Natural Variability in the AMO

The Arctic Multi-Decadal AMO Oscillation (AMO), has a strong link to observed Global temperatures, and is far better correlated to observed global temperature trends then any single atmospheric parameter (including carbon-dioxide).

The AMO operates over a 20 to 40 year period and is poorly predicted in Global Climate Models (GCMs). When the AMO is in the warm phase, droughts are more prevalent and hurricane activity tends to be enhanced. The cause of a negative phase shifting in the AMO, is a direct result of a slight weakening in the Gulf Stream. The temperature fluctuations resulting from the AMO extend from the equator to the north-Atlantic basin, with temperatures up to +0.5'C between extremes.

The AMO is a major factor in determining the mild climate of the Northern-hemisphere and Arctic ice-sheet. The AMO makes attribution of carbon-dioxide to temperature rises very difficult. Since the 1990's the AMO has been in a strong negative phase, but recently there are signs of an abrubt cooling due to a weakening (not shut-down) of the Gulf stream flow.

The negative phase of the AMO is likely to lead to far lower temperatures in North and West Europe, and the entire Northern-Hemisphere.

http://www.cdc.noaa.gov/Timeseries/AMO/

Sea Temperature Anomalies (SST)

"Switch" to North-westerly Flow noticeable from October 2007

A gradual shifting of the prevailing wind between October 2007 to present was noticeable in the North-West Atlantic close to the United Kingdom, which contributed to the wet and cool Summer of 2008 due to a strong (unstable) polar maritime flow. OnlineWeather.org.uk hedged bets that this "cut-off" to the usual tropical maritime flow into the UK, would produce below average temperature for northern-Europe during Winter 2008. The circulation effects are consistent with a warm temperature anomaly in the North Atlantic, but also indicate a longer-term shift in the climate system, which could result in a partial recovery or ease of Arctic ice melt. There is a strong signal that a warm temperature anomaly in the mid-Atlantic may have been present in 1981, when a long period of Arctic air resulted temperatures "well-below average" during December, and caused a "cool and wet summer", though reliable ocean data on a local scale is scarce during this period making this observation "inconclusive".

A significant weakening of the Gulf Stream flow would induce identical effects, and hence the Meriodional Overturning Circulation (MOC) plays a key role in dictating Global temperatures. Northern hemisphere ice cover during Winter and Spring, combined with high latitude ice coverage is consists a large negative feedback if MOC weakening is coincident with a warmer world. This Ocean-atmosphere coupling is essential in prediction of future climate change. There is evidence that the MOC has fluctuated in intensity naturally, though it is likely that the weakening seen is of a result of unprecedented ice-melt at the poles, well above the IPCC predictions. The MOC weakening is consistent with a global temperature leveling off during the early 21st century, when temperatures were otherwise (all thing equal) expected to accelerate in line with high levels of anthropogenic emissions.

Christmas / December Forecast 2008

Update: 7th November, 2008 [2105 UTC]

Seasonal Update: December / Christmas Outlook, 2008

Are you dreaming of a White Christmas ?

Analysis of the warm temperature anomaly in the Mid-Atlantic to the West of the United Kingdom was undertaken. The macro-physical behaviour of this Ocean anomaly has been compared and contrasted to the UK climatology archive, by a weighted pattern match-up. This analysis is suggestive of a 65% probability of a BELOW AVERAGE December, with a strong tendency towards Arctic maritime airstream near the middle part of December. The Summer / Autumn follows the general trend of 1981, when an Arctic flow resulted in well below average temperatures during December. In 85% of cases the North-Westerly or Westerly domination resulting from the mid-Atlantic pattern persisted into late December for close significant comparison years, when the feature was prevalent during November. In general the warm anomaly propagated Westwards allowing colder and drier continental air to affect the SE of England, whilst Arctic Maritime air becomes a key feature.
Careful weighting of the significantly correlated years with Winter 2008 enables a prediction of temperature generally below average. The CET (Central England Temperature), is expected to be below average, and heavy wintry showers or snow is expected to dominate more northern and western counties.
December 2008 Anomaly: -0.3 +/- 1.0'C [CET: 4.0'C +/- 1.0'C]

Subconsious Weather Forecasting

3) Subconscious is smarter than you.

Subconscious is smarter than you. In other words, it is more powerful. In a recent study, a square was attributed to a location on a computer screen through a complex pattern. After watching it out, people began to get results better than the chance of recognizing where the square would crop up next. However, when they were inquired to consciously find out the pattern, even given a few hours, nobody really did it!

Hot forecast [October 2008]

Mild UK Weather set for the next 8 days:
[remember that the temperature is variable. On a Sunny day in October the temperature around London can range by up to 6'C within a 50km range. Some of this is due to the Urban Heat Island effect, but most of which results from patchy low cloud or fog. On the 8th of October London's outskirts reached 15'C, whilst parts reached 22'C. I used a representative London value, and will keep to the same one throughout. The GFS provides a smoothed mean of the temperatures, averaged over a 6 hour time window, and does not consider the urban heat island, so days with a high dynamic range in temperature, max T is underestimated and min T is overestimated. The mean temperature should remain unaltered if the chosen locations are sufficiently far from Urbanized sprawling.]
The GFS forecast interpretation was made independently, without access to a TV weather forecast or BBC sources.

My forecast from Global Forecast (GFS) 8 day forecast outputs:


Date: --------------- London: --------------- Edinburgh:

Tue 7th, Oct--------------- 15'C/13'C Rain --------------- 13'C/10'C Rain
Wed 8th, Oct --------------- 15'C/9'C partly cloudy--------------- 12'C/8'C Rain
Thu 9th, Oct --------------- 15'C/15'C Cloudy --------------- 12'C/12'C Rain pm
Fri 10th, Oct --------------- 17'C/10'C Sunny--------------- 15'C/12'C Rain pm
Sat 11th, Oct --------------- 18'C/15'C partly cloudy--------------- 13'C/10'C Rain
Sun 12th, Oct --------------- 18'C/13'C rain --------------- 13'C/8'C showers
Mon 13th, Oct --------------- 18'C/15'C partly cloudy --------------- 10'C/12'C Heavy rain pm
Tue 14th, Oct --------------- 15'C rain --------------- 12'C rain

Mean temperature --------------- [16.375'C/12.857'C] --------------- [12.500'C/10.287'C]
Temperature anomalies--------------- [+1.275/+5.407] --------------- [+0.100'C/+4.337'C]

Mean anomaly--------------- [+3.341 +/- 0.5'C] --------------- [+2.2185'C +/- 0.5'C]

----------------------
BBC 5 day forecast

Tue 7th, Oct --------------- 17/9 Rain --------------- 14/8 Rain
Wed 8th, Oct--------------- 17/5 Partly cloudy --------------- 14/7 Partly Cloudy
Thu 9th, Oct--------------- 17/10 Sunny --------------- 15/12 Cloudy
Fri 10th, Oct --------------- 19/10 Sunny --------------- 16/8 Rain
Sat 11th, Oct --------------- 17/10 Partly cloudy --------------- 13/8 Sunny

Mean temperature--------------- [17.4'C/8.8'C] --------------- [14.4'C/8.6'C]
Temperature anomalies--------------- [+2.300/+1.350] --------------- [+2.000'C/+2.650'C]

Mean anomaly--------------- [+1.825 +/- 0.5'C] --------------- [+2.325'C +/- 0.5'C]


Observations:

An atmospheric block near the UK ended explosive during the beginning of the period, causing an "explosive" surge of tropical maritime moist air driving into the UK. The following was observed ...

(1) Strong subsidence occurs either side of the SW'ly jet of moisture, causing cooler dryer bands and low level cloudiness which acts as a negative feedback. In some cases this "significantly reduced" the expected rainfall in both the BBC and GFS forecasts. The GFS poorly resolves boundary layer issues, and secondary convective processes associated with a highly confined stream of moisture.
(2) Possibility of "Fog" dragging down temperatures in the SE of England by Monday. [Prediction of 5:1 made for Fog causing disruption to Heathrow air travel, made on Wednesday 8th].
(3) It is likely that the urban heat island "pushed" up the average temperature in London by up to +0.5'C

Probability Estimates; Observations are shown in the boxes:

Place your bets wisely [66% of the probability lies in the range 1.5'C to +4.5'C]
There is enough water vapour in the atmosphere this week, to produce a doubling-effect of carbon-dioxide. How will this influence the UK weather. Perhaps we might see a negative feedback take place?

Truth (Tues 7th Oct, 2008) London [Greenich - London]: 18/8 rain Edinburgh [EGPH - Edinburgh Airport]: 16/11 rain Truth (Wed 8th Oct, 2008) London [Greenich - London]: 18/6 Sun Edinburgh [EGPH - Edinburgh Airport]: 15/8 Partly cloudy Truth (Thurs 9th Oct, 2008) London [Greenich - London]: 19/11 Sun Edinburgh [EGPH - Edinburgh Airport]: 15/4 Rain pm (;, but mostly cloudy Truth (Fri 10th Oct, 2008) London [Greenich - London]: 18/8 Sun Edinburgh [EGPH - Edinburgh Airport]: 17/11 Rain Truth (Sat 11th Oct, 2008) London [Greenich - London]: 20/9 Sunny Edinburgh [EGPH - Edinburgh Airport]: 12/2 Sunny Mean Temperatures London 18.6/8.4 [+3.025/+0.95] Mean anomaly = +2.4875'C Edinburgh 15.0/7.2 [+2.60/+1.25] Mean anomaly = +1.925'C

Delete

Christopher James Nankervis wrote at 10:37am on October 12th, 2008 5 Day GFS London +2.925'C Edinburgh +2.525'C 5 Day BBC London +1.825'C Edinburgh +2.325'C 5 Ensemble (BBC+GFS)/2 London +2.375'C Edinburgh +2.425'C 5 Observation London +2.4875'C Edinburgh +1.925'C Delete

Christopher James Nankervis wrote at 2:12pm on October 14th, 2008 Truth (Sat 12th Oct, 2008) London [Greenich - London]: 24/15 Sunny Edinburgh [EGPH - Edinburgh Airport]: Partly Cloudy: 15/11 Truth (Mon 13th Oct, 2008) London [Greenich - London]: 18/11 Mist/Partly cloudy Edinburgh [EGPH - Edinburgh Airport]: 14/6 Partly Cloudy Truth (Tues 14th Oct, 2008) London [Greenich - London]: 15 Partly cloudy/Rain pm Edinburgh [EGPH - Edinburgh Airport]: 12 Partly Cloudy Delete

Christopher James Nankervis wrote at 2:45pm on October 14th, 2008 8 Day GFS London +3.341'C Edinburgh +2.219'C 8 Observation London +2.957'C Edinburgh +2.770''C

Cold forecast [October 2008]

Friday 24th
4.0'C/9.0'C [20mm rain pm [mostly rain]] 25mph SW

Saturday 25th
8.0'C/15.0'C [5mm rain am [mostly cloudy]] 35mph W

Sunday 26th
5.0'C/9.0'C [2mm rain [light showers / partly cloudy]] 25mph NW

Monday 27th
0.0'C/8.0'C [Sunny!!] 15mph NWW

Tuesday 28th
-2.0'C/7.0'C [Sunny!!] 15mph NWW

Wednesday 29th
-2.0'C/10.0'C [Rain; 25mm, possibly some sleetiness] 20mph NWW

Thursday 30th
4.0'C/10.0'C [Partly cloudy] 25mph NWW

--------------------------

---------
Prediction (GFS)
+2.4'C / +9.7'C

Mean (1960-1990)
+4.2'C / +10.5'C

Anomaly
-1.8'C / -0.7'C [-1.25'C +/- 0.5'C] BELOW AVERAGE

Truth:
5/10
9/13
4/9
0/8
-2/5
0/6
-2/8

Truth
+2.0'C / +8.4'C
Anomaly
-2.2'C / -2.1'C [-2.15'C +/- 0.5'C] BELOW AVERAGE

White Christmas

A north-westerly flow has become a semi-permanent feature of the UK weather over the past couple of years. Combined with an enhanced North-Westerly Jet, this flow gave rise to a polar-maritime type heavy rainfall scenario, with enhanced cyclonic activity leading to flooding in the Summers of 2007 and 2008.

The cause of this weather feature, is thought to be either (1) related to the La Nina, a cool water phase of the Pacific, which tends to cause an intense polar jet in the northern hemisphere, which interacts with upper level vorticity near Greenland, causing a northwesterly flow into the UK.
(2) A slight weakening of the north-Atlantic drift / Gulf Stream circulation, could induce a stronger polar jet. Literature tends to suggest that the Meridional Overturning Circulation (MOC) is weakening, which could be part of a longer term cycle, (3) Diminished solar activity and ionization by solar particles, or changes in northern hemisphere cloud cover particularly near the Arctic, (4) Arctic Oscillation / North Atlantic Oscillation changes due to ocean cycles.
Since the ocean and atmosphere are intrinsically coupled, it is unlikely that the atmospheric changes are not related or linked to changes occurring simultaneously in the Ocean. (5) Ice melt in the Arctic causing some feedback on the climate, which I don't understand (6) Other feedback process of unknown origin ....

Projecting the northwesterly flow / sinking Rossby waves pattern scenario into Winter 2008, I provided a forecast (Seasonal 2008) at OnlineWeather.org.uk. This was based on increased storminess, and changes to the mean (prevailing) airstream arriving into the UK.
In "normal" conditions, a Tropical Maritime flow dominates the weather of the UK (mT on figure 1.), yet during the past couple of years, the flow has been shifting gradually to a semi-permanent returning polar maritime (rPm) or polar maritime (Pm) flow, which coincided with a super-La Nina phase.