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.
October 2024 – Mean Pressure Read More »
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 CFS, ERAERA ERA 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 NOAANOAA NOAA 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 hPahPa A 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.
The grid of images above, is for daily MSLPMSLP Mean 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.
Winter 1963 – Daily MSLP and 500 hPa heights Read More »
Unusually high pressure in September to the southwest of Iceland and Greenland (+8 hPahPa A 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.
Sep 2024 – MSLP Anomalies Read More »
Anomalies of -15 hPahPa A 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 UKUK The 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.
August 2024 – MSLP Read More »
Pressure was lower (-3 hPahPa A 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.
Much lower than average pressure to the north (-8 hPahPa A Hectopascal is the SI unit of pressure and identical to the Millibar), and higher than average pressure in the central Atlantic (+5 hPa), produced a W’NW flow and lower than average temperatures across IONAIONA Islands 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..
June 2024 – Mean Pressure and anomalies Read More »
Mean pressure across IONAIONA Islands 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. in May was around 3 hPahPa A Hectopascal is the SI unit of pressure and identical to the Millibar below the LTALTA Long Term Average. This is usually defined as a 30 year period by the WMO.. In fact lower than average pressure was strung out westward across the central Atlantic all the way to the United States. Mean higher than average pressure persisted across Scandinavia (+6 hPa) resulting in a very slack pressure pattern across the country.
May 2024 – Mean Pressure & anomalies Read More »
The resident Icelandic low for April was displaced southeastward again this month by higher than average pressure across Greenland, and lower than average pressure in the northern North Sea, leaving the British Isles in a slack cyclonic westerly flow on the mean pressure chart.
April 2024 – MSLP Read More »
Look no further for a reason for all the depressing cloudy, mild & wet weather in March 2024. The anomalous Icelandic low that’s a resident feature of anomaly charts in any month of the year, decided to take a holiday.
March 2024 – MSLP anomalies Read More »
February 2024 was a cyclonic month across the IONAIONA Islands 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., with a strong broad W’SW gradient that stretched from central Atlantic into northeast Russia. The Icelandic low was elongated further east into the northern Norwegian sea (-9 hPahPa A Hectopascal is the SI unit of pressure and identical to the Millibar), and the Azores high displaced to the southeast towards the Canaries (+4 hPa). Mean MSLPMSLP Mean 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. was below normal across the whole of IONA by as much as -9 hPA in northern Scotland.
February 2024 – Circulation Read More »
Temperatures across IONAIONA Islands 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. were close to average in January. I suspect the mean MSLPMSLP Mean 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. chart is not telling us the full story, because with a mean flow like this, you might have expected temperatures to have been well above average.
If you turn up the granularity the pentad mean pressure charts reveals why January wasn’t much milder. The 7th to 11th was cold and anticyclonic, the 12th to 16th NW’ly and the 17th to 31st was a milder W or SW’ly.
January 2024 | Circulation Read More »
It looks like this January (2024) could turn into a very anticyclonic month from this weekend, so I thought I would take a look back in the objective LWTLWT Lamb Weather Types are often used in UK-based analyses, with individual weather patterns based on the eight primary cardinal directions (N, NE, E, SE, S, SW, W, NW) plus cyclonic (C), anticyclonic (A) and unclassified (U) types. records, which started in 1871, and found that January 1992 was the most anticyclonic on record., although despite it being so anticyclonic, it never really managed to generate more than a few easterly days at the start of the third week.
MSLPMSLP Mean 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. that month across the UKUK The 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. got close to 1050 hPahPa A Hectopascal is the SI unit of pressure and identical to the Millibar on the 26th as you can see from the chart for 12 UTCUTC Coordinated 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)., the highest on that chart was 1049.0 hPa at Cynwyd in Denbighshire. I only have main synoptic hour data so it may have broken through 1050 hPa. Notice that they’re also plotted SYNOPSYNOP SYNOP (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. reports from Cape Wrath, Butt of Lewis and Binbrook on that chart, those were the days 😉
One other point about January 1992 is that it was also a El NinoEl Niño El Niño 'The Boy' is the warm phase of the El Niño–Southern Oscillation and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific month.
The most anticyclonic January – 1992 Read More »
At a glance it looks like MSLPMSLP Mean 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. across the UKUK The 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. in 2023 was more often below average than it was above. There were a couple of notable anticyclonic spells in January and February, and again from mid May into Mid June, but that was about it, with extended cyclonic spells in January, March, July and from mid October to mid November.
Mean Sea Level Pressure – 2023 Read More »
MSLPMSLP Mean 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. anomalies in December were not too dissimilar to those of November, with the Icelandic low pushed further south into mid-Atlantic by higher than usual pressure across Greenland. Pressure was lower than average across the 55N latitude from Scotland east into the southern Baltic(-8 hPahPa A Hectopascal is the SI unit of pressure and identical to the Millibar) and higher than average (+5 hPa) to the west of Portugal. This all added up to a tight W’SW flow from the central Atlantic across England and Wales, and eastward on into Germany and Poland. All a result of a south shifted jet stream for much of the month.
Circulation – December 2023 Read More »
In November it looks like the semi-permanent Icelandic low decided to do some early Christmas shopping and head southeast towards Scotland. Thanks to blocking, from Greenland across to northern Scandinavia, for much of the month, anomalies were low from Denmark to eastern Russia (-12 hPahPa A Hectopascal is the SI unit of pressure and identical to the Millibar) and higher (+8 hPa) to the northeast of Iceland. Much of the cyclonic activity in the first half of the month took place at latitude 50° north, the North Atlantic’s answer to the roaring forties. 😉
Here’s a closer look at the daily charts and associated LWTLWT Lamb Weather Types are often used in UK-based analyses, with individual weather patterns based on the eight primary cardinal directions (N, NE, E, SE, S, SW, W, NW) plus cyclonic (C), anticyclonic (A) and unclassified (U) types. and GIGI Gale Index.
November 2023 – Mean Pressure Read More »
October 2023 – MSLP Read More »
I had never heard what an Hovmöller diagram was until I watched the Deep Dive video produced by the Met OfficeUKMO The 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 and put out on their Youtube channel yesterday. The Hovmöller diagram was first introduced by Ernest Aabo Hovmöller (1912-2008), a Danish meteorologist, in a paper that he published in 1949. I had seen charts like it before used to display climate data, but hadn’t realised that they had a name. In reality they’re very similar to a heat map as far as I can see, but I decided to see if I could reproduce one in software that was as similar as possible to the one that Alex Deakin showed.
As you can see the X-axis displays values of longitude for a fixed line of latitude, in this case 55° north. The Y-axis displays dates over the last month. In the Hovmöller diagram above I’ve displaid MSLPMSLP Mean 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. values from six hourly reanalysis data. It clearly shows various anticyclonic spells in red and hot spots of cyclonicity in blue. I think it will come in very handy as another way of looking at global MSLP or temperature climate data over a longer period although I’ve still to write the code for that😉
Hovmöller diagram Read More »
I was watching the Deep Dive video produced by the UKMOUKMO The 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, and presented so well by Alex Deakin about the weather in September 2023 on Youtube as you do. He showed two anomaly charts for MSLPMSLP Mean 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., one for the first half of September and the other for the second half that showed how anomaly charts for the whole month can sometimes be misleading. In this case it was how the remarkable warm spell in the first half of the month contrasted with the more mobile second half. The resulting anomaly chart for the whole of the September cancelled out the anticyclonic SE’ly in the first half that brought all the high temperatures.
September 2023 – When anomaly charts hide the real picture Read More »
A classic mean pressure chart for September that bears a striking resemblance to charts of mean pressure for the whole year that you might see in many geography textbooks. Pressure was much lower across the eastern Atlantic (-5hPa) than usual, and much higher across the Ukraine and eastern Russia (+6hPa), resulting in a fairly strong SW’ly flow across the country.
September 2023 – Mean MSLP Read More »
It’s easy to see why August 2023 was such an unsettled month across Ireland and the UKUK The 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. with temperatures just below the average when you study the MSLPMSLP Mean 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. anomalies.
August 2023 – Circulation Read More »
As always the mean pressure chart can reveal a lot about the weather, and in July 2023 it showed why it was so wet and changeable, with near average temperatures across the British Isles. It’s also apparent from it why Iceland was so cold due to the squeeze in the pressure gradient between higher than average pressure across Greenland, and lower than average pressure across NW Europe, resulting in a persistent and strong N or NENE North East flow of air across the island. It’s not so revealing about the causes of the heatwave across North Africa, which happened in a very slack pressure field in a ridge of high pressure that extended eastward into the Mediterranean from the Azores high.
July 2023 – Mean Pressure & anomalies Read More »
Well the first thing to say is that low’s are not at all unusual in August. Remember the Fasnet storm of 13 August 1979? Tomorrow’s low has a forecast central pressure of 983 hPahPa A Hectopascal is the SI unit of pressure and identical to the Millibar for midday and is situated close to Birmingham. Below is a graphic of charts drawn using reanalysis data from 1948 so you can make your own minds up. The one that immediately stands out to me is the chart for the 2nd of August 1986, with a GIGI Gale Index of 38. Remember this chart uses reanalysis data in a coarse 2.5°x2.5° grid of MSLPMSLP Mean 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. values so contours may well be lower.
It just so happens that I have this chart, but as you can see the low close to Tiree is already a filling feature, with a minimum central pressure of 988 hPa at 06 UTCUTC Coordinated 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)., and can’t match the forecast depth of tomorrow’s low. So tomorrow’s low looks very unusual, and is likely the deepest low to affect the UKUK The 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. on this date in over 75 years!
2 August 2023 – How unseasonable is Wednesday’s low? Read More »
