Tracking The Developing French Low

[WINTRY WALES]

Right here we go!

Been snowing lightly here all afternoon and then had a much heavier spell for about 30 mins which left a good dusting.

What is expected for the rest of the night and tommorow???

I thought we were in the firing line of a low pressure system moving up from the southwest(Roger J Smith opened a thread about it)

Also what are peoples thoughts for the rest of the week, the countryfile forecast yesterday showed snow all week for much of Wales and the southwest, has things changed guys??

Cheers all

WW

[Roger J Smith]

Update at 1730 GMT ...

Complex situation evolving about as expected. Low (990 mbs) now on French coast moving NNW, about due south of Brighton at present, should slop over to west Sussex and then make more of a NW turn through Hampshire-sw Wiltshire to near Bristol by 00z and south of Dublin by 09z.

Visualize four zones and how they are likely to move with this low, to get some idea of the weather sequence.

Zone one is the warm sector which is almost all offshore from the UK at present, an occlusion appears to be near central Essex, warm front almost due north cutting East Anglia in half, cold front pivoting round east Kent. This warm sector is more dramatic over Belgium (4-5 C) and is losing its integrity as it's dragged NW over snow-covered England with decreasing upper support. Still, it is likely to bring 1-2 C temps and 0-1 C dew points northwest into coastal east Midlands and northern East Anglia before mixing out and ceasing its rain-making tendencies. As it goes further northwest, its integrity is blurred by the coastal rain-snow division of sea effect squalls that it is gathering up and merging into sloppy sleet band.

Zone two is a dry slot behind the low extending up from France into parts of inland southeast England. This dry slot will rotate around and probably be found as a thin dry corridor heading west for central Wales. Temps in the dry low are about zero C and so snow melt will be a weak process at worst as it moves through.

Zone three is frontal forcing ahead of the low, and appears as a NNW-SSE oriented band of heavy snow currently in the central to west Midlands and north. This will tend to be rotated towards Northern Ireland overnight.

Zone four is wrap around precip being augmented by sea effect rotating out of the Irish Sea into the Bristol Channel in a flow that will probably back from NNE to NNW and hit inland southwest England especially Dartmoor with heavy snow for most of the night. This zone will see thunder snow develop at times, could mix with rain or hail at sea level but will eventually be rotated around the west-moving low to form squally bands over Channel for tomorrow morning, at which time they will push further east as well as back to north and try to force the dry slot off the surface as it stretches to breaking point near Cotswolds. At this point, the storm will be wrapped around with sub-528 dam thickness and could start to regenerate as a snowstorm.

So it's a complex pattern that favours some areas staying in snow despite nearby mild air moving north past them, for example higher parts of greater London, while for others it promises heavier snow later as features rotate overhead and intensify (the low itself is getting stronger and will have an energy boost from the Channel).

More later if there is more later.

[doublebarrel]

Many thanks for the update Roger

[willitbsunny]

Okaaay...so does this mean that it could be looking good for South East Wales??

[Bristawl Si]

Excellent post Roger! That's dedication posting from Canada! Just as the one earlier today.

You certainly called it right for us today in BTL. I wasn't expecting much going by the BBC last night and early this morn.

Had about 3 inches here in North BTL and it's just started snowing again.

[BristolBlizzard]

Excellent post Roger! That's dedication posting from Canada! Just as the one earlier today.

You certainly called it right for us today in BTL. I wasn't expecting much going by the BBC last night and early this morn.

Had about 3 inches here in North BTL and it's just started snowing again.

You had a bit more then me but still a good day <_<

You think we've had our lot mate or more to come?

[slinky1989]

Not likely to get any more here as the band that has just passed is moving westwards and the band that's over london (which I'm guessing is part of the french low?) is moving north <_<

Edited February 2, 2009 by slinky1989

[Bristawl Si]

You had a bit more then me but still a good day <_<

You think we've had our lot mate or more to come?

Well it's still snowing now.

From Roger's post i reckon we might get some more, but dunno whether it'll be a lot. it's just starting to freeze as well.

Where in BTL are you?

[Solar Cycles]

Update at 1730 GMT ...

Complex situation evolving about as expected. Low (990 mbs) now on French coast moving NNW, about due south of Brighton at present, should slop over to west Sussex and then make more of a NW turn through Hampshire-sw Wiltshire to near Bristol by 00z and south of Dublin by 09z.

Visualize four zones and how they are likely to move with this low, to get some idea of the weather sequence.

Zone one is the warm sector which is almost all offshore from the UK at present, an occlusion appears to be near central Essex, warm front almost due north cutting East Anglia in half, cold front pivoting round east Kent. This warm sector is more dramatic over Belgium (4-5 C) and is losing its integrity as it's dragged NW over snow-covered England with decreasing upper support. Still, it is likely to bring 1-2 C temps and 0-1 C dew points northwest into coastal east Midlands and northern East Anglia before mixing out and ceasing its rain-making tendencies. As it goes further northwest, its integrity is blurred by the coastal rain-snow division of sea effect squalls that it is gathering up and merging into sloppy sleet band.

Zone two is a dry slot behind the low extending up from France into parts of inland southeast England. This dry slot will rotate around and probably be found as a thin dry corridor heading west for central Wales. Temps in the dry low are about zero C and so snow melt will be a weak process at worst as it moves through.

Zone three is frontal forcing ahead of the low, and appears as a NNW-SSE oriented band of heavy snow currently in the central to west Midlands and north. This will tend to be rotated towards Northern Ireland overnight.

Zone four is wrap around precip being augmented by sea effect rotating out of the Irish Sea into the Bristol Channel in a flow that will probably back from NNE to NNW and hit inland southwest England especially Dartmoor with heavy snow for most of the night. This zone will see thunder snow develop at times, could mix with rain or hail at sea level but will eventually be rotated around the west-moving low to form squally bands over Channel for tomorrow morning, at which time they will push further east as well as back to north and try to force the dry slot off the surface as it stretches to breaking point near Cotswolds. At this point, the storm will be wrapped around with sub-528 dam thickness and could start to regenerate as a snowstorm.

So it's a complex pattern that favours some areas staying in snow despite nearby mild air moving north past them, for example higher parts of greater London, while for others it promises heavier snow later as features rotate overhead and intensify (the low itself is getting stronger and will have an energy boost from the Channel).

More later if there is more later.

I have to say Roger your forecasting skills are second to none. What with that and your LRF, you should be raking in the cash. After all, it's what you deserve, with all the time and effort you put into all!

Edited February 2, 2009 by Solar Cycles

[marksp]

many thanks for that Roger, have enjoyed posts over the years covering all weather topics. I have been trying to get to grips

with the snowfall event here and your comments have helped tremendously. I'm hopig for some more snow tonight here.

precipitation is still snow (just) more small ice crystals, but it is still accumalating but very slowly.

[jacksdad]

Not likely to get any more here as the band that has just passed is moving westwards and the band that's over london (which I'm guessing is part of the french low?) is moving north

Marvellous Swindon is the new Abingdon whilst not quite snowless only about 2" here today whilst further east 8"+ and now our six fingered friends to the west may get a good covering.

[kumquat]

Great post Roger. The area of precipitation extending around the M5 south of Bristol has just been spinning and dumping. I thought we'd had our lot around 19:30 but now the Eastern flank is coming back to get us!

Edited February 2, 2009 by kumquat

[Mondy]

And here's another on the way. Consistently showing on every GFS run for days:

[oldsnowywizard]

thought i would post in this one to discuss the latest radar soundings and to keep an eye on where the precip goes..

i was led to believe that the front from the south and north would combine, stall somewhere and drift back SE..

from the looks of things.. the north front just kept on goign south, the southern front has kept on going north..?

it does look like the western edge of the band over Bristol is heading SE.. i would imagine this will start dragging the rest of the eatsern band SE but with the precip filtering in a SW direction possibly?

result should be that central and perhaps eatern midlands and then SE of this area should see more precip later in the day.. possibly 3-4 hours...

[oldsnowywizard]

update..

larger area of precip is now heading NE out into the north sea.. finally a thin band of snow working very slowly SE.

ive had non stop snow now since 7am.. looks like at least another 3/4 hours at this rate.

polar low hitting Scotland bringin a band of heavy showers in.. i wonder where this will end up..