Archives For March 2015

eclipse shadow

eclipse shadow

Sadly in Reigate and across the SE of England a blanket of thick cloud persisted throughout the eclipse period and we had no direct view of the amazing spectacle. Elsewhere in the UK views were mostly better, so we had about the worst possible situation: thick stratus and stratocumulus that stubbornly didn’t move until midday.  Nevertheless, effects of the eclipse were recorded and experienced. The afternoon was cloudless blue sky, so the weather played with us.  On the bright side, our student weather club eclipse forecast turned out spot on here! NewEx RESULTS: scroll down

cloudy in the SE

cloudy in the SE

Darkening skies: eyes adjusted to the fading daylight but the timelapse below shows the light fading as the camera exposure and shutter speed were taken off auto and set to manual. Spot the lights automatically coming on.

Cooling down: as solar radiation faded, temperatures locally fell a little but only by less than 0.5C or so.  As the eclipse was relatively early in the morning it seems that the usual climb in temperature was somewhat held back by the eclipse cooling.  Dew point, rather surprisingly, also dipped somewhat showing a somewhat drier atmosphere for a short period during the eclipse.

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Pressure change? Although we cannot directly experience this, pressure fell markedly towards the end of the eclipse period.  The overall forecast for the day was for pressure to fall… but was the pressure “held up” somewhat by cooling subsiding air from aloft?  Well, we won’t know for sure but the pronounced “pressure cliff” seems to nicely coincide with the maximum of the eclipse period.  The wind moderated somewhat through the eclipse which can been seen by the slight lowering of max wind gust speeds below.  Nationally, NewEx found little evidence of the “eclipse wind” (see below).

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Overall, the eclipse in the South East and for us in Reigate was spoilt by cloud and we didn’t get to see this rare event.  Nevertheless, there is some good meteorology that will come out of this, not least to investigate the influence of solar radiation on weather models.

another eclipse shadow

another eclipse shadow

National Eclipse Weather Experiment: summary of findings quoted from University of Reading Meteorology Department “StarGazing Team”.

“After the data had been uploaded, we collected together the observations from the different sites and averaged them. From combining the measurements from all the participants, these show a clear drop in temperature across the country.

Temperature

Temperature change

A reduction in cloud in central England during the eclipse is also apparent. This is a very interesting result for further analysis, and one which would be hard to obtain other than through the efforts of a disciplined group of distributed human observers such as yourselves.

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cloud cover change

This finding is therefore almost certainly unique to NEWEx. As you may have noticed, winds were mostly light across the country during the eclipse, which meant the circumstances were not well suited for detecting changes in the wind. The so-called “eclipse wind” unfortunately remains elusive, so more work will be needed on this.”

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wind change

more here from NewEx http://www.met.reading.ac.uk/outreach/newex_2015/index.html

Low cloud on a slack N/NE flow has sat over the SE overnight left by the weak Channel low.  This low cloud will clear during the morning, the question is will it clear by the eclipse maximum at 9.30am?  Low cloud can be seen on the satellite image below but the cloud mask image shows clearance occuring in Wales, parts of N England and E England.  This is behind a weakening frontal feature (no rain) which is slowing as it moves south. Our student forecast still holds true from yesterday.. so check our original BBC school report eclipse forecast here

Sat pics this morning suggest the NetWx charts are doing well with cloud forecasts. If this turns out to continue then we can expect a relatively prompt clearance of cloud between 9 – 10am. As cloud is likely to remain in some places locally it will be down to a lot of luck but regionally some in the SE, especially further NORTH should get a view of the eclipse between 9-10am. **as we know it stayed cloudy across Reigate and SE England during the eclipse and didn’t clear until midday. London had a better view so the clearer weather was never far away but took its time to arrive: better luck next time!** UPDATE ON IMPACTS OF ECLIPSE ON WEATHER FOLLOWING SOON

Watch out for subtle weather impacts such as an eclipse wind, changes in cloud formation and a slight dip in temperature during the event.  More on this from our weather students here 

Here is a reminder of the times and % cover of the sun during the eclipse.  Remember not to look directly at the sun at all.  Use a pin hole camera.

Most models currently forecast HIGH pressure ridging in from the west by Friday.  Update Sunday 00Z run: shows more agreement.  ECM has been out-performing other models recently so this might prove to be most accurate: high edges in from west, cool N/NE flow, then pressure falls by next weekend as HIGH regresses back west allowing spell of cool northerlies.

Latest charts show clearest view over Midlands/Wales/N England… SE is hanging on to lingering cloud from a shallow LOW passing south into France from N Sea, this will enhance cloudy N/NE winds through Thursday.  Cloud should be clearing from the North quite quickly during Friday morning so hopefully it’ll hurry up and so by 9.30am!  It could turn out to break quite suddenly with little high and medium cloud above to hinder views thereafter.

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more model agreement on high by Friday

If this forecast comes out then the weather looks reasonably good    iffy! (update Mon: dirty high : lots of cloud, especially in east nr North Sea coasts) for chances of catching a view of the partial eclipse passing over the UK. Latest chart for Friday am from UKMetOffice shows a band of cloud / light rain moving S/SE during the early morning over SE England.  Further west and north and away from east / SE coast currently looks more promising for seeing the eclipse.

metoffice cloud Friday eclipse 9am

UKmet weather cloud chart

The partial eclipse peaks around 9.30am for us in Reigate and the SE.  Details of local cloud cover are not reliable at this range especially circulating round a high pressure such as this.  So, if a view is important to you, continue to check professional forecast providers carefully throughout the week.  On Thursday our student RGS weather team will be putting together a video weather forecast for the eclipse for a BBC School Report so please check back then for details!

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Reminders: never ever look at the sun, even in an eclipse (check here for methods of viewing).  Also, without taking away any of the excitement and value of viewing and understanding this awesome spectacle, let’s check the comment from our expert friends at Meteorwatch so we know what to expect… 🙂

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OK, back to the weather… the GFS chart below shows the current synoptic situation: a Scandinavian HIGH pressure is bringing cool, dry but mostly cloudy easterlies through this weekend.  A weakening front from the continent will bring cloudier wetter conditions on Sunday and cloud could linger on Monday as pressure ebbs away slightly.   A lighter southerly flow looks to warm and brighten things up by mid week and it should stay dry.

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Saturday 14 March synoptic : Scandinavian HIGH

By Friday, eclipse day, the HIGH over Scandinavia is forecast to ebb south and melt away to be replaced rather quickly by a LOW pressure over Scandinavia.  At the same time, the GFS shows the Azores HIGH building a ridge from the SW.  The GFS and GEM has this anticyclone building somewhere to the W/NW or even over the UK by Friday.  The exact position and strength of the HIGH will determine wind direction and cloud cover.

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Partial Eclipse day chart Friday 20 March

The ECM chart below puts the HIGH further west and introduces a purposeful northerly wind with a hint of a cold front moving south down the N Sea during Friday morning.  Though the ECM is on its own with this it is worth watching as this could be a spoiler for those wanting a view of the eclipse.

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cold front on ECM

The GFS Atlantic charts below show a ribbon of cloud stretching the length of the total eclipse path, roughly between Iceland and the Faroes and Svalbard.  This ribbon of cloud is associated with a humid SW air stream and frontal cloud ahead of low pressure nudging into the HIGH from Greenland.  If this HIGH pressure comes off as shown below then the UK could well be the best location to get a relatively cloud-free view of the partial eclipse.  Unfortunately the charts show that views along the path of totality through the Faroes might be less clear, but it’s early days and cloud forecast charts are notoriously flakey!

The position of the HIGH to the west / NW of the UK will bring in North or NE flow through the North Sea and into SE England.  Such a flow will be cool and places near North Sea facing coasts might risk low cloud off the sea or even fog early on.  Fog may not ruin a view of the eclipse and could add to the mystery but lifting low cloud might spoil things of course.  Eclipses can influence cloud cover and shape, so watch for any subtle changes to cloud as the eclipse occurs. Reports to NEWEx welcomed by Reading University Meteorology Department.

Temperatures you experience if out viewing the eclipse from 8-10am will vary locally depending on sunshine(!), cloud cover and fog and exposure to the N/NE breeze. Temperatures first thing are cool 2-3C but should climb to 8-9C, though a dip of 1-2C is expected during the eclipse.  Windchill is likely to be a factor near coasts and hills.

So: exact details tricky to pin down: but the outlook seems reasonable for seeing the eclipse in Reigate on Friday morning.  The risks will be if the N/NE wind picks up and drags in low cloud from the coast, which is quite possible; or if the ECM chart comes off that cold front pushing down the North Sea could be a spoiler too.  However, the overall pattern looks to be optimistic.  Updates nearer the time and please check back to view our student video forecast on Thursday!

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eclipse in the UK

Pleasant mild sunshine of late looks to give way to some cool drab easterly winds this weekend as high pressure builds over Scandinavia.

Easterlies this time of year are less cold than in winter as the continent warms under stronger Spring sunshine.  In any case, the continent has had a relatively mild winter so there is not much deep icy cold in our continental source regions so we cannot expect much real cold in this easterly episode.  Cool, drab cloudy skies are most likely … called anticyclonic gloom.  This is built when a large scale temperature inversion occurs: a cold cloudy air mass near the surface stays cold while above the air warms in sunshine and prevents convection going higher.  Low level convection, unable to rise, creates low cloud that spreads out as a thick low blanket of stratocumulus often with occasional drizzle. Most unimpressive!

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Further ahead there are hints of a possible colder mid/late March as some models suggest northern blocking: the Greenland high joining in with increasing pressure over the Pole and lower pressure blocked to the south.  This situation can allow polar air to escape into mid-latitudes given the right pressure pattern.   A forecast Arctic Oscillation (below)  diving steeply negative is also an indication that this might be on the cards.  Similarly there is a negative tilting North Atlantic Oscillation too.  Both these show indications of going negative.  The Madden-Julian Oscillation (below) is an indicator of the activity and location of  cyclical tropical convective wave systems that travel east along the Equator.  Different phases of the MJO have been connected with influencing different global weather patterns – including tenuously with European/Atlantic weather. The MJO is moving into Phase 7 and this has been correlated with northern blocking and a negative NAO, at least 50% of the time anyway!

Some of the models are hinting at the idea of some colder weather this month, but it’s a way off so not certain, worth watching though as a possibility of winters last gasp might catch people out.

 

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February 2015 Reigate weather summary

 

Weather statistics summary for Reigate during February 2015

Average temperature 3.9C (UK 3.5)

Tmax 10.8C 25/02

Tmin -3C 22/02

Total precipitation 59mm

max wind gust 32mph 06/02

February was around the long term average at 4C in Reigate.  The CET stood February at just 0.3C above the long term average.

After an intially cold start to the month the temperature rose.

Overall February came out around average temperature but note the much warmer continent.

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A notable cirrostratus halo occured around moon on 02 Feb and this accompanied by some brief excitement over a snow band moving south down the eastern side of the country.

This band delivered an insignificant snow flurry on 03 Feb, overnight, with  a cm or so of briefly lying snow that melted rapidly during the morning.

Models threatened easterly winds on occasion but this didn’t arise.  In any case Europe and the continent experienced a warmer than average month so the deep continental cold was not available.  In fact after another brief flirt with snow at the beginning of the month, the temperature climbed through the middle of the month with westerly influences with temperatures exceeding 10C overnight on occasions.

Rainfall 58mm was just a little below average and sunshine hours, at 90 hours, was about average.

 

 

 

MetOffice February summary

http://www.metoffice.gov.uk/climate/uk/summaries/2015/february

 

How high can we expect temperatures to go and how Spring-like is this weekend set to be in Reigate? Find out below!

This weekend and possibly for much of March, the weather is set to be dominated by HIGH pressure nearby to the south and low pressure to the NW which will bring in mild southerly or SW winds for Reigate.  Cooler and cloudy easterly wind directions are also possible later next week if the high pressure slips NE to Scandinavia which models are suggesting.  Whilst this weekend is expected to be pleasantly mild and spring-like and initially sunny on Saturday, temperatures are not going to break any Spring records because cloud cover is gradually going to spill from the north on a weakening cold front.

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synoptic chart Fri 6 March

The synoptic chart above shows the HIGH over the continent to the south of the UK and a deep low to the NW between Iceland and Greenland.  This is dragging in, with the help of a lively SW jetstream, a SW moist airflow over Scotland.  In fact NW Scotland has an amber warning for huge rainfall totals above 140mm over the next few days assoicated with the stalled cold front that will sit near or over Scotland for much of the time.  Warm air flow ahead of this cold front is advecting large amounts of moisture in a plume over the mountains which is causing the high totals over the NW. The charts below show the unsettled NW compared to the calm, mild and dry SE of the UK under the influence of the HIGH pressure.

The charts below show the story for this weekend.  Initially a dry airmass sits over the SE on Saturday morning but this is gradually replaced as cloudy conditions slip SE.  Temperatures through the weekend are looking mild, with Tmax 15C possible on Saturday, but anything higher is less likely on Sunday as cloud further thickens with the arrival of a weak cold front.  Saturday is probably the most pleasant day with brighter sunnier conditions especially in the morning.  The cold front in Scotland slowly migrates SE during the weekend but weakens as it does so.  By the time it reaches the SE on Sunday evening it is probably only going to bring low cloud and some drizzle.  Throughout the weekend wind in the SE is set to be light, especially on Sunday.  Misty conditions might occur overnight into Sunday and later Sunday evening in light winds.

Next week is looking generally mild and with HIGH pressure not far away to the south mostly dry.  A couple of LOW pressure systems are forecast to pass across the NW of the country and their trailing fronts will be weak in the SE but could bring cloud and some light rain.

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LOW passes to the NW on Monday

Overall the high pressure looks set to dominate Europe during next week bringing dry and warmer than normal conditions.

The GFS and ECM both suggest that the HIGH could slip over Scandinavia by the end of the week, as the chart below suggests.  This would introduce cooler easterly winds to the UK but nothing too icy at this time of year, it would also remain mostly dry. Unfortunately, easterly winds are often cloudy as they pick up moisture from the North Sea that creates days of anticyclonic gloom under an inversion.

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Scandinavian HIGH… would bring dry, cool but gloomy March weather

The charts below summarise the weather outlook: high pressure domintating bringing mostly dry and mild conditions.  Nights next week could turn colder with possible frost returning.  The longer range models suggest March could turn out to be a very dry month especially in the south.

BBC summary

http://www.bbc.co.uk/weather/feeds/31774369?ns_mchannel=social&ns_campaign=bbc_weather&ns_source=twitter&ns_linkname=news_central