Lettucing Gutted

1740 was indeed the coldest year on record in Britain. However September 1740 was surprisingly warm with a C.E.T of 14.0c. It was also only 0.7c cooler than August 1740.

Thank you for the data Mr_Data. Sorry warm weather lovers but if I wanted to go back in time, I would go back to 1816. This was a phenomenally cool year in Britain due to Indonesia's Mount Tambora volcano erupting in 1815. It appears there was a dramatic 6.4c temperature drop between October 1816's slightly cool 10.3c and November 1816's very cold 3.9c. It seems that 1816 and 1879 were two of only a few years in the last 1000 years in Britain not to have a single month equal to or above the 1960-1991 C.E.T averages for Britain.

Does anyone know the C.E.T for every month in 1816? It would be interesting to know because there might have a few months that were slightly "warmer" than average.

Another example of a warm October followed by a cold December is found below:- 1996 October 11.7c > 10.6c 1960-1991 C.E.T December 2.9c < 4.3c 1960-1991 C.E.T

There are two other examples of a "White Christmas in a mild winter". These are Christmas 1993 and Christmas 2004. See the website listed below for more information on those Christmases:- http://www.personal.dundee.ac.uk/~taharley...in_december.htm

The Santa Ana wind I know it sounds a bit of a paradox having "hot Northeasterlies" Nick F. However the Santa Ana's source regions - The Great Basin and Colorado Plateau are very high up and are positioned between The Rockies in the east and The Sierra Nevada Mountains in the west. This means that any cold wind that develops up there has to travel downslope to Los Angeles in Southwestern California. All downslope winds experience adiabatic heating. Adiabatic heating is caused by downslope winds moving from a low thickness tropospheric layer (500mb in the middle troposphere and on a high plateau) to a high thickness tropospheric layer (1000mb at sea level). The movement of air from a low to a high thickness layer compresses the air that is descending from the high plateau to the sea level. Compression generates Adiabatic heating - a non-solar heating effect on the downslope wind. To understand the heating effect of compression you have to think of the warmth that is generated by inflating a car tyre with air. The valve on a car tyre feels very warm after it has been inflated. Another example of generating heat by compression is by increasing the air pressure in a pressure cooker. In a downslope wind - compression causes the air molecules to move closer together in descending air as it descends from the middle troposphere to the surface. As the air molecules move closer together - friction caused by the colliding air molecules generates heat. The Western Sierra Nevada Mountain slopes - which the Santa Ana downslope wind MUST descend are very high and steep. This means that the adiabatic heating effect usually warms the Santa Ana's maximum air temperature from a max of about -5c on the High Sierra Nevada Mountain slopes to a max of at least +30c in all seasons by the time the Santa Ana wind reaches Los Angeles, California. The above adiabatic heating process modifies the Santa Ana downslope wind in all seasons UNLESS the High Sierra Nevada Mountains are unusually very cold. When the air temperature on top of the High Sierra Nevada Mountains is unusually cold for example -20c - adiabatic heating would only rise the maximum temperature in the Santa Ana wind to maybe a max of 17c in the winter in Los Angeles and a max of 24c in the summer in Los Angeles. For more information on the Santa Ana wind follow the website link listed below:- http://www.islandnet.com/~see/weather/alma...06/alm06sep.htm The Shamal (Seistan) wind Another example of "hot Northerlies" is the hot, humid and dusty Shamal (Seistan) Northwesterly winds that effect Afghanistan and the Middle East in the summer. In the winter the Shamal (Seistan) Northwesterly winds produce cool, dry and dusty weather in the Middle East and Afghanistan because the Shamal is an extension of the Maritime Arctic Northwesterly winds from Greenland. However in the summer the Shamal (Seistan) Northwesterly wind picks up heat and moisture as it crosses the hot Persian Gulf and hot Red Sea. The maritime modified Shamal Northwesterly wind brings hot, humid and dusty weather to the Middle East and Afghanistan in the summer. For more information on the Shamal and Seistan winds follow the website link listed below:- http://www.netweather.tv/forum/index.php?s...9&hl=Shamal

I wish we would get a proper autumn again like that one... :unsure:

Southwestern California's Santa Ana northeasterly wind is often hot - even in the winter. However according to this website there were unusually COOL Santa Ana winds in November in Southwestern California. B) http://www.topix.net/content/trb/387303151...327800901494139 Does anyone have any theories as to why the Santa Ana wind was so cold?

Yeah thank you Brick the pages on the warm and core systems was a very interesting read. :lol: I just have something extra to add about an anonomly in Siberia. The upper low that exists above the cold cored Siberian High Pressure System in Siberia in winter causes high level rising motions due to positive vorticity in the upper troposphere that allow high level Cirrus and Cirrostratus clouds to form via adiabatic cooling. These clouds produce very cold but light diamond dust snowfall. Anomalously in the Siberian winter these clouds also slightly offset radiational cooling over Siberia as well by absorbing long wave radiation from the surface and re-radiating it back to the surface.

A couple of questions about warm and cold core systems:- -In a warm core high is there subsidence from the lower stratosphere right down to the ground? -In a warm core low is there uplift in the lower troposphere but subsidence in the upper troposphere and the lower stratosphere? -In a cold core low is there uplift from the ground right up into the lower stratosphere? -In a cold core high is there subsidence in the lower troposphere but uplift in the upper troposphere and the lower stratosphere?

As BBC weatherman Paul Hudson said back on 22nd August 2000: "I've never seen anything like. This was a mother of a storm". B)

A similar process (Icy downdrafts) to this must have allowed a thunderstorm that traveled northeast from North Wales to Northeast England to dump some snow at Hedon, East Yorkshire on the 21st August 2000! In The Mirror Newspaper on the 22nd August 2000 there was a picture of snow on the ground and a snowball fight! There is also a picture of a snowman!!!! Elsewhere on that August day there was six inch thick accumulations of hail on the North York Moors in addition to flooding from an hour long "monsoon deluge". York railway station was hit four times by lightning causing disruption to train services whereas a 50 foot wide waterspout formed off the Lincolnshire Coast near Cleethorpes which then swirled over near the mouth the Humber. However a sunny heatwave continued on Bournemouth Beach!

November 1952 was also a cold one with a C.E.T of 4.2c. In fact that November together with a cool October 1952 C.E.T of 8.8c and the coldest September 1952 (C.E.T of 10.7c) of the 20th Century make autumn 1952 with a C.E.T of 7.90c the second coldest autumn of the 20th Century in Britain. There was a 5.1c drop in C.E.T temperatures between the average of 15.8c in August 1952 to 10.7c in September 1952. The following December 1952 was also cold with a C.E.T of 2.8c together with the deadly London Smog.

Below are three types of unusual British winters from the 20th Century:- 1. There are two examples of a cold November proceeding an overall mild winter in respect of the 1960-1991 Central England Temperature (C.E.T) averages which include the following:- -1919-1920 November 1919 3.3c (below the 1960-1991 C.E.T of 6.0c), December 1919 5.5c (above the 1960-1991 C.E.T of 4.3c), January 1920 5.2c (above the 1960-1991 C.E.T of 3.2c), February 1920 6.0c (above the 1960-1991 C.E.T of 3.3c) -1993-1994 November 1993 4.6c (below the 1960-1991 C.E.T of 6.0c), December 1993 5.5c (above the 1960-1991 C.E.T of 4.3c), January 1994 5.3c (above the 1960-1991 C.E.T of 3.2c). Interestingly February 1994 was slightly below average with a temperature of 3.2c below the 1960-1991 C.E.T of 3.3c. 2. Below are two examples of a warm February ending an overall cool winter:- -1981-1982 December 1981 0.3c (below the 1960-1991 C.E.T of 4.3c), January 1982 2.6c (below the 1960-1991 C.E.T of 3.2c), February 1982 4.8c (above the 1960-1991 C.E.T of 3.3c) -1996-1997 December 1996 2.9c (below the 1960-1991 C.E.T of 4.3c), January 1997 2.5c (below the 1960-1991 C.E.T of 3.2c), February 1997 6.7c (above the 1960-1991 C.E.T of 3.3c) 3. Below are two examples of an overall cool winter that contained one mild month that was NOT February:- -1984-1985 December 1984 5.2c (above the 1960-1991 C.E.T of 4.3c), January 1985 0.8c (below the 1960-1991 C.E.T of 3.2c), Febuary 1985 2.1c (below the 1960-1991 C.E.T of 3.3c) -1995-1996 December 1995 2.3c (below the 1960-1991 C.E.T of 4.3c), January 1996 4.3 (above the 1960-1991 C.E.T of 3.2c), Febuary 1996 2.5c (below the 1960-1991 C.E.T of 3.3c) I determined this using the following websites:- http://www.personal.dundee.ac.uk/~taharley...av_temperat.htm http://www.personal.dundee.ac.uk/~taharley...ther_months.htm