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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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#1
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Was expecting today to be quite a good day in the south (south
Hampshire specifically), particularly given the cold front was weak down here and it was fine late yesterday. Was hoping to get out today given the prospects of "Bill" tomorrow but seems to be turning into a disturbed day with heavy showers about, possibly the most disturbed day in the south since the 6th. Temperatures really struggling as well, e.g. 17C at Heathrow or 16C at Cardiff at 1100BST which seems a couple of degrees below the norm for that time of day. Looking at the Met Office suggestion of "Bill" not doing much in the southeast maybe today will be the worst day of the week round here! Nick |
#2
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"Nick" wrote ...
Was expecting today to be quite a good day in the south (south Hampshire specifically), particularly given the cold front was weak down here and it was fine late yesterday. Was hoping to get out today given the prospects of "Bill" tomorrow but seems to be turning into a disturbed day with heavy showers about, possibly the most disturbed day in the south since the 6th. Temperatures really struggling as well, e.g. 17C at Heathrow or 16C at Cardiff at 1100BST which seems a couple of degrees below the norm for that time of day. .... one of those situations when the surface charts doesn't really do justice to the situation; there is a marked upper trough (colder air throughout troposphere in this case, relative to either side) swinging from west to east, being hustled along by events further west and relaxing (i.e. lessening the dynamic / vorticity forcing), but still enough of a force hereabouts to give short-lived moderate, locally heavy showers - they're not lasting long (15 mins at most). http://www.wzkarten.de/pics/Rtavn001.png should improve as the trough moves on and we get descent to its rear. On the GFS timing, the axis of the trough should be passing overhead here ~midday GMT. Martin. -- Martin Rowley West Moors, East Dorset (UK): 17m (56ft) amsl Lat: 50.82N Long: 01.88W NGR: SU 082 023 |
#3
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"Martin Rowley" wrote in message ...
... one of those situations when the surface charts doesn't really do justice to the situation; there is a marked upper trough (colder air throughout troposphere in this case, relative to either side) swinging from west to east, being hustled along by events further west and relaxing (i.e. lessening the dynamic / vorticity forcing), but still enough of a force hereabouts to give short-lived moderate, locally heavy showers - they're not lasting long (15 mins at most). http://www.wzkarten.de/pics/Rtavn001.png should improve as the trough moves on and we get descent to its rear. On the GFS timing, the axis of the trough should be passing overhead here ~midday GMT. .... and just about on time, we duly had a complete change in 'skyscape' with Cu now much shallower - not capped as the air is still unstable, but I suspect that the mid-level moisture has changed and won't sustain the taller convective towers, at least hereabouts - obviously still perky over the spine of Devon & Cornwall & over Wales. Also, scrappy elements of layer Ac which indicates some medium-level descent/stabilisation going on. However, the trough can't be as straightforward as that image posted (ex GFS) as looking carefully at the cloud elements I can see that the cloud winds aren't following the simple shape indicated. Going back to the 00Z plots of actual upper winds at 700 and 500hPa, it's clear that the trough was being distorted by the developments further out in the Atlantic (ex-Bill), and Valentia winds in particular didn't verify too well against background: a common problem with such developments. Even the model 700hPa trough isn't anything like as symmetrical as the 500 hPa for example. .... in major forecasting centres (such as Exeter), they will overlay water vapour imagery in particular against other imagery and model fields - modern NWP suites can produce 'pseudo WV' fields - and such errors are quickly picked out and can be allowed for. However we seem to be poorly off for real-time WV imagery - I can't find a loop of such - does anyone know of a source? Martin. -- Martin Rowley West Moors, East Dorset (UK): 17m (56ft) amsl Lat: 50.82N Long: 01.88W NGR: SU 082 023 |
#4
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"Martin Rowley" wrote in message
... ... in major forecasting centres (such as Exeter), they will overlay water vapour imagery in particular against other imagery and model fields - modern NWP suites can produce 'pseudo WV' fields - and such errors are quickly picked out and can be allowed for. However we seem to be poorly off for real-time WV imagery - I can't find a loop of such - does anyone know of a source? Martin. http://oiswww.eumetsat.org/IPPS/html...2/BW/index.htm click on the region of interest to access the loop I'll endeavour to provide a pseudo water vapour example that Martin mentions. Jon. |
#5
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On Aug 25, 1:41*pm, "Jon O'Rourke" wrote:
"Martin Rowley" wrote in message ... ... in major forecasting centres (such as Exeter), they will overlay water vapour imagery in particular against other imagery and model fields - modern NWP suites can produce 'pseudo WV' fields - and such errors are quickly picked out and can be allowed for. However we seem to be poorly off for real-time WV imagery - I can't find a loop of such - does anyone know of a source? Martin. http://oiswww.eumetsat.org/IPPS/html...2/BW/index.htm click on the region of interest to access the loop I'll endeavour to provide a pseudo water vapour example that Martin mentions. Jon. Thanks for that link Jon. That is excellent. One question that puzzles me, and concerns the contrast on the IR frames. North Africa looks very dark (due to the high temperatures there), but the cloud contrast does not seem to show the thick cloud associated with ex-Bill as particularly white. Could this be my laptop, or are the cloud tops relatively warm? Or is it just that the really bright white shade is reserved for the added coastlines? Stuart |
#6
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"Jon O'Rourke" wrote in message
... http://oiswww.eumetsat.org/IPPS/html...2/BW/index.htm click on the region of interest to access the loop I'll endeavour to provide a pseudo water vapour example that Martin mentions. .... thanks for that Jon: a 'red face' moment coming up, as I had found that site (one of the first I looked at), but couldn't get it to do anything: now I've just realised - you have to click on the *name* of the area to get it to respond! Martin. -- Martin Rowley West Moors, East Dorset (UK): 17m (56ft) amsl Lat: 50.82N Long: 01.88W NGR: SU 082 023 |
#7
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On 25 Aug, 13:26, "Martin Rowley"
wrote: "Martin Rowley" *wrote in message ... ... one of those situations when the surface charts doesn't really do justice to the situation; there is a marked upper trough (colder air throughout troposphere in this case, relative to either side) swinging from west to east, being hustled along by events further west and relaxing (i.e. lessening the dynamic / vorticity forcing), but still enough of a force hereabouts to give short-lived moderate, locally heavy showers - they're not lasting long (15 mins at most). http://www.wzkarten.de/pics/Rtavn001.png should improve as the trough moves on and we get descent to its rear. On the GFS timing, the axis of the trough should be passing overhead here ~midday GMT. ... and just about on time, we duly had a complete change in 'skyscape' with Cu now much shallower - not capped as the air is still unstable, but I suspect that the mid-level moisture has changed and won't sustain the taller convective towers, at least hereabouts - obviously still perky over the spine of Devon & Cornwall & over Wales. Also, scrappy elements of layer Ac which indicates some medium-level descent/stabilisation going on. However, the trough can't be as straightforward as that image posted (ex GFS) as looking carefully at the cloud elements I can see that the cloud winds aren't following the simple shape indicated. Going back to the 00Z plots of actual upper winds at 700 and 500hPa, it's clear that the trough was being distorted by the developments further out in the Atlantic (ex-Bill), and Valentia winds in particular didn't verify too well against background: a common problem with such developments. Even the model 700hPa trough isn't anything like as symmetrical as the 500 hPa for example. ... in major forecasting centres (such as Exeter), they will overlay water vapour imagery in particular against other imagery and model fields - modern NWP suites can produce 'pseudo WV' fields - and such errors are quickly picked out and can be allowed for. However we seem to be poorly off for real-time WV imagery - I can't find a loop of such - does anyone know of a source? Martin. -- Martin Rowley West Moors, East Dorset (UK): 17m (56ft) amsl Lat: 50.82N * Long: 01.88W NGR: SU 082 023 Down here the trough seemed to clear eastwards around 08:00, but then another line of stratocumulus/embedded cumulus around 10:30, with a few spots of rain. Since then good sunny periods, with the cumulus mainly in it's normal 'spinal' location After the coolest night since 9th (Min 11.5C) the temperature was initially very slow to rise, but has risen steadily since 11:00 to reach 19.7C currently, making it the warmest day here since 20th (yesterday 19.1 max). Noticeably cooler inland under the cloudy strip. 19C and still fine out on Scilly. www.scillyman.co.uk/Web_Cam.html / www.scillyman.co.uk/Web_Cam.html In fact it sill looks pretty calm out there. On a slightly different topic, maximum temperatures on Scilly & coastal west Cornwall, seem to have been relatively high this year compared with inland parts of Devon/Cornwall. I can't see that this is due to the SST anomalies, so I can only put it down to the differential between the sunshine on the coast, and that inland, being greater than normal this summer. (It may be I'm being influenced by the cold conditions in the far SW last year, when average maximum temperatures in August were easily the lowest I've recorded - since 1991). If anyone has access to maximum temperature data for St Mary's (I've got Penzance!) and for a scattering of other locations in Cornwall/ Devon, for July/Aug for say the last 3 or 4 years, it would allow me to compare the differentials. I hope to get data for St Martins. Well, as there's still no sign of the cloud steaming ahead of 'Bill', and the breeze is only of Force 3 or so, I'm off to Lamorna to do a bit of snorkelling before it all gets stirred up. Graham Penzance www.turnstone-cottage.co.uk/recent.html |
#8
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"sutartsorric" wrote in message
... One question that puzzles me, and concerns the contrast on the IR frames. North Africa looks very dark (due to the high temperatures there), but the cloud contrast does not seem to show the thick cloud associated with ex-Bill as particularly white. Could this be my laptop, or are the cloud tops relatively warm? Or is it just that the really bright white shade is reserved for the added coastlines? I would hazard a guess it's largely down to the way the image is being processed. Other sources, e.g. http://wind.met.fu-berlin.de/cgi-bin...laymode=Endlos perhaps offer better contrast and show some fairly vigorous ascent on the forward side of the system. VT 18Z WAFC data puts the tops at 26000FT http://www.lfv.se/Tor/wc18/swc_18.asp about 10000FT less than the CB over the continent in terms of a comparison. Jon. |
#9
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On Aug 25, 2:43*pm, "Jon O'Rourke" wrote:
"sutartsorric" wrote in message ... One question that puzzles me, and concerns the contrast on the IR frames. North Africa looks very dark (due to the high temperatures there), but the cloud contrast does not seem to show the thick cloud associated with ex-Bill as particularly white. Could this be my laptop, or are the cloud tops relatively warm? Or is it just that the really bright white shade is reserved for the added coastlines? I would hazard a guess it's largely down to the way the image is being processed. Other sources, e.g.http://wind.met.fu-berlin.de/cgi-bin...=12&count=16&i... perhaps offer better contrast and show some fairly vigorous ascent on the forward side of the system. VT 18Z WAFC data puts the tops at 26000FThttp://www.lfv.se/Tor/wc18/swc_18.asp about 10000FT less than the CB over the continent in terms of a comparison. |
#10
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in 57197 20090825 115604 Nick wrote:
Was expecting today to be quite a good day in the south (south Hampshire specifically), particularly given the cold front was weak down here and it was fine late yesterday. Was hoping to get out today given the prospects of "Bill" tomorrow but seems to be turning into a disturbed day with heavy showers about, possibly the most disturbed day in the south since the 6th. Temperatures really struggling as well, e.g. 17C at Heathrow or 16C at Cardiff at 1100BST which seems a couple of degrees below the norm for that time of day. Looking at the Met Office suggestion of "Bill" not doing much in the southeast maybe today will be the worst day of the week round here! Nick It was fine all day, though very windy, at Hayling Island after an early heavy shower. |
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