Lettucing Gutted
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Posts posted by Lettucing Gutted
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Warm spells in March can be damaging to the CET if you want a really cold March.
Yeah talking of March warm spells I think March 1965 is one of the few Marches which have achieved 20C or higher extreme maxima and yet still finished below average.
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12C. The cooling trend is over.
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The south-westerly type can bring very different kinds of weather depending on the airmass history and the amount of frontal activity. For instance, it will always be drier and sunnier towards the SE rather than the NW. The tropical maritime type will give dull wet weather in the NW and sunshine in the SE (the extent of the sunshine depending on how close by the high pressure is), while the "returning polar maritime" type usually heralds sunny mornings followed by bands of sharp showers moving SW-NE during the afternoon. The "west based negative NAO" scenario with low pressure stalling to our west or north-west and blocking to the east and west of it tends to promote the "sunshine and showers" scenario whereas a mobile Atlantic will mean more fronts, cloud and moderate persistent rain.
In terms of temperature does the "Returning Maritime Polar" Southwesterly type give cool weather especially by night whereas the "Mobile Atlantic" Southwesterly type gives very mild/warm weather especially by night? Interestingly June 2003 had a Negative North Atlantic and Southwesterly pattern and yet was very warm due to deep long draws of Maritime Tropical air.
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Its funny how these things work out. Anyone remember February 2008? That was incredibly sunny with the kind of clear skies and unbroken sunshine we have currently enjoyed. However maxima got as high as 16C for Manchester and that was the 12th of February. Yesterday was 10C colder even though it is 3 weeks later in the calendar than the 12th of February and the sun is obviously higher and stronger. Shows how much impact different airmasses can have.
Indeed Mr Data it all depends on the airmasses. The high from February 2008 was warm and sunny due to an early Continental Tropical air plume:-
http://www.wetterzentrale.de/pics/archive/ra/2008/Rrea00120080212.gif
http://www.wetterzentrale.de/pics/archive/ra/2008/Rrea00220080212.gif
Whereas the current high is cold and sunny due to its Continental Polar air origin from the North Pole similar to the very cold March 1962:-
http://www.wetterzentrale.de/pics/archive/ra/1962/Rrea00119620316.gif
http://www.wetterzentrale.de/pics/archive/ra/1962/Rrea00219620316.gif
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Certainly a notable cold snap for many, more so for the low minima than the low maxima, but at the same time, not exceptional for this early in the spring. The first weeks of Marches 2001 and 2006 were often colder than this over most of the country.
What is unusual about this instance is that it's associated with high pressure rather than a full-on blast of cold air like in the 2001 and 2006 cases.
It seems like the current sunny and cold scenario is the result of the Arctic High ridging south.
Also these cool anticyclonic spells are not exclusive to the winter and spring months. They can also occur in the autumn and summer months like August 1993.
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So we need around +0.7C months from now onwards to reach 10C by the end of the year and thats without March possibly coming in below average...
The last year that didn't produce any months 1.0C or more above their respective CET average was 1996.
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One of the reasons why its easier to get a large negative anomaly in winter compared to summer is the wider range of sources of cold air in winter compared to summer. In winter you can get cold Continental Polar air from the Arctic, cold Maritime Polar air from the Atlantic during Cold Zonality and cold Continental Polar air from the Continent. However in summer you can only get cold Maritime Polar air from Atlantic Cold Zonality and Continental Polar air from Arctic originated Northeasterlies, Northerlies and Northwesterlies. The Continental Easterlies always bring warm, humid and sunny weather in the summer rivaling southerly and southwesterly warm, humid and sunny plumes.
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I was interested by this post in the model output discussion thread today.
Apparently easterlies can bring widespread cold and bright weather even in May however when was the last time we had a "cold easterly with a "northerly" source" in May?bright snowy weather from the east is still possible during March and indeed well into May, but it requires a source from high latitudes- in essence an easterly with a "northerly" source.
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And how on Earth will it be 14 in a row, 2006 had the coldest start to Spring in 30 years or something like that.
If what I said wasnt clear enough I meant the whole combined March-April-May 2010 CET average will be the 14th warmest in a row.
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10C ushering in yet another mild blowtorch spring. 14 in a row... :lol:
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A cold winter will help, but ironically winter has been the most common season to record a 1C below average anomaly in the last 20 years. We have to go back to 1986 since that last happened in spring, 1972 in summer and 1993 in Autumn!
The mild springs and autumns since after 1996 have been real killers for recording years below 10C.
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It would be remarkable to have two sub-3C months in a row after such a long gap, but with the models the way they are it's hard to rule it out.
1) The last winter were 2 sub 3C months occured in a row was 1996-1997 with December 1996 2.9C and January 1997 2.5C.
2) The last winter were all 3 months were sub 3C was 1962-1963 with December 1962 1.8C, January 1963 -2.1C and February 1963 -0.7C. This was also the last winter were all months were sub 2C.
3) The last winter were all 3 months were below their own 1961-1990 averages was 1990-1991 with December 1990 4.3C, January 1991 3.3C and February 1991 1.5C.
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And also a nina-like low GLAAM signal should reinforce a southerly tracking jetstream.
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Does this mean your CET predictions are using some kind of reverse psychology, Craig?
Of course. I'd rather be pleasantly surprised if we had a cold year despite me predicting a very mild year than being very disappointed if we had a mild year despite me predicting a cold 'un.
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January-March for me should be cold, sunny and snowy remaining cool, sunny and showery for the rest of the whole year.
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This makes sense that Scandinavian ridges, at least in more recent climatology, are products of eddies in the northern arm of the jet when this is more dominant during Nina (low angular momentum) years.
What are the other ways of forming Scandinavian Ridges?
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But even in March, a solid 8cm snow cover will usually survive longer under unbroken sunshine, highs of 4C and sharp night frosts than under cloud, highs of 2C and lows of 0C- in the latter case higher dewpoints and higher ground temperatures come into play.
Indeed in pages 51 to 52 of Philip Eden's book a "Change in The Weather" he said of the March 1970 cold wave in Britain that the snowman he made called Snowman Ted persisted till the 22nd March 1970 despite unbroken sunshine.
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I get the impression that there is at least two types of Arctic High Pressure system. An Arctic High is a high with its centre north of 80deg North.
The Cold Arctic High
This is the true beast for cold weather fans and are affectionately known as "cold blocks". The great feature of this Arctic High is that it can send big pools of cold air all over the mid lattitudes such as Britain, for long periods and with hardly warming out of the Arctic cold pool due to displaced warm airmasses as long as both the polar and subtropical westerly jet streams flow at low latitudes. The fact that the Arctic cold pool doesn't warm out in a cold Arctic High is important for sustaining cold spells otherwise the warming of the Arctic troposphere creates cyclogenesis leading to strong low pressure systems and secondary features near the North Pole which cut of the flow of cold air and strengthens the Ferrel cell which can bring very warm weather to the mid latitudes associated with the subtropical high pressure systems.
The cold Arctic High was responsible for almost all of the cold months and seasons upto the end of the 20th Century. As the name suggests the cold Arctic High is related almost directly to the intensity, depth and extent of the Arctic cold pool. The intensity, depth and extent of the Arctic cold pool is in turn dependent on the extent of the Arctic ice sheet. There was a large Arctic ice sheet and cold Arctic High in the cool Arctic summer of 1985 and there was an even larger Arctic sheet and large cold Arctic High in the cold Arctic winter of 1969. An interesting feature of the best cold Arctic Highs is that eventhough the cold high forms in a deep cold Arctic airmass there is anticyclonic circulation at all levels of the Arctic atmosphere from the surface, through the troposphere and into the stratosphere. Although the Arctic upper troposphere is colder than normal there is anticyclonic circulation in the upper arctic troposphere and stratosphere due to direction of planetary wave energy from Siberian snow cover and the intense surface Arctic High and/or Siberian Highs themselves.
Below is an example of a cold Arctic High in the cool Arctic summer of 1985:-
http://www.wetterzentrale.de/pics/archive/ra/1985/Rrea00119850601.gif
In the chart below notice that in addition to the plus 5C, 0C and even the -5C 850 HPA isotherms plunging into the Western Mid lattitude North Atlantic Ocean the Arctic is also under sub -5C 850 HPA air associated with the cold Arctic High:-
http://www.wetterzentrale.de/pics/archive/ra/1985/Rrea00219850601.gif
Below is an example of a cold Arctic high in the cold Arctic winter of 1969. The central pressure of this high is 1045mb and is north of Novaya Zemlya:-
http://www.wetterzentrale.de/pics/archive/ra/1969/Rrea00119690117.gif
In the chart below notice that in addition to the -5C and even the -10C 850 HPA isotherms plunging into the Central Mid lattitude North Atlantic Ocean the North Pole is also under sub -22C 850 HPA air associated with the cold Arctic high:-
http://www.wetterzentrale.de/pics/archive/ra/1969/Rrea00219690117.gif
The Warm Arctic High
Effectively this is a displaced subtropical high pressure system. Eventhough deep cold cutoff lows can be displaced into mid lattitude locations such as Britain (hence a Negative North Atlantic Oscillation and Negative Arctic Oscillation)the warm "Arctic" High brings record breaking "warmth" to the Arctic itself. This happened during the very warm Arctic summer of 2007 which saw a record low Arctic ice extent.
Below is an example of a warm Arctic High in the warm Arctic summer of 2007:-
http://www.wetterzentrale.de/pics/archive/ra/2007/Rrea00120070807.gif
In the chart below notice that eventhough the 5C isotherm at 850 HPA surges towards Spain there is a pool of very mild plus 0C and even plus 5C air at 850 HPA associated with the warm Arctic High over the Arctic:-
http://www.wetterzentrale.de/pics/archive/ra/2007/Rrea00220070807.gif
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At 16.6C it was 0.8C above the 1961-1990 August average of 15.8CHow could August possibly be mild?
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Its interesting that most of the warmth this year has happened in two months.
March 2009 was also mild and in the eastern 3rd of the UK August 2009 was a very mild month as well.
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Assuming the December 2009 CET finishes at 3.5C the December 2010 CET will have to be cooler than 7.6C in order for the 1981-2010 December CET average to be cooler than the 1971-2000 December CET average of 5.1C.
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I was just thinking this myself John. The GFS was predicting maximums of -2 or -1c across large swathes of central England earlier in the week, here it is still -4c, so there is more proof that the GFS doesn't always go insane with the minimums.
It seems to be spring and summer when the gfs has minimum and maximum temperatures below reality.
Why Are People Still Looking For Cold And Snow?
in Spring Weather Discussion
Posted
I hate the heat and prefer the cold. The reason I keep predicting record warm CETS all year around is because really cold April-August months become rare since the late '80s.