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Weather Patterns And The Ash Cloud

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Uk airports are re-opening this evening for the first time since Iceland's Eyjafjallajokull ( prounounced ay-yah-FYAH'-plah-yer-kuh-duhl) volcano erupted last Wednesday.

Although seismic activity at the volcano has increased, the ash plume appears to have shrunk during today. Though there is still the possibility that the activity could trigger an even larger eruption at the nearby Katla volcano, which sits on the massive Myrdalsjokull icecap and has erupted every 80 years or so, the last time was in 1918.

VAG_1271785386.png


Despite the latest volcanic ash map by Met Office (above) showing parts of Britain and Ireland as a no-fly zone today and tomorrow, along with other parts of Northern Europe, planes were being allowed to fly above 20,000 feet (7,000 kilometers) over the United Kingdom today and now those restrictions have been lifted to allow aircraft to take off and land below this over the UK. The ash cloud also spread westward from Iceland, toward Greenland and Canada's eastern coastline.

The Plumes of ash did rise as far as 5.5 miles into the air in the early days of the eruption, however, the ash cloud has decreased to below 1.8 miles in height today, even though the eruption continues. This is good news for northern European flights as there less ash being dispersed into the atmosphere towards Uk and mainland Europe due to not gaining height to transport further. The decrease in ash height also means it will have less of an impact on flight paths which are well above the ash cloud. Although ash production has slowed significantly, the potential still exists for yet another large release of ash. So if an abundance of ash once again originated from the Iceland volcano this week the upper-level wind flow will bring it yet again over the UK and northern Europe. so Northern Europe is perhaps not out the woods yet! At least the next few days as winds at 500mb and 300mb (below) and winds nearer the surface still continue to blow down from the NW and the Iceland area towards the UK tomorrow, Thursday and Friday:

jet_w12.png w500_w12.png - Weds 1200hrs

jet_th18z.png w500_th12.png - Thurs 1200hrs

jet_f12.png w500_f12.png - Friday 1200hrs

... however, by Saturday, we see a ridge and Atlantic trough upstream move east towards the UK, which will tend allow winds to finally back away from there recent N or NW direction to a SW'erly direction which will tend to keep continuing ash from the volcano to keep away from the UK:
jet_sa12.png w500_sa12.png

From the weekend and into the medium range, it looks like this evening that the Atlantic trough arriving to the west will slow and amplify in length to allow ridging to build N and NE across the UK, due to warm air advection ahead of the trough, see below the 8-10 day ECM/GFS 500 HGT comparisons ... this will be further good news for keeping the Ash Cloud at bay in the coming few weeks:

ecgfs_12.gif

6-10day prognostic chart for 500mb heights also shows trough/low height anomaly (blue) to the west of UK, and ridge/positive height anomaly (red) across UK with settled weather and upper winds from S or SW:
610day_03.gif

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