With each new GFS run seeming to produce even more sensational charts regarding long-fetch southerlies and unseasonable warmth, here's a little look at what drives this major broad-scale synoptic development:
https://max.nwstatic.co.uk/gfsimages/gfs.20140922/12/147/h850t850eu.png
https://max.nwstatic.co.uk/gfsimages/gfs.20140922/12/147/hgt300.png
Day 6, we have a strong, flat jet raging across the U.S. and starting to exert influence on the Atlantic, and a low pressure system positioned NW of the Azores, in a prime position to exploit the incoming jet energy and rapdily intensify.
https://max.nwstatic.co.uk/gfsimages/gfs.20140922/12/171/h850t850eu.png
https://max.nwstatic.co.uk/gfsimages/gfs.20140922/12/171/hgt300.png
Day 7, the storm system has deepened substantially, and acts to buckle the jet in the mid-Atlantic. Where the jet slows, marked upper air convergence occurs, driving subsidence from the upper levels down to the surface and hence increasing pressure over the UK, in turn tilting the jet SW-NE, which then further builds the ridge, and so on...
https://max.nwstatic.co.uk/gfsimages/gfs.20140922/12/252/h850t850eu.png
https://max.nwstatic.co.uk/gfsimages/gfs.20140922/12/252/hgt300.png
Day 11, the above processes are reinforced by a sharp trough in the jet near to the Azores - a truly immense blocking high stands strong.
The LP to the SW does lift N during the following few days, but the resulting WAA reinforces the block yet further, meaning that even 16 days from now, it's still driving our weather:
https://max.nwstatic.co.uk/gfsimages/gfs.20140922/12/372/h850t850eu.png
Yep - that's two very long fetch southerlies in one GFS lower-res period (days 9-16).
Staggering stuff, but it all comes down to that storm system on day 6 being able to rapidly intensify as the strong jet out of the U.S. interacts with it. This has been predicted consistently across the past few GFS runs.
UKMO seems to have the pieces in the right place on day 6:
http://www.meteociel.fr/ukmo/archives/2014092212/UW144-21.GIF
In fact the HP is just a little stronger at this stage, which would help with developing the strong block days 7-10
http://modeles.meteociel.fr/modeles/gem/runs/2014092212/gem-0-240.png?12
GEM doesn't build the HP north and east so readily, but still produces that strong pressure build - just more UK-based. Looks very good going forward from there if you like settled October weather with the potential for a true Indian Summer depending on mist and fog amounts.
http://www.meteociel.fr/modeles/jma/archives/2014092212/J192-21.GIF
JMA has the storm system on day 6 positioned a bit further south before interaction with the jet. This results in an even stronger build of HP - what a chart that is for day 8!
http://www.meteociel.fr/modeles/ecmwf/archives/2014092212/ECM1-192.GIF
ECM follows suit and is a marked improvement on the preceding few runs from a warmth perspective
If you have any problems or queries relating to TWO you can Email
[email protected] https://twitter.com/peacockreports 2023's Homeland Extremes:
T-Max: 30.2°C 9th Sep (...!) | T-Min: -7.1°C 22nd & 23rd Jan | Wettest Day: 25.9mm 2nd Nov | Ice Days: 1 (2nd Dec -1.3°C in freezing fog)
Keep Calm and Forecast On