Model output discussion - after the beast, what next?

[feb1991blizzard]

12 minutes ago, Summer Sun said:

Arpege 12z shows a gap as well obviously impossible to take this overly seriosuly this far out

 

Also I don't buy into the 9cm IMBY either, we didn't have that much more level snow in the last cold spell (maybe 5 inches - difficult to tell with drifts) and the heights and 850's are not as low this time.

[Whether Idle]

49 minutes ago, blizzard81 said:

Very welcome northward adjustments on most of the main players on the 12z runs. Perfect easterly hit this Saturday running into Sunday. This should create some significant convection. Just hope the colder than normal north sea doesn't temper things too much. 

The North Sea is not far off the LTA. Id be more focussed on inland solar convection in your locale.

[SMU]

14 minutes ago, Summer Sun said:

Arpege 12z shows a gap as well obviously impossible to take this overly seriosuly this far out

 

20-25cm ^^ in that dark bit over NW Kent ( 7 stages of shading on the scale )

[SMU]

Just now, feb1991blizzard said:

Also I don't buy into the 9cm IMBY either, we didn't have that much more level snow in the last cold spell (maybe 5 inches - difficult to tell with drifts) and the heights and 850's are not as low this time.

Core heights are lower & more concentrated this time ( but over shorter space of time )

[MattTarrant]

5 minutes ago, Steve Murr said:

20-25cm ^^ in that dark bit over NW Kent ( 7 stages of shading on the scale )

It states 18cm as MAX. 

[Whether Idle]

2 minutes ago, MattTarrant said:

It states 18cm as MAX. 

Agree.  Correct.

 

[SMU]

1 minute ago, MattTarrant said:

It states 18cm as MAX. 

Yes reviewed it - 6 stages not 7 so 15-20cm scale 

Still 18cm plus elevation @1.5x gives the downs about 25-30cm in the sweet spot same as 2009.

[Dancerwithwings]

11 minutes ago, Steve Murr said:

20-25cm ^^ in that dark bit over NW Kent ( 7 stages of shading on the scale )

A good example of a 'Thames Streamer', parts along that look very good for ppn

Edited March 14, 2018 by Dancerwithwings

[feb1991blizzard]

5 minutes ago, Steve Murr said:

Core heights are lower & more concentrated this time ( but over shorter space of time )

Also though last time it was 3-4 days of solid window for convection, less than 24 for Northern areas assuming ECM / UKMO (ish) is the verification, possibly only 12 hours of heavy convection although theres a more persistent band of snow showing on Friday first for NE areas of UK, Ive not seen that mentioned yet although its probably been mentioned on the short range thread.

[MattTarrant]

1 minute ago, Steve Murr said:

Yes reviewed it - 6 stages not 7 so 15-20cm scale 

Still 18cm plus elevation @1.5x gives the downs about 25-30cm in the sweet spot same as 2009.

Not convinced. We do though need to allow the time range to reduce to allow for greater confidence in the locality and intensity of potential streamers, maybe even a notable trough feature?

[JamesL]

I'm thinking along the same lines as Steve M. 

Having lived in Kent for over 23 years (on the N Downs) I have seen some tremendous LOCALISED totals where shower trains just dump snow for hours on end. 

The last Beast my parents had 8.5" of level snow between Faversham and Sittingbourne on the N Downs, whilst people down the road barely got a covering. 

You hit the jackpot here you could be looking at 25cms easily, even with precipitation limited to around 48 hours (maybe a little longer in Kent) 

Don't be surprised to see MO warnings turn orange in localised areas. The winds this time seem a little more NE so expect mid Kent to get hit hard rather than west Kent IMO 

[IPredictASnowStorm]

Its only Wednesday and they have put a warning out already so there's definitely going to be some decent amount of snow for most ?

[snowray]

15 minutes ago, Dancerwithwings said:

A good example of a 'Thames Streamer', parts along that look very good for ppn

I'm not sure that this is a Thames streamer to start off with any way, winds start off NEly then slowly veer more ENEly on Sunday. It will be interesting to see how convection pans out and the various streamers, thunder snow looks likely I would have thought in some of the showers?

Edited March 14, 2018 by snowray

[IPredictASnowStorm]

Snow Showers should fly in I think this will be better for snow than the last beast 

[Frosty.]

Discussing potential snow amounts at this range is fun but it's still too early to know where the sweet spot (s) will be!..get the cold in first etc.etc..

Wonderful model output if you're a coldie, especially the Ecm 12z..and especially if you're in the southern half / third of the uk....it's going to be a great weekend, especially in the regional threads.

Edited March 14, 2018 by Frosty.

[IPredictASnowStorm]

3 minutes ago, Frosty. said:

Discussing potential snow amounts at this range is fun but it's still too early to know where the sweet spot (s) will be!..get the cold in first etc.etc..

Wonderful model output if you're a coldie, especially the Ecm 12z..and especially if you're in the southern half / third of the uk....it's going to be a great weekend, especially in the regional threads.

Just too excited ? Week is going so slow 

Edited March 14, 2018 by IPredictASnowStorm

[SMU]

32 minutes ago, JamesL said:

I'm thinking along the same lines as Steve M. 

Having lived in Kent for over 23 years (on the N Downs) I have seen some tremendous LOCALISED totals where shower trains just dump snow for hours on end. 

The last Beast my parents had 8.5" of level snow between Faversham and Sittingbourne on the N Downs, whilst people down the road barely got a covering. 

You hit the jackpot here you could be looking at 25cms easily, even with precipitation limited to around 48 hours (maybe a little longer in Kent) 

Don't be surprised to see MO warnings turn orange in localised areas. The winds this time seem a little more NE so expect mid Kent to get hit hard rather than west Kent IMO 

Nice post & just to add to this - Ive often thought of how to forecast snow without the aid of models due to there inability to quantify PPN totals from Streamers -

you can do the same for anywhere but The following parameters are important:

This is a very crude way -

A) Timeline of optimal instability - 24 hours

B)Max PPN rates from showers - ~2cm per hour

C)% of time You can optimise from the optimal instability time - max 75% (0.75) because the streamer locale usually changes.

This means the equation to the 'top out' values at sea level is A X B X C

so my forecast sweet spot at sea level would be 36cms within the window available.

In terms of elevation ( again crude ) based on reports I have seen from scotland then corresponding reports from Glencoe - that when sea level got a fall of 15cm, the Glencoe car park would be 2X (600M) ~ 30cm

So I would go with a 0.33 increase in depth per 100M

Tops of the downs are @ 200M Mostly - So 'top out' for the downs would be 59CM.

This is on a par with 2009 where low ground of NW kent got to 30-35cm in a 30 hour window & the high downs were in the 50's.

Taking the beast from the last week the GFS ppn rates/ snow depths look to be about 5-8X to low under convection where as the high res models like Hirlam / Aperge feel about 1.5X to short

Best

S

Remember that top out forecast. 36cm which is in the streamer sweet spot location TBC?

 

Edited March 14, 2018 by Steve Murr

[fazzafarrand]

50 minutes ago, feb1991blizzard said:

Also I don't buy into the 9cm IMBY either, we didn't have that much more level snow in the last cold spell (maybe 5 inches - difficult to tell with drifts) and the heights and 850's are not as low this time.

5*25.4=12.7cm that is more ? 

 

[Frosty.]

Cracking Ecm 12z ensemble mean for this weekend, especially across southern uk..amazing charts considering the time of year, this being spring and all!!

Edited March 14, 2018 by Frosty.

[london-snow]

11 minutes ago, Steve Murr said:

Nice post & just to add to this - Ive often thought of how to forecast snow without the aid of models due to there inability to quantify PPN totals from Streamers -

you can do the same for anywhere but The following parameters are important:

This is a very crude way -

A) Timeline of optimal instability - 24 hours

B)Max PPN rates from showers - ~2cm per hour

C)% of time You can optimise from the optimal instability time - max 75% (0.75) because the streamer locale usually changes.

This means the equation to the 'top out' values at sea level is A X B X C

so my forecast sweet spot at sea level would be 36cms within the window available.

In terms of elevation ( again crude ) based on reports I have seen from scotland then corresponding reports from Glencoe - that when sea level got a fall of 15cm, the Glencoe car park would be 2X (600M) ~ 30cm

So I would go with a 0.33 increase in depth per 100M

Tops of the downs are @ 200M Mostly - So 'top out' for the downs would be 59CM.

This is on a par with 2009 where low ground of NW kent got to 30-35cm in a 30 hour window & the high downs were in the 50's.

Taking the beast from the last week the GFS ppn rates/ snow depths look to be about 5-8X to low under convection where as the high res models like Hirlam / Aperge feel about 1.5X to short

Best

S

Remember that top out forecast. 36cm which is in the streamer sweet spot location TBC?

 

If correct 2009 gave me the biggest snowfall seen nigh on a foot and the meto issued a red warning albeit very localised other parts of the region received copious amounts also a great event that stands out in my memory although a quick thaw occurred and within a day or two the snow was gone. Would be great if we see even half that total over the weekend more runs needed however.

[feb1991blizzard]

The Icon 18z is going to be a stonker.

[bluearmy]

Incidentally, the impending reversal around 20th is pretty short lived and shallow as a gentle zonal flow returns at 60N  after a day or so. There is plenty of reverese flow north of 70 throughout the strat though in the trop, areas of reasonably solid  zonal flow remain which no doubt is reflected in the positive AO/NAO phase we see next week 

[Chertseystreamer79]

19 minutes ago, Steve Murr said:

Nice post & just to add to this - Ive often thought of how to forecast snow without the aid of models due to there inability to quantify PPN totals from Streamers -

you can do the same for anywhere but The following parameters are important:

This is a very crude way -

A) Timeline of optimal instability - 24 hours

B)Max PPN rates from showers - ~2cm per hour

C)% of time You can optimise from the optimal instability time - max 75% (0.75) because the streamer locale usually changes.

This means the equation to the 'top out' values at sea level is A X B X C

so my forecast sweet spot at sea level would be 36cms within the window available.

In terms of elevation ( again crude ) based on reports I have seen from scotland then corresponding reports from Glencoe - that when sea level got a fall of 15cm, the Glencoe car park would be 2X (600M) ~ 30cm

So I would go with a 0.33 increase in depth per 100M

Tops of the downs are @ 200M Mostly - So 'top out' for the downs would be 59CM.

This is on a par with 2009 where low ground of NW kent got to 30-35cm in a 30 hour window & the high downs were in the 50's.

Taking the beast from the last week the GFS ppn rates/ snow depths look to be about 5-8X to low under convection where as the high res models like Hirlam / Aperge feel about 1.5X to short

Best

S

Remember that top out forecast. 36cm which is in the streamer sweet spot location TBC?

 

I was always rubbish at maths...! 

 

What regional thread you now in Steve?  The bookmark I had for the last beast is now closed. 

 

 

Cheers for the ever interesting input.

[shaky]

18z icon upgrade so far!!cold air coming in quicker and scandi high pushing further west!!cant believe it!

[Mike Poole]

Doesn't this one look like a giant freezing Monty Python style foot coming in?  Tapping the big toe too.

ICON at T57.   And it looks further north than the 12z which is perhaps more pertinent.