Tracking The Developing French Low

[Roger J Smith]

Sometimes the model guidance is just a foundation for meso-scale forecasting. This may be one of those occasions.

The Atlantic low that was approaching Portugal yesterday has disintegrated over Spain and what's left of it will drift towards Barcelona and the French Riviera over 24-36 hours. Meanwhile, a meso-scale low is developing in the lee of the Pyrenees near Bergerac and Bordeaux, and this is associated with an inverted trough running NNE towards Belgium. This takes advantage of an upper level trough following the coldest upper level low-thickness slug that is currently advancing rapidly towards Wales and southwest England.

The arctic front has stalled at about a line from north of Nantes to Le Mans and about 100 miles south of Paris. This is advancing very slowly north against the strong easterly flow, and generating moderate snow, reported as heavy by some co-op observers on meteociel. This band of meso-scale snowfall will be pushed north into the Channel over the next six hours and the inverted trough will sharpen until a meso-scale low forms near mid-Channel south of Brighton.

At this point over-running will add to the heavy meso-scale sea-effect complex over southeast England and a widespread blizzard like snowstorm may develop across southern England including much of the southwest, and south Wales. Separate heavy sea-effect bands will sweep into eastern Ireland.

Through the day on Monday, the meso-scale frontal snow will pivot with the low trying to push inland. Although it may make some progress, the main deformation will come with a further inverted trough feature running north up the east coast of England. This may introduce sleet or rain to some east coast locations but it will tend to hold back the actual progress of warm air at the surface, I feel, and will hold relatively cold air in place near the surface as the low deepens. This could allow heavy snowfall rates to continue in many inland portions of England and Wales as the low begins to drift towards the Bristol Channel. Meanwhile, new low pressure is likely to be forming offshore from Portugal. Eventually, the low drifting west to the south of Ireland will be pulled back into this stronger low, while the remnant old low in the Med will make some progress north into southern France, forming a three-part complex low that is likely to pull back into the Bay of Biscay.

The overall result of all this may be a massive snowfall in many areas, so people should be prepared for the possibility that very large snowfall totals will begin to accumulate not only in the Thames streamer zone as at present but more widely across southern England and some parts of central England well into Yorkshire in terms of the inverted trough feature creating a secondary band of heavy snowfalls. Hard to estimate the potential here as much of this event has not even begun to activate at this hour, but let's say conservatively 20-30 cms could accumulate in some parts and I would not rule out larger amounts locally over some of the higher terrain of inland southern England, so 30-50 cms would be possible, and on top of that there could be some drifting in places.

Will update this once the events start to come together, but with the temperatures as low as they are now in places like Lyneham and Little Rissington, I feel that the ingredients are there for a historic snowfall event.

[stoke weather watch]

When do you think this could hit the south coast?

[summer blizzard]

When do you think this could hit the south coast?

Around dinner time.

Current FAX has a single 986mb low just off Portugal at the moment. However xcweather has a secondary low centred just east of Bourdoex in south western France at 988mb.

[Hot*Snow]

What would you expect the track of the weather system to be - will this be a southern event only or would you expect it to travel further north. Do you think the north-west could be in the firing line.

Good spot anyway! Adds another twist to a fascinating tale.

[mezzacyclone]

all this and i`m just getting over another monumental superbowl roger

great days indeed!

[stoke weather watch]

But how far north do we think it will go and why have the met office or the bbc said anything bout it?

[Ross B]

But how far north do we think it will go and why have the met office or the bbc said anything bout it?

They have? Is this not the snow that is meant to move the whole way up the UK and give snow to Scotland on monday night/tuesday? In which case they were going for very heavy snow towards the east coast of England

[stoke weather watch]

I though this was a new low? i know about the main band coming in from the southeast later on but will that get up to stoke on trent?

[tom_f123]

Fantastic post roger, thanks for that.

What do people think the chances of the west mids are, i think ill literally cry tommorow if we get nothing again and the south get more dumpings.

Edited February 2, 2009 by tom_f123

[weatherobsuk]

Thanks Roger, made for intresting reading. I think I grasped the basics of it but im still confused as to what the chances for the central Pennine region areas are going to be?

With the introduction of milder air behind the front that pivots over Central England to the East, would the freezing level to the West ensure that any precip thats likely to fall be guaranteed to fall as Snow to the West? FAX charts also had the Front as a Trough so whats changed the Models predictions back into a frontal system again?, is it the introduction of the airmass from Belgium causing forcing thats going to enchance any precipitation over Southern and Central England?

[fatyido]

Thats made me sooooooooo excited reading that. It seems that although we are 50 miles north up the A1 from Londons heavy overnight snow,

it appears that we in West Cambridgeshire should see some heavy snowfall later this afternoon.

I cant wait. Bring it on - and please dont downgarde..!!

[azores92]

Thats made me sooooooooo excited reading that. It seems that although we are 50 miles north up the A1 from Londons heavy overnight snow,

it appears that we in West Cambridgeshire should see some heavy snowfall later this afternoon.

I cant wait. Bring it on - and please dont downgarde..!!

the graphics are fairly poor atm. could get better spose.

[03jtrickey]

Will update this once the events start to come together, but with the temperatures as low as they are now in places like Lyneham and Little Rissington, I feel that the ingredients are there for a historic snowfall event.

So it's not all over then!!!! I'm only 20 miles West of Little Rissington!

Only had 1cm so far

[snowking]

So it's not all over then!!!! I'm only 20 miles West of Little Rissington!

Only had 1cm so far

Fantastic read and great potential there roger, what would be the key ingredients to watch for across france to see if these developments are occuring?

James more on the way soon my friend it seems to have encirculated us in the last few hours and the northern extremity of the streamer now feeding us some energy, first few small flakes coming down as i speak

SK

Edited February 2, 2009 by snowking

[Nights King]

Doesnt look good for west country from what i can see. had a quick look and met and bbc both have few showers from this low. Any chance of a change?

[Graeme B]

How potent will this low be as it moves northwards into Scotland ?

[sarah7meme]

is this likely to hit kent? as there are lots of speak about west...

i am above folkestone in rural valley

[tom_f123]

is this likely to hit kent? as there are lots of speak about west...

i am above folkestone in rural valley

Lol yes its going to track up the eastern side of the country

[Mondy]

How potent will this low be as it moves northwards into Scotland ?

Fax chart shows the front right over our heads on Tues. That should bring plenty!

http://212.100.247.145/fax/PPVG89.png

Edited February 2, 2009 by Delta X-Ray

[Severe Siberian icy blast]

Lol yes its going to track up the eastern side of the country

in pretty sure us midlanders will get it as well . i no the graphics arent that great but its a developing area remember

[*Stormforce~beka*]

is this likely to hit kent? as there are lots of speak about west...

i am above folkestone in rural valley

Just watched the bbc weather online and seems liek the main areas to miss out are Sussex and Hampshire close to where the low is sitting. Shows no dumping here.

[Thunder Snow]

Is it going to hit Northern England

[Roger J Smith]

Update, the area of moderate snow in northern France is approaching the Channel now, expect some fairly extensive development of heavy snowfall into southeast and south central England by mid-day (where not already in progress from sea-effect bands). Further north, it will be a case of the existing sea-effect becoming heavier later on as this energy phases, the situation will still essentially be a nowcasting radar-watching exercise for many, but I do expect the spread of heavier snowfall amounts to be a big factor in the total outcome of this situation. Some have already seen a lot of snow and will get a lot more, others have seen very little and will get a lot in a while ... and some will miss out, but this has the possibility of spreading snow into districts that cannot get any from sea effect bands. Much depends on the actual path and strength of the meso-scale low, which is just beginning to push into the frontal band now in south-central France.

[East Herts Snow]

The Northern edge of the front will be hitting the English channel around 9am.

Will this also help to pep up the ppn?

[*Stormforce~beka*]

Roger - Do you think that Hampshire will miss out on this one as its so close?