Model output discussion - winter proper underway

[Chesil View]

10 minutes ago, damianslaw said:

In projected mobile periods always worth keeping an eye on the jetstream, and the latest forecasts are for it to trend south next week, so whilst unsettled looks the theme it could be a cold unsettled spell, at least in the north increasing chances of some wintry precipitation to low levels at times with frost, further south more average conditions. Indeed secondary low, and sudden trough development looks likely to happen, making forecasting each day ahead quite difficult, timing of fronts and low pressure and path not easy to forecast. I too am not expecting a particularly stormy spell, windy yes, but nothing remarkable, jet will have some oomph but the wind will be taken out of it so to speak.

Until Christmas Day - one of those miserable murky grey descents into christmas, that has plagued the UK for the seventh year in a row now, maybe next year will bring something different, very very uninspiring, but at least nothing to interfere with pre-christmas travels. 

ECM showing a arctic high developing next week thanks to pacific ridging, UKMO going for a more NW influence for christmas day, and GFS trending colder once we get to christmas day.

 

Quite so Damianslaw the only genuine white xmas (falling and lying snow on the day itself) I ,ve had here in coastal south Dorset was in 1993 from a little runner running round the base of a trough to the north.

[feb1991blizzard]

1 minute ago, frosty ground said:

Which will change again in the morning.... 

Not in the 15d period from now.

EDIT : It might change but not significantly enough for a proper cold spell to suddenly develop.

Edited December 19, 2017 by feb1991blizzard

[Daniel*]

27 minutes ago, Man With Beard said:

Spreads suggest some runs with low pressure quite far south into Europe. We'll see the detail later

That’s unusual to see that’s interesting late December wintry but not overly cold? Possible.

[northwestsnow]

22 minutes ago, feb1991blizzard said:

Not in the 15d period from now.

EDIT : It might change but not significantly enough for a proper cold spell to suddenly develop.

Think you would very well on tonights EC Feb- certainly from 192 onwards

[Dennis]

some are showing .... we need to wait

[ANYWEATHER]

Hello! After the benign conditions before Christmas things have not changed on recent output with a very strong jet stream coming out of North America because of some extreme cold over there interacting with the sub tropical high pressure further further south in the North Atlantic Ie The Azores High! There is no point at this moment looking at detail , but expect the unexpected , Loads of weather coming to us via a turbulent Jet stream. Watch This Space ...

[feb1991blizzard]

2 minutes ago, northwestsnow said:

Think you would very well on tonights EC Feb- certainly from 192 onwards

I wont ever be looking at those charts again - unless someone else asks on here for a specific snow depth for their location - two words spring to mind - fingers and burnt.

[knocker]

There is nothing in tonight’s NOAA, GEFFS and EPS mean anomalies to suggest any shift away from remaining unsettled from the end of the  coming weekend for fourteen days with temps varying around the average.

Upstream in the 6-10 day period we have the NE American ridge displacing the Canadian vortex lobe to the Hudson Bay area with a trough running south.  There is a strong jet running around south of  the latter across the Atlantic to connect to a secondary lobe with troughs across the UK and Eastern Europe with little sign now of the east European ridge.

Thus this portends unsettled weather over the UK as systems track east on the strong upper flow which doesn’t of course rule out some wintry interludes as they traverse the country and gales could be part of the package as well, all of which the det. runs will need to sort.

Although not total agreement in the ext period there are some adjustments upstream with the ridge tending to reorientate west allowing the vortex to slip back to northern Canada. Still a strong upper westerly flow although the complex subsidiary lobe north of Scandinavia is simplified with the trough to the north west of the UK. So still unsettled with temps around average and the usual caveats apply.

[Ukwoody]

Hi all. I'm confused. In this mornings post by Paul, he suggests there may be a "storm" on Boxing day with strong winds.  Yet toning some seem to be suggesting rather mild benign conditions. Have things changed?  Certainly the charts around lunchtime seemed to suggest strong winds...

[Dennis]

Just now, Ukwoody said:

Hi all. I'm confused. In this mornings post by Paul, he suggests there may be a "storm" on Boxing day with strong winds.  Yet toning some seem to be suggesting rather mild benign conditions. Have things changed?  Certainly the charts around lunchtime seemed to suggest strong winds...

Its all about what we see at HIGH LVLS or also called stratospheric signs - there are some strong activities at the moment

[January Snowstorm]

It all looks average winter fayre to me 

Cold / mild interludes with nothing too severe. Very little wintry weather away from mountains in the Northwest.

[Summer Sun]

3 minutes ago, Ukwoody said:

Hi all. I'm confused. In this mornings post by Paul, he suggests there may be a "storm" on Boxing day with strong winds.  Yet toning some seem to be suggesting rather mild benign conditions. Have things changed?  Certainly the charts around lunchtime seemed to suggest strong winds...

Up to Saturday looks fairly quite exact timings for the storm remain open to doubt but one arriving sometime between the 25th and 27th looks fairly likely

[Frosty.]

Certainly the Ecm 12z ensemble mean charts look a lot more interesting next week compared to the benign snooze fest this week. How the balance between mild / cold air works out is still all to play for but I'm encouraged that there is at least a chance of something wintry at times next week and hopefully into the new year too.

[Paul]

Latest blog from @Nick F looking at the potential for stormy weather between Xmas and New Year:

Potential Stormy Pattern Developing Between Christmas Day & New Year

[West is Best]

Things are starting to get very, very, interesting ...

There's a clear pattern shift signal around 26/12 - actually heralded on Christmas Day. Whether it goes the way of the pear, turns into 1962-3 (which began on Boxing Day) or much more likely sits somewhere between those two extremes remains to be seen. What's not really in doubt is that there's something for cold lovers to grasp hold of here.

[comet]

Way to much emphasis in here on EPS, GEFS, GloSea, Met etc etc they have all proven to be wrong many times in the past including the not to distant past and they will be again. The trend in the operational runs of the nwp  models look quite positive and so does the progression of downwelling in the strat. I would expect to see  further increases in northern blocking and a much colder pattern developing post Christmas. below are 30mb composite charts from the 14th and 16th this forcing downwelling from 10mb. This forcing started from wave breaking around the 8th and another slightly  weaker one around the 16th.

Below the composites for 50mb

below the composites for 100mb on the 14th and 16th

 

[nick sussex]

Continued debate in the US as to whether the outputs have  the correct MJO amplitude.

Regardless of the RMM forecasts they expect an active MJO into phase 8 and then 1.

MJO forcing is the catalyst for the surge of cold air into the US plains which suggests it’s signal isn’t being over ridden by other factors .

Thats off todays further MJO update from the Global Tropics Hazards outlook.

[JBMWeatherForever]

Seems to be that the potential for very cold conditions to affect the UK at times after Christmas and into the New Year is currently being under emphasised, given the current output in front of us. It may be that things can go pear shaped, however at the moment the trend is very much in the right direction. The end of 2017 is looking very interesting !    

[Bobd29]

11 minutes ago, West is Best said:

Things are starting to get very, very, interesting ...

There's a clear pattern shift signal around 26/12 - actually heralded on Christmas Day. Whether it goes the way of the pear, turns into 1962-3 (which began on Boxing Day) or much more likely sits somewhere between those two extremes remains to be seen. What's not really in doubt is that there's something for cold lovers to grasp hold of here.

Hi WIB, interesting hypothesis but seems totally at odds with Nick F’s storm chart in the post above. Looking at the 200 mph jet stream spawning very deep lp systems our way does not show any indication of blocking far south of the pole so hard to see anything more than transient nw spells of interest to cold lovers. Glad to hear your views on this.

[Frosty.]

I don't know what anyone else thinks but I'm looking forward to a chance of some cold zonality during the expected disturbed potentially stormy weather at times through next week and into the new year. Weather like we have this week is a waste of space, a waste of time and I can't wait until its shown the door next week!

[Nick F]

9 minutes ago, comet said:

Way to much emphasis in here on EPS, GEFS, GloSea, Met etc etc they have all proven to be wrong many times in the past including the not to distant past and they will be again. The trend in the operational runs of the nwp  models look quite positive and so does the progression of downwelling in the strat. I would expect to see  further increases in northern blocking and a much colder pattern developing post Christmas. below are 30mb composite charts from the 14th and 16th this forcing downwelling from 10mb. This forcing started from wave breaking around the 8th and another slightly  weaker one around the 16th.

But is that of evidence of downwelling though? They are anomaly charts you posted rather than geopotential height structure of the polar vortex at different heights in the stratosphere.

Certainly the strat forecasts from GEFS and EPS to day 10 suggest the SPV will stay displaced off the pole and centred towards the Barents and Kara Sea areas north of Russia by New Year, though extended forecasts from GEFS take it back to the pole.

My concern would be if the SPV becomes elongated and aligned with the tropospheric PV close to our NW, as if they become coupled, it would keep low heights intact to our NW for a protracted period in January. Though no evidence of this yet ... with signs of the -EPO ridge building heights toward Greenland, which will help drive the jet stream south. The question is, will the cross polar heights be sustainable into the New Year?

[Dennis]

GFS18z colder air incoming from the west

Edited December 19, 2017 by Dennis

[Nick F]

Sneaky strong northerly veering northwesterly developing next Wednesday on the back of those dumbbell lows affecting the UK Christmas and Boxing Day. Could be some wintriness for northern and western areas, especially hills.

Certainly a signal for some cold zonal polar flow after Boxing Day.

[January Snowstorm]

Further good news on the 18z as the cold gets upgraded after Christmas. 

Right now the trend is our friend

[comet]

23 minutes ago, Nick F said:

But is that of evidence of downwelling though? They are anomaly charts you posted rather than geopotential height structure of the polar vortex at different heights in the stratosphere.

Certainly the strat forecasts from GEFS and EPS to day 10 suggest the SPV will stay displaced off the pole and centred towards the Barents and Kara Sea areas north of Russia by New Year, though extended forecasts from GEFS take it back to the pole.

My concern would be if the SPV becomes elongated and aligned with the tropospheric PV close to our NW, as if they become coupled, it would keep low heights intact to our NW for a protracted period in January. Though no evidence of this yet ... with signs of the -EPO ridge building heights toward Greenland, which will help drive the jet stream south. The question is, will the cross polar heights be sustainable into the New Year?

I was of the thinking that by showing the anomaly charts you could see where any forcing is taking place rather than the broad brush of the mean. The wave breaking several days back at the 10mb level is without doubt the reason behind the Alaskan ridge and cold surge that we engulf a number of states in America over the coming days rather than MJO, Glaam , GWO etc.