Bartlett Highs in general and when they occur

[North-Easterly Blast]

Looking at charts, a Bartlett High only seems to develop during the winter months. To help anyone understand what I mean I would refer to a Bartlett as a high pressure area that sits over France, Spain or the Bay of Biscay, no further north than the north of France. You only seem to see these patterns develop in the winter months, and you never see a Bartlett in the summer months. Does anyone know why this is?

The closest you possibly get to a summer Bartlett with a chart in the summer months resembling a winter Bartlett High is when ridges of high pressure cross southern UK in between lows moving east across the UK giving the north / south split, of rain for the north but drier further south.

On the other hand, many people confuse a Bartlett with a Euro High. To explain the difference I would refer to a Euro High as a high pressure area that sits over central or eastern Europe with possibly a ridge over the UK. As Bartletts only seem to develop in the winter, a Euro High seems to be able to develop at any time of the year. A Euro High with a ridge over the UK is what brought the heatwaves of August 2003, July 2006, and of summer 1995. A Euro High has also been largely responsible for much of the warmth of this April. With increased solar radiation by this time of the year, the persistence of the Euro High this month has allowed very warm conditions to build up over the UK and Central Europe. Whereas these type of Euro Highs do occur during the winter months too, such as in late December 1992, February 1993, mid January 2001, February 2003 and this type of pattern also brought the cold temperature inversion of early February 2006.

Can anyone explain the reason why only the winter months see Bartlett Highs, whereas any time of the year see Euro Highs?

[North-Easterly Blast]

It is also true to say that, very similar to the summer Azores High ridge over the UK, that setup does also occur in winter too. Last December was an example of when a displaced winter Azores High became a mid-latitude ridge over the UK. The winters of 1991-92 and 1992-93 were characterized by a mid-Atlantic Azores ridge displaced NE over the UK with the jet in a zonal position to the north of the UK. Months also like January 2001 and February 2003 featured the Euro High.

[Summer of 95]

To help anyone understand what I mean I would refer to a Bartlett as a high pressure area that sits over France, Spain or the Bay of Biscay, no further north than the north of France. You only seem to see these patterns develop in the winter months, and you never see a Bartlett in the summer months. Does anyone know why this is?

Has the definition of a Bartlett changed over time? When I first encountered the term on uk.sci.weather about 4 years ago it was defined as an Azores High extending to Biscay and sometimes the Alps area, it did not have to be centered over France although those that did still qualified. As for Euro High, I often think of that as an overgrown Bartlett, sometimes the result of a Bartlett merging with a pre-existing high over SE Europe or southern Russia (never Scandi though). I thought I would be able to find examples of summer Bartletts (using the uk.sci.weather definition) in Wetterzentrale charts post-1988; here are a few dates:

10th June 2002: Azores extending to France/Spain: UK under deep low

11-15 Aug 2002: repeatedly tries to join with one over the Black Sea to make a Euro High but a stubborn low over Poland/Czech Rep area stops it (I remember this area getting some serious flooding caused by that low) in the end gives up and turns NE and gets as far as Denmark- leaving the UK except the far SE in no-mans land throughout.

17-21 June 1998: migrated until it ends up centered over the Alps; on 21st-22nd a new Azores forms which also launches Bartlett extensions into Europe until the 25th; all the time the UK is under depressions.

19-20 Aug 1994: another Azores launching Bartletts although not very strong ones (1015-1025mb): low between Britain and Iceland; moist westerlies. The following week there are more Azores extensions to France/Spain briefly forming a Euro on 27-28th; lows pass close to or over Britain all the time.

1-15 Aug 1992: strong Azores high repeatedly throws Bartletts into SW Europe; at times they meet another high wandering around between Russia and the Balkans to make Euros; however Britain plagued by a series of lows with only brief (~24hr) ridges in between.

24 Aug 1992: that's a Bartlett if ever I saw one! 25th-28th reaches all the way to Turkey; huge low covering Britain, Norway and Iceland. August 1992 one of the worst summer months I can remember in Britain, easy to see why.

[North-Easterly Blast]

Many thanks for quoting dates when a summer Bartlett High occurred.

I started this thread to question why we hardly ever see weather charts in the summer months that resemble / look virtually the same as the Bartlett winter charts of 1988-89, Jan/Feb 1990, Feb 1998, Jan/Feb 2002 and Jan 2007.

In winter in the UK, well nowadays and for the last twenty years a Bartlett High and an Icelandic low and SW'lies across the UK has become a familiar chart, but does anyone else know of any more that occurred in the summer. I find it so strange as to why it is rare to see a weather chart in the summer months that show a Bartlett High / Icelandic low and SW'lies over the UK.

I mean to say that weather charts in the summer months often feature an Azores ridge across the UK, weak lows to the north and to the south of it, or a more meridonal Atlantic flow with lows over the UK rather than a flat jet and a Bartlett High. Why is this?

In the past cooler than average summer months such as the very cool wet July of 1988, have often been characterized by "cold zonal" looking charts, and a meridonal Atlantic flow, similar to the "cold zonal" setup in January 1984, but why is it that summer months are rarely charcterized by "mild zonality" and a Bartlett High and SW-NE tracking lows across the UK, similar to the setups of last winter 06-07, and the very mild winters of 88-89, 89-90 and 97-98.

[BrickFielder]

As autumn approaches Canada cools down, due to slow ice build up to the north of the UK the result is a high pressure area developing over Canada with a strong ridge. This leads to a mid atlantic trough as cold air spills out of canada and meets warm gulf air which spins up low pressure systems. These are quite intense systems usually because of the temperature differences and tend to blaze across the Atlantic flattening the Azores high pressure into a ridge towards spain. This is a difficult pattern to dislodge and usually takes either high pressure ridging out of siberia or a stratospheric warming to shift.

During summer the temperature differences are less and so the low pressure systems spinning up tend to have less power. Hurricanes and tropical depressions can affect this as can the atlantic tripole/bipole SST (Sea Surface Temperature) Pattern. The current Atlantic SST pattern is for cool water of the eastern seaboard of the US which tends to give a cut off low towards Spain and high pressure towards greenland. Warm water of the coast of the US tends to give us more of a Bartlett pattern. This pattern changes over multidecadal (multiples of 10 years) periods. This is why I think bartlett pattern are less common (still possible though) during current summers.

Edited April 26, 2007 by BrickFielder

[Thundery wintry showers]

I always think of June 2002 as having been quite a Bartlett-dominated month. South-westerly winds blew almost without a break, and here in the North East the month was quite warm in spite of the frequent cloudy wet conditions- and entirely due to high minima.

The average minimum for June 2002 at Durham was the highest since 1982.

July 1985 had frequent south-westerlies and a pronounced north-west/south-east split, with the southeast having a fairly warm sunny month, and the north having a very dull wet month, as part of what was a very dull wet summer. I'd say June 1976 and August 1989 often had a Bartlett in occupation as well, though in those cases high pressure was often further north, resulting in the warm sunny weather affecting most of England & Wales.

[North-Easterly Blast]

A high pressure moving north to cover the British Isles is therefore not a Bartlett High. These Azores ridges will give warm dry conditions in summer and frequent fogs in winter, sometimes with temperature inversions such as in the 1991-92 winter and in early February 2006 and in December 2006.

Also what is the current situation with stratospheric warming / cooling? Has there ever been significant stratospheric warming / cooling events before in the past in years gone by?

[Summer of 95]

A high pressure moving north to cover the British Isles is therefore not a Bartlett High. These Azores ridges will give warm dry conditions in summer and frequent fogs in winter, sometimes with temperature inversions such as in the 1991-92 winter and in early February 2006 and in December 2006.

Also what is the current situation with stratospheric warming / cooling? Has there ever been significant stratospheric warming / cooling events before in the past in years gone by?

I think of the 1991-2 and Jan/Feb 2006 anticyclonic charts as different to the classic Bartletts like Feb 1998 and Jan 2005; the late Jan 1992 one I'd be tempted to say is a Scandi High displaced 1000 miles southwest, rather than an Azores one displaced 1000 miles northeast like the Feb 1998 one was. I say this because going through the charts it sems to be as much of continental as Atlantic origin, and at one point reaches 1045 mb; while this is not uncommon with Scandi, Siberian and Greenland highs an Azores/Bartlett one seldom hits 1040, often not even 1030. (Feb 1998 peaks at just over 1035). Of course I remember well the difference in the weather- Jan 1992 frosty and foggy with some ice days; Feb 1998 warm and sunny with temps hitting the high teens- fully 20C warmer at its peak than the 1992 one was- surely a sign that they were different airmasses of different origin and classification?