May 13, 2013 — Leave a comment

The UK is trapped in a “cold washing cycle” with no end in sight this week.  The meandering north-south flow of the jetstream mentioned earlier is partly to blame for fixing LOW pressure over the UK which simply is not budging. Our LOW is sandwiched between a HIGH to the west (Atlantic) and the east (Baltic) and is going nowhere for a while. Hence the heavy showers are set to continue and there is worse to come… starting tomorrow!
A deepening wave depression is set to form on the polar front and spin out from the Atlantic across SW, Central and Southern UK during Tuesday and Wednesday. Heavy rain, gusty winds, cool temperatures and even wet snow are predicted. The worst of this will be in the south west, Wales and parts of central southern England but Reigate and the SE will get continuous rain for 24 hours peaking in intensity overnight Tuesday into Wednesday. Once the fronts move away during Wednesday morning cool unstable north westerly winds and warming surface temperatures will create unstable conditions with a risk of heavy showers and thunderstorms through Wednesday and Thursday pm.
Rain is likely to arrive Reigate Tuesday during the morning and it won’t stop until sometime Wednesday am, to be replaced by heavy showers and a risk thunderstorms. Reigate could see >30mm of rain before the end of the week.
The weekend looks utterly dreadful, especially for the SE: LOW pressure swings close to the SE from the continent and this could bring heavy thundery showers close to Reigate for the weekend.

Throughout the convective weather later this week: points to watch out for are tremendous cumulonimbus clouds and even tornadic conditions with mamatus clouds and perhaps the odd funnel cloud?
Some models show a ridge of HIGH pressure building from the west next week – this is forecast to bring a decent end to May.

Classic short wave depression: the following synoptic charts show how the wave depression forms out of the polar front jet stream.  An innocent kink in the front is the first indication of lower pressure.  Thereafter the fronts become more pronounced, central pressure falls and the whole circulation moves across the UK. Note that, throughout this episode, the “mother low” to the north of Scotland barely moves.

p.s. “cold washing cycle” is not a meteorological term!

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