Archives For January

2016-02-21_10-45-50

Reigate, Surrey January 2016 summary weather statistics

  • Tmax 12.8C
  • Tmin -5.1C
  • T av 5.2C
  • Total rain 137.2mm
  • sunshine hours 94.1 hours
  • mean pressure  1009mb
  • max gust 35mph

January 2016 was a modestly unsettled month in Reigate with frequent wet days (21 in total with >1mm) and total rainfall amounting to 137.2 mm, this was some 160% of normal expected rainfall totals for the SE as a whole for January.  This caused some surface water flooding and soggy fields but, whilst a few flood alerts were issued, the River Mole behaved itself as no one rainfall event occurred with sufficient intensity to cause significant flooding problems in the Mole catchment.

In comparison with recent years, January 2016 turned out moderately wet sitting between the very wet January 2014 183 mm and the drier Jan 2015 69mm.  Of note locally was a spectacular display of mammatus cloud on 10 January as a squall line brought a thundery trough that passed over the area bringing some hail and cumulonimbus cloud.

It was a mild month with average temps 5.2C, Tmax 12.8C and only 7 days with minimum temperatures dipping to or below freezing. The highest January max temp ever recorded occurred in N Ireland. Whilst no weather record was broken in Reigate it was still a mild month with about average sunshine.

2016-02-21_11-01-09

sunshine Reigate January 2016

At 5.4C the CET temperature for the UK was 1.6C above the long term average. At 1.13C the global average January temperature turned out to be another record breaking warm month.

Returning to local events, one brief marginal wet snowfall event occurred in Reigate and Surrey overnight 16-17 January.

Snow lay during the morning of 17 January and was just sufficient to allow families to enjoy sledging and snowman building in Reigate and Priory Park for a few hours before it all melted by midday.

 

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The mean 500mb pressure anomaly pattern for January shows the UK in a mostly stormy Atlantic regime with storms rattling through especially the NW bringing high rainfall totals there. Storm Gertrude at the end of the month did not impact the sheltered SE much. As usual the SE was relatively protected sitting nearer the higher pressure over S Europe.

2015-02-04_18-44-20

January 2015 summary for Reigate, Surrey

Average temp 4.5C (UK av 3.7C, CET 1C above long term average)

Tmax 14.7C (12.2C 2014)

Tmin -4.9C (-1.5C 2014)

Total precipitation 69mm  (183mm 2014)

Max wind gust 42mph (52mph Jan 2014)

snowfall was recorded on 3 days, snow lying on 2 mornings

Total sunshine 96 hours (98hrs 2015)

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January was mostly under the influence of an occasionally strong westerly and NW airstream with some stormy weather for the NW of the UK but, predictably, Reigate and the SE was sheltered from most of the weather action and our rainfall total was about on the long term average for the South East at 69mm. This was, of course, considerably less than the 183mm rainfall last January 2014!

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Overall, January was just about average temperature in the UK. This average hides the variation though… the start of January was extremely mild with some very warm Tmax temperatures early in the month reaching nearly 15C in Reigate.  The end of January was considerably colder than average although nothing extreme.

The end of January cold snap ran into the first week of February.  During this period Reigate saw temperatures drop modestly below average and we experienced 3 spells of modest wet snowfall, albeit lying snow from night time falls rapidly melted by early morning and the lowest temperatures we a mere -4C.  Reigate experienced one notable but brief “thundersnow” event on the afternoon of 29 Jan. This caused some local traffic disruption.

The cause of our swings in weather a neatly summarised in the mean monthly sea level pressure and 500hPa anomaly chart from the JMA.  Here you can see the building high pressure over the Azores towards Iceland and the low pressure to the North and NE nudging towards Scandinavia.  It is this configuration of building ridge in the Atlantic and LOW over Scandinavia that eventually brought our modified “Arctic blast” through the last week of January.  As is normal for an Arctic airmass the SE of England away from the North Sea coast of Kent rarely sees any prolonged snowfall and this was the case.  An interesting feature developed on the 29/01/2015 within the Arctic airmass: a polar low may have spun up and moved South through the Irish Sea.  This was controversial and not accepted as a true polar low by everyone but it seemed to have many of the characteristics.  A post on this polar low can be found here.

 

The evolution of the January 2015 cold snap was interesting because it was initiated by an unusually cold and unstable NW airstream on the back of a deep low that crossed Scotland.  The NW airstream was unstable enough to bring the thundersnow event to Reigate. Oddly the original NW “blast” from Greenland pushed through so quickly that a lot of polar maritime returning and tropical maritime air was secluded in the low core over Scandinavia.  It was this secluded / occluded warmer airmass that a) probably contributed to the polar low feature and b) modified the Arctic blast and , at least initially, made it much less cold than is usual for such an airmass direction.  It took several days for any truly cold air to reach the SE of England and, even then, 850hPa temps never fell below -6 or -7C.

The CET for January was nearly 1C above average for the long term average, quite a lot more than the MetOffice.  As can be seen from the chart below this January was not exceptionally warm, being moderated by the cold snap at the end of the month.  Only 6 of the last 20 years have come out colder than the long term CET average.

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Globally January was +0.35C above the long term (30 year) average temperature.  The northern hemisphere was +0.55C above the long term average.

2015-02-08_21-10-04

 

http://www.metoffice.gov.uk/climate/uk/summaries/2015/january/regional-values

http://www.metoffice.gov.uk/climate/uk/summaries/2015/january

 

January 2014 summary

February 2, 2014 — 1 Comment

Brief summary of weather this January in Reigate. January 2014 has been one of the wettest on record for SE England.  UKMO say that January 2014 in Southern England and SE has been the wettest for 250 years (since “records began 1766”).  Records specific to Reigate do not go back that far (c4 years) but the town had over 180mm of rain in January, more than 3 times the rainfall in January last year.   Kenley, our nearest official met office wx station, recorded just over 200mm of rain.  Kenley is on top of the North Downs so is likely to experience more rain due to orographic uplift, especially in the convective downpours on squall lines and thunderstorms that occurred this month (posts here).

A significant proportion of Reigate rain arrived in the form of intensive downpours brought by humid unstable Southerly / SSW air masses bringing thundery cells from the Channel Coast, notably on 28 January when Reigate had thunderstorm activity and spectacular cumulonimbus clouds (one big clap over the town at 1:00pm).  This was during the cut-off low warm-through at the end of the month.

On 23-24 Jan a squall line arriving from the NW brought the highest gust of wind recorded in Reigate for at least 4 years: 52mph.  The squall line brought more trees down locally and recorded gusts over 60mph on the Downs. Posts on that event here.

The month began wet with the Mole running high and ended with the river still in a flood state.  Here are some pictures illustrating January 2014 around Reigate.

http://www.metoffice.gov.uk/news/releases/archive/2014/Early-January-Stats

Chart showing January weather for Reigate, Surrey; collected by Reigate Grammar Weather Station. Data for January available NOW on the DATA page (link above).  More analysis on our collected data will appear soon.