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Lettucing Gutted

Cold Zonal Months That Failed

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The scary thing we're supposed to be in cool zonality and we still clocking up well above temps so far. I presume the warm Atlantic isn't helping much here though.

Below is a list of months that reinforces the above quote about how useless westerlies are becoming for achieving cool monthly C.E.Ts:-

Eventhough all of the months below had shortlived cold northerly and warm southerly spells, the vast majority of these months were dominated by westerlies that had a source near Greenland. Yet these months all recorded C.E.Ts above the 1961-1990 C.E.T averages. And all of the months below except for August 1999 and August 2006 even achieved C.E.T means above the 1971-2000 C.E.T averages.

January 1999

February 1999

March 1999

August 1999

December 1999

September 2000

April 2004

April 2006

May 2006

August 2006

May 2007

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I can add another few to that list Craig; November 1977, which was dominated by frequent northerlies after the 10th and often from well up into the Arctic yet the daily CETs were not especially low on those days and the month still failed to fall below the 1961-90 average.

Another period to add to the list is December 24th-28th 2001. Those five days had N-NW'ly airflows over the UK with a source from up into the Arctic Circle and yet the daily CET means were still close to average for late December on all five days, and given the synoptics the daily CETs should have been lower, so December 2001 ought to have been even colder overall than it actually was. The final four days of Feb 2001 were not especially cold at least for the CET given that a polar low crossed the UK in a north-north-westerly flow. The late Feb 2005 easterly was also a very lacksture affair and still saw no real cold compared to February easterlies of the past, and given the synoptics overall it ought to have achieved a below par CET, similar to Feb 1994, but it didn't.

September 2007 is another northerly month that failed. That often had winds from a northerly quarter and still ended up a shade above average.

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I think November 1977 and December 2001 were more cases of Greenland blocking and northerlies, rather than a cold zonal westerly type.

November 1977 seemed to have an anomalously warm Arctic, so the second half of the month had repeated northerlies where anomalously warm air at high latitudes kept modifying the airflow somewhat, resulting in snowy-looking synoptics being very marginal (although there was still snow for some). 24-28 December 2001 had a mild anticyclonic NW type and cold northerly type for the most part, with just the one brief Arctic surge on the 25th/26th.

September 2007 was more of an anticyclonic/northerly month, so while it should have been cooler than it was, it didn't feature the sort of long-draw northerly weather that characterised the likes of Septembers 1952 and 1986.

Agree re. February 2005- again, the main issue was the lack of cold pooling to the east.

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What many of the months listed in Craig's post did have in common though was a lack of outstandingly high maxima; although they ended up with close to average CETs (usually that so 1990s/2000s culprit that is above average minima); especially in the non-winter months only the odd day or two (24-25th April 2004 and 5-7 Aug 2006) achieved maxima more than a degree or two above the average for the time of year. April 2006 I particularly remember for this; even though it had an average CET with many mild nights (and not a few days of SW'lies) it consistently failed to rise above the mid-teens C by day; I think it was the first April since 1986 (which was well below average) not to reach 20C anywhere. A month not mentioned that was even more noteworthy for this was October 2004; cyclonic cold W'ly with a CET almost bang on average, it was very dull and wet with a remarkably low temperature range in these parts; the coldest nght was about 3C and the warmest day about 15 or 16; we've had greater ranges than that in 24 hours this week.

Mays of 2006 and 2007 perhaps have unrepresentative CETs as both had a very warm first few days before weeks of cold wet weather set in; remember May 1995 despite its (as I remember) strikingly cold middle part still had an average CET because of a warm first week.

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