UK meteorology

My dad's health continues to be a concern, and it isn't helping my anxiety either. It's therefore possible that I might not be around for a while, or my contributions might be intermittent. To complete my 'lesson' posts on areas of low pressure, U thought I'd post a diagram of a Cut-Off Low (abbreviated in the diagram to COL), which is a low which ends up to the south of the jet, usually as a result of the jet streak accelerating and, rather than curving to the south of the low centre, cutting straight across the north of it.


Here is a simplified chart for an actual cut-off low over southern California in 2005:
 
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Update from Malcolm, with the ECM showing a different orientation for the upper trough by the weekend which would draw in a colder easterly flow, while the GFS shows the trough with a less-pronounced negative tilt, therefore pulling in a warmer south-easterly:
Given that the GFS and ecm diverged quite early this morning a quick early glance at the gfs 0600 det, run and it is still at odds leading up to the weekend

The GFS surface and charts for 00 Friday and Saturday and the 500mb and 850mb anomaly





The ecm for 00 Saturday



clearly this pattern change is causing some problems
 
Tonight's anomalies:
Time to relax tomorrow as the transient ridge promises a reasonable day.


In fact Wednesday may well be not a bad day either for most to start with but heavy rain and strong southerly winds will slowly take over as the front associated with the major trough to the west struggles east.



A similar story on Thursday although the strong winds will abate apart from the north east.



Still unsettled on Friday but changes are afoot with the trough to the west becoming negatively tilted (forcing the jet south as Interitus mentioned earlier in a much more detailed and complex post
) whilst the high cell amplifies in the north east.



 
My dad's health continues to be a concern, and it isn't helping my anxiety either. It's therefore possible that I might not be around for a while, or my contributions might be intermittent. To complete my 'lesson' posts on areas of low pressure, U thought I'd post a diagram of a Cut-Off Low (abbreviated in the diagram to COL), which is a low which ends up to the south of the jet, usually as a result of the jet streak accelerating and, rather than curving to the south of the low centre, cutting straight across the north of it.


Here is a simplified chart for an actual cut-off low over southern California in 2005:
You take out as much time as is needed C. Best wishes to you Dad.
 
This morning's view from Malcolm (GFS outputs first):
Today, once the patchy rain associated with the low in the south east and the occlusion to the west has fizzled out, will be dry and fairly sunny in most areas, particularly the west with maybe just the isolated shower, as the ridge sidles in from the west.This will continue to be the state of play overnight for most areas but through the night cloud and rain will encroach from the west as a front associated with the complex area of low pressure to the west, courtesy of a deep upper trough, tracks east. It will also become increasingly windy in the west. (Do not look at the fax chart if you are of a nervous disposition)





Wednesday continues to be dry and fairly sunny for many areas to the east, albeit with a southerly wind increasing in strength but cloud and rain, sometimes heavy, will continue to encroach from the west as a low associated with the aforementioned low pressure area deepens and tracks slowly NNE to be 956mb by 1800. But at the same time a glance at the 500mb chart indicates that things are-a-changing with high pressure building to the NE and the trough adjusting alignment.



Eventually overnight and through Thursday the front struggles across the country taking patchy rain with it but the strong winds do abate apart from in the north east. But aloft the pattern is still evolving with the trough to the west increasingly becoming negatively tilted and another trough swinging south west to the east bringing much colder air.



Friday sees a SW/NE split as the upper pattern continues to adjust with showery rain pertaining in the south west but a strong south easterly wind bringing wintry conditions to the north east with snow showers on the high ground as temps start to plummet.





Saturday it becomes colder for all of the UK as the wind backs easterly and strengthens with snow showers and perhaps longer periods in eastern and central areas. This is compounded by the GFS developing an upper low in the Denmark area and tracking it west overt the UK by 00 Sunday.





There is a caveat vis the end of the week as last evening's fax charts are not as doom laden as the GFS and do not totally agree albeit the general prognosis is still rapidly downhill

 
What's the reckoning on snow for the weekend?
More likely further east, I'd have thought, Colum, as it's going to be an easterly flow, however, with the increased UV output you'd expect by mid-March, diurnal heating of the ground will tend to increase lower-level instability, so wintry showers may well set-off further inland than normal in an easterly flow. Given your altitude above sea level, if you do see shpwers, I'd expect they'd be of snow. One fortunate aspect of it is that it shouldn't last beyond Monday if my understanding is correct.
 
I just thought I'd post this complex FAX chart as it's an example of what the senior forecasters at the Met Office produce nowadays. I say that as our retired Met Office forecaster and Malcolm, the ex-Met man whose posts I quote, have moaned that several of the short sections of fronts on these charts are superficial and don't seem to follow meteorological logic, especially where there are several close together in a relatively small area. You can, however, see the front that cleared my are (east of England) earlier and the small ridge of higher pressure in the isobars that has given many areas a nice day:
 
There could be a great deal of rain for Johnny and possibly the Count as well today:
The main problems over the next 36 hours or so are going to be rain and strong winds associated with the fronts and complex low pressure system just to the best of the UK. This will mainly affect the south west, Wales and N. Ireland, where gales are possible as the rain is quite slow moving so some quite high totals are likely in places. Elsewhere sunny intervals but the wind will pick up during the day. During this evening and overnight the rain will gradually move north east clearing by morning









Through Thursday the rain will continue to affect the north east, perhaps some snow in eastern Scotland, leaving brighter conditions in it's wake but later a low associated with the aforementioned complex low pressure are will drift into the south west bringing more showery rain. Temps still a little above average but breezy.



By midday Friday the pattern change is well under way with the upper trough to our west becoming negatively tilted as high pressure surges to the north east with another trough and much colder air swinging south west around the latter. On the surface the low changes tack into Ireland and a fresh south easterly wind is introduced to the north east.and much lower temps.



The new pattern continues to become established over Saturday with strong easterly/ south easterly winds affecting all of the UK and much colder with snow showers quite likely in the east and south with a dying cold front moving slowly west.



Sunday feeling very bitter in the strong easterly wind with the possibility of snow showers in the east and central areas and perhaps some more persistent snow in the S/SE as the cold pool associated with the upper low tracks west and swings into France. Still to be decided.



 
From the ECM:
It's obviously far too early to attempt to call the possible snow event in the south on Sunday but for the record this morning the ecm has the cold pooll/upper low a little more north and west than the GFS. At 00 Sunday it is in the eastern Channel Over the next 12 hours the main snow belt remains in the Channel as it moves west but the norther edge would impact the south coast. But the main point is the temp which will not get above freezing in many places and in the strong easterly wind the wind chill be very nasty indeed.

 
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