Bone dry (mostly!) for Reigate and SE for next week…

October 4, 2013 — Leave a comment

Update: BIG cool off likely from mid-week as high slips west and draws down COOL Northerlies / NE polar winds for E UK: Tmax drop from 19c to 10c by mid week! Matches Northern blocking suggested by NAO (see text below) Likely to bring first snow cover for continental Europe. ( check @RGSweather)

cool off mid week

The movement of this high has changed in latest models – update coming later:

Rainfall, or lack of it, is the theme for next week in / update: cool off is the theme now for Eastern UK, SE and in Reigate. Warm upper air flowing from the South and SW is building a blocking HIGH pressure which will sit to the South of the UK and then migrate WEST keeping rainfall and LOW pressure way out west in the Atlantic for much of the coming week. Tmax temps during the day could top 20c and night time temps could even stay in double figures.  Given these high nighttime figures and low dew points it is unlikely that fog will be much of problem with low humidity in the SE, unless the cloud clears at night and ground temps fall away. Is this an Indian Summer? Read here. http://www.bbc.co.uk/news/magazine-15127159

The NAO (north atlantic oscillation) is a measure of pressure difference between the Azores and Iceland.  If the pressure difference is high then it yields a positive NAO and this usually accelerates westerly winds and the jetstream and brings fast moving wet and warm (winter) Atlantic weather to the UK.  Negative NAO usually indicates a weak pressure difference, weak westerly winds and a blocking pattern with higher pressure than usual and slow blocked weather which sticks around for ages.  The weaker westerlies in mid-winter can allow cold polar air to flow out of the Arctic depending on the location of the HIGH. Slow moving conditions can mean extreme weather if a HIGH causes dry weather for weeks (drought) or a static slow moving LOW accumulates a lot of rainfall.  So negative NAO is not necessarily “good” weather.  For us, at present, we have a very negative NAO, one of the most negative NAO’s of this year but the ridge is bringing in a warm flow from the continent.

The longer range CFS chart shows a major gear change down to cooler conditions later in October. To be expected of course, but it looks rather a harsh step function in the weather.  It’s long range so things can change.
Enjoy the warm dry weather and Autumn sunshine but think of the USA today where Winter storm Atlas is bringing blizzards to S Dakota and Wyoming, Tropical Storm Karen is making landfall this weekend over Louisiana and Mississippi and, in between, there are tornado warnings in Iowa, Kansas and Nebraska. Update: severe tornadoes breaking out near Sioux City, NE Nebraska. Thoughts to people there. Stay safe.

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