Editing Chelmsford (section)

==Geography and climate==

===Geology===
From over 600,000 years ago, during the [[Pleistocene]] [[ice age]], until the [[Anglian Stage]] around 478,000 to 424,000 years ago, the early [[River Thames]] flowed through the area where Chelmsford now stands, from [[Harlow]] to [[Colchester]], before crossing what is now the [[North Sea]] to become a tributary of the [[Rhine]]. Consequently, gravel deposits are frequently found in the area and current and former [[gravel pit]]s in the district are common.

Chelmsford has two rivers, the [[River Can]] and the [[River Chelmer]]. Although often confused to be the same river in the city centre, they are quite separate until they join towards the east of the city to form the [[Chelmer and Blackwater Navigation]] which heads out towards [[Maldon, Essex|Maldon]] before flowing into [[tide|tidal]] waters at the [[Blackwater Estuary]]. In the other direction, the Chelmer comes from the north from its source near [[Thaxted]] while the Can comes from the West from [[Writtle]] where it separates from the River Wid.

Until the 1960s, these rivers were extremely prone to flooding the city centre area including two disastrous floods in August 1888 (known locally as 'The Great Flood') and in September 1958 (which also badly affected nearby [[Wickford]]) causing widespread damage. Flood prevention schemes in the 1960s on both rivers have largely prevented any further incidents here although the natural floodplains to the north and east such as The 'Baddow Meads' and The 'Chelmer Valley' continue to see flooding after prolonged heavy rainfall.

===Climate===
As with most of the UK, Chelmsford has a [[oceanic climate|temperate oceanic climate]] (''Cfb'' in the [[Köppen climate classification]]), however due to its proximity to continental Europe, Chelmsford enjoys warm summers and cool but not cold winters, with a relatively narrow annual temperature range and few extremes of temperature. Being in the southeast of England, the city enjoys a warmer climate than most of the United Kingdom and is one of the driest areas in the country. The nearest [[met office]] weather station is in [[Writtle]], {{convert|2|mi|km|abbr=off|0}} west of the city centre.

The record highest temperature recorded in Chelmsford was {{convert|39.1|C|F}} on 19 July 2022<ref>{{cite web | url=https://www.chelmervillage-weather.co.uk/FreshWDLmaster.html | title=FreshWDL }}</ref> beating the previous record of {{convert|37.7|C|F}} which was set on 25 July 2019.

The coldest temperature recorded in Chelmsford was {{convert|-20.6|C|F}} on 29 January 1947. A low of {{convert|-18.0|C|F}} was recorded during December 1981, and more recently the temperature fell to {{convert|-13.0|C|F}} on 20 December 2010. [[Frost]] is common, occurring on an average of 53 nights of the year.

Rainfall averages 591.8&nbsp;mm a year, with daily totals of over 1&nbsp;mm falling on 108.1 days of the year. Thunderstorms are rare and mostly occur during July and August. All averages refer to the 30-year observation period 1981–2010.

Chelmsford was struck by a F1 [[tornado]] on 23 November 1981 as part of the record-breaking nationwide [[1981 United Kingdom tornado outbreak|United Kingdom tornado outbreak]] on that day causing some damage in the city centre.<ref>{{cite web|url=http://www.eswd.eu/cgi-bin/eswd.cgi|title=European Severe Weather Database|website=eswd.eu}}</ref>

{{Weather box
|location = [[Writtle]],{{efn|Weather station is located {{convert|2|mi|0|abbr=out}} from the Chelmsford city centre.}} elevation: {{convert|32|m|ft|0|abbr=on}}, 1981–2010 normals, extremes 1960–present
| collapsed    = 
| metric first = y
| single line  = y
| Jan record high C = 15.1
| Feb record high C = 18.4
| Mar record high C = 22.8
| Apr record high C = 27.0
| May record high C = 30.0
| Jun record high C = 33.6
| Jul record high C = 39.1
| Aug record high C = 35.7
| Sep record high C = 32.1
| Oct record high C = 28.6
| Nov record high C = 18.5
| Dec record high C = 16.6
| Jan high C = 7.4
| Feb high C = 7.7
| Mar high C = 10.7
| Apr high C = 13.6
| May high C = 17.0
| Jun high C = 20.2
| Jul high C = 22.9
| Aug high C = 22.7
| Sep high C = 19.3
| Oct high C = 15.0
| Nov high C = 10.5
| Dec high C = 7.7
| year high C = 14.6
| Jan mean C = 4.5
| Feb mean C = 4.4
| Mar mean C = 6.7
| Apr mean C = 8.7
| May mean C = 11.9
| Jun mean C = 15.0
| Jul mean C = 17.5
| Aug mean C = 17.3
| Sep mean C = 14.5
| Oct mean C = 11.1
| Nov mean C = 7.2
| Dec mean C = 4.8
| year mean C = 10.3
| Jan low C = 1.5
| Feb low C = 1.0
| Mar low C = 2.7
| Apr low C = 3.8
| May low C = 6.8
| Jun low C = 9.8
| Jul low C = 12.0
| Aug low C = 11.8
| Sep low C = 9.7
| Oct low C = 7.1
| Nov low C = 3.9
| Dec low C = 1.8
| year low C = 6.0
| Jan record low C = -20.6
| Feb record low C = -13.3
| Mar record low C = -11.1
| Apr record low C = -6.1
| May record low C = -2.8
| Jun record low C = -1.7
| Jul record low C = 2.2
| Aug record low C = 0.6
| Sep record low C = -1.1
| Oct record low C = -6.7
| Nov record low C = -8.1
| Dec record low C = -18.0
| precipitation colour = green
| Jan precipitation mm = 53.2
| Feb precipitation mm = 39.2
| Mar precipitation mm = 40.2
| Apr precipitation mm = 41.6
| May precipitation mm = 48.7
| Jun precipitation mm = 49.9
| Jul precipitation mm = 44.3
| Aug precipitation mm = 51.7
| Sep precipitation mm = 48.6
| Oct precipitation mm = 64.1
| Nov precipitation mm = 58.0
| Dec precipitation mm = 52.3
| year precipitation mm = 591.8
| unit precipitation days = 1.0 mm
| Jan precipitation days = 10.8
| Feb precipitation days = 8.6
| Mar precipitation days = 9.2
| Apr precipitation days = 9.2
| May precipitation days = 8.7
| Jun precipitation days = 8.5
| Jul precipitation days = 7.3
| Aug precipitation days = 7.7
| Sep precipitation days = 7.8
| Oct precipitation days = 10.1
| Nov precipitation days = 9.9
| Dec precipitation days = 10.2
| year precipitation days = 108.1
| Jan sun = 58.0
| Feb sun = 76.1
| Mar sun = 112.4
| Apr sun = 165.7
| May sun = 196.6
| Jun sun = 198.2
| Jul sun = 209.9
| Aug sun = 204.0
| Sep sun = 147.4
| Oct sun = 113.9
| Nov sun = 68.7
| Dec sun = 47.4
| year sun = 1598.2
| source 1 = [[Met Office]]<ref name="Met Averages">{{cite web |url=https://www.metoffice.gov.uk/research/climate/maps-and-data/uk-climate-averages/u10q3cdwd|title= Writtle 1981–2010 averages |access-date=22 December 2020|publisher=Met Office}}</ref>
| source 2 = [[Royal Netherlands Meteorological Institute|KNMI]]<ref>{{cite web| url = https://eca.knmi.nl//download/millennium/millennium.php| title = Indices Data – Writtle STAID 1845| access-date = 22 December 2020| publisher = [[KNMI (institute)|KNMI]]| archive-date = 9 July 2018| archive-url = https://web.archive.org/web/20180709010608/https://eca.knmi.nl//download/millennium/millennium.php| url-status = dead}}</ref>

}}