Hi everyone. Back to normal today with my report on the midnight outputs from GFS, UKMO, GEM, NAVGEM and ECM for today Friday December 13th 2013.
All models show a more unstable but still relatively mild SW flow now establishing over the UK with a series of troughs crossing slowly East through today and again over the weekend. A brief chillier and brighter period tomorrow will be followed by the flow strengthening and pressure steadily falling with the risk of heavier rain increasing for all with time. Winds will reach gale or severe gales at times as we move from the weekend into the new week with a brief lull likely on Tuesday as a ridge crosses East over the UK, meaning a drier and less windy day is likely when it would feel a little less mild.
GFS then ratchets up a very disturbed Atlantic with a lot of cold air coming out of the States and spinning up some powerful storm systems which lie to the North of the UK for some considerable time including the Christams period. This will allow some potentially very strong gusts of wind at times as squally bands of rain sweep West to East across the UK with showery weather following quickly behind. In the colder air there could be a surprise white Christmas for some as squally wintry showers are shown to affect the UK over the period with even the potential for some longer spells of rain, sleet and hill snow for a time in the South. Overall average temperatures look likely before it turns rather cold over the Christmas period. Little change in the unsettled and windy spell then concludes this morning's run.
UKMO this morning closes it's run next Thursday with very deep Low pressure near Iceland with a strong and increasingly chilly WNW flow over the UK. Rain will sweep East early in the day and clear East to be followed by frequent showers with hail and thunder and some sleet or snow over Northern hills as it begins to feel colder, especially in the North.
GEM today shows very unsettled weather towards the end of next week and on to the end of it's run with showers or longer spells of rain in strong to gale SW winds affecting all the UK at times. This run shows only brief colder incursions with showers before milder air sweeps back NE again.
NAVGEM also shows a colder and more showery period towards the end of next week quickly replaced by a return to milder air with gales and rain at times by the weekend.
ECM also shows a fast changing pattern later next week alternating between short showery and rather colder conditions with spells of rain on milder SW winds with only very short drier interludes in between in constantly strong to gale winds for many.
The GFS Ensembles today show a sine wave pattern between milder and colder interludes from alternating air masses between tropical and polar maritime air indicative of a fast changing and mobile Westerly airflow. The operational described above was a colder option, especially over the Christmas period with most members keeping Christmas mild and wet with some heavy rainfall for many, especially in the South as wave depressions sweep through.
The Jet Stream shows we have a powerful and changing little surge of energy crossing the Atlantic and the British Isles throughout the entire run keeping a very unsettled and potentially stormy spell of weather for many parts of the UK in the run up to Christmas and probably beyond.
In Summary today we are staring down the barrel of sustained and quite powerful at times Atlantic driven weather setup with deep depressions centred close to Northern Britain for much of the time. It will take some time for the deepest unsettled and stormy conditions to affect the South in a big way as it's not until the middle of next week that the removal and influence of High pressure embers to the SE finally leaves the South. Thereafter all areas will see spells of very windy and wet weather alternating with colder and more showery air and yes there will be some snow at times over Northern high ground and even the chance of a little on Southern hills too if the cold air digs far enough South behind the squally cold fronts. Any such wintryness will be transient though as the next system would quickly sweep milder air back NE again with gales and rain. So all in all a typical wintry and potentially stormy period of weather is to come when the day to day forecasts from the output will change markedly run to run within a pattern that is likely to change little.
Martin G
Kilmersdon Radstock Bath Somerset