I have a theory that northerlies don’t last as long as they did in the past, the general life expectancy of one is probably no more than 48 hours tops. The cold from the current ‘Arctic blast’, has already moved south to allow warmer temperatures to come down from of all places the Arctic. It’s not evident until you run a comparison of temperatures differences that are 24 hours apart that you’re ever likely to notice it though (fig 1). I’m not saying that temperatures aren’t several degrees below average for this time of year, but it’s warmer 2 or 3°C warmer than it was at the same time yesterday over much of the north, and conversely it’s up to 7°C colder across many central and southern areas.
The earlier low that’s now scooted off down the east coast of Scotland may not have been a proper polar low, but as I suspected might happen, the one that’s just south of Sule Skerry at 1600 UTC is. Figure 1 is not from a kindergarten by the way, it’s my attempt to draw up the 1600 UTC chart using my Wacom tablet, so excuse the state of the isolines, it’s very difficult to get any kind of smoothness or get your hand inside a radius to draw a curved isobar, but it’s the best I can do under the circumstances!
The circulation around the feature is clearly seen in this 1545 UTC visible satellite image (fig 2) with curl of cloud marking the associated trough that lies to the west of the polar low and stretches north-northwest from Stornoway.
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).
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.
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.
The takeover of the BBC weather contract by MeteoGroup must be imminent if it’s to happen this spring as promised. I’ve read recently that Meteogroup are going to provide the graphics for the new service, and I wonder if they are of the same standard that they push out on their Twitter account. It seems that the Met Office are using all forms of social media including Twitter to show of their new graphics engine – Visual Cortex. If these couple of examples I have included from their respective Twitter accounts are anything to go by (figs 1 & 2), I think I much prefer the graphics and animations from the Met Office than those of MeteoGroup, which do look a little dated. Corporately, I think that the Met Office are still smarting after being dropped by the BBC, it’s quite obvious from how they’ve upped their game in the last couple of years on social media.
Of course MeteoGroup could surprise us, and have their own new bespoke graphics engine ready to go from the start, or maybe getting that in place and tweaked has delayed the takeover. It seems that all the various staffing changes concerning the presenters in London have now taken place, and all we are waiting for now is the big switchover.
For some reason this article is the most popular one that I’ve ever written. Now, five months later, I’ve written a new article with the latest news about the takeover, the graphics system and the model data that they intend to use.
At first I thought that this was low AC when I first saw it, which shows you what a poor observer of cloud I was in my day, but the LCBR at Exeter airport reckons the base is 5,000 feet, and I’m not going to argue with that. Feel free to tag on some extra supplementary varieties to the description such as undulatus, perlucidus (gaps between), or stratiformis.
The dry theme that started in late March continues into the last week of April, especially over central southern parts of England (where some stations are still in a state of partial drought), as this graph of precipitation illustrates from Benson in Oxfordshire since the start of this year (fig 1).
A big part of why it’s been so dry is the anticyclonic weather of the past month, as you can see from the Benson barograph (fig 2).
A state of type is now well under way, with cold air set to flood south across the country in a N or AN, but according to the latest NWP guidance that meridional type looks like it will be a relatively short-lived affair, before things become more mobile from Sunday, putting an end to the dry spell even across southern counties.