UK/Ireland: Pattern changing Storm Deirdre brings flooding rain, freezing rain, snow and severe gales

Written by on December 15, 2018 in Rest of Europe, United Kingdom & Ireland with 0 Comments

The Atlantic is making it’s comeback after a near week dominated by cool, easterly winds. Storm Deirdre is making the change from cold continent back to milder, stormier Atlantic as the jet stream strengthens.

Credit: Tropical Tidbits

The tight thermal gradient marked by the storm is helping it deepen on final approach to the UK and so the weather conditions are highly varied depending upon where you are.

Credit: Met Office

The storm at outside dynamics look good for possible sting jet formation.

Strong warm air advection increases freezing rain potential.

Deirdre is driving a lot of moisture in and this is falling as rain over Ireland, snow over Highland, Southern Uplands and N Pennines but freezing rain in other parts.


Tricky day for forecasting precipitation type…

Essentially we have a mild Atlantic low which marks a pattern change but as it an environment of tighter thermal gradient, it’s deepening and therefore strengthened at it’s moved over the UK this Saturday afternoon. The increase in temperature gradient has aided the tightening of pressure within the low. As a result, fairly widespread gale force winds have exceeding 50 mph at sea level while near 120 mph over the tops of some Scottish mountains.

Ahead of the storm’s main cold front, it remains cold but behind it, the mild Atlantic air has taken over the lowest mile of the atmosphere, primarily over Ireland and Northern Ireland where heavy wind driven rain has caused flooding, aided by already saturated ground.

For low level parts of mainland Britain, rain has been falling and some of this rain has frozen on the below freezing ground but led to flooding in areas of southwest England and Wales where it’s reached 10-13C thius afternoon.

However, from the Midlands to Central Lowlands, it’s struggled to get above the freezing mark. Factor in the strong winds and it’s felt bitter. However, a warm layer associated with the system has managed to punch through the cold air and so this makes for a trickier forecast precipitation wise.

Mid afternoon temps and wind chill.

Credit: Meteoceil

Credit: Meteoceil

While freezing or below at ground level, it was above freezing at around 850mb or 5,000ft.


With this in mind, a rare AMBER warning for ICE was issued.

Credit: Met Office

In the warm windy air, Ireland experiences flooding!

In the cold air but with warmer air above, Co Durham and other parts of England and Scotland are observing freezing rain.

and where the lowest mile of the atmosphere remains at or below freezing, like in the Highlands, it’s snow!

Once Deirdre passes, mild Atlantic air will fill our atmosphere and by next week we’re in warm southwest winds ahead of another front.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

The GFS ensemble shows a warmer than normal pattern now through Christmas Day.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Despite this, just keep in mind what’s going on way up in the stratosphere…..

Tags: , , , ,

Follow us

Connect with Mark Vogan on social media to get notified about new posts and for the latest weather updates.

Subscribe via RSS Feed Connect on YouTube

Leave a Reply