Another breezy day across the country

Figure 1

Another breezy day across the country, bright in the south and with an unusual band of cloud in the visible satellite image, its aligned SW-NE and stretches from Cornwall, through Dorset, and into Norfolk. There are some showers associated with it across south Devon, but none elsewhere.

Figure 2

It’s not too different to a similar band that developed on Thursday and stretched from Cornwall NE with a line of heavy showers along it. There’s obviously some kind of geo-thermal hot spot over Cornwall that’s triggered the convection in both events…

Figure 3 – 1445 UTC 8 June 2017

 

Find the cold front

There’s plenty of orographic rainfall evident in the warm sector across the southwest of England and Wales in this morning’s 0815 UTC weather radar image (fig 1), but you would be hard pushed to find a cold front in the Celtic sea between here and SW Ireland on it though. This reminds me of an almost identical situation that occurred earlier this week.

Figure 1

The cold front is well-marked by the cloud in the visible satellite image (fig 2), it’s just not producing any precipitation at the moment.

Figure 2

Figure 3 – Courtesy of the Met Office

Something not quite right about this cold front

There’s a cold front – or should I say that there should be a cold front straddled across southwest England this morning. But you would be hard pressed to find it on the plotted 10 UTC chart (fig 1).

Figure 1

You might think that the cold front is associated with this batch of rain that’s now cleared through the southwest and is now moving northeast across the Midlands, but that rain can’t be the cold front because it’s just too far on (fig 2).

Figure 2

The cold front according to the T+06 forecast chart (and why do the Met Office not release their latest 6 hour analysis quicker than they do) is only across Cornwall at 12 UTC (fig 3).

Figure 3

So why is it, that if the cold front went through the Scillies at around 06 UTC (fig 4) (with moderate rain and a slight pressure kick), does the dew point there continue to climb, as if a warm front rather than a cold front has passed through?

Figure 4

Answers on a postcard please, or why don’t you just leave a comment. It would be so educational if the Met Office released the Synoptic Review (part II) that the Chief forecaster produces every six hours on the internet for all to read. I always found it fascinating reading as an outstation assistant, and am sure that a lot of people interested in the day-to-day weather across the country would find it fascinating too, I bet the answer is in there.

A little bit too optimistic

Figure 1 – Courtesy of the BBC

There was a little bit more rain than expected in Spotlight forecast at 6.55 PM yesterday (fig 1), and the front was a lot slower and more reluctant to clear Cornwall, with some kind of secondary feature following on behind the initial band of rain (fig 2).

Figure 2

Now that I’ve seen the midnight analysis (fig 3), I now realise that the secondary feature is the cold front, and that the initial rain band is the warm front.

Figure 3 – Courtesy of the Met Office

Here’s a quick look back at yesterday’s estimated rainfall totals in the southwest (fig 4), most of it falling before 15 UTC if truth be said. It finally did brighten in the late evening, as the upper cloud finally began to retreat eastward.

Figure 4 – Courtesy of the Met Office

22 May 2017 – Mesoscale trough?

Figure 1

I know I shouldn’t have tempted fate going on as I did about how warm it had been today. I wasn’t paying attention to the visible satellite image sequence this afternoon, but finally noticed the increasing cirrus and cumulus bubbling up over northwest Devon (fig 2). From the observations there’s certainly evidence of some kind of trough pushing into western areas of Wales and the southwest at 15 UTC, with a band of thick cirrus strung out along it. The increased humidity must have been enough to cause the convection, and if you look closer you’ll see a wind veer and increase in dewpoint, behind some small falls of pressure over East Wales (fig 1). It could all simply be down to a southward extension to the first of two occlusions that the Met Office are showing in their 06 UTC analysis (fig 3), but it’s certainly put paid to what had been a lovely afternoon here in south Devon till then.

Figure 2

Figure 3 – Courtesy of the Met Office

Classic dumbbell lows

Some classic dumbbelling going on between these two lows in the latest forecast frames from the GFS model as they orbit around the British Isles during the next week. I would challenge any broadcast meteorologist to find anything good to say about the weather if these charts are accurate.

Courtesy of OGIMET

If this wasn’t a polar low the next one could be…

Figure 1

The small low pressure in the Moray Firth at the moment (fig 1) doesn’t quite fit the bill as a classic polar low according to my old copy of the Meteorological Glossary. It describes a polar-air depression as:

A SECONDARY DEPRESSION of a non-frontal character which forms, more especially in winter, within an apparently homogeneous polar AIR MASS; near the British Isles the development is usually within a northerly or north-westerly airstream. The chief characteristics of this type of depression, which seldom becomes intense, are a movement in accordance with the direction of the general current in which the depression forms, and the development of a belt of precipitation near the depression centre and along a trough line which often forms on the side farther from the parent depression where also the pressure gradient (and surface winds) is increased.

Meteorological Glossary (6th edition 1991) Courtesy of the Met Office ©Crown Copyright

In this morning’s visible satellite image (fig 2) the trough, which the Met Office have as a wrap round occlusion in their midnight analysis, would usually occur on the western side of the low in this situation, or so says the glossary, but not with this feature looking at the imagery and the weather radar (fig 3).

Figure 2

Figure 3

The precipitation is of snow across the north of Scotland down to quite low levels this morning, and warnings have been issued by the Met Office (fig 3). I hadn’t notice that the Met Office had finally updated the dreadful mapping that they use in their warnings, a lot smarter, but about time.

Figure 4 – Courtesy of the Met Office

Although this low might not be classed as a classic polar low, a proper one might be developing off the coast of eastern Iceland, because the latest pressure falls at Torshavn (fig 5), indicate either a trough or maybe even a proper polar low might be squeezing itself into the tight northerly flow and head southward later today (fig 6), so you never know.

Figure 5 (the wind directions maybe spurious at times)

Figure 6 – Courtesy of OGIMET

Sign of things to come at Baltasound

The cold air has dug back in behind the cold front at Baltasound, turning the rain to snow, as the low pressure whizzes across the Northern Isles.

I wish someone would sort out that anemometer at Torshavn, I’m sure that the wind direction is the exact reciprocal of what it should be, it’s happened before, you just can’t trust those AWS.

 

The midnight analysis

Figure 1 – Courtesy of the Met Office

I suppose that the occlusion straddled across central England in the midnight analysis (fig 1) could be classified as a ‘cold’ occlusion, because it’s certainly brought lower dew point air south and west across the UK today. The cold front that preceded it actually raised dew points as it came south yesterday evening as far as I can see. I see the occlusion/trough lying from Tiree southeastward to Lincoln as the real cold front, although there is little or no weather on it (fig 3), but it does separate the 6 to 8°C dew points in the west from the +1 to -2°C dew points further east and north (fig 2).

Figure 2

Neither the IR satellite image or the weather radar provide any good evidence of any triple point system centred over North Norfolk at midnight, with the bulk of the rain having transferred into the continent during the previous evening (figs 3 & 4).

Figure 3 – Courtesy of the Met Office

Figure 4 – Courtesy of the Met Office

Looks like I’ve lost this particular argument though, because the Deutscher Wetterdienst midnight analysis confirms the Met Office analysis (fig 4), low Peter turned out to be rather an unusual synoptic feature.

Figure 5 – Courtesy of the Deutscher Wetterdienst

Extreme Easters since 1772 in Central England

Figure 1 – Data courtesy of NCEP/NOAA 20th Century Reanalysis

The Met Office beat me to a story about extreme Easters of the past, but undaunted, and without the masses of climate data they have at their disposal, I pressed on with a bit of research of my own.

Because Easter is not at a fixed time each year it’s difficult to compare one with another. Easter Sunday can fall as early as the 22nd of March or as late as the 25th of April. I’ve used the daily CET series from 1772 (now there’s a surprise), and calculated a five-day mean, from Maundy Thursday to Bank Holiday Monday to do my comparison with. Because of the time range that easter can fall, I have base it on mean temperature anomalies rather than the mean temperature. So from what I’ve found the coldest Easter period since 1772 occurred in 1892 (fig 3). The Easter Sunday that year fell on the 17th of April so it was by no means early.

Figure 2 – Data courtesy of the Met Office

The mean temperature for the five days between Maundy Thursday and the Bank Holiday Monday in 1892 was 2.1°C, which was -6.4°C below the long-term average for that period (fig 3). The weather chart for the Sunday (fig 1) shows just what a bleak and cold Easter that must have been in eastern parts.

Figure 3 – Data courtesy of the Met Office

I couldn’t resist including the Monthly Weather Report for April 1892 after using it to check out my story because I was taken with some of the phrases that were used by whoever wrote the report. I have highlighted some of them from the PDF that I accessed courtesy of the Met Office (fig 4). The remark about Vapour Tension exceeding 0.25 on the south coast of Ireland and England was a real charmer, I bet sixpence was a lot of money in 1892, and what happened to the Weekly Weather Report?

Figure 4 – Courtesy of the Met Office and ©Crown Copyright

Conversely, the warmest Easter using the same method, fell in 1926 in Central England at any rate.  Easter Sunday that year fell on April 4th, and the five-day mean was +6.5°C above today’s long-term average, and if you look at the synoptic situation (fig 5) you can understand why. I did look for any weather related news for Easter 1926, and mistakenly thought that this was the year of the Easter Rebellion in Ireland, but I was 10 years too late, that occurred in 1916.

Figure 5 – Good Friday 1926, data courtesy of NCEP/NOAA 20th Century Reanalysis