Model output discussion - deep cold inbound?

[ancientsolar]

4 minutes ago, weirpig said:

The only concern i have  and to be fair its not really that a big deal   but if the uppers are so low  we get that  alpine type powdry snow   which in my opinion is bloody awful.  You can have a foot of the stuff and the ground is clear  but up the corner of some terrace house it upto the upstairs bathroom. 

with a gradual cool down, there will probably be a very thick layer of snow already on the ground before any powder snow arrives, possibly 2 days worth 
, oh and powder snow in the wind is beautiful and makes you really feel like you are part of the north pole


 

[Bristawl Si]

3 minutes ago, Scott Ingham said:

The south west will hopefully benefit after tuesday during a battleground period. Its very hard for the south west to do as well as the east in a south easterly

A south easterly can be quite decent re snow for the Bristol area.

[Scott Ingham]

11 minutes ago, weirpig said:

I think we are in danger here of going a tad OTT   im sure there will be places that receive some snow  and im sure those eastern areas  may well get around those values.   but all of those regions  bordering on a foot of snow?.    highly unlikley 

Its obviously not every single town is it.

When the met office put out a warning for a county or two they also know some areas will miss out but i think at least one location in each of those area will hit between those amounts.

It wouldnt surprise me dropping into each one of those regionals to find one poster to hit between the freshholds by wednesday 12am.

I never said widespread? But i honestly think a big swathe of the eastern portion of this country will hit at least 20cms

[weirpig]

3 minutes ago, Djdazzle said:

Prior to the February 2009 snow event, they were predicting 10-15 cm. South of London was quite widely in excess of 20-25cm.

Yep  some areas could do  great.   but a vast swath of the country  under a foot of snow?.   bear grills would be running for cover. 

Edited February 4, 2021 by weirpig

[Polar Low]

4 minutes ago, weirpig said:

The only concern i have  and to be fair its not really that a big deal   but if the uppers are so low  we get that  alpine type powdry snow   which in my opinion is bloody awful.  You can have a foot of the stuff and the ground is clear  but up the corner of some terrace house it upto the upstairs bathroom. 

 

 

As for some of the snow depth predictions in this thread I think - quite understandably - that some people are going into hype overdrive. 

There's absolutely no evidence suggesting totals of a foot of snow widely in the SE/EA. I doubt we'll even see that locally. 

I imagine the average falls in favoured areas will be closer to GFS - up to 15cm.

[That ECM]

7 minutes ago, Kasim Awan said:

There's a difference between what we could expect vs what is likely to happen

If we plotted a histogram of probabilities of outcome vs severity of that outcome I would say your prediction sits at 30% on the probability axis which is conservative territory

I'm going with 50% atm which is more > 20cm quite wildey

 

Eh? If I go out in the rain what I could expect is to get wet and what is likely to happen is I will get wet. love your posts and detail. This one was just a ramp.

[Nick L]

Just now, Djdazzle said:

Prior to the February 2009 snow event, they were predicting 10-15 cm. South of London was quite widely in excess of 20-25cm.

And for every snow event suggested where totals exceeded what was forecast, I will show you an example where totals were lower than expectations. It's not a reliable form of forecasting.

[seabreeze86]

I honestly have no idea what the snow totals will be but what I do know from experience is that in every decent/severe cold spell snow amounts where I live anyway have always been underplayed. 2010 was the best example of this ,happened repeatedly 

[Battleground Snow]

Huge scatter on the GFS at 162 almost 17 degree range = GFS struggling to resolve the outcome...

It's probably it's biggest weakness. Atlantic being too progressive v a cold block, amplified by how cold the block and how big the low is.

[DIS1970]

Seems to me a few need to cut back on the old G & T's, looking beyond 3 days and estimating depths of snowfall is a little premature.

[Scott Ingham]

6 minutes ago, Kasim Awan said:

I share this POV tbh, as we've seen 6-8" from 12 hours of a flow with say 1.5x more instability in 2009

The upcoming flow > lasts say 36 hours at 1x the instability

12 hours x 1.5 intensity = 18 units. 18 / 7.5 inches = 2.4 units to an inch

Upcoming flow > 36 hours x 1 intensity = 36 units. 36 units / 2.4 = 15 inches

 

Yeah exactly that is my exact thinking i think well see the hi res firm up soon om this

[Kasim Awan]

2 minutes ago, That ECM said:

Eh? If I go out in the rain what I could expect is to get wet and what is likely to happen is I will get wet. love your posts and detail. This one was just a ramp.

Better rephrased as what you'd expect vs what could happen

You expect to get wet but you could slip and fall

Don't discount slipping

It's basic statistics but important when analyzing what could happen in this set up

Edited February 4, 2021 by Kasim Awan

[BLAST FROM THE PAST]

The Atlantic isn’t coming steaming through.  There’ll be some wild outputs coming over next few days but like we saw over last week, the troughing will disrupt and happen further west.  There’s a major push of arctic air into mid latitudes around the NH...this is some hemispheric event.  January saw another drop in global temps as did December...there’s serious ‘widespread’ cold around.

 

BFTP

Edited February 4, 2021 by BLAST FROM THE PAST

[Scott Ingham]

2 minutes ago, Bristle boy said:

A south easterly can be quite decent re snow for the Bristol area.

I cant disagree and this looks likely tuesday i just see nearer 5-10cm before you get hammered thursday 

[Don]

Just now, Battleground Snow said:

Huge scatter on the GFS at 162 almost 17 degree range = GFS struggling to resolve the outcome...

It's probably it's biggest weakness. Atlantic being too progressive v a cold block, amplified by how cold the block and how big the low is.

Wow, not often you see a scatter like that!

[MattStoke]

I think a few favoured eastern spots could see close to a foot but more widely it will be 10-15cm, maybe some largish patches up to 20cm. Reducing to 5-10cm for central areas, and 0-5cm for western areas. More over high ground and less in sheltered spots. Highest amounts in unsheltered areas prone to streamers.

Edited February 4, 2021 by MattStoke

[TEITS]

4 minutes ago, Nick L said:

There certainly is. But there is no evidence in either case to suggest the snowfall depths that were suggested there. There is no way that we're going to see in excess of a foot of snow through London and the SE on Sunday. If people want to post the evidence from the models that suggests otherwise then be my guest. EC has totals no higher than 10cm, GFS closer to 15cm, UKV could see closer to 20cm in places. Absolutely no evidence that I'm seeing to suggest in excess of a foot.

I'll be writing the forecast for TfL later, so if anyone wants to provide evidence for it I will gladly change my mind! 

Sometimes you need to use instinct and experience rather than simulated models. I have a very good idea of snowfall distribution across my area under the conditions suggested by the models for next week. Never forget how in the 80s an E,ly brought 1ft of snow in Peterborough in under 2hrs from a band of snow showers.

At times we can become too dependant on computer models. For example I just knew the GFS was way off with its handling of the low for this weekend. At one stage it even had the low move NW to Iceland against the huge block to our N. Instantly I knew this was wrong.

[Djdazzle]

Just now, Nick L said:

And for every snow event suggested where totals exceeded what was forecast, I will show you an example where totals were lower than expectations. It's not a reliable form of forecasting.

Agreed - but to rule it out at this range is taking a risk. Things could upgrade quite easily.

[Howie]

2 minutes ago, Battleground Snow said:

Huge scatter on the GFS at 162 almost 17 degree range = GFS struggling to resolve the outcome...

It's probably it's biggest weakness. Atlantic being too progressive v a cold block, amplified by how cold the block and how big the low is.

This makes no sense, why is there such significant scatter only 3 days out? Clearly has lost the plot

[Kasim Awan]

Just now, Djdazzle said:

Agreed - but to rule it out at this range is taking a risk. Things could upgrade quite easily.

 

3 minutes ago, Nick L said:

And for every snow event suggested where totals exceeded what was forecast, I will show you an example where totals were lower than expectations. It's not a reliable form of forecasting.

Localizations from streamers & too low of an intensity in forecast is only a real issue in unstable convective flows, not so much with fronts. So streamers & shower set ups more regularly outdo forecasts.

[Mapantz]

The level of ramping in here is quite something.. 

It is suited to the moans/ramps/banter thread, as it is over the top quite frankly.

[Don]

6 minutes ago, Scott Ingham said:

I cant disagree and this looks likely tuesday i just see nearer 5-10cm before you get hammered thursday 

Not sure what my location can expect at this range but I suspect the best chance for significant snow will be later next week, although I'm sure there will be some early in the week, but probably nothing like the potentials for the south east?  Still all to play for....

Edited February 4, 2021 by Don

[Scott Ingham]

8 minutes ago, bluearmy said:

 

Yes - rather over excited 

widely 5/10 cms up the eastern side of England ....locally 15/20 cms, especially in coastal counties 

But those 5/10 cms could easily end up 2/5 cms .....that’s just how snow is .....

Locally is a figure spoken about.

The numbers i throw out arent wide spread and werent suggested as but ill be surprised if one poster from all those areas hasnt hit 20cm or 30cm in the soutb east by tuesday pm

[Allseasons-Si]

Evening all

firstly i would just like to comment on the PPN,there is no way of telling how much snow we will likely to see on the ground from this easterly until it has settled,...fact,you have to take in to consideration what troughs might there be in the flow and not everywhere will see these streamers,the models will not pick these out yet and they won't take into account the convective state of these,SST'S is another factor with the differential in temps and uppers

as for the models,great runs again today and if more of an upgrade again today

the latest gefs ens gets my area down to -10.8c on the 8th Feb,that is pretty good going.London not bad at -8.7c.

 

[Kasim Awan]

GFS snowfall accumulations initialized on 26th February for 28th Feb midday. Only 4-5cm for most of the East Midlands, East Anglia, Essex. Boy were they underestimations @Scott Ingham

Edited February 4, 2021 by Kasim Awan