FAX - LP ca 995mb south of Iceland continues to push fronts across Britain, especially the north, but weakens by Sat 20th allowing continental heat to have more influence.
GFS Op 0z - As FAX to the weekend; on Sun 21st rise of pressure in the N Sea brings up heat from the south which stagnates over Britain under the influence of a new ridge of HP from the SW, lasting to Sun 28th. This HP loses its influence and for a couple of days from Mon 29th LP from France moves up and encourages some mixing with cooler conditions from the NE before more HP returns 1030mb Ireland Thu 2nd with more heat from the east/southeast.
ECM - as GFS to 28th. The ridge of HP is then present but lies first across England Fri 26th with cool westerlies for Scotland but then moves north delivering more heat to the south on a SE-ly Thu 2nd
Potential uncertainty - weak pressure gradients mean that either heat from France (aways likely to be dominant in S England) or cool Atlantic air (always present around Shetland) could be wafted one way or the other at a day or two's notice. AIFS and GEFS have contrasting outcomes for N & S.
AIFS - London maxima 30C or thereabouts Fri 19th, Tue 23rd and Mon 29th dropping back to 25C in between. A splash or two of rain this week, else dry. Edinburgh, maxima around 18C to Tue 23rd, cooler for a couple of days then 22c from Sat 27th. Significant rain this Friday, bits and pieces after that.
GEFS - in the S, mean 10C above norm Fri 19th after which mean continues above norm by 7C at first dropping back to 2C above by Thu 2nd - but during those two weeks there is a persistent ens range of some 20C, op and control amongst the warmest. Very little chance of rain. Less extreme further N & W, and for Scotland a somewhat different picture; peak on 19th about 5C above norm, then mean close to norm throughout. The ens spread is there, but more tightly packed than in England with only few outliers, and there are chances of rain at any time.
War is God's way of teaching Americans geography - Ambrose Bierce
Chichester 12m asl