Amazing clear blue skies this weekend in Reigate! Subtle changes at first this week, then more significant deterioration by the end… probably 😉
HIGH pressure stays in charge through the first half of this week but with more cloud building and a few scattered showers possible. We are on the cool side of the HIGH with an airflow from N/NE and occasionally brisk cool winds on the coast circulating round the HIGH.
Easterlies / NE winds are due to build on occasions this week especially on the south coast as super-geostrophic wind circulating round the HIGH draws cool air from the North East. Cool nights are likely in a generally cool airmass when skies are clear of cloud and heat escapes.
Could even be a touch of frost up north on first few nights early this week.
The thickness chart above shows how the east side of the HIGH has a less “thick” airmass which is cooler as measured between 1000-500mb height). This means that, despite the overall high pressure, surface warming during the day can increase lapse rates lifting thermals into the cool air which can spark scattered showers as land warms through. There have been big thunderstorms in Europe along the front separating this cooler airmass from the building heat of the Med.
Later in the week warmer thicker airmass is due to fold round the top of the HIGH but this might bring more cloud. Things are on the change by the end of the week as a LOW forms in Biscay and threatens to edge north / NE to bring possibly wet weather to the SE by Friday. The MetOffice fax chart shows a triple point crossing into the South by Friday and these can yield a lot of rain. Spanish Plume potential brewing … (updated Tues)
Whilst this is unlikely to be a full-on classic plume plume (update Tues… yes it could be best for some time!) it could sweep unstable air into the south and possibly cause thunderstorms. Heavy rain is possible too.
Thereafter the scene into the weekend looks more unsettled as a trough over the UK replaces the HIGH as it regresses (moves west) into the Atlantic. An Atlantic LOW from the NW looks on the cards for the weekend while pressure remains low. June has started cool (especially due to cool nights) and will continue to be overall cooler than average for the next 10 days. Note the change visible on the charts below.
There is general agreement for this deterioration amongst models. So this week is likely to see a change to less agreeable conditions: lower pressure and a bit more rain at times and staying rather cool for summer!