The lame NW theme continues after the milder blip at the end of the working week. Not much snow on offer for many but the Scottish ski industry should be pleased. Thereafter anyone’s guess but disappointing non the less.

Originally Posted by: JACKO4EVER 

The NWP show a very cold NWly. Nothing lame about. Many people’s ability to read charts is lame. The London ensembles are clearly cold with some touching-10 C between 29 Jan & 1 Feb.

 There is crystal clear potential for snow next week in the south as well as the north according to current NWP.

Originally Posted by: Iceman 

Agreed. Effectively we’re back to the pattern that was emerging a week ago, before the 2-3 day dance with the promise of an easterly.

The phantom easterly had the effect of destroying the calm but upbeat mood in here. Hopefully we can get it back. 

Originally Posted by: Gandalf The White 

The lame NW theme continues after the milder blip at the end of the working week. Not much snow on offer for many but the Scottish ski industry should be pleased. Thereafter anyone’s guess but disappointing non the less.

Originally Posted by: JACKO4EVER 

Quite right Jason. ECM this morning shows what might happen in FI if the Azores high retrogresses to Greenland, but this scenario is unlikely and the window of opportunity will surely expire soon as the SSW propagation will have long ceased before met office’s mirage cold spell has a chance to manifest before April. 

Originally Posted by: White Meadows 

No. The theoretical maximum is 23 * 16 = 368.

Originally Posted by: Brian Gaze 

Any chance of another SSW?😁 we could see another one.

Originally Posted by: tallyho_83 

Quite right Jason. ECM this morning shows what might happen in FI if the Azores high retrogresses to Greenland, but this scenario is unlikely and the window of opportunity will surely expire soon as the SSW propagation will have long ceased before met office’s mirage cold spell has a chance to manifest before April. 

Originally Posted by: White Meadows 

On the subject of all things SSW, an excellent article here from Dr. Judah Cohen on AO, NAO and the Polar Vortex - where we are now, and what's likely to happen for the rest of winter. A long read, but very worthwhile.

https://www.aer.com/science-research/climate-weather/arctic-oscillation/

Originally Posted by: Arcus 

Agreed. Effectively we’re back to the pattern that was emerging a week ago, before the 2-3 day dance with the promise of an easterly.

The phantom easterly had the effect of destroying the calm but upbeat mood in here. Hopefully we can get it back. 

Originally Posted by: Gandalf The White 

I quite agree WM, the split vortex is doing us no favours either. Considering the end of this month was supposed to be “blocked” it’s a big step backwards. No matter how this NW outbreak is dressed up- it’s a pig. We can put lipstick on it and send it to the beauticians, but it will still be a pig nonetheless.

Originally Posted by: JACKO4EVER 

On the subject of all things SSW, an excellent article here from Dr. Judah Cohen on AO, NAO and the Polar Vortex - where we are now, and what's likely to happen for the rest of winter. A long read, but very worthwhile.

https://www.aer.com/science-research/climate-weather/arctic-oscillation/

Originally Posted by: Arcus 

Brian - sorry to come back to this.  1) Do the TWO ensemble charts generate from the same base data as the Wetterzentrale ones?  2) the only reason I ask is the snow row % they show are shown for every 6 hour increment of the output, so they give 4 values per 24 hours.  the TWO ones on give 2 per 24 hours.    How is there a difference?

This is not a criticism, just curious. 

Originally Posted by: kmoorman 

But many have said that's what we look for for a true major SSW is to see the PV split!? Which was what happened hence zonal winds reversal so you're saying that the split in the PV isn't helping?

Originally Posted by: tallyho_83 

1) Almost certainly. The only possibility is they use one of the adjusted data sets provided by NCEP, unlikely though because it would most likely be labelled differently.

2) The GEFS data sets are stepped at 6 hour intervals so there are 4 steps per full day. There are 23 runs - 20 GEFS, Control, Mean and GFS Operational. The TWO snow row is calculated by:

i) Check each run

ii) Check ALL steps for a given day (usually 4, but not always. eg. 12z day 1 only has 2 steps, 12 and 18) to see whether snow is forecast

iii) If one or more steps for a given day show snow then add 1 to the snow row value for that day

The key difference between the TWO and WZ ones (if they are as you describe) is this:

1) WZ is showing the chance of snow for a given time step

2) TWO is showing the chance of snow for a given day

A quick example:

Assume only 1 run shows snow for all 4 time steps on day 2.

TWO will display a snow row of 1 for day 2.

WZ will display a snow row of 1 (or the % equivalent) for day 2 00:00 GMT, 1 for day 2 06:00 GMT, 1 for day 2 12:00 GMT, 1 for day 2 18:00 GMT.

Originally Posted by: Brian Gaze 

As a Kentish Man, my world view is that the north begins at Watford and Manchester is a town on the Scottish border.

So conversely you may well think, being from Kilbride, that the south begins at Durham, or maybe York. Those places may well get a bit of snow, but let me assure you that the true south, south of the M4, NEVER gets snow from a NW-ly.

Originally Posted by: DEW 

Thank you. 

Does your method round to the nearest integer then, as there will be times when the number don't easily divide by 4 for a single day.

So, if the figures for a day are  1 1 0 1     or   2 2 3 2     would TWO give us  1   and  2 respectively?      

And to get a 23 on TWO we'd need at a minimum 22 23 23 23    for the 4 data points on that specific day.

Is that correct?

Originally Posted by: kmoorman 

6z rolling out... and by 120 things are changing again... a slight adjustment and things look less wintry ... However. That HP out east seems to look like it has the potential to influence our weather charts again.

Originally Posted by: Russwirral 

6z rolling out... and by 120 things are changing again... a slight adjustment and things look less wintry ... However. That HP out east seems to look like it has the potential to influence our weather charts again.

Originally Posted by: Russwirral 

It has split, it just hasn’t split in the right place, so we still get troughing where we don’t want it. 

Some odd looking charts around again this morning, eg look at the pressure patterns on the GFS 0Z 300hr chart!

Originally Posted by: Rob K 

Just for fun!

differences in the Greenland and HLB between the 00z run of the OP and 06z run from N. Hemisphere view:

06z @ 384:

Originally Posted by: tallyho_83