*Someone at the Met OfficeUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy forgot the minus sign.
Here are some of the plotted charts from eleven of the lowest temperatures that have occurred in the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland. since 1961. I’ll add to the charts when I get more time, but as I only have SYNOPSYNOPSYNOP (surface synoptic observations) is a numerical code (called FM-12 by WMO) used for reporting weather observations made by manned and automated weather stations. SYNOP reports are typically mad hourly and consist of groups of numbers (and slashes where data is not available) describing general weather information, such as the temperature, barometric pressure and visibility at a weather station. data back to 1973 I can’t include the ones from the early 1960’s. So to start the show, here are the joint coldest temperatures of -27.2°C from 1982 & 1995.
It’s a shame Braemar has never been a SYNOP station, but the -16°C and 18 cm of snow reported at Dyce, will give you an idea of the condition further up Deeside.I’ve caught the 18-06 minimum temperature at Altnaharra of -27.0°C. The UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy had started to include temperatures to one decimal place by then, so the minimum must have occurred between 06-09, or even later. Similar synoptic conditions to those in 1982, but a much tighter SE’ly gradient, who knows it could have been even colder if the wind hadn’t go up.🤔
December 2024 was a month dominated by very much higher than average pressure in the central North Atlantic (+14 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar). The resulting strong and broad, west southwesterly flow, stretched right from Canada in the west, across the North Atlantic and Baltic, and on into Siberia in the east. There’s little wonder that December turned out to be one of the mildest on record in IONAIONAIslands Of North Atlantic.
Yes I know there's an island called Iona, but this is so I don't have to use the term 'British Isles' when referring to the whole of Ireland and the UK..
Due to the New Year’s revelry we were enjoying until 6am this morning, this story of torrential rain & flooding across N England totally escaped me. Overnight 30 to 50 mm of rain fell quite widely, with more that 80 mm on the Pennines in the 15 hour period until 09 UTCUTCCoordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT). on New Years day, resulting in local flooding across the region.
1 Jan 2025 1230 UTCUTCCoordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT).
A well defined, and remarkably straight, squall line across the southeast of England.
December 2024 ended up with a mean of 6.8°C, that’s 1.9°C above the 1991-2020 LTALTALong Term Average. This is usually defined as a 30 year period by the WMO., making it the joint 12th mildest since 1659.
The view of wave clouds over Ben Wyvis from Culloden (circa 1990)
ChatGPT said:
Yes, lee waves and gravity waves are related phenomena, but they are distinct in their context and characteristics:
1. Gravity Waves
Definition: Gravity waves are oscillations in a fluid medium (e.g., the atmosphere or ocean) where the restoring force is gravity. These waves can occur when fluid layers are displaced vertically and gravity works to restore equilibrium.
Occurrence: They occur in various settings, including atmospheric layers, oceans, or any medium where buoyancy plays a role.
Examples:
Ocean waves created by wind.
Atmospheric waves generated by storms or other disturbances.
Internal gravity waves propagating within stable atmospheric layers.
2. Lee Waves
Definition: Lee waves are a specific type of atmospheric gravity wave that forms when stable air flows over a mountain or similar topographic obstacle. The obstruction forces the air to oscillate vertically, producing a wave pattern on the lee side (downwind side) of the mountain.
Occurrence: They are a subset of gravity waves that specifically arise due to the interaction of airflow with terrain.
Characteristics:
They often result in standing waves that do not move relative to the mountain, giving them a fixed appearance.
Associated with features like lenticular clouds, which form at the crests of the waves.
Can produce turbulence, affecting aviation.
Key Differences
Aspect
Gravity Waves
Lee Waves
Definition
General waves caused by gravity as a restoring force.
A specific type of gravity wave caused by airflow over terrain.
Cause
Broad (e.g., buoyancy, storms, etc.).
Flow of air over topography.
Location
Atmosphere, oceans, or other fluids.
Downwind side of mountains or ridges.
Motion
Can be traveling or standing waves.
Typically standing waves.
Relationship:
Lee waves are a subset of gravity waves, specific to atmospheric conditions involving terrain-induced airflow.
6 Dec 2024 12 UTCUTCCoordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT). Surface analysis MSLPMSLPMean sea level pressure is the pressure at sea level, or, when measured at a given elevation on land, the station pressure reduced to sea level assuming an isothermal layer at the station temperature. falling 10.4 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar in the last 3 hrs at Belmullet (1), with dewpoints of 11°C coming into Valentia (2).
6 Dec 2024 13 UTC 3 hr Pressure Tendencies The central pressure of Storm Darragh may not be explosive cyclogenetic, but 3 hr pressure falls of 12 hPa across W Ireland at present are not to be sniffed at. 🤨 The Belmullet barograph is showing a roller coaster ride 😉
6 Dec 2024 15 UTC Surface analysis Dewpoints of 13°C into SW Ireland. Cold front getting close to Valentia Big pressure fall across Ireland of 10 hPa or more over 3 hrs. Weather buoy K2 goes offline – can you beleive it! No double structures here!!
6 Dec 2024 18 UTC 3 hr pressure changes
6 Dec 2024 21 UTC Surface analysis Big pressure rises at Valentia (1) First signs of very strong northerly to the W of Ireland Sleet at Aboyne (2)
7 Dec 2024 08 UTC Highest overnight gusts It looks like Capel Curig, aka as the Snowdonia wind tunnel, has recorded the highest gust of 81 kts or 93 mph overnight.
7 Dec 2024 09 UTC Total Precipitation [33 hrs] Estimates from weather radar A wet night in many places away from the far SE, with areas of 40-50 mm over high ground of Argyll & Bute, N Ireland, Lake district & Snowdonia,with white pixels indicating >80 mm in wettest places.
7 Dec 2024 09 UTC A selection of anemographs Notice the high gust-mean ratio at Capel Curig. The rapid increase of speed at Crosby at 06 UTC. Inland gale at Yeovilton.
7 Dec 2024 03-14 UTC Total Precipitation [11 hrs] Estimates from weather radar. The heaviest of the rain in Wales seems to have been further W than the AMBER warning area so far, with >80 mm over Snowdonia.
7 Dec 2024 16 UTC Aberporth Still blowing a force 10 NW’ly with gusts of 85 mph. Gale force 8 for 24 straight hours. 😱 That’s where the BBCBBCThe British Broadcasting Corporation (BBC) is the national broadcaster of the United Kingdom, based at Broadcasting House in London. It is the world's oldest national broadcaster, and the largest broadcaster in the world by number of employees, employing over 22,000 staff in total, of whom approximately 19,000 are in public-sector broadcasting. & ITV should have sent their film crews today 😉
7 Dec 2024 19 UTC Max Gusts [mph] You can hear the wind moaning in the bell tower at Notre-Dame… The bells, the bells…
7 Dec 2024 19 UTC 24 hr MSLP difference The pressure is close to 47 hPa higher at Belmullet than it was last night.
Was there a gust of 96 mph or not at Berry head? The original tweet from the UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy has just vanished.
Snow on CairngormCairn GormCairn Gorm (Scottish Gaelic: An CÃ rn Gorm) is a mountain in the Scottish Highlands. It is part of the Cairngorms range and wider Grampian Mountains. With a summit elevation of 1,245 m (4,085 ft) above sea level, Cairn Gorm is classed as a Munro and is the seventh-highest mountain in the British Isles..
A very bland kind of month temperature wise across much of NW Europe. In the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland. a mild first half to November was cancelled out by a colder second half. The central Atlantic was above average, but both to the north and south it was a little colder than average.
Higher than average pressure in a band from southern Greenland, across Iceland (+9 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar), the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland. and down into Italy, with lower than average pressure south of Newfoundland (-11 hPa) and the Barents Sea, helped produce a drier than average November across large parts of the UK.
Despite a pause for much of July, and another at the end of August that lasted into the first week of September, the 2024 tropical cyclone season in the North Atlantic ended up being quite a busy affair, thanks in a large part to a very active September & October, and of course SSTSSTSea Surface Temperatures in the Atlantic, Caribbean and Gulf of Mexico being at all time record highs.
I haven’t examined all the forecasts that predicted a record breaking season, but I’m sure that 2024 ended up being a bit of a disappointment, despite the record SST.
As far as the raw statistics of the matter were concerned I made it â—¾The joint 5th for number (two category 5) â—¾The 22nd for total ACEACEAccumulated cyclone energy (ACE) is a metric used by various agencies to express the energy released by a tropical cyclone during its lifetime. It is calculated by summing the square of a tropical cyclone's maximum sustained winds, measured every six hours. The resulting total can be divided by 10,000 to make it more manageable, or added to other totals in order to work out a total for a particular group of storms. (162.5) â—¾The 31st for total longevity (99 days) â—¾The 54th for total distance (27,127 NM) All data is of course provisional until the HURDAT2 data series is updated next spring.
Added a bit more logic to the Extremes viewer in my Reanalysis MSLPMSLPMean sea level pressure is the pressure at sea level, or, when measured at a given elevation on land, the station pressure reduced to sea level assuming an isothermal layer at the station temperature. application to distinguish if the centre of the vortices it found, be it high or low, was on the edge of the chart. Here are the results from all Decembers back to 1948.
I’ve just added a search routine to find the lowest and highest MSLPMSLPMean sea level pressure is the pressure at sea level, or, when measured at a given elevation on land, the station pressure reduced to sea level assuming an isothermal layer at the station temperature. in a given rectangular area for any period back to 1948 from reanalysis data I’ve downloaded. It was not too difficult to do in code, except when the area spanned the Greenwich meridian! Unfortunately the grid is rather coarse at 2.5° x 2.5°, but it suffices because the amount of data for a finer grid would be enormous. Here are the results I’ve generated for the highest and lowest MSLP around the British Isles for all Novembers back to 1948. The latest reanalysis data I have only extends to the 19th of November this year, so it may well be that storm Bert has beaten the 950.8 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar from 2010 in the last few days.
Highest MSLP November 1948-2024Lowest MSLP November 1948-2024
Just a compilation of posts to my new Blue Sky account of this week long early cold spell across the country.
15 Nov 2024 1500-2100 UTCUTCCoordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT). Temp changes I generated this chart to see how the cold air was progressing into the NW behind the cold front. Then I noticed just how quickly this evening had cooled across S England under near perfect radiation conditions.
15 Nov 2024 06-20 UTC Precipitation Totals Estimates from weather radar. Just 0.6mm of rain from cold front in StrathpefferStrathpefferStrathpeffer (Scottish Gaelic: Srath Pheofhair) is a village and spa town in Easter Ross, Highland, Scotland, with a population of 1,469..
16 Nov 2024 1112 UTC 1097 M Snow already starting to accumulate on the Cairngorms at 1097 M. It’s -3°C at 1245 M so freezing level ~500 M 🤔
16 Nov 2024 2153 UTC Some snow in these heavier showers on the Velux windows in Strathpeffer.
18 Nov 2024 1610 UTC Looking down from the Nevis range over Ft William & the top end of Loch Linnhe if I’m not mistaken. It looks like the SW end of the Great Glen has been in fog all day.
18 Nov 2024 NASANASAThe National Aeronautics and Space Administration is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. Worldview You can see the extent of the snow cover across the N of Scotland this lunchtime. Loch shin stands out very sharply.
18 Nov 2024 21 UTC Surface analysis An absolutely fascinating chart, I wish I had more time to analyse it more properly. It’s already -8.3°C at Glascarnoch, beating this mornings -7.8°C at Tulloch Bridge, and it’s on[y 21 UTC.😮 Heavy snow at Waddington 🤔
16-19 Nov 2024 12 UTC Temp anomalies The cold air has slowly extended further and further S each day since Saturday.
19 Nov 2024 1445 UTC The sky has grown very dark in Strathpeffer as it fills in with CBCBCumulonimbus cloud. Well-developed cumulonimbus clouds are characterized by a flat, anvil-like top’s coming down from the N. It’s an active trough and deep convection, with thunderstorms in the Moray Firth. It’s just started to snow – big flakes – vis down t0 800 M.
20 Nov 2024 0855 UTC Strathpeffer A good ~4 cm level snow cover from overnight snow showers which continue this morning. The old wives tale that temperatures increase when it starts to snow are true this morning 🤔
20 Nov 2024 12 UTC Strathpeffer-Knockfarrel Plenty of CB coming down from the N but moving fairly rapidly. An icy wind & a little drifting on the top. Still sub-zero this lunchtime 5 cm of snow lying.
20-29 Nov 2024 12 UTC 2M Temp anomalies ECMWFECMWFThe European Centre for Medium-Range Weather Forecasts is an independent intergovernmental organisation supported by most of the nations of Europe. It is based at three sites: Shinfield Park, Reading, United Kingdom; Bologna, Italy; and Bonn, Germany. It operates one of the largest supercomputer complexes in Europe and the world's largest archive of numerical weather prediction data. Its lasted a full week in N Scotland not bad for an early cold spell. It’s a winter wonderland in Strathpeffer today, with a max of just 0.2°C so far. I imagine the kids will be sledging down the golf course shortly.
20 Nov 2024 1630 UTC Snow showers all day long in Strathpeffer, despite the fact that we’re 100 km away from the N coast of Scotland. I’ve just measured 10 cm of lying snow by the traditional Met OfficeUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy method of the mean of 3 measurements. 😉
20 Nov 2024 2345 UTC Quite sharp pressure falls & an ominous blob of cloud on the IR satellite imagery, combined with a lot of mod/heavy ppn across the N of Sutherland at the moment.
21 Nov 2024 08 UTC Snow Depths Certainly much deeper than 14 cm just after midnight, but temps rose from -3°C to 1°C and the snow turned sleety from 02 UTC. Still only 0.7°C with some light snow in Strathpeffer.
21 Nov 2024 09 UTC Surface analysis This cold warm front solution seems to kind of fit the weather we’ve seen in Strathpeffer overnight.
21 Nov 2024 07 UTC (31 hr total) Total precipitation Estimates from weather radar Most of this, inland at least, fell as snow. Estimates look a bit too high.
21 Nov 2024 1040 UTC It’s snowing again in Strathpeffer, although you can’t see it so well in this webcam image. Temperature dropped back to 0.3°C. It’s a rather nasty day out there all in all. But it’s not over to the fat lady starts to sing. Apologies to any fat ladies out there 😉
Higher than average pressure across southern Greenland and central Russia, with lower than average pressure in the central North Atlantic help produce a fairly strong SW’ly mean flow for the month across the British Isles. The track of a number of tropical cyclones helped dig a path of lower anomalies from Florida by the look of it too.
00 UTCUTCCoordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT). 16 Oct 198706 UTC 16 Oct 1987
Only three hourly Synops I’m afraid, and many of them missing from the worst affected regions. At a glance, and from this limited SYNOPSYNOPSYNOP (surface synoptic observations) is a numerical code (called FM-12 by WMO) used for reporting weather observations made by manned and automated weather stations. SYNOP reports are typically mad hourly and consist of groups of numbers (and slashes where data is not available) describing general weather information, such as the temperature, barometric pressure and visibility at a weather station. data, although it looked a pretty windy night, you wouldn’t have thought it had been as severe as it was across the southeast of England. I’ve no idea if my hind sight analysis was anywhere close to the analysis on the day. I was an observer at Kinloss at the time, and missed all the excitement after being posted to Scotland that summer.
Christmas Day 12 UTCUTCCoordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT). 1979-2023
This post is more of a reminder to myself about an application I wrote to display a grid of charts it downloads from Wetterzentrale. You can choose to display CFSCFSThe Climate Forecast System or coupled forecast system (CFS) is a medium to long range numerical weather prediction and a climate model run by the National Centers for Environmental Prediction (NCEP) to bridge weather and climate timescales. Version 2 became operational as CFSv2 in 2011., ERAERAERA stands for 'ECMWF Re-Analysis' and refers to a series of research projects at ECMWF which produced various datasets (ERA-Interim, ERA-40, etcetera). or NOAANOAANOAA is an agency in the Department of Commerce that maps the oceans and conserves their living resources; predicts changes to the earth's environment; provides weather reports and forecasts floods and hurricanes and other natural disasters related to weather. reanalysis charts either as charts of isobars overlaid over colour filled contours of 500 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar heights, or as charts of isolines of 850 hPa geopotential heights, overlaid on colour filled contours of 850 hPa temperature. I think it produces a pretty useful grid of charts to view a month, or a season, but in truth I haven’t used it that much in the last 12 years. The example above displays surface pressure charts for Christmas day.
Winter [DJFDJFMeteorological Winter comprising the months of December, January & February] 1962-63
The grid of images above, is for daily MSLPMSLPMean sea level pressure is the pressure at sea level, or, when measured at a given elevation on land, the station pressure reduced to sea level assuming an isothermal layer at the station temperature. and daily 500 hPa geopotential heights for each day of the infamous winter of 1962-63.
The other innovative thing that I added to the application, was a colour analyser (above image). This does a lookup on the colour of each pixel across the map of the British Isles in the downloaded image, and calculates an overall average which it uses to plot a graph and fill a table with the daily 850 hPa temperature or the 500 hPa geopotential height. A crude but quite effect way of gauging just how warm or cold it is on any given day. There are problems with the app, but out of my control, in that Wetterzentrale for some years, use a slightly different resolution and size for their images. I could fix it but it’s fiddly. They also seem now not to load the ERA reanalysis images on their server. Who knows for how much longer they’ll maintain the CFS and NOAA images, it would be a real loss if this went.
Unusually high pressure in September to the southwest of Iceland and Greenland (+8 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar) and across Ukraine (+11 hPa). This effectively neutralised the usual Icelandic low, effectively pushing a band of lower pressure from northern France to the Black Sea. That left the British Isles in a col as far as mean pressure for the whole month was concerned, which doesn’t quite tell the whole story.
Anomalies of -15 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar to the SE of Iceland displaced the usually shallower Icelandic low east to produce a broad SW’ly flow across the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland. and Ireland during August. The semi-permanent Azores high remained with pressure a little higher (+2 hpa) than average enhancing the flow.
The Met OfficeUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy have just introduced a new feature to their forecasts you find on their weather app or on their website. As well as including the probable daily maximum and minimum temperatures for the next seven days, they also now include values for the highest and lowest possible temperatures for that day too. The BBCBBCThe British Broadcasting Corporation (BBC) is the national broadcaster of the United Kingdom, based at Broadcasting House in London. It is the world's oldest national broadcaster, and the largest broadcaster in the world by number of employees, employing over 22,000 staff in total, of whom approximately 19,000 are in public-sector broadcasting. do the same thing in their forecasts, but as far as I know, it remains hidden and unused in the HTML. Personally, I can’t see what benefit this ‘fudge factor’ is to any forecast, other than adding a degree (pardon the pun) of uncertainty to the end user – which temperature is it going to be today or tonight, probable or possible? It also makes a bit of a nonsense of having fixed hourly temperatures, which remain presumably of the ‘probable’ variety. I’ve been doing some verification work on forecast three hourly temperatures over the past year, and I’ve found their forecast temperatures vary dramatically from the actual reported values beyond T+36. It’s a little bit early but I’ve not noticed any significant improvement since I started using the new beta data. All I can say is if that people do complain to them about the accuracy of their temperature forecasts in the future, this will be a very neat way of getting them out of a fix. 🤨
Here are some random images, tables and animations that I posted regarding Storm Lilian to my Twitter account @xmetman. Nothing particularly devastating about the winds or the rain from the storm itself, which the Met OfficeUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy should really have never named. It was gone in a flash, and although there were gusts in excess of 70 mph on the Lancashire coast, only eight SYNOPSYNOPSYNOP (surface synoptic observations) is a numerical code (called FM-12 by WMO) used for reporting weather observations made by manned and automated weather stations. SYNOP reports are typically mad hourly and consist of groups of numbers (and slashes where data is not available) describing general weather information, such as the temperature, barometric pressure and visibility at a weather station. stations recorded a gale. Gale Index wise the storm didn’t register above the 200 mark because of its size, with the extratropical cyclone that had been Hurricane Ernesto scoring much higher earlier in the week. I should have written a piece about Ernesto, but when you have so few followers as I have, I thought what’s the point 😪
Pressure was lower (-3 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar) close to the Azores during July, with higher than average pressure to the west this displaced the usual Azores high further west in the North Atlantic. This, combined with much lower than average across Greenland and Iceland, resulted in a fairly strong mean zonal W’SW flow across the Atlantic for the time of year, running from Canada to the Baltic across the British Isles.
Despite central England temperature series being a composite temperature from three separate sites, it’s still possible to use the UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy 25°C heatwave temperature as the threshold to calculate a heatwave day in Central England, and thereby calculate the number of three day consecutive days that have occurred there since 1878. I added this functionality to my Daily CETCETCentral England Temperature application a number of years ago, and have recently added a second method of using the maximum anomaly to do it, rather than by using a fixed temperature. At the same time I gave it all a bit of a spring clean, hopefully it’s still accurate. 🤞 The program allows you to adjust the threshold from 25°C to 30°C, and the anomaly from +6°C to +10°C, it also allows you to change the number of consecutive days from 3 to 7.
If you plot a bar chart for the number of heatwave days since 1878, as I’ve done with an accompanying 5 year centred average and linear trend, you’ll see that the number of days >=25°C has increased from 4.6 days to 10.8 days in the intervening 146 years.
The most number of distinct heatwaves (using the 25°C and three consecutive days or more rule) in a single year was six and occurred in both 1911 and 1995. The most number of heatwave days in any one year was 33, and occurred in 1976 and 1995.
The longest heatwave I found, using the 25°C and three consecutive days or more rule, was 16 days which occurred in the golden summer of 1976, between the 23rd of June and the 8th of July 1976 this was closely followed by the 15 day heatwave covering an almost identical period in 2018.
The results using anomalies are a horse of a different colour and a story for another day. Suffice it to say I used the 1878-2023 LTALTALong Term Average. This is usually defined as a 30 year period by the WMO. as a level playing field to produce the results in the table below. The year 1995 still ends up with most heatwave days of 32, and 1976 the longest run of anomalies of 6°C and higher of 16 days.
