Just thought I'd post a quick update regarding the output of the numerical prediction models. After mild, cloudy conditions tomorrow morning, the High pressure will shift position slightly, thereby cutting-off the maritime, north-westerly flow, and briefly reintroducing cooler, brighter continental air for Saturday night and Sunday. Much of mainland UK will see a ground frost tomorrow night, and Sunday for most will be chilly, bright with plenty of sunshine, and a light south-easterly flow. Sadly, from Monday onwards, more cloud will be caught-up in the circulation, and, as the blocking High 'sinks' south-east into the continent, a mild, cloudy and generally dull tropical maritime flow will establish, with temperatures rising (initially in south-west England), such that, by next Thursday, daytime maxima in the south will be in the 13-15 degree Celcius range; between 8 and 12C further north.
By the end of next week, the models are suggesting that the unsettled weather which will have already developed in the north-west of the UK will be spreading south. This is due to indications that the high will merge with the Azores anticyclone, thereby drifting west and switching our airmass from a returning tropical maritime one to returning polar maritime. Winds by this stage will be westerly, with average temperatures (8-12C generally by day) and periods of rain and showers, possibly with blustery winds, interspersed with drier and brighter periods between frontal systems. Rain amounts are expected to be greatest in the north-west, though there are few indications at this stage of amounts which would cause widespread flooding.
Towards the end of the model run, there are hints that the jet may move to our south, placing us on the colder side of the jet. If this verifies (and it is a BIG "if"), low pressure systems would be likely to pass to our south, possibly pulling colder polar maritime and arctic maritime masses into their circulation. This would probably cause precipitation in the north and on high ground further south to become wintry, though low levels south of the Humber would probably see rain.