The North Atlantic Oscillation (NAO) is an index often used to describe the weather where +NAO means westerly flow and widely warm/wet/windy and -NAO means blocked and widely cold/calm/dry. The expected weather pattern for Week 4 of 2021 (25th-31st Jan) from the ECMWF model - run on Monday 18th Jan 2021 is shown below:
It shows Greenland high and thus -NAO (as shown in the NAO forecast below from NCEP dated 19th Jan 2021) but we still have strong Atlantic (ATL) low pressures feeding into UK/Northern(N.)mainland Europe - ending up warm/wet/windy across much of mainland Europe - this being an example where NAO doesn't tell the full story.
With 29 Grosswettelage patterns, this allows the Met-Set Weather service to deliver a much more detailed picture to describe the expected weather in the outlook and the energy impacts for Europe and provide answers to questions such as; where is the focus of the wind likely to be, is it expected to be cold/windy or cold/calm for UK/Germany etc..
The ECMWF forecast from 19th January 2021 shows a clear signal for a WS pattern for Week 4.
In fact this has been a persistent signal in the forecast for week 4 as shown in this gif below of 7-days worth of forecasts:
WS means Westerly South-shifted - still a dominant westerly flow from the ATL - just shifted further south than it's usual position that focuses more of the wind into S Europe/FR and turns Nordic cooler/calmer/drier overall.
We can see two main alternatives patterns to this idea - HNZ (High pressure NorthSea-Iceland with low pressure over Europe) where the Jet-stream shifts even further south with gaps between the incoming lows to allow cooler/calmer conditions to spread south from Nordic more into N.mainland Europe which shows up as a temporary risk for working week 4.
The other being SWZ (South-Westerly Low pressure) where the Jet-stream ends up a bit further North and pushes more wind/warmth into UK/S Nordic shows up as a risk for the weekend of week 4 on ECMWF.
The beauty of the Met-Set tool is you can keep track of these alternative risks run by run / model by model - for example the GFS/GEM ENS runs from the day this was written (19th Jan) kept the HNZ risk more for first half of week 4 and a greater risk for SWZ second half of week 4 - Thurs onwards.
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