day across the bulk on England and Wales tomorrow. Here are the streamlines for 12 UTC across the south (fig 2).
Temperatures across large parts of England and Wales never fell much below 16°C last night (fig 1). The broad warm sector has southwesterly winds which are feeding tropical northeastward from close to where category 2 Hurricane Ophelia is located (fig 2).
Northwest severe gale force nine to storm ten along the Dutch Coast and soon across the German Bight. as storm Xavier rushes across northern Germany this morning and still deepening quite rapidly.
There’s an interesting article in this months Weather magazine (September 2017) about a severe thunderstorm that occurred over East Devon over 20 years ago. I can add little to the article except a plotted chart for 18 UTC on the 7th of August 1997 (fig 1). Unfortunately my records don’t list any observations from Exeter airport which might have been of interest. At first I thought the article was about the severe hail storm that left hail a foot deep in Ottery St Mary, but after a quick Google, I realised that this was a totally different event that had occurred on the 30th of October 2008 and not in 1997.
It’s always good to see an article about some weather event that happened in the UK, but it’s strange that it took all this time before it got a mention in the Weather Magazine. Anyway, here are the streamlines that accompany the contoured chart for what they are worth (fig 2).
Another interesting week in the Atlantic coming up. The GEFS model takes the long-lasting hurricane Jose (1) finally northward, and just skirting the east of the American eastern seaboard (fig 1). Of the two new tropical storms that have recently formed, Lee and Maria (3), it looks like Lee will perish but Maria is forecast to flourish into a category four hurricane by Wednesday. Maria looks likely to follow a similar track to that of Jose, but maybe come a little further west and cause more problems to the Lesser Antilles, before turning northward as Jose did (fig 1). Further north in the Atlantic, the warm air associated with the remnants of Jose looks like it may trigger the formation of a major extratropical cyclone in the central Atlantic by next weekend (3). This is probably science fiction, but the T+156 from the latest GFS run has an intense low of 959 hPa at 60° north and 21° west by Saturday (fig 2). This
If this does come about, the southwesterlies ahead of this intense low, could pump up some warm air across the British Isles for the first time this month.
I would say, writing as a non-expert, that the showers over West Wales and the Celtic Sea have lost their intensity from earlier this morning (fig 1), due to encroaching upper and medium cloud that’s streaming south across Southwest Wales and the extreme west of Cornwall (fig 2), from an upper warm front that was lying across Western Scotland at 06 UTC (fig 3). I reckon warmer air aloft is stabilising the atmosphere and limiting the convection. The showers certainly haven’t lost any of their potency across the south of Devon at the moment though, and I don’t think I’ve ever seen the sky so full of towering cumulus and CB, or lines of CB, as I can see looking out of the window at the moment. The showers are sharp, but have been relatively brief so far today.
I think the Met Office have come up with a new type of surface feature on the 12 UTC analysis today (fig 2), it’s marked on the chart as a trough and is aligned north-south from Anglesey in the north, extending south through West Wales and Cornwall, before ending in the SW approaches almost in Brittany. It doesn’t fit the definition of a trough as outlined in the Meteorological Glossary as far as I can see (fig 1), and runs parallel with the isobars, in fact if was a little further west, it would be indistinguishable from the 1016 hPa isobar. To be fair, a feature like this would explain the long period of heavy rain that started in West Wales at about 10 UTC this morning, but I have no idea of what it is.
The rainfall from this feature, was very heavy in places from 10 UTC to 15 UTC today, and the totals from it easily merited a yellow warning, but maybe because its Friday afternoon, or maybe it’s because they’ve already had a bit of a bad week with Aileen, the Met Office didn’t bother issuing one, hoping perhaps that people wouldn’t notice, which is probably a good idea on their part, because issuing a warning retrospectively would only draw people’s attention to the failings of their NWP mesoscale model. Here are my estimated 12 hour accumulations so far from weather radar images from 03 UTC this morning (fig 3).
It’s been a thoroughly wet day in the small town of Llandysul in Ceredigion, which I reckon has seen around 48.3 mm of rain in the last 12 hours. There are fairly large areas of 24-32 mm of rain across West Wales and East Cornwall/West Devon region, and an inner region within that of green and yellow pixels 32-50 mm, with isolated red pixels 50-75 mm across Ceredigion.
The Caribbean will shortly have the intense vortex of Hurricane Irma to contend with, but we have our own interesting mini-vortex across the southwest of England this morning. It doesn’t seem that noticeable in the plotted synoptic chart (fig 1), but you can easily identify it in visible satellite imagery (fig 2), and to some extent the decaying spiral rainbands in the weather radar (fig 3).
I tried to analyse the frontal position on the 09 UTC chart as you probably noticed (fig 1), albeit with a little help from the visible satellite image. The only trouble with that approach is that you end up with a nephanalysis and not a surface analysis, talking of which here is the 06 UTC analysis from the Met Office looked like (fig 4), even before I downloaded it I suspected that an upper cold front would be part of the answer!
After the passage of the warm front into the southwest of England today, the surface wind at Plymouth and Cardinham always seem reluctant to veer around into the southwest behind it. I’ve marked the warm front on the strength of the 16°C dew points, but couldn’t hold it back any longer over west Devon (fig 1). I’ve seen this kind of thing happen before on occasions, but I thought that this time I would make a blog of it in the hope that someone can tell me why the wind continues to back rather than veer, and despite the fact that the gradient is ~20 knots from 210° (fig 2).
Here are the weather charts for the August Bank holiday since 1971 (fig 1), that was the year that they officially moved the old Bank holiday from the first Monday in August, to the last Monday in August to spread them out a bit. The Bank holiday in 1992 stands out a bit as being exceptionally cyclonic with westerly gales across Scotland on that day (fig 2), luckily, 2017 looks very likely to be the warmest one on record, good old Gravesend Broadness, where would be without you. The thumbnails in the grid are courtesy of Wetterzentrale , and are a combination of NCEP reanalysis charts before 2014 and GFS analysis after.