Four troughs and two convergence zones

Courtesy UKMO

Trough man, or woman, has been on duty again today down in Exeter. In his or her 12 UTC analysis, he or she has outdone themselves by identifying two convergence zones and four separate troughs across IONA. We’ll never know what happened to the remains of the two short occlusions that were in the 06 UTC analysis, or for that matter any continuity or credulity. In a slack showery situation like this one you could draw a line just about anywhere and claim that it was a trough or the result of some convergence, which I suppose is exactly what they’ve done.

2 thoughts on “Four troughs and two convergence zones”

  1. …just because the London area has quite dramatic weather right now ! 12Z analysis looks spot-on to me – they fit with the shower lines exactly. Also the s coast sea br front conv line. Too many fronts on the earlier analysis though.

    1. Yes, they kind of loosely fit the weather radar (more so the visible satellite image) but there’s no real continuity to any of it, and it’s more akin to a nephanalyis than a surface analysis. I couldn’t detect any marked wind veer or pressure rise across the Midlands behind any of today’s multiple troughs. In the 18 UTC analysis, the trough running N-S down the east coast of Scotland at 12 UTC has turned into a convergence line, and a short occlusion (marked frontolysis!) has now suddenly appeared just to the north of Shetland and ahead of the cold front.

      Here’s what the Met Office Glossary has to say about troughs:-

      A trough (of low pressure) is a pressure feature of the SYNOPTIC CHART; it is characterized by a system of isobars which are concave towards a DEPRESSION and have maximum curvature along the axis of the trough, or ‘trough line’. The trough is said to be ‘deep’, or ‘shallow’, according as the maximum curvature of the
      isobars along the trough line is great, or small, respectively; the former corresponds to the V shape referred to in the obsolete term ‘V-SHAPED DEPRESSION’. If the isobars of a depression are circular the trough line is generally taken to be the line through the centre perpendicular to the line of advance of the centre.

      A FRONT is necessarily marked by a trough but the converse is not true. Those troughs which are not frontal in character are, however, also generally marked by
      cloudy, showery weather. The term ‘trough’ is also used in meteorology to signify an elongated region of low values of any specified element, e.g. ‘thickness trough’, ‘temperature trough’.

      How many troughs have you seen that which have isobars that have not been concave towards the low in a Met Office analysis? At times drawn along the axis of a ridge of high pressure.

      There might have been some degree of convergence along the south coast today, but as far I could see the WNW’ly gradient prevented any sea breeze incursion.

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