Guest weather analysis by Joe D’Aleo, CCM, AMS Fellow.
It has been for northern Europe a hot summer. Is it climate change as the media would like to have us believe? Or, is it something much simpler? For example, ocean patterns. Off the coast of Africa, water was coldest in the entire record back to 1950. A temperature change in one place of the oceans, means a change elsewhere also.
The UK July ranked 3rd warmest since 1950 in the very long term (starting 1659) temperature data-base from Central England.
The last 30 days has been warm in most of Europe but cooler in Iberia, Italy and the Balkans
The heat intensified the last week.
Anomalies were very large Wednesday in the northeast.
Portugal was in the news because of developing heat though they actually had an unusually cool summer.
The driver for the warmth was the cold tripole in the Atlantic sea surface temperature anomalies. Off Africa, water was coldest in the entire record back to 1950.
The TNA (Tropical Northern Atlantic) Index will update for July in a few days but June was a record negative (cold) in sharp contrast to 2017. This should lead to a quieter hurricane season in the Atlantic Basin.
For years with greater than 1 STD negative TNA in June, the ACE Index was negative.
But it has major impacts also downstream. See how in the upper atmosphere low heights were seen over colder water and positive anomalies over warm water. Downstream from the North Atlantic trough, a ridge built in the north.
Surface pressure matched the 500mb heights.
Warmth built in the ridges, cooler than normal temperatures lingered in the troughs.
In southern Europe in the lower pressures, it was wet, while it was dry in the northern ridges.
The EPS seems to be trying to evolve the pattern to one less extreme after the heat today with an impressive transient trough. Given the ocean patterns, it probably will be brief or limited as the ensemble model shows.