Short range model discussion - into 2018

[PompeyFC]

3 minutes ago, knocker said:

Temps much better behind the front but of course France is not subject to the double whammy

Knocker. Thanks for the link earlier. Does the approaching system pick up more moisture as it crosses the channel due to 850s thickness etc and does the precipitation increase as it hits the cold air over south west and se wales ?

[PompeyFC]

Is the system likely to stall and pivot off north west aswell hence the long hours of snow forecast?

[knocker]

47 minutes ago, PompeyFC said:

Is the system likely to stall and pivot off north west aswell hence the long hours of snow forecast?

The system already has plenty of moisture and the direction and speed that it's moving, along with the increasing wind, are the main problems

[Nick L]

UKV has trended this afternoon/evening's snow eastwards by some extent. The 6z had negligible snow for Bucks through to Essex, it's now wanting to bring in 3-5cm through these areas going into this evening.

Edited March 1, 2018 by Nick L

[knocker]

You can also see the upper front quite clearly on that geostationary

 

[swebby]

5 minutes ago, knocker said:

You can also see the upper front quite clearly on that geostationary

 

The warm front N-france tying in nicely with the observations of the snow to rain line

[knocker]

Just think the temps down the west coast of France might be in west Cornwall this evening

[knocker]

The high resolution MODIS at 1300 illustrating the convergence zone of the midday analysis 9Image courtesy Dundee Satellite Receiving Station)

[tyson99]

Does this low system seem to be a lot further east than originally predicted or am I miss reading the charts ?!?!?

[Interitus]

3 hours ago, knocker said:

Funny enough as the 06 GFS shows it in a couple of areas tomorrow morning I've been looking for a good sounding that might illustrate it. Not brilliant but close

Midday sounding from Brest, not much of warmer slot above at the time but shows the potential in the region -

And further east at Trappes -

[Nick L]

25 minutes ago, tyson99 said:

Does this low system seem to be a lot further east than originally predicted or am I miss reading the charts ?!?!?

I think it's a bit further east than initially expected, not by a huge amount though.

[shotski]

4 minutes ago, Nick L said:

I think it's a bit further east than initially expected, not by a huge amount though.

How’s central beds looking nick ?

looks like we could be in the game. 

[knocker]

3 minutes ago, Interitus said:

Midday sounding from Brest, not much of warmer slot above at the time but shows the potential in the region -

And further east at Trappes -

Yes I agree and it looks increasingly likely as if some parts of the south west/Wales will cop a little of this. Not good

[Nick L]

1 minute ago, shotski said:

How’s central beds looking nick ?

looks like we could be in the game. 

If the UKV is anything to go by, absolutely. It has shifted the potential a long way east, but I'm remaining cautious as it's a bit isolated with this.

[Sawel]

2 minutes ago, Nick L said:

If the UKV is anything to go by, absolutely. It has shifted the potential a long way east, but I'm remaining cautious as it's a bit isolated with this.

Still plenty of snow showers showing for up here in Dundee and Eastern Scotland between now and Tuesday I imagine? 

[Nick L]

7 minutes ago, Nick L said:

If the UKV is anything to go by, absolutely. It has shifted the potential a long way east, but I'm remaining cautious as it's a bit isolated with this.

GFS is doing the same. Confidence increasing.

[SilverWolf]

16 minutes ago, Nick L said:

GFS is doing the same. Confidence increasing.

Hi, what does this mean for tomorrow potentially? Is the cold less likely to hold, or is the cold stopping it’s movement north? Thanks 

[Swave Snow]

Has Emma Pivoted yet. On the radar seems to be travelling northwards encroaching much more of the East than even this morning's forecasts? If it has pivoted please tell me and I apologise if I have made a mistake or please confirm if it has not pivoted yet.

[knocker]

Still possibilities of freezing rain overnight

[captaincroc]

39 minutes ago, Nick L said:

GFS is doing the same. Confidence increasing.

Hi Nick.

South Cheshire was always on the edge of the predicted area for this front...could the eastwards shift help us this evening?

[swebby]

12 minutes ago, knocker said:

Still possibilities of freezing rain overnight

That's stretching over a wide area, hopefully wrong but an eye on MetO warning this evening to see if further warnings go out.

[Day 10]

Wrong thread

 

 

Edited March 1, 2018 by Day 10

[knocker]

Apart from the far south west the warmer air struggles to get north but finally gains some traction over the weekend.

[feb1991blizzard]

1 hour ago, Nick L said:

GFS is doing the same. Confidence increasing.

Any chance that PPN expected N Wales might get a bit further North as well as East?

[Interitus]

8 hours ago, Buzz said:

Kind of.

Thanks for the explanations but I'm still a bit puzzled - the west of Wales doesn't look like getting that much snow. However past easterlies have always given a good amount in the same area from frontal systems approaching from the west or south west. Presumably the main factor causing the relative lack of western Wales snow today/tomorrow is that the fronts are approaching from the south ? (Then of course the mountains do their bit as you have described).

Well it would depend on many things such as the angle of the fronts, the actual wind direction and strength at various altitudes and the strength of the frontal uplift etc. Carmarthen might see a reasonable snowfall this time, though all things being equal on occasions like this, it is unlikely to be as much as higher ground to the east most of the time.

So for example here is the precipitation across south Wales later this evening, from the Arpege model -

The black line is a cross-section from Carmarthen eastwards to Monmouth. Looking at the vertical velocities along this line, the easterly wind flow (from the right hand side) shows strong uplift on the eastern flank of the Brecon Beacons, with descent on the western end through to Carmarthen (at the left hand edge) -

The descending air warms (not shown here but 850 temp varies roughly between -8°C and -2°C) and dries out, shown in the relative humidity cross-section -

This drier air limits precipitation forming, and also evaporates or sublimates snow falling into it; the fall speed of the flakes from upwind to Carmarthen will likely take them on a journey right along the drier section of lower humidity air.

(whatever happens, Dydd Gŵyl Dewi Hapus!)

 

Edited March 1, 2018 by Interitus