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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

Polar Continental (Pc) air is most common in winter as HIGH pressure forms over cold northern continental interiors and pushes out freezing air to mid-latitudes.  In summer, when it does occur, Pc brings dry stable and warm conditions to the UK as the continents warm up.  Pc has been an unusually frequent visitor this March and effectively reversed our usual south westerly prevailing wind. As Spring sunshine warms the surface and Atlantic LOW pressure systems edge closer to the UK next week dragged by a more northerly migrating jetstream, we can be assured that moist maritime air will be making a return and any remaining incursions of polar continental air will increasingly lose their frequency and ferocity, Russia has to warm up sometime!
air masses UKMOBefore we bid “farewell” to the freezing Polar Continental air until next winter it is worth remembering the good times.  Pc has occasionally brought crystal clear skies with excellent visibility and dramatic views of the sky both day and night (as anyone staying up to see the ISS will testify). The long picture series shows Cumulus Congestus building over Stratford on Avon last week and an unusual Pileus Altocumulus Lenticularis veil forming over the dramatic rising thermals. Pileus is a fleeting, ephemeral cloud type and forms as convective up-draughts in the cumulus force upper winds over the rising congestus, just like air being forced to rise over a mountain range.  Moisture in the air condenses, or sublimes into ice, and forms a beautiful veil called Pileus.  The photos were taken over just two minutes and then the Pileus melted away.  Pileus is a beautiful cloud but has a darker side because it sometimes forms above rising nuclear mushroom clouds and volcanic eruptions.

Cloud streets, lines of Stratocumulus, were also a feature of the easterly winds: where an isothermal “cap” (temperatures staying the same with increasing height) kept a lid on rising thermals and clouds remained flat and formed lines in the airstream.  Cloud streets seem to urge us to follow them, pointing the way to something important over the horizon.  Finally, the “sundog” (mock sun) was another fleeting feature of polar continental air, though not exclusive to it: apparently only 5/100 people have ever seen a sundog, so here is a picture of one in case you haven’t caught one yet.  They occur as low-angled sunlight refracts through hexagonal ice crystals.

Pc air wasn’t all as beautiful as this of course: freezing grey blankets of dull stratocumulus dominated the weather for days in the south east and deposited icy snow grains right through to Friday.  Nevertheless, I do hope you had the time to look up and admire the best of the Polar air show this March.  So, Polar Continental may crack our cheeks and rage and blow but we’ll kind-of miss it… won’t we?  “Adieu, adieu, adieu… remember me.” Exit Ghost of Pc! (The photos above were all taken along the Stratford canal last week, the statue is William Shakespeare in Bancroft Basin).

n.b. March summary for Reigate coming soon!