Archives For January 2013

Main roads remain clear around Reigate after the evening snow and temperatures are rising above freezing, where they will remain throughout the night and through tomorrow. The main snowfall moved away north west by 10 pm and further light snow showers will peter out overnight. The weather radar shows showers becoming increasingly limited to the south coast. Any further showers overnight are likely to be light and fall as sleet as temperatures rise above freezing. Wednesday and Thursday’s forecast remains cloudy and cold with the risk of any light snow decreasing all the time as a HIGH pressure builds from the north east.  Look to Friday afternoon and through the weekend for the next exciting weather installment for Reigate weather!

Run for it!

January 22, 2013 — Leave a comment

The front this evening has come further North than expected so snowfall over Reigate could amount to 3-4cm by end of tomorrow: snow should die out overnight, only light flurries tomorrow likely, if any.

Above is an “ensemble run” of temperatures and precipitation for London until early February (850hPa represents 1500 metres above the surface – so temps are not for ground level). To get an accurate forecast, weather super-computers run complicated models several times, called runs, with slight “perturbations” in the data (labelled P1-P20). Perturbations are deliberate “errors” fed into the initial weather data which are designed to see how far each run agrees with each other. If all the runs (lines shown) are close together then weather forecasters can place more confidence in their predictions. Naturally, things get a lot less certain into the distant future: hence the increasingly squiggly lines towards February: i.e. anything could happen between those lines! The above runs all agree that we are due to warm up over the weekend. However, look closely at the detail from Friday 25 Jan to Sunday 27 Jan and it shows the warming could take a little while and significant precipitation could arrive from the west on Saturday BEFORE our cold dense block of air budges out the way. The incoming warm air is less dense and will tend to ride up and over the cold air mass still sitting on Reigate. Any initial precipitation is therefore likely to fall as snow or freeze-up when it hits the cold layer and turn into icy rain. This can be nasty stuff and coat freezing surfaces with ice too boot. The warmer air will eventually arrive (Sunday) but the transition could potentially be quite messy. Next week looks wet and windy with a return to Atlantic westerlies.

“…All that snow had to go… ” (Dr Suess) … but not until Saturday!

This time next week it could be 12°C with heavy rain! The icy HIGH pressure block controlling our weather is about to be broken down by a deep depression due to hit sometime this weekend. This might yet turn out to be a brief warm interlude and a return to cool conditions is certainly possible before the winter is out… it all depends on the weather over Canada and Greenland and air pressure 15km above the North Pole.

Back to this week: staying cold and mostly snow-free for Reigate (falling from the the air that is; snow underfoot will stay put ;-))
A close shave Tuesday for Reigate: Snow, with sleet behind, pushing in on a warm front edging across the Channel from NW France is not due to reach us in any quantity, and probably not at all (it is due to hit the South West and Wales significantly).
There could be some light snow Tuesday evening and overnight to Wednesday morning but dying out quickly.

The rest of the week looks cold and frosty with light snow flurries possible, but nothing amounting to much. There is snow around but nothing like we have had and little of any significance coming Reigate way.  It will stay chilly with an easterly wind with very cold nights until…
Friday evening and the weekend is when the exciting change to milder conditions is due to start. It won’t be a quick change and may involve a lot of snow preceding rainfall…but, by this time next week this scene of Reigate Hill in the snow might be a distant happy memory!

Nothing to do with current weather…

 

A strong jet stream (high altitude wind) blowing across the Atlantic to the south of the UK is likely to maintain the LOW pressure over Europe this week: which will mean our weather stays cool. Jetstreams direct weather systems on the ground, like a good theatre director bosses around their actors on the stage! Winds blow anticlockwise round LOW pressure systems and when they sit to the south of the UK they drag in cold Easterly and Northerly winds from a freezing continent. Warm air is currently trapped to the south of the jetstream and it won’t budge north because of a blocking HIGH over the North Pole. What does all this mean for Reigate this week?

Sunday snowfall will clear off from Reigate soon and temperatures will drop low overnight (-5°C) under clearing skies. Possible snow/sleet showers Monday pm, temperatures will rise above freezing briefly.  More cold easterlies on Tuesday and Wednesday with snow showers possible. Thursday and Friday look like bringing a cold frosty and foggy HIGH pressure: clear skies = cold overnight temps.  Details might change but that’s about it.
The BIG question is what changes will happen from Friday through next weekend? The mighty computers that use complex models to supply forecasts are at odds on this: US and European models suggest a big Atlantic storm will finally bring in milder weather behind lots of rain (briefly preceded by snow) to the UK. The Canadian (graph pictured) and Japanese models suggest  instead that this LOW will be beaten back yet again with heavy prolonged snow and a continuation of the cold spell through to February. Weathermen say this is a “developing situation” aka: we don’t know yet but it’s exciting to find out which model will win! Watch posts this week for developments on this. 

Good news! RGS weather is now the 39th most popular world weather site and 14thUK weather site on the WEATHER TOPSITES list with nearly 6000 hits since we started in September.

 

Update Sunday: 5cm of fresh snowfall in Reigate on top of the snow on Friday.  Main roads round Reigate remain clear but freezing temperatures expected overnight (possibly down to -6°C) could create problems for journeys tomorrow morning. RGS parents and students please refer to HM message on the school website ; RGS staff please refer to emails. More details on weather outlook later.

RGS snowfall for RGS catchment Sunday 20 JanTwo LOW pressure systems will do a strange spinning dance around the South East on Sunday and Monday, depositing more snow and maybe some icey rain. This unusual pirouette of storms starts on Sunday with a LOW moving North out of France and skirting the East coast and then curving north west across the country. This will bring cold Easterly and Northerly winds to Reigate and up to 5cm more snow starting late morning (actually started 8am: moved much quicker than expected: snow front moving 30mph+ 😉 !) with moderate falls after lunch, dying out in the evening. Reigate is on the edge of heavier snowfalls which will affect Kent, where 10cm is possible over the hills. Skies will clear overnight and temperatures could drop to -6°C.

Monday sees the next LOW, tracking up the English Channel from the West, with a risk that it will bring snow or icey rain to Reigate in the afternoon.  The exact track of this little LOW remains uncertain: the UK Met Office suggest it will track into Belgium (and we will miss any snow attached) but other models (NAE & ECMWF) suggest it will come much closer to the South East which would bring more snow: uncertain – so watch for updates!  Every wind direction will be represented during the next two days: the coldest directions from the East and North will dominate but occasionally warmer wind directions from the South and West will cut into this weather dance lifting Reigate above freezing, but not for long.

Whilst more weather systems early this week will approach from the west, usually a warmer direction, these LOWS will mostly track south of the UK and this will drag in cool winds from the east and north.  The jet stream remains south of the UK and until it shifts north we will be stuck in cool Polar air.  Nevertheless, temperatures in Reigate should creep above freezing during the day this week, bringing a slow thaw. Advanced charts show a vigorous LOW pressure arriving next weekend which could drive in proper mild Atlantic air: probably a return to rain and wind.

In Reigate snow started falling lightly at 8:00 am and continued throughout the morning building to a peak moderate snowfall intensity for a few hours  around midday, thereafter gradually dying out through to (approximately) 4.00 pm when the main period of snow stopped.  A total of 8 cm of snow was measured lying at our observation site at Reigate Grammar School (see post below). This is equivalent to approximately 8 mm of rainfall (i.e not much).  So, a total of 8 hours of snowfall delivered just 8 cm of snow, which fell as light or moderate falls. The maximum temperature for the day was +0.2°C at 12:15 am in the morning! The lowest temperature recorded was -2.1°C at 10:00 am.  The lowest wind chill temperature was -7.8°C recorded at 8:00 am, just as the snow started.  

It’s NOT over yet! Another significant snowfall event is possible on Sunday through to Monday with a LOW winding up over the continent and bringing our own special snow just to the South East! We will post details as they become clearer. Please measure snow depth where you are and send in the cm depth! Who has got the most?!  Follow us on twitter @RGSweather for updates and Facebook.

Photos: scenes from today around Reigate Grammar and Reigate.

SOLVED! our anemometer and wind direction transmitter on the school roof malfunctioned early Friday due to snow on rooves interrupting wireless signal from the anemometer and wind vane unit.  Wind records for Friday are therefore invalid because they got stuck! The problem has been fixed.

How do you measure snow depth properly (i.e.World Meterological Organisation approved method)?
Measuring the depth of lying snow is not quite as simple as sticking a rule (ruler) in and taking a measurement. To be really accurate and “by the book” do the following:

  1. Place a white board down before it snows, away from trees and buildings. 
  2. Find a graduated ruler or graduate your own stick in cm / mm.
  3. Find a patch of untrampled and undrifted snow which has a clear sky view, away from trees and buildings.
  4. Take 10 measurements holding the rule vertically and read the depth carefully in cm. Note down the measurements. Disregard the highest and lowest reading.
  5. Take the average of the rest as the “depth of snow” reading.
  6. Note the maximum and minimum depths within the area too.

how to measure snow fall

Note that old snow (>1day) will become compacted so increasing depth of snowfall on top of old layers becomes inaccurate.
To measure “fresh snowfall” on top of old snow place a “board” (snow board?!) over the old layer before it starts snowing again.  Remember where your board is (mark with a stick!) and measure fresh snowfall there. Repeat with further boards if you live somewhere like Alaska.

So, you don’t need any high tech equipment to measure snow, infact, technology has lagged behind in this regard. All you need is YOU, a stick, a pencil and paper and… some snow.

Now have fun and get measuring snow depth where you are and please send us some measurements from your area! 🙂

 

RGS school email has been sent to parents

Further to the message yesterday, please be aware of the timings for the rest of the day. Morning lessons will continue as normal but we are planning to let students leave from 1.30pm, once they have had lunch. The coaches are due to leave between 1.45pm and 2pm. The school will remain open until 4.30pm and any students who wish to stay will be supervised by staff. The GCSE French Mock Examination this afternoon has been postponed; however the Public Exams (Maths C1 and C2) will continue.

If you would like your son or daughter to leave early after lunch, please contact them directly via text or email, or contact the school office via email. We will only give permission for children to leave early if we have seen a message from you.

So – will the SKYFALL or is it just some normal winter snow over Reigate tomorrow? Let’s see…

The worst of the snow on Friday is reserved for places like Wales near the leading edge of occluded fronts associated with the LOW which will slowly creep off (called a “slider low”) to the South East, unable to make headway against that brutish HIGH over Scandinavia! This HIGH isn’t budging and has stopped the LOW zipping right over the UK which would have delivered mild air from the Atlantic.  Mild air probably won’t reach the SE for at least a week so any snowfall will stick around.  The problem for Reigate tomorrow is that fronts edging slowly east (and weakening as they edge into higher pressure) will slow right down and bring persistent light snow most of the day and through to Saturday. Snow could be heavier at midday for a while on Friday.
Starting around 8-9am in Reigate light snow will accompany very cold South Easterly winds of up to 20mph and gusting over 25mph, giving a severe windchill of -8°C. Given the very low temperatures the snow will be dry and might blow around a bit in exposed areas. Nevertheless, total snowfall should be quite low but spread out over a long period: by end of Friday possibly around 8cm for Reigate, which isn’t a show-stopper… or wouldn’t be in Sweden!
Saturday sees more snow and cold, more on that later.
So … will we see the SKYFALL in Reigate tomorrow and over the weekend?! … hopefully not but it will be very cold, windy and snowy, so wrap up and enjoy!  Spare a thought for Wales and the west where there will be REAL BLIZZARDS. (Video shows rain and snow (hatched) from Friday am through to Sunday in 3 hour intervals).