November 2011 Forecast

[Thundery wintry showers]

Following on from my analysis of the October forecast, I present an analysis of the November forecast that I issued at the start of the month.

Southerly and anticyclonic types are likely to remain dominant for most of November with a persistent trough in the Atlantic and blocking highs over the continent. The most likely source of any colder weather will be the east rather than the north, but I think, in contrast to the end of last November, any snowy easterlies are unlikely.

Following the clearance of rain on the 2nd/3rd, a returning polar maritime incursion will bring sunshine and showers on the 3rd and 4th, with temperatures falling close to the seasonal average. The 5th-7th November will then see high pressure building across northern Britain. It will be cloudy in eastern and southern areas, with some light rain in East Anglia and south-east England, while most of central and western Scotland will be sunny with widespread ground frosts and patchy fog by night.

During the second week of November, it will start off dry, with south-easterly winds, plenty of sunshine in the west, but rather more cloud in the east due to winds off the North Sea, and maximum temperatures will be close to the long-term average at 9-12C. From the 10th onwards, however, low pressure will attempt to push in from the west. It will make slow progress, but there will be some slow-moving bands of rain for western areas. With southerly winds it will become increasingly warm again with highs of 15-16C possible in southern areas and also areas prone to the fohn effect in southerly airstreams (e.g. the north coast of Wales).

There is no substantial evidence for a significant pattern change into the second half of November. The third week of November is likely to continue much as the second week left off, with a persistent trough in the mid-Atlantic and high pressure to the east, giving more southerly winds. The trough will generally be far west enough to keep most places dry, but particularly around midmonth we may continue to see rain belts try to push in from the west. Long-range teleconnection outputs suggest that we may see the trough relocate further west during the last third of November, with high pressure becoming more extensive and bringing in south-easterly winds. However, the continent doesn't look likely to be especially cold then, so we are unlikely to see a repeat of the snowy easterly of the 20th-22nd November 1993. Instead, the weather will most likely end up dry and sunny in the west with night frosts, and cloudy with warm nights in the east.

Overview

November will be a warm month, but not exceptionally so, as the Atlantic influence is set to be relatively limited due to the placing of the Atlantic trough well to our west. I predict a Central England Temperature of 8.0C. Mean temperature will be about 0.5 to 1C above the 1971-2000 average in the west and 1 to 1.5C above in the east.

All parts are expected to have a dry November. In some eastern parts the rainfall shortage will exceed 70%, while shortages of 30-50% will be widespread elsewhere, with only Ireland and south-west England likely to approach the average. Unlike in October, sunshine totals are not expected to mirror rainfall totals, due to the frequency of dry cloudy weather in the east. Sunshine will be 10-30% above average in the west and 0-20% below in the east.

Weather patterns- I thought these were picked out pretty well during the first two-thirds of the month, but I predicted that high pressure would extend westwards during the final third of the month, when in reality the opposite happened- the Atlantic came roaring in and pushed the block well away. One major reason for this discrepancy was that the MJO was projected to head through phases 3-4-5 towards late November when I issued the forecast (and composites suggest more high pressure further west), whereas it currently lies only at phase 3. Another factor was the cold stratosphere which usually hinders the retrogression of high latitude continental anticyclones.

Temperatures- underestimated by 1 to 2 degrees Celsius, positive anomalies have come out at 2.5 to 3.0C in most regions. Again this is mainly due to the fact that the colder last third with continental air did not materialise.

Rainfall and sunshine- both came out much as predicted.

In summary I thought that the forecast went very well up until around the 22nd November, and correctly identified the overall character of the month as a whole, but the last week of November saw much the opposite progression to what I had predicted.

[A Winter's Tale]

Following on from my analysis of the October forecast, I present an analysis of the November forecast that I issued at the start of the month.

Weather patterns- I thought these were picked out pretty well during the first two-thirds of the month, but I predicted that high pressure would extend westwards during the final third of the month, when in reality the opposite happened- the Atlantic came roaring in and pushed the block well away. One major reason for this discrepancy was that the MJO was projected to head through phases 3-4-5 towards late November when I issued the forecast (and composites suggest more high pressure further west), whereas it currently lies only at phase 3. Another factor was the cold stratosphere which usually hinders the retrogression of high latitude continental anticyclones.

Temperatures- underestimated by 1 to 2 degrees Celsius, positive anomalies have come out at 2.5 to 3.0C in most regions. Again this is mainly due to the fact that the colder last third with continental air did not materialise.

Rainfall and sunshine- both came out much as predicted.

In summary I thought that the forecast went very well up until around the 22nd November, and correctly identified the overall character of the month as a whole, but the last week of November saw much the opposite progression to what I had predicted.

Interested to see what you're December/Winter forecast will be like when it's released.

[Methuselah]

Aye Ian. Not a bad forecast at all!