11 December – morning satellite and radar images

Figure 1

A very dramatic visible satellite image of the British Isles this morning, with yesterday’s snow clearly evident across Wales, along with the shadow of the frontal band from Yves, Ana or whatever they ended up calling the low over northern France (fig 1). The convective streamers are already in place down the Irish Sea, running from just south of the Isle of Man aligned N’NE-S’SW to the west of Cornwall, and are now showing up in the weather radar (fig 2). Moderate rain is edging into Sussex and Kent, if temperatures had been just a degree or so colder this would have fallen as snow even to low levels and caused travel chaos.

Figure 2

Today’s precipitation totals and risk of flooding in Devon

Figure 1

Apart from the bright banding from the Dean Hill radar, the two interesting  areas of precipitation accumulations for today are one northwest of London which produced a lot of snow today at High Wycombe, and the other area across central Devon and the Blackdown hills on the Devon-Somerset border (fig 1). The estimates from the weather radar for that area are in excess of 50 mm from 06 UTC this morning. I imagine that most of this will have been rain, but it has been snowing for most of the afternoon a little further northeast at Bristol Airport, so you never know. The only thing that I can attribute the band of higher totals to is the occlusion that aligned itself across central Devon for most of today. A severe flood alerts has been issued by the Environment Agency for the rivers Clyst and the Culm in south Devon (fig 2), that’s according to the FloodAlerts.com web application.

Figure 2 – Courtesy of floodalerts.com

10 December 12 UTC

Figure 1

I finally managed to get a visible satellite image out of the Met Office today and what a good one it is too (fig 2). I reckon their whole website has been under severe strain this morning because of the snow.

Figure 2

The worst now looks like it’s out-of-the-way, so I’m now going to lie down for a bit and have a rest and leave you with the 12 UTC chart (fig 3). The Met Office did fairly well with the various warnings for snow and strong wind despite low Xanthos tracking a little further south than forecast, although I’m not sure the people of Buckinghamshire would agree with that.

Figure 3

If you notice the 12 UTC observation from the weather buoy M6 to the west of Ireland, is already showing signs of the new low that sets to deepen rapidly and sweep into France overnight. I wonder if that one will behave itself?

Radar problems

Classic radar problems across the UK and Irish weather radar network overnight undoubtedly caused by the effects of snow. The Shannon radar is showing bright banding, as was Dean Hill for much of the night, Chenies is now showing spoking (fig 1).

Figure 1

This may have screwed up the estimates of overnight precipitation from 18 UTC yesterday but here’s what it looked like anyway (fig 2).

Figure 2

The estimated totals from the weather radar seem to fit with the measured totals on the ground across the southwest (fig 3).

Figure 3

Today’s showers, the Cheshire gap, the Cat and Fiddle and the jet stream

Figure 1

Today’s gradient across Liverpool bay has been slightly more backed than it was yesterday, which as allowed a continuous stream of showers to feed through the Cheshire gap throughout today towards the White Peak (fig 1). Estimated accumulations since 06 UTC today in the wettest areas are in the range 16-24 mm. Most of the showers today have been of rain near the coast, but on higher ground inland of snow. The weather certainly looks very wintry at the Cat and Fiddle pub at dusk this afternoon (fig 2).

Figure 2 – Courtesy of the Cat & Fiddle

The ubiquitous jet stream may have something to do with this continuous feed of showers, but I am no expert. This afternoons visible satellite image has been very dramatic, with the sun casting long shadows on the frontal system that’s approaching the west coast of Ireland from the west. There was also a tongue of upper and medium cloud that stretched across Northern Ireland, across Liverpool Bay and East Anglia associated with the band of showers (fig 3).

Figure 3

Compare the 300 hPa winds as the GFS see’s it for 12 UTC today with the curve in the frontal system coming in from the west (fig 4).

Figure 4 – Courtesy of wxcharts.eu

Yesterday’s showers and the Cheshire gap

I thought that I’d just look back at yesterday’s showers across the country using estimates that I make from the 5 minute weather radar images (fig 1).

Figure 1

Most of these showers inland yesterday of course were of snow, so I imagine the Northwest Highlands and Snowdonia must have a good covering by now. I did see reports that the showers where feeding through the ‘Cheshire gap’ in the northwesterlies, but as far as I can see looking at the orography of the region, the ‘Cheshire gap’ is synonymous with the Cheshire Plain (fig 2), and a little further east of where the tongue of greatest precipitation (32-40 mm) totals were yesterday. If anything the showers were feeding through the North Channel and diagonally across the Irish Sea in the northwesterly, and getting that extra bit of impetus as they come up against the high ground of the Isle of Man and North Wales.

Figure 2 – Courtesy of ESRI

Line convection across SE

Figure 1

Impressive line convection evident in the weather radar images across the southeast of England during this lunchtime (fig 1). A three degree drop in temperature, and a gust to 32 knots on the passage of the cold front at Northolt for example (fig 2), looks fairly typical for the area.

Figure 2