Phantom Warm Fronts

[Lettucing Gutted]

Has anyone noticed that after we have had a summer cold spell that we sometimes get a return to above average temperatures without the passage of a classical warm front cloud band and wind shift over Britain?

This scenario often happens when the Azores High Ridge moves into Western Britain from the west and displaces a summer Northerly cold spell from us.

As soon as the displaced Azores High Ridge moves over Britain we get a return to above average temperatures.

The link below leads to a diagram that shows the air mass changes that Britain experiences in a "Phantom Warm Front" summer warm up. In the image on page 1 Britain experiences a cool Northerly Maritime Polar flow. However in the image on page 2 the air flow has changed to a very warm Returning Maritime Tropical flow as the Azores High Ridge moves over Britain.

Phantom_Warm_Fronts.doc

I call this warm up method a "Phantom Warm Front" since no classical warm front cloud band and wind shift crosses Britain during the warm up.

Below is a recent fax chart example of a "Phantom Warm Front":-

On the 21st August 2007 the daily mean in the C.E.T zone was a cool 14.8C courtesy of a Maritime Polar Northeasterly wind.

http://www.wetterzentrale.de/archive/2007/...cka20070821.gif

On the 25th August 2007 the daily mean in the C.E.T zone had risen to a very warm 17.4C courtesy of a Returning Maritime Tropical West-Northwesterly wind brought by the Azores High ridging northeastwards into Western Britain.

http://www.wetterzentrale.de/archive/2007/...cka20070825.gif

http://hadobs.metoffice.com/hadcet/cetdl1772on.dat

You will notice that during the warm up between the 21st August 2007 and 25th August 2007 there was no warm front cloud band and wind shift crossing Britain.