As much of north-western Europe battles with some seriously soggy weather while the southeast struggles to leave summer heat behind, many will be looking for signs of change to come this autumn.
Let’s look at what the most relevant historical years suggest. The November pattern might raise a few eyebrows!
2nd Half Oct: Unsettled North, Warm Iberia & East
When historical years are filtered down to those which saw, among other factors, a weak to moderate strength La Niña event and a negative phase to the Pacific Decadal Oscillation, some weak but interesting signals are identified.
Most prominent in the above-left chart is a belt of below-normal mean sea level pressure (MSLP) spanning from Scotland to around the eastern Baltic Sea. This suggests a raised likelihood of low pressure systems (‘lows’) affecting that region.
“The UK may have a hard time drying out much”
With those come spells of rain, sometimes strong winds too. No surprise, then, that the tendency map below shows above-normal rainfall in many spots. Successive storms could lead to a risk of flooding in places. The UK may have a hard time drying out much, while France fares better.
In north-eastern Europe, lows following such a path will tend to draw up some warm air ahead of them. So, it may be an anomalously warm second half to October there (and wet in some places).
To the west of there, temperatures mostly look average overall, but as lows come and go, a lot of day-to-day variation can be expected.
Shifting our attention further south in Europe, we see a slight signal for higher than usual MSLP in the west.
Coupled with lows throwing across mild air from the North Atlantic, this is a warm setup for Portugal and Spain. Not necessarily a very dry one, though – it’s only a weak high pressure signal. Some wetter spells are likely.
East of there, it’s an unremarkable outlook. This is 15-day averaged guidance, though, so please don’t take this as a guarantee that conditions won’t be unusual at any point.
November: Signs of Winter in West, Still Mild in East
For this month, the weather tendency changes substantially for Iceland, Portugal, and Spain (see below). Elsewhere, the only change of note is an expansion of the anomalously warm area in the east.
The change in the west is connected to a substantial pattern shift in the North Atlantic. In the pair of maps posted at the start, note the switch from blue to orange shading in the middle-left.
Frequent lows give way to a predominance of high pressure, which may be strong at times. Now here’s the big deal: Around high pressure, the air circulates in a clockwise direction. So, when positioned west of Europe, it moves cold air toward western Europe from near or over Greenland.
“I would not rule out some unusually cold spells of weather reaching as far east as Germany”
The MetSwift analogues suggest that in November 2020, it will tend to locate just a bit too far west to bring much of that cold air further east than Ireland. This is a monthly average and subject to uncertainty, though, so I would not rule out some unusually cold spells of weather reaching as far east as Germany.
When such cold conditions move across the Mediterranean Sea, it tends to cause unsettled weather to develop there. Adjacent lands can see a lot of rainfall. We can see that represented by wetter than average tendency for both north-eastern Spain and central Italy. Allowing for uncertainty, locations in between could easily be included.
Another Slow Slide into Winter for eastern Europe & north-western Asia
In eastern Europe, it’s looking like an unusually warm autumn season overall. This will be down to both weather patterns and climate change. As of early October, the Arctic sea ice edge lies a record-large distance from the Eurasian north coast. There’s an unprecedented amount of warmth and moisture available from the exposed Arctic Ocean. So, the seasonal development of cold conditions is likely to be unusually slow in the coming weeks.
James Peacock MSc
Head Meteorologist at MetSwift