Archives For March

2016-04-23_10-19-23

Reigate weather summary statistics for March 2016:

  • Tmax 14.8C
  • Tmin -2.8C
  • Taverage 6.3C
  • Total rainfall 80mm (66.4 aws)
  • Max gust 51mph
  • Total sunshine 118.6 hours

March in Reigate started and finished unsettled with Storm Jake (no impact locally) on 2 March and Storm Katie (moderate impact, see previous post) on 27-28 March.  High pressure located to the north of the UK mid-month kept things more settled and mostly dry here.

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Here’s a time-lapse video from Reigate of showers and a defined cold front passing through associated with Storm Jake on 2 March.  Note the distinct drop in temperature as the cold front arrives (windows fog up) and then the change (veer) in wind direction as the front passes and skies clear.  Spot the wind shear too during the cold front passage.

March was sunnier than average for Reigate with 118.6 hours of sunshine.

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UK-wise the month was sunnier but wetter in the south, mostly due to heavy rain associated with a deep low on 9 March and Katie later in the month.

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deep LOW brought most of March rain to the South

March was also slightly below average temperature in the south.  The CET came out 0.1C above average for March at 5.8C.

Air pressure was lower across the south of Europe than the north during March, hence the drier conditions to the north.

The Atlantic cool blob sea surface temperature anomaly continued to develop during March and this may have had some influence on moderating temperatures regionally.

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Globally, March was the warmest ever recorded March by a considerable margin at over 1.29C above the long term average for the month.

 

Whilst Europe was about average temperature, there were notably extreme temperatures across the Tropics, in particular Indonesia, parts of India and Australia, as well as tropical North and South America and parts of Africa.

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This continues the trend of warming shown in the graph below. Note the correlation of anomalously warm years with El Nino events.

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The current record breaking 2015-16 El Nino is fading fast and is forecast to be replaced by cooler than average Pacific equatorial sea surface temperatures known as a La Nina by the autumn.  This might have implications for a more active Atlantic hurricane season.

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Met Office March summary

refs

http://www.metoffice.gov.uk/climate/uk/summaries/2016/march

 

2016-03-21_19-02-57

The Atlantic is showing off some classic visible cloud features of cyclone birth and decay today.  Systems labelled 1-4 on the satellite photo above show different features including stages of cyclone / mid-latitude depression formation and decaying high pressure ridge all on one satellite picture.  The chart below shows the same view with fronts.

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Starting with LOW number #2 (why not?!): the spectacular classic cloud spiral of LOW #2 indicates a mature low occluding and filling.

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This maturing occluding LOW has a couple of interesting extra vortices near the low core.

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Despite their angry look, classic cloud spirals like this on satellite photos are actually decaying and filling lows, losing their strength as pressure rises in the low core.  This particular LOW has a spectacular cold front of over 1500 miles stretching from 60N to the sub-tropics. The red colours on the RGB false colour eumetsat image below shows the cold continental polar air surging in behind the cold front.

Low #1 is a rapidly intensifying LOW off the coast of Labrador.  It looks harmless as a smudge of cloud but this shape … a so called “baroclinic leaf” indicates the birth of an angry developing storm: rapid cyclogenesis.

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This will deepen and pressure will fall rapidly in the next 24 hours as frigid continental air collides with humid maritime air under the influence of an active 200mph jetstream.

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LOW #1 is expected to form a big storm in the Labrador Sea by Wednesday. The fronts on this storm are then forecast to stretch clean across the Atlantic and bring the SE our first frontal rain for over a week by later Thursday.

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System #3  on the top satellite photo shows the HIGH pressure lingering over the South of the UK but regressing into the Atlantic.  This ridge has dominated mid to late March weather in the UK but brought a lot of anticyclonic gloom to the SE.  The deflating ridge will allow a more unsettled Atlantic westerly regime to dominate late March and early April weather.

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Low pressure #4 is an interesting developing depression in the Mediterranean, courtesy of a southward limb of the jetstream. Currently a disturbance dumping snow over the N Atlas in Morocco, this LOW is set to deepen across the Mediterranean through the week.  It will track directly ENE through the Med and bring snow to the Atlas mountains, rain to N Algeria and foul wet, windy and wintry conditions to Italy and then more snow and wintry weather to the Balkans.

Finally, for the UK our weak ridge is deflating to the SW and this will open the door to zonal westerlies and frontal systems bringing rain and wind from later Thursday and into the weekend.  Ensembles below show the dry spell ending this week and some notable rainfall spikes in the days to come, especially over the weekend.

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2016-03-20_09-26-16

High pressure has dominated the last week of our weather but it has turned out disappointing here due to cloud cover lingering under a persistent temperature inversion, not unusual for this time of year.  Lingering decaying fronts have caused drab stratocumulus cloud to spread out beneath an anomalously warm upper air mass causing anticyclonic gloom for much of the SE.

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Any convection has been limited to the lowest 1km and been unable to break the inversion, so cloud, unable to rise into cumuliform tufts associated with the stronger sunshine in April, simply spreads out into a boring grey blanket, especially when the flow arrives from the North Sea bringing additional moisture in the lower layers. An inversion is when temperatures increase with height through a part of the atmosphere, usually referring to a lower layer.

So, whilst upper air temperatures have been anomalously warm, the surface temps have been kept disappointingly low.  Somewhat “upside-down” weather.

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This is because the Spring sunshine has been unable to break through the cloud and warm the surface.  The exception has been the north and west of the country, especially the hilly parts of Wales and NW England, which have enjoyed more sunny days.

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anticyclonic gloom

Today it was the turn of the E/NE coast to get the sunshine as weakening fronts shifted south around the high.

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The coming week sees the HIGH slowly deflating, like a sad party balloon, into the sub-tropical Atlantic.  A couple of powerful late winter storms emerging out of the NE US and Newfoundland start the onslaught to break a westerly unsettled flow back across the Atlantic by Easter.

For us in the SE this change to unsettled conditions happens slowly but ensemble runs are showing around 20mm of rain is possible before the end of March. So we might expect some wet and windy days before the end of March, including a risk of a wet bank holiday period.

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A return to more mobile frontal conditions is not all bad news, especially in the SE.  A westerly flow with weakening Atlantic frontal systems will break the gloomy cloud cover and bring sunny intervals and showery episodes to clear the pollution phase we have experienced lately.  The risk for us is any fronts stalling over the SE in front of a European HIGH – this situation can dump fairly large amounts of rain. Chart below shows wind speed and an active cold front for Sunday, too far off to be reliable but worth watching.

 

The multi-model charts below show this change from HIGH to LOW during the next week.

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Note the model agreement below by Saturday for SW winds, bringing temperatures up possibly into the mid-teens in the SE.

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In short, we can expect the weather to turn the “right way up” again and we should enjoy more mobile, fresher, brighter conditions, albeit with breezy episodes of potentially heavy rain at times. The charts below show temperatures rising in the SE but rain returning by Friday.

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Further into April there are hints that pressure rises across the Pole which will bring the potential for further unsettled cooler conditions during the school holiday period. RGSweather is off to Iceland (East fjords) again so this could mean some nice cold conditions for our trip there as the AO is expected to turn negative and the flow northerly, at least for the N Atlantic.  The UK appears to get stuck in an unsettled trough for early-mid April. Worth watching as JMA and CFSv2 both agree on this blocked pattern.

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2015-04-07_11-05-58

March 2015 Reigate summary

Reigate March 2015 weather summary

  • Average Temperature 6.9C
  • Tmax 14.4C
  • Tmin -1.9C
  • total rainfall 23.8mm
  • max wind gust 46mph
  • sunshine 143.2 hours

Anticyclonic conditions controlled a good chunk of March bringing a lot of dry weather to Reigate.  Total Reigate March rainfall of 23.8mm is around half of that expected from the long term average for March recorded since 1873.  Whilst March rainfall this year was low it was not outside the “normal range” with mean monthly rainfall for March in South East England being 49.8mm and the mode (most frequently occurring) at a relatively dry 38.7mm.  March 2015 turns out to be the 36th driest year since 1873, the lowest being 1929 with a paltry 2mm of rainfall.  So March 2015 was dry but not super-dry!

With high pressure around March was sunny and not terribly windy, especially through the middle month.  Mid-Month the temperature dipped notably (see top chart) as a slack easterly set up with the high moving over Scandinavia.  It was not a beast from the east because the continent was warm and there was no really cold air available.  The slack conditions finished at the end of March, however, as a significant NW gale blew across the UK.  This broke our daily wind run record at 305.4 miles.  Wind run is the “fetch” or distance that the wind has travelled passing a point during the day.  Imagine a balloon drifting in the wind during the day… how far would it travel? This is the wind run.  The NW wind also turned lorries over on motorways further north, gusting over 70mph in places.  In Reigate the max gust was 46mph, pretty strong but with no leaves on the trees it did not cause damage.

143.2 hours of sunshine in Reigate exceeded the long term average.

March will be remembered for the “deep partial” solar eclipse that crossed much of the UK on 20 March.  Sadly for us in Reigate and much of the SE we saw nothing of it except a gathering gloom and slight dip in temperature.  More on our eclipse observations here: https://rgsweather.com/2015/03/21/reigate-some-eclipse-effects-on-weather/

2015 overall is above the long term CET average but not by much. Nevertheless, as a moderate El Nino is set to start properly this summer it is likely that 2015 will be break more temperature records globally as a hot year overall for the planet.

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All our weather data can be downloaded from the data page here.

MetOffice March summary 

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

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

A system stirred up by a low pressure tracking out of Mexico into the Gulf of Mexico this week is on track to bring unsettled conditions for part of the weekend to the UK.  It’s nothing too severe for most but is an interesting feature that will bring some wind and rain everywhere.  Below is a satpic showing the development of this system as it interacted with a lively jetstreak on Saturday 28/02/2015.

development of LOW on jetstreak

development of LOW on jetstreak

 

This LOW illustrates nicely how extra-tropical systems can rattle clean across the Atlantic in a few days if they are picked up by an active jetstream.   This one does precisely that.  Spot the system leaving Florida on the chart below for today and the sat pic.  This system started as a low pressure crossing from Mexico into the Gulf of Mexico mid-week, so for weather systems it will be an aged fellow on arrival here in the UK.  Its’ longevity is partly due to the exceptional COLD over NE US which interacts with the warm tropical air and causes further deepening.

The Gulf low pressure is tracking quickly NE skirting the US east coast before being picked up and deepened further by an active jetstream.  The jetstream itself is particularly powerful at the moment due to intense cold spilling out of an exceptionally wintry NE USA meeting warm tropical air issuing from a strong subtropical Azores HIGH pressure converging with the moist Gulf airmass.  A result of the powerful jetstream is a positive North Atlantic Oscillation: the NAO is a measure that indicates the difference in pressure between Iceland and the Azores.  In positive NAO conditions the jetstream is often active, producing a strong westerly zonal flow keeping Europe mild and unsettled especially in winter, or early spring!

Our Gulf LOW is due to pass over Reigate fairly rapidly through Saturday pm and overnight into Sunday am and bring some moderately wet and windy weather, likely to go unnoticed because of the nocturnal transit.  Winds gusting in excess of 40mph are possible for Reigate into Sunday am in exposed places.  Notably, due to the TROPICAL origins of this airmass the temperature overnight Sat-Sun could climb to double figures in Reigate.  Tropical air crossing the Atlantic also picks up a tremendous amount of moisture so attendant fronts are likely to bring a lot of rain too, possibly exceeding 10mm overnight, which is a moderately wet night.

Here are the synoptic charts showing the Gulf low progress across the Atlantic, deepening and occluding into the North Sea.  Note the secondary wave which could bring additional rain later on Sunday to the South.

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The additional rain later Sunday afternoon / evening looks potentially heavy for the South and SE.  It’s a rapidly developing wave feature that needs attention as, on the northern edge, it looks to raise the possibility of snow across the Midlands.  Heavy rain is possible for the SE and #Reigate with a period of gales on the south coast.

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The outlook for next week is for the Azores HIGH pressure to extend a ridge to the north and cause a NW then northerly airflow for the UK.  This will bring cooler temperatures to the UK.  Whilst it is likely to be mostly dry for Reigate and the SE with pressure rising, wintry showers especially on east facing coasts of the North Sea could be possible depending on how the HIGH develops.  Frost is likely with temperatures dipping below freezing at night from mid-week.

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Atlantic ridge builds to the west and brings in northerlies

How long this Atlantic block persists, and the cooler weather, is uncertain.  The coldest scenario would depend on the HIGH moving north and east and building over Scandinavia to pull in easterlies from a cold continent.  This scenario is preferred by the ECM by later next week whilst the GEFS topples the high to the SE and brings back a zonal mild westerly flow from the persistent Icelandic LOW pressure that erodes the edges of the HIGH from the NW.  The charts below show the uncertainty as a wide spread of possible pressure and temperature towards the end of the first week in March.

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Gulf low for the weekend, then pressure builds

The cool start to March is shown below.  The overall outlook is for a persistent positive NAO and Arctic Oscillation to persist and this would suggest a brief cool epsiode without the formation of a persistent Scandinavian High.  Models have flirted with possible easterly winds by the end of next week but the outlook is for the positive NAO to persist and this rather suggests a quick return to milder zonal westerlies.  As the high builds in early in the week various troughs and fronts could even push some wintry precipitation as far as the SE on Tuesday (spot the pink on the rainfall chart below for Tues)

First week of March starts cool: MetOffice synoptic chart for mid-week shows Azores high briefly ridging north to block mild zonal westerlies and usher in a cold polar airmass, albeit briefly as this ridge looks to topple SE and by next weekend we could be in a pretty mild SW flow hitting mid-teens possibly.  So a cool, mostly dry middle part of the week for Reigate and much of S England but precipitation, some even wintry, pulling in on NW / N winds is not ruled out with a North Sea low possible.  As the Atlantic is likely to push westerlies back in later in the week we can expect more purposeful frontal rain pushing east across the whole country.

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link to accuweather take on this system

http://www.accuweather.com/en/weather-news/winds-to-whip-uk-north-sea-coa/43063930

 

March 2013: “In like a lamb and out like a lion!”  

March 2013 in Reigate recorded an average temperature lower than January and a minimum temperature lower than February and the lowest dew point of -7.1°C so far this year. It was an exceptionally cold month and got colder and colder from the the one lovely day at the beginning.

The opposite of what should happen, did happen.  March started with rapidly rising temperatures reaching over 16°C in the first week but things deteriorated rapidly after that as a Polar blocking HIGH built to the North and pushed vigorous easterlies and north easterly winds towards the UK for much of the month.  A number of Atlantic LOWS tried to bust the BLOCK but were pushed to the south of the country where fronts between freezing polar air and milder air created exceptional blizzard-like conditions for some areas.  The Channel Blizzard created exceptional snowfall on 11 March for the Channel Islands but Reigate got away with 1cm of lying snow which melted in the town quite rapidly and left a day of severe wind chill down to -12ºC at 5am.  Mini snow drifts persisted on the North Downs and Reigate Hill for several days.  Arctic air arrived later on the 12 March as the LOW drifted SE and dragged northerly winds in creating brighter conditions with spectacular cumulus snow and sleet showers through to the 13 March.  Reigate had episodes of heavy sleety rain mid-March and even a clap of thunder (first recorded since Christmas Day!) on 18 March as milder air met colder air creating unstable conditions on complex fronts.  March 23 saw another snow event over the UK: record-breaking snow fall occurred to the NW over the Isle of Arran, Cumbria and Wales but Reigate again escaped the worst with a few cm falling but melting rapidly while a covering of snow lingered for a few days over the Downs.  Cold easterlies then dug-in and pushed dew points to -6°C with temperatures hovering around freezing through to the end of the month.  Dull blanket layers of stratocumulus caused by a persistent isothermal layer at around 900m in the easterly winds brought occasional flurries of sleet and snow grains and severe wind chill but little sunshine.  Temperatures fell throughout the month and Spring was delayed in the coldest UK March since 1962. 

Very low dew points (down to -7ºC) show that dry air persisted for much of March.  People with lots of hair to manage may have had a difficult time through March with curly hair going straight or fly-away due to drying out in the low humidity and dry, skin-cracking north-easterly winds.  Low dew points have a bad impact on curly hair, dragging out the moisture from the hair into the dry air.   Whilst dew points in the UK are usually high in our moist humid climate which is good for keeping curly hair curly, anyone with lots of hair to manage should check dew points on weather forecasts very carefully, especially in winter and avoid expensive hair-dos on days with low dew points… just a thought.  More seriously, farmers across the UK struggled with lost livestock in deep snow and delayed sowing of spring crops.  The weather sparked some debate over climate change and the possible causes of the cold which gripped the whole of the northern hemisphere.

January av 3.7ºC; HIGH 11.9ºC LOW -5.9ºC RAIN 58.4mm
February av 3ºC HIGH 11.6ºC LOW -2.4ºC RAIN 42.9mm
March av 3.3ºC HIGH 16.2ºC LOW -3.3ºC  RAIN 67.8mm