Archives For April 2016


Today we put up a new weather station at our sports ground at Hartswood outside Reigate. This location will complement our established town weather station located at Reigate Grammar School. Hartswood is an out of town location with more exposure from all wind directions. It is already recording different conditions to the town (see links below).

The new weather station is a robust self-contained Davis Vantage Vue automatic weather station (AWS).  This model was chosen for its ability to cope with exposed sites and it has a reputation for being relatively maintenance free for longer periods.  It is commonly put on masts on rooves, as we have done here.


This AWS is unusual because it uses the new Vantage Connect system.  The Connect system uses the mobile phone network to transmit data at 15 minute intervals to the Weatherlink website where it is pushed onwards to other websites, such as Weather Underground.  There is also a handy local live read out of weather on a console in the Tea Hut window.

The Vantage Vue weather station is simple to set up being a single housed unit. Attaching the anemometer and wind vane involves tightening screws with a tiny allen key. The Connect System is also easy to set up. Insert and connect batteries, start both systems up and they will endeavour to discover each other with little intervention.

The console unit also discovers the AWS and starts displaying data almost immediately with little user input.


Once the systems are working and data is uploading reliably to the internet then assembly and fitting onto the roof is the next step.  An aerial expert was employed for this bit.


Orientation to the South is important for both the Vantage Vue and Connect systems. Not only do they both use solar panels to maintain battery power (used at night of course) the Vantage Vue also requires a southerly orientation to ensure that wind direction readings are accurately recorded by the wind vane.  This is all explained in the manuals.


Roof top sites for AWS are popular but they have pros and cons.  Whilst wind readings benefit greatly from a clear wind run at height (so long as the mast exceeds a metre or so above the roof line to avoid eddies and turbulence), the accuracy of rain recordings can sometimes suffer with greater wind speed rendering totals somewhat less reliable than traditional ground based rain gauges (although ground based AWS often do not entirely satisfy strict meteorological conditions for rain gauge placement either).  Roof locations benefit from better security and connectivity.  Overall, with single-unit compact weather stations a roof top location is a good compromise and the most effective use of this technology.  Our Vantage Pro 2 AWS in town allowed us to divide the rain gauge and temperature sensor units on the ground from the anemometer on the roof, a better solution.


“Live” weather data from Hartswood can now be viewed on the internet in these locations:

Weatherlink summary

It is hoped the data will prove to be useful for checking the weather conditions before matches for staff, students, players and spectators preparing for their match or visit.


Eventually a ground frost sensor can be added to issue alarms when ground temperatures fall to near zero. This will save some guess-work and early visits to check if pitches are frozen or not. Data will also be useful for students doing weather studies in urban micro-climate and the data can also be used by computing and maths students amongst many other applications.

RGSweather will also be able to compare data between town and edge of town locations.


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.


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.


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.


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.


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.


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


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.


Met Office March summary




Currently Reigate and the SE is enjoying a settled sunny spell under the continental flow of a HIGH pressure sat directly over the UK.

Light surface easterly/SE winds and unbroken sunny skies under high pressure have brought temperatures up to 17C locally today.


The 500mb chart above shows the upper southerly / SE flow bringing recently warm conditions in the daytime.  Unfortunately things change by the end of the week as the upper flow swings round to arrive from the north over the weekend and push temperatures well below average for the time of year.


The jetstream will be arriving direct from Greenland by Sunday, as HIGH pressure builds over the Atlantic and falls to the east of the UK.

Airmass temperatures in this northerly polar flow (measured at 850hPa) could even be low enough for showery wintry precipitation.

Cold late Springs are not unheard of in the SE, 1981 was a cold Spring with snow, for example. Recent Springs over the last 25 years have been milder than the long term, so this event is still “normal” weather.



The HIGH is set to regress NW into the Atlantic and merge with a high pressure over Greenland.  Pressure over the Poles is rising as well, shown by the swing to negative Arctic Oscillation and related NAO.


The result of higher pressure over the Polar regions and low pressure in mid latitudes is to push cold Arctic air south.  If this was January it would be a truly cold period coming up.


With LOW pressure over the North Sea the resulting funnel of cold northerly winds will dig south across the UK and into Europe especially from Sunday into next week.  Sunday is the London marathon and, whilst showers are forecast coming down the UK during the day, it looks a mostly dry but cool start for runners.

Most of the wintry action looks set for Benelux but here the Tmax during the daytime are likely to be around 10C, but fall to near freezing at night, with frosts under any clear skies.  Occasional wintry showers are possible, especially Monday. Note the Tmax temperatures on Monday daytime shown below.

Cool for the time of year for sure, as shown by the contrasting anomaly charts below between this week and next.

During this cold spell next week fresh falls of snow are expected across mountain regions of Europe, especially Norway and the Alps and the highlands of Scotland and Northern England.


At lower elevations snow might fall at times during this cold spell, however, strong April sunshine (as strong as August) will quickly raise temperatures between showers so that, even with any wintry precipitation, ice and frost will melt rapidly away.  Icy roads overnight are also unlikely at lower elevations because soil and surface temperatures have risen well above freezing.  Nevertheless, gardeners should be aware of the chance of frost and 10cm soil temperatures will fall to near 5C over the course of next week.


How long will this last?  Charts show the cool spell lasting for much of next week but with some amelioration throughout likely.  Stronger sunny periods will make it feel satisfactory out of any wind but night time on east coasts in heavy wintry showers, for example, will feel distinctly chilly!

Where’s the heat gone?  It’s worth pointing out the very high temperature anomalies over N Africa and Greenland at the moment.  The highest and earliest surface melt across the Greenland ice cap is likely to continue next week in the upstream flow around the Atlantic block. The build up of heat in N Africa (shown below) could, in the right conditions, bring continental heat to the UK later and, perhaps some decent thunderstorms, but this is all just speculation.