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.
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.
The storm at outside dynamics look good for possible sting jet formation.
Possible #StingJet has been resolved in the ARPEGE & AROME models. Violent winds will be possible as high momentum air ejects from the cloud head of the rapidly developing cyclone –> https://t.co/jMVBmlVkF4
Credit to @severeweatherEU for schematic. pic.twitter.com/yCSPuyml0N
— wxcharts (@wxcharts) December 14, 2018
Strong warm air advection increases freezing rain potential.
#StormDeirdre will make for an interesting Saturday in the UK! This Shapiro-Keyser cyclone is modelled to produce a sting jet with strong gusts, with some notable warm air advection from the warm front allowing the risk of freezing rain and heavy snow for many northern regions! pic.twitter.com/NsCY2pOg3y
— Ollie Millin ⚡️ (@MillinMan1) December 15, 2018
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.
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.
In the warm windy air, Ireland experiences flooding!
Flooding on the River Derneen and River Derry in Carlow and Wicklow. More expected today and then potentially a lot more on Monday night and Tuesday. Those in areas prone to flooding near to be on alert. #StormDeidre pic.twitter.com/khf8N7XoeQ
— Carlow Weather (@CarlowWeather) December 15, 2018
In the cold air but with warmer air above, Co Durham and other parts of England and Scotland are observing freezing rain.
Just captured this gate which has become a victim of the freezing rain here in County Durham this afternoon. #uksnow #FreezingRain #StormDeirdre @StormHour @UKSnowUpdates @StormchaserUKEU @metoffice @Lauratobin1 pic.twitter.com/0vVOphujx1
— PAUL KINGSTON (@PaulKingstonNNP) December 15, 2018
Freezing rain in North Yorkshire near Settle. Take care everyone in the North. #StormDeirdre #FreezingRain @metoffice @bbcweather pic.twitter.com/HR6u2Q9EgC
— Richard P (@RichardPeasland) December 15, 2018
Thanks to Leeds Bradford @LBIAirport for this photo of the freezing rain that has formed an icy glaze over parts of the airport #icy #StormDeirdre pic.twitter.com/irZGy48a5K
— Met Office (@metoffice) December 15, 2018
Today's 12z Nottingham tephigram is about as classic as a freezing rain event gets. A layer of above-freezing temperatures helps to melt the snow, this rain then falls through a sub-zero layer below and becomes supercooled, forming an instant ice glaze on contact with the ground. pic.twitter.com/6MFwqsClGf
— Dan Holley (@danholley_) December 15, 2018
Incredible 12Z sounding from Nottingham. Raging warm advection (SE sfc. winds to SW at 700 hPa) generating a warm nose (2°C at 850 hPa) atop a cold boundary layer (-5°C at 925 hPa). Rare to see this in the UK, and can cause #FreezingRain. pic.twitter.com/IdFDns3yaI
— Simon Lee (@SimonLeeWx) December 15, 2018
and where the lowest mile of the atmosphere remains at or below freezing, like in the Highlands, it’s snow!
On our way to Inverness and taking double the time because the #A9 conditions are horrific for driving in. When we left there was no snow and there wasn’t any in Inverness, but it’s come fast. ❄️ we’ve passed 2 very bad accidents so please be careful if you’re travelling ?? pic.twitter.com/towyOWeXNI
— Amber Zoe (@imamberzoe) December 15, 2018
⌚16.40⌚
A number of route are affected by heavy snow and rain this afternoon.
Stay up to date here: https://t.co/jtiyFWHXwE
Stay up to date with @metoffice here: https://t.co/HeOAt2nKw6#PlanAhead #DriveToRoadConditions pic.twitter.com/4HR9IJEmnr— Traffic Scotland (@trafficscotland) December 15, 2018
Once Deirdre passes, mild Atlantic air will fill our atmosphere and by next week we’re in warm southwest winds ahead of another front.
The GFS ensemble shows a warmer than normal pattern now through Christmas Day.
Despite this, just keep in mind what’s going on way up in the stratosphere…..
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