Interitus

A good time to dig out the interesting and thorough analysis by Steven Burt and Philip Eden from the journal "Weather" - "The August 2003 heatwave in the United Kingdom. Part 2 - The hottest sites" https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1256/wea.10.04B Conclusion - the 2003 Faversham reading was considered to be 2 degrees higher than expected.

Could've been worse - despite the widespread heat, temperatures of 30.6°C at Hawarden and Trawscoed were a whopping 4.6°C off the Wales record, just a typical hot summer's day. Belgium and the Netherlands just added roughly 2 degrees to their national records dating back to the 1940s from 38.8 and 38.6°C to 40.7°C. On the one hand this could suggest that it would be well within scope to happen here....though on the other perhaps it re-establishes a natural 2 degree difference between their maximum and ours which was 36.7°C at Raunds and Canterbury in 1911 and has been closed in recent years.

Arpege wasn't bang on then was it? Lol

Note - two stations for Cambridge - the airport with rounded Metars and the Meto site at Cambridge NIAB (National Institute of Agricultural Botany)

Hottest place in the country yesterday.

34.6°C Nantwich, 34.5°C Knutsford and Bidston 3/8/1990, 34.3°C Crosby 19/7/2006 - Met Office - https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/weather/learn-about/uk-past-events/regional-climates/north-west-england--isle-of-man_-climate---met-office.pdf Incidentally, the official Man Airport weather station closed, produces Metar only, last one shows 32°C. Where is this reading from?

Non standard sites (but top quality instruments) the Manchester Uni Whitworth Meteorological observatory is reporting 32.56°C at roof level and 34.42°C at street level at 13:28 UTC (14:28 BST) - http://whitworth.cas.manchester.ac.uk/current/index.html

METARS = rounded values

More significant is the heat over the low countries - the Netherlands and Belgium records of 38.6 and 38.8°C would be obliterated. Interestingly in contrast to the SE UK seemingly recent increasing warmth, these records date back to the 1940s (23/08/44 and 27/06/47 respectively).

No it's not the potential for the absolute maximum which is in question, it is the relative frequency of local records, which just happen by and large to be national ones also in the southeast.

It's a little curious the seeming increase in frequency of record breaking or potential near-record breaking heatwaves in various months that affect the southeast. May be a misperception, but for example Wales and northwest England records go back to 1990. Some parts of nw England got close to those levels in 2006 but in general these heatwaves don't get close to the 34/35+ record values in these areas. 2003 was a non-event in the NW!

You don't have to tweet to view though, Twitter search right now brings lots of great images from last night, too many to post! https://twitter.com/search?f=tweets&vertical=default&q=noctilucent clouds&src=typd

Some decent NLCs visible from north Cheshire at the moment, look forward to some good pics later. Plenty of good images on Twitter.

Think that honour has gone to Achnagart, exactly 30°C at 4pm, temperatures in the south west don't seem to be progressing. Bummer, posted above at same time!

Another windshift and just as quickly the temperature is back down from 27.8°C to 21°C. All the while, Kinloss on the same stretch of coast 10 miles to the west hasn't been above 18°C!

Good grief, with a change of wind direction from onshore to off, Lossiemouth has apparently seen a rise of 10 degrees in an hour to 27°C, with 7 degree increase in 20 minutes.

29.3°C at Achnagart in the northwest Highlands at 15:00 up from 9.2°C at 1 am.

Indeed, as above, weathercast.co.uk Chivenor figure actually rounded up from 28.5°C -http://www.weathercast.co.uk/world-weather/weather-stations/obsid/3707.html Still it pips Porthmadog stuck on 28.4°C, while Caernarfon has been struck by sea breeze, now down to 24°C

Apparently Carpentras 44.3°C, but Villevieille 45.1°C

Or perhaps high latitude...was clear all night Wednesday but couldn't see a sausage further south from north Cheshire so didn't bother looking last night even though I was awake and turns out there were some present duh!

Caernarfon airport, just to the north of Porthmadog, also reached 27°C yesterday though rounded values on METAR, and today reported 28°C at 11 and 12 BST before dropping back to 26°C at 13:00 with a switch to a westerly breeze off the sea. Porthmadog was behind at this stage but now hit 28.4°C at 13:00.

Good and reasonable analysis, there was indeed a cold pool of air that moved from the Icelandic region, it's just that the motion of air parcels tends to be so complicated that there should be caution when relating temperatures to a direct source of SSTs. For example, here is the GFS 3 day backward trajectory plot of air at 640m asl for a matrix of points across the southern North Sea area to 27/06 00z using isobaric motion - This motion is pretty much as would be expected by eye, the air follows the isobars and remains at the same height. Temperatures were between 5-7 degrees probably in the Faroes region where the trajectories converge before uniformly warming to 11-13 over the southern North sea. Prior to this though there is quite a scatter of temperatures from the source regions, with also some surface warming over ground in Iceland. However, this assumes that the air parcels remain at the same height ignoring vertical motion which can be examined using the model vertical velocity - This gives a wider source area, but none of the air parcels originate near the surface, ranging from roughly 1400-4000 metres asl. Motion largely follows isentropes of potential temperature so finally here is the isentropic analysis - This gives a range of source altitudes from near surface to 2000 metres though all reach above 1000 metres where the trajectories converge. The caveat with this adiabatic approach however is that ignores significant diabatic effects from eg condensation, precipitation, strong insolation, mixing etc and can have problems with discontinuities across frontal boundaries. Trajectory plots courtesy NOAA Hysplit - https://www.ready.noaa.gov/HYSPLIT.php

Why is it assumed that air at 950 hPa, which the charts show is at 640 metres asl hence expectedly colder than the North Sea surface, has originated at sea level thus must be from north of Iceland?

Understandably, there's been a lot of focus on the 850 temperatures. Of course this is above any land surface in the UK. However, the cool marine boundary layer which is pegging back surface temperatures is quite shallow so theoretically there is the possibility that some of the highest temperatures, particularly on Thursday and Friday, could be achieved at altitude across the peaks of the highest Welsh mountains, above the inversion. For example, using the Arpege model, for 10pm Thursday, temperatures near sea level in parts of south Wales are around a warm 18 or 19 degrees. The 850 mb temperature is a ridiculous 24+ degrees, but the warmest values are actually a bit lower down such that it is around 26 degrees at and above the 925 mb level which at 865 metres altitude could be encountered on the highest of the Brecon Beacons. Similarly on Friday afternoon, with 850 temps around 22°C in north Wales, there is approaching 27 degrees at 900mb at the height of Snowdon and the highest Carneddau mountains.