| Analysis of the development of Storm Udo | |
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| Tweet Topic Started: May 29 2011, 03:07 PM (545 Views) | |
| Fergal (IWO) | May 29 2011, 03:07 PM Post #1 |
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http://www.irishweatheronline.com/news/analysis-of-the-development-of-storm-udo/16333.html As one of the windiest Mays for several decades comes to an end, it is interesting to look back at the evolution of the most noteworthy event, Storm Udo, which affected Ireland and Scotland on the 23rd. This was the strongest May storm since the one of May 27th, 1986, with the strongest gusts recorded at Belmullet (78 knots / 144 kph) and Malin Head (72 knots / 133 kph). A look at the synoptic situation at 00UTC on Saturday 21st May shows a strong zonal setup, with a distinct north-south divided between polar and sub-tropical airmasses. This thermal gradient led to the formation of an unseasonably strong jetstream of around 140 knots across the north Atlantic region, from New Foundland to west of Ireland. Udo can be seen as a small area of low surface pressure over New Foundland, located along the strong polar frontal zone, and in the Right Rear Quadrant (RRQ) of the jetstream, in an area of upper convergence (indicated by the + in the 300 hPa wind chart). This upper divergence removes mass from the upper troposphere, and air from below must move upwards to compensate, lowering the pressure at the surface. ![]() Animation showing three different charts for 00UTC Saturday 21st May 2011. An embryonic Udo can be seen as a small area of low pressure over New Foundland. (Images: www. wetter3.de) A look 24 hours later shows Udo now taking on a distinct baroclinic leaf shape on satellite imagery, with a strong temperature advection dipole now evident at 700 hPa. This is an illustration of what the goal of the depression is – to mix out the temperature gradient that existed between the polar and sub-tropical airmasses, by pumping warm air northwards, and cold air southwards. ![]() Situation at 00 UTC Sunday 22nd May 2011. (Base image: Satreponline.org) At this stage Udo’s core surface pressure has not fallen by much, but that changes withing the next 24 hours, plummeting to 982 hPa by 00 UTC Monday. Six hours later it has fallen further, to somewhere between 976 and 973 hPa, depending on the analysis chosen. The UK Met Office analysed it as 976 hPa, but Meteocentre was lower at 973 hPa. It shows a highly impressive structure on satellite, with its wrap-around occlusion showing 1.5 turns, and the strong downflux of dry stratospheric air, shhown by the reddish colour. ![]() Udo, 06 UTC, Monday 23rd May 2011. (Image: EUMETSAT) By 12 UTC, however, there is more agreement in a value of around 976 hPa, which is still several hPa lower than the models had been forecasting. The low is located just west of the Outer Hebrides, with a very strong pressure gradient on its southern flank bring storm force winds to the north of Ireland and western Scotland, with mean speed of up to 52 knots recorded at Malin Head. ![]() 12 UTC Monday 23rd May 2011. (Image: Satreponline.org) The largescale pattern is on the change for this week, with strong troughing in the Canadian Maritimes pumping warm air northwards towards the northeast Atlantic, extending the Azores High to our region around midweek. This promises us a pleasant Bank Holiday weekend, and of course the start of the exams would not be the same if we didn’t have good weather to go with it! Edited by Fergal (IWO), May 29 2011, 03:08 PM.
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8:18 PM Jul 11