Archives For February 2013


Anti-cyclonic stratocumulus cloud continues to blanket Reigate and the SE of England in a cold, gloomy weather underworld.  A temperature inversion (where temperatures rise with height, instead of fall) at 1000 metres is trapping any rising air which inhibits convection spreading out the cloud mass to cover the entire sky: good to reduce rainfall, bad for any views of the sun!  Regrettably no light at the end of the tunnel yet: the north-easterlies circulating round the HIGH pressure to the North are likely to continue for much of the week and bring in blankets of stratocumulus cloud from the North Sea. This spectacular view from the EU Meteosat satellite today at midday clearly shows the cloud blanket voering SE England from 22,300 miles away.
Temperatures will struggle to exceed 5C in the days to come; this time last year temperatures were well above 12C and even hit 17C on a few days.

 

The very cold upper atmospheric pool of air which put Reigate in the freezer this half term (-11ºC at 1500m, -35ºC at 5000m!) is moving off South… to be replaced by warmer air aloft moving in from the North (-1°C at 1500, -25ºC at 5000m).  Watch the video below to see the warm air moving in from the north and pushing the cold air south.  This is rather upside-down to what we would normally expect and is being caused by warm air being squeezed through by an active jetstream in the Atlantic: this is feeding warmer air into the HIGH pressure sitting atop the UK currently.  Reigate weather will be dominated by the HIGH pressure during this week making things mostly dry but, as we are located on the edge of the high pressure weak fronts will be able to influence our weather as they nudge across the Channel early in the week and bring light snow turning to drizzle through Monday and maybe more light rain on Tuesday. Temperatures remain uninspiring at 5°C.

Here is a table showing the effects of wind chill, familiar to mountaineers.  The blue zones are what Reigate and the SE has experienced in recent days with gusts of 15mph in freezing air taking “feels like” temperatures down to -13ºC.  Note that this is the zone of “maximum” danger for hypothermia because people tend to underestimate the effects of any breeze in temperatures hovering around freezing and under-dress.  Note that a slight breeze is enough to cause the greatest chilling effect.  These cool and breezy conditions are also more common in mid-latitude populated areas like the SE of England where winter temperatures frequently hover around 0ºC.  Dry air feels colder than humid / moist air: there’s more evaporative cooling into dry air and dry air also conducts heat away from your warm body more readily than does moist air.

Met Office article on wind chill

The cool pattern of winter weather we have experienced in Reigate during February has not been reflected everywhere across the Northern Hemisphere.  Greenland, in particular, has been warmer than usual. Whilst Reigate has experienced Polar air incursions pushing temperatures 2ºC colder than average, Greenland has experienced more frequent warm southerly air masses than usual and it’s HIGH pressure has not developed so strongly this month to keep out the warm air, until recently. The Greenland ice sheet doesn’t usually start melting until April or May (average 1980-2010). In 2013 surface melting has started already in SE Greenland. So, the 2013 Northern Hemisphere winter climate appears to be acting strangely with extreme storms in the USA (Sandy and Nemo), heavy snow in Russia, severe storms in the Atlantic and now the early onset of melting on the Greenland ice sheet being startling reminders that weather patterns have been far from “average”.  Reigate is fortunate to have  escaped any severe weather on this scale!


Wrap up!  Spring is cancelled for at least another week!  Mainly dry but some light snow showers and a really cold wind will be around through the weekend for Reigate, albeit mostly very light snow flurries and with little or no accumulation. Air temperatures will climb slowly above freezing to 3ºC during the day but a stronger breeze of 15mph, gusting 20mph, will make it feel even colder, especially Sunday with wind chill as low as -6ºC during the day. Night air temps will fall to -3ºC.  A tad warmer and damper by mid-week with daytime temps rising to +5C; the HIGH shifts directly over the north of the UK so winds, still easterly or northerly, will be lighter and track more across the North Sea rather than central Europe: this will feel balmy in comparison! 


The cold easterlies predicted have created interesting and unusual cloud patterns across the country. The satellite photo from today shows ripples in the breaking cloud to the west of the hills in Wales and the SW.  The easterlies driving the cloud are part of the cold sinking dry air created by the anticyclone to the north east of the UK.  The easterlies are  forced to rise over the hills and then sink the other side (the “lee-side”), creating this wavy cloud pattern.
Another feature of this cold snap is illustrated in the video below which shows how temperatures have changed over the last few days.  Notice how inland temperatures drop significantly lower than anywhere near the sea. The sea stays warmer for longer during winter as it takes 5x longer to cool down (and warm up) than land surfaces.  The video shows temperatures rapidly falling to low temperatures inland but coastal areas are moderated by the warmer seas surrounding the British Isles.

The cold easterly winds and some light snow flurries will continue over the weekend as a weak short-wave trough (a “blip” in the isobars surrounding the HIGH) passes to the north of our region.  The very cold pool of upper air is drifting away to the south, so temperatures will recover very slowly through to Monday.  However, spring is certainly on-hold at the moment and, despite being a mostly dry week,  temperatures will remain lower than average in the continuing easterly air flow.  Watch next weekend as a low passes to the north of the UK which could bring a “last hurrah” for real winter conditions as a cold northerly is possibly on the cards.  Longer range forecasts give little cheer for us in Reigate and the South East as HIGH pressure seems to stick around to the North and bring in Channel lows to the south of the country bringing wet and cool weather.

Not about the weather but arguably still just about in the atmosphere … the small dot here is the International Space Station taken from Reigate last night on my Lumix GX1 with 45-200 zoom; f8 1/1000, ISO1600. ISS ~300 miles away: population 6; Moon ~240,000 miles away: population 0; … amazing! p.s. light snow possible for Reigate at weekend with a trough circling round the HIGH pressure bringing cold easterlies. High pressure looks like continuing but shifts in wind direction will vary the temperature … signs of warmer conditions next week.: scrap that!!… latest charts show cold Arctic plunge on 5 March – keep watching!


Cloud is spreading from the East tonight associated with the cold easterly winds approaching tomorrow but the sky will hopefully remain clear over Reigate for a siting of the International Space Station this evening. The ISS will make a visible pass over Reigate at 18:57hrs this evening moving from west to east across the sky in just over 2 minutes. Where do we look? Start by looking due west and then nudge a few degrees to the north. The ISS will make an appearance some 40′ above the horizon near Andromeda at 18:57:04 hours. It will ascend to a position almost vertically above our head when it will be only 260 miles away. It is brightly illuminated by the sun and will disappear into the shadow of the Earth as it moves down across the eastern horizon. The ISS is orbitting at over 17,000 mph and takes about 1hr30mins to orbit the Earth.

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This week for Reigate: dry and increasingly cold!  Watch the video which shows cold air (at 1500 metres) flooding in from the east.

Wind direction is so important in controlling our winter and early spring weather: many of the “source regions” (where our winds originate from) are at their most extreme at this time of year: the continental interiors, for example, are at their coldest and driest in late winter, so any air mass coming from the continent will be very cold indeed, despite Spring being just round the corner.  These cold and dry easterly winds contrast with our usual warm and wet SW Tropical winds that arrive from the Atlantic.  This week it is the turn of Easterly winds and HIGH pressure to dominate our weather: this means cold and dry.
UK unusual dry patchThe HIGH to the north east and the LOW to the south is a perfect set-up for dry and icy Easterly winds to flood across the South East, arriving from a very cold Russia on Tuesday and strengthening through to the weekend.  It should stay dry with a low risk of snow flurries reaching Reigate.   Actual max temperatures will be +1 or 2°C during the day but the 15 mph wind will make it feel very chilly at -3°C in the daytime and, during the night, as low as -8°C wind chill.  Cloud cover will control how low air temperatures actually fall at night: clear skies could see temperatures drop to -4°C with frosty mornings.  Want to warm up?  Get to Reykjavik in Iceland which will be the warmest city in Northern Europe this week with unseasonably high temperatures of +8°C with a “warm” and wet southerly Tropical wind.  Next week looks warmer and staying dry for Reigate with temperatures up to 10°C. An early taste of Spring perhaps?

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The “Russian ice bear” is escaping again and will arrive in Reigate from Tuesday!  A HIGH pressure developing over Scandinavia and a LOW over Europe will open the cage and let the Russian ice bear gallop across Northern Europe and arrive freezing and growling in the UK from mid-week.  Expect cold easterly winds on the back of the bear.  The frigid continental interior, where the bear lives, has had the whole winter to cool down: the source region is now -10ºC and frequently lower. (View the Urals meteorite shower youtube clips again to get an idea of how cold the source region of this air mass is!) There is the potential for some of the coldest temperatures of this winter yet to be recorded in the SE as the bear bites back.  The week looks mostly dry but snow showers are also possible, especially further east.  The easterly winds warm up on their journey west and also pick up some moisture from the Baltic and comparatively warm North Sea; any warming causes instability (a tendency for air to rise and form cloud and rain/snow) and snow showers are therefore possible on the east coast, some of these could reach further inland on the strong easterly winds forecast.  Whilst the duration of this cold snap is not certain, the end of this sort of episode often sees westerly winds return with substantial snow on the leading edge of fronts.  How and when the bear returns to it’s cage remains uncertain,  but it will be prowling around Reigate from Wednesday on wards this week.