If you’re a regular reader of this blog, you will know that I’ve been talking about a pattern as we move towards the middle of November and the models have started to hint at this more and more in recent days. We’re seeing some fairly unseasonal warmth at the moment and that’s down to High Pressure over Europe and Low Pressure in the Atlantic drawing up Southerly winds across the United Kingdom.
What will this pattern change mid-month bring then? There’s no real clear signal, though it would seem there are two or three possible outcomes, conflicting signals make it hard to determine which one we’ll see.
In recent days, the Polar Stratosphere has begun to warm fairly rapidly, this can bring about a weakening of the Polar Vortex allowing High Pressure to establish itself across the Arctic, this in turn would send the current Positive AO, negative.
The current 500mb height anomaly charts also show a pattern change with the High Pressure currently over Europe, pushing further North and West, though having said this, the ECM shows a continuation of the current pattern we are in, so as I say there are some conflicting signals to contend with.
So, what are the three possible outcome
1. High Pressure edges further North and West allowing much colder, Arctic air into Europe, the Polar Vortex weakening and allowing heights to rise will displace much colder air into lower latitudes, if this pattern does indeed setup, we will see gradually colder temperatures and an increased possibility of snowfall as we move through the second half of the month. The signal for this is tentative, but it is there.
2. High Pressure sinks Southwards over Europe allowing the Jet Stream to flatten out across the UK turning things very changeable with a mixture of sunshine, showers and strong winds. Signals for this outcome are generally rather weak, this outcome isn’t very likely.
3. High Pressure continues to hold its position over Europe, keeping Low Pressure stuck to our West and we see a continuation of above average temperatures with rain trying to push in across Western areas and then stalling against High Pressure, this outcome seems as likely as cooler outcome number 1.
So, due to many conflicting signals, there is currently no clear picture or trend as we move into the second half of November, though the models are hinting at a change, whilst some hint at a continuation of this pattern.