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Weather news and views from Brian Gaze.
Posted 21st October 16:12
In the short to medium term the weather is looking quite unsettled. How are things shaping up as we head into and through November?
The recent upgrade to the GEFS model means charts and data going out to 35 days ahead are now available. This and the extended range ECM model are increasingly useful tools when trying to identify longer range weather trends. Needless to say they are not intended to provide day to day details!
One thing of note is there was a suggestion of cold spells being more frequent during the late part of the meteorological autumn. That could still turn out to be the case but recent model runs have been backing away from the idea.
The chart below from the GEFS model shows forecast 850hPa temperature anomalies for the week beginning November 3rd. Over the UK things are looking pretty close to the 1981 - 2010 average. There's more hint of a negative (colder) anomaly in the north west. It suggests the likelihood of colder incursions from the west or northwest being more frequent than in the south and east.
By the week beginning November 10th a positive (milder) anomaly is present over most of the UK as can be seen on the chart below. It doesn't suggest VERY mild conditions and also remember it is averaging the values over the entire week. Therefore, a mix of warmer and colder days is possible. Nonetheless, it doesn't support the idea of an early winter.
The chart below for the week beginning November 17th is very similar. Again it leans towards milder than average conditions.
Taking the above into account the present suggestion is that November temperatures are looking quite close to the norm. There earlier colder signal has faded.
The GEFS 35 day pressure plot for London is below. The green shading indicates the standard deviation which is a measure of the forecast spread. The trend currently appears to be towards somewhat higher pressure.
My interpretation is it is pointing towards pressure increasingly building to the south of the UK. That often suggests mild weather, although if the high pressure area builds far enough northwards it can begin to turn colder as the Atlantic flow is cut off and calm conditions allow it to cool quickly at the surface.
To summarise the signal for colder conditions in November which I spoke about a while ago has faded if computer models are to be believed. There are caveats, for example, La Nina conditions are believed to increase the likelihood of early wintry outbreaks.
Therefore, the old saying "Ice in November to bear a duck, rest of the winter be slush and muck" may not be put to the test this year. However, there is still plenty of time for things to change.
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