A jetstreak is a thread of extremely strong winds embedded into the jetstream. The jetstream is now in charge of our weather and is directing a family of LOWS across the NW of the UK this week. Tomorrow, Wednesday, a strong jetstreak is forecast to develop overhead across the south and SE of England and reach a maximum strength Wednesday afternoon through to evening and overnight to Thursday early hours. At 5500 metres and above wind speeds will exceed 120 mph and this will lead to rapidly rising air motion which, in turn, causes excessively deep cloud formation throughout a saturated atmosphere and … heavy rain. In Reigate, totals of over 10mm are forecast tomorrow, not terribly much really, but most of this will fall in a few hours in the afternoon. It will also be quite windy at ground level, possibly exceeding +35mph gusts. Temperatures will be strangely warm during all this (+19ºC) as the air is largely tropical in origin, so it could feel quite balmy and humid if you happen to rush between shelter or as you battle with your umbrella.
Needless to say, the thread of heavy rain in the south, shown left, associated with the jetstreak could move north or south and we might miss the big action altogether. Nevertheless, put summer on hold for a while and grab the wet weather gear!
Rapidly developing lows to the left exit region of this jetstreak will also cause heavy rain to the North as well.This system is associated with the decaying remnants Tropical Storm Andrea which soaked the east coast of the USA last week before crossing the Atlantic to throw some of her dying fury at the UK. She is rather weary but still capable of lashing out, let’s wait and see what she has left tomorrow!