All Hail the Jet Stream

Hail in Bruton, Somerset
Image: Stuart Anderton

In the sea of storms and the deluge every day, for what seems like weeks now, Friday 3rd January was particularly notable for the ferocity of the squalls and the hail widely reported around the country. Sue, a subscriber of WeatherAction described the situation as

Wuthering Heights conditions in Cambridge UK. Howling gale, black sky and sleet in large quantities. Don’t know about Armageddon but this is looking quite [apocalyptic] in the short term.

ITV also reported on the conditions is Cambridge and it was quite a major talking point for those caught in the storm’s wake,  being reported in many local media sources

At the University of Reading, rainfall overnight amounted to 6.5 mm, and another 1.2 mm fell shortly before midday as a line of hail and heavy rain crossed the town.

Dr Roger Brugge of the University of Reading’s department of meteorology said this hail was accompanied by a increase in wind speed and gusts of up to 52mph.

Dr Brugge said: “After some sunshine earlier in the morning conditions changed by early afternoon to those of daytime darkness – due to low, thick cloud. Reading Post Readers’ flood pictures from Reading and Wokingham

See also the Daily Mail report with many more pictures

Like many others I took a video and some images (submissions welcome leave a comment asking not to publish and I will email you back).



Note the size and quantity were minimal compared to that being reported across a vast swathe of the country (see below) and minute compared to the enormous ‘boulder’ sized hail reported in Southern India on Tuesday 31st December 2013.


Boswinger, Cornwall

Illminster, Somerset

Caerphilly, South Wales

Hemel Hempstead, Hertfordshire

Lowestoft, Suffolk


This was also reported by Nino Van Eeckhout in the comment section at WeatherAction

Belgium was quite hit Friday afternoon by a heavy storm passing the country. Severe winds with thunder, lightening and hail passed our country with substantial damage inplaces. The soccer stadion from KV MECHELEN for instance was severly damaged. Although the national Belgian MET Office didn’t warn us for this, WEATHERACTION did warn for very heavy weather on Friday and Saturday. Well done Piers. First goal achieved in my action to persuade more people to check your forcasts. Use this link for pictures

Background Factors

The proximity of the polar jet axis (pink line) before this weather action is seen here


Satellite image of the British Isles 0900 3rd January 2014
Image: KNMI


Polar jet streams are typically located near the 250 hPa pressure level, or 7 to 12 kilometres (4.3 to 7.5 mi) above sea level, while the weaker subtropical jet streams are much higher, between 10 and 16 kilometres (6.2 and 9.9 mi) above sea level…The northern hemisphere polar jet stream is most commonly found between latitudes 30°N and 60°N Wikipedia Jet stream

Cross section of the two main jet streams, by latitude
Image: Wikipedia

As can be seen in the image directly above the Polar and Ferrel air cells were mixing on our doorstep.

This was the geomagnetic K indices during that time


And it is worth noting that, as SpaceWeather noted, at the time

Earth is inside a stream of solar wind flowing from the indicated coronal hole.


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