Archives For cold polar air

A medley of photos showing Reigate today: heavy snow in the morning melted rapidly as air and surface temperatures remained above freezing most of the day.  Colder air is on the way overnight and tomorrow.  Read on to find out why…

Here is the weather synopsis for this week: HIGH pressure to the north, LOW pressure to the south and a weak jetstream well to the south of the UK: result = POLAR NORTH EASTERLIES flood across the UK…again! Crazy low temperatures for March are forecast early/mid week with 850hPa temps at 1500m as low as -8°C over Reigate and surface temps struggling above freezing: wind chill as low as -9°C possible at night, daytime wind chill as low as -5ºC with winds up to 20mph feeling outrageously cold for this time of year, or any for that matter!

Sunday: watch out for snow streamers developing across the SE and East Anglia as the cold easterly wind crosses a comparatively warm North Sea. The 12°C difference between sea surface temps (+6°C) and air mass temps (-6°C at 1500m) could cause instability on decaying fronts lingering near the SE. This could cause the formation of perky showers in “lines” (snow streamers) which could mean some areas get prolonged snow whilst others, a few miles away, see none at all.
Monday and Tuesday: colder, drier, brighter; but snow showers always possible.

update Sunday 24: Big uncertainty about the end of the week: less uncertainty now: COLD set to continue: snow storm for Easter? 😦

Here is a summary of the causes of the March 11 2013 “Channel Blizzard” which brought extra-ordinary “Spring” weather to SE England and the Channel Islands and N France. At RGS we had record low wind chill temperatures of -10°C at 9.30am, 36mph gusts and sub-zero temperatures all day.  Follow the numbers on the map to get a quick view of why it all happened!

1. Cold source region for Polar Air: the NE winds originated from the Polar regions with temperatures below -15°C and traveled across an extremely cold continent to reach the UK.

2. On their journey, the North Easterlies warmed a little over the North Sea (by now +4-5°C) which caused showers to form in unstable air (warming causes air to rise, clouds form and it snows). These showers formed lines called “snow streamers” which fed snow to the SE for most of the day and into Tuesday morning.

3. Much warmer SW winds at +10°C met the frigid cold Polar air mass somewhere over the Bay of Biscay but they didn’t mix well and they certainly didn’t get on!  In fact, the cold, dense polar air pushed the lighter, less dense tropical air right up off the ground, to over 4000m, where all the moisture condensed, formed cloud and snowed!  The high winds experienced across SE England were “squeezed” like toothpaste between the HIGH over Iceland the LOW over France (a high “pressure gradient”: look how close together the isobars are over SE England and the Channel!).

4. Next? Things will stay cold during mid-week as the UK remains firmly in Polar air and enjoys some dry weather courtesy of a HIGH over Iceland (unusual).  Clearer skies and frosts.  However, a Polar Low forming SE of Greenland at the moment is due to break through the Icelandic HIGH later in the week and bring unsettled conditions to the end of the week / weekend: as Polar air is still involved this may bring further snow and sleet.

Greenwich Lightship is a UK Met Office weather station in the middle of the English Channel. 3 metre waves, 50mph winds, sow and 10 foot waves were recorded.  Unbelievably horrendous conditions which the Channel Islands experienced as a blizzard.

Watch the satellite animation below and spot the storm winding up in the Bay of Biscay before it hits the Channel and says “Hello” to France and the UK!