Focussed Model Discussion

[knocker]

Outlook - very unsettled. cold with snow

The 500mb and surface analysis for midnight

With the center of the low now in the North Sea, once the band of shower rain/sleet, currently over the Midlands, has cleared the south east this morning, the whole of the UK will be in the the cold northerly airstream  This will reach gale force, or even severe at times, in coastal areas. initially in the west and then later the east, before easing. There will be a lot of squally wintry showers with snow to quite low levels in places and again these tending to move fro west to east during the day. Quite a severe wind chill

The strong winds will continue down the east coast for a time this evening with the wintry showers which will also be prevalent in northern Scotland but generally a clear night with a widespread frost with some ice by morning.

Monday a dry and sunny, albeit cold day, for many areas, but an occlusion associated with the low east of Greenland is edging in from the west and this will bring some patchy rain and snow on the higher ground very early and this will move slowly east during the day. Not feeling as cold as Sunday.

You will have noticed that the aforementioned occlusion trails back into the Atlantic and overnight Monday  and through Tuesday a wave forms on this and tracks east to be near Brest at midday Tuesday, Also cast a glance back to NE america where an intense upper trough is emerging  The low will then track across northern France through the rest of Tuesday and overnight into Wednesday bringing a fair amount of snow to southern regions of Britain.

By midday Wednesday the low is over Germany so a quieter day with perhaps a few wintry showers in the west but very cold. but note the aforementioned upper low is now south east of Greenland.

 By Thursday midday the Greenland trough has tracked south east and a deep surface low of 967mb is west of Ireland and the associated fronts are moving north east across the country with bands of rain, sleet and snow, the detail of which will be determined over the next couple of days.

Edited January 27, 2019 by knocker

[knocker]

Continuing briefly with the gfs. Friday unsettled and cold with wintry showers as the trough resides over the UK and much the same for Saturday as it continues to drift east

[knocker]

The ecm has the main low about 10mb higher and a tad further west than the fax at 1200 Thursday and then tracks it west of Brest over the next 24 hours, any frontal snow will be confined to the higher ground in the south west of England and south Wales  This is of course far from a done deal. By midday Saturday the low is over Italy and Britain id in a north easterly airstream with showers along the east coast and temps around 3-4C as high pressure ridges to the west. The ridge then comes under pressure as the next frontal system arrives over Ireland on Monday

[knocker]

This morning's updated fax charts early Tuesday

[knocker]

Forecast sounding (gfs) for Tuesday. You wouldn't discount snow on the back edge of the front

[Catacol]

Interesting week coming - but still blocking looks to be eluding us so winter scenarios are extremely marginal. The EPS 240 image is not a good one for a cold feed, with pressure rising over the UK and quite strongly to the SE but still with a trough anchored to the NW and the AH in play. Tick tock....and more delays.

[Guest]

It looks like we are nearly there!  What to look for in the models

 

I've still very little time to produce a full post, so I'll do a summary.  I'm writing this report for several threads on two weather forums (US and UK) with a full spectrum of readers - so I'll use simple terms. There have been some excellent posts on here in recent weeks and this post will pick up on the timing and coupling issues.

Despite the great advances in our understanding of the teleconnections and how they influence the atmosphere and the broad scale patterns, there are still challenges at certain times in understanding how they interact with each other, constructively or destructively and which ones dominate at particular times. The GSDM (global synoptic dynamic model) pulls this together and gives us a great heads up into what is going on and what we "might" expect and look out for in the coming weeks, months and seasons.  It's just as important to understand what can go wrong and why as it is when everything goes according to plan. 

 

This winter has been both truly fascinating and (so far) pretty frustrating for the cold and snow brigade.  We know that a major SSW (sudden stratospheric warming) and particularly a split SPV (stratospheric polar vortex) usually leads to widespread HLB (high latitude blocking) in the Arctic with a lot of cold displaced towards the middle latitudes. No two SSWs are alike.  Occasionally the wind reversals in the strat never down well to the trop (troposphere), to influence the surface patterns. More often they do produce surface impacts but this can be pretty quickly (in just one or two weeks) or after a protracted period.  These timing issues are mostly in relation to the "coupling" between the strat and the trop.  When they are in harmony, down welling can proceed much more smoothly.  Since the 2018 SSW and the final warming in the Spring, the strat and trop have been pretty decoupled. In fact, it is this which has delayed and prevented (so far) a full El Nino from developing despite a number of attempts and this has defied most of the main ENSO forecasts.  We have seen short periods of El Nino like conditions but with brief La Nina like setbacks.

 

This SSW started off in late December as a displaced SPV which quickly split in early January. The wind reversals in the middle and lower strat lasted for most of this month.  There is a recovery underway up there now (which does not mean that the event is over - far from it) and the reversals are at last down welling through the trop.  It looks like full surface impacts will be seen in the high Arctic within a week or so.  We still need the trop to be receptive (with other teleconnections acting constructively) and it was back in late December but far less so for much of January but the next cycle of tropical forcing has been underway during the last few days. This is where +ve GLAAM (global atmospheric momentum) anomalies push polewards from the tropics. We saw +ve mountain torque events and the GWO (global wind oscillation) is in a higher orbit in phase 6.  GLAAM and the torques are key parts of the GSDM.  Another part of this forcing mechanism is shown by the MJO (Madden Julian Oscillation) with areas of tropical convection progressing from west to east.  This too is entering key phases in its cycle which are more favourable for HLB.  In fact ECM has now joined GEFS (and several other models) with increased amplitude from phase 6 into phase 7 within a few days (indicated on both the VP200 and RMM charts).  There are the usual time lags and the benefits from both the GWO and MJO in favourable phases are usually seen some 7 to 10 days later - ie: on this occasion very much in harmony with the Arctic surface impacts.  

 

There are still two mores ingredients.  One of these is the ENSO state with weak El Nino conditions considered to be most favourable for tropical forcing.  A WWB (westerly wind burst) is underway in the western tropical Pacific and progressing steadily eastwards.  This will be associated with an upturn in the Nino region temperatures which is just getting underway right now.  The final ingredient is FT (frictional torque) which has been stubbornly -ve all month - in fact it was last +ve at the equator and northern tropics in late December.  FT has been rising for the last 3 or 4 days and on the Jan 24th chart (always produced 2 days afterward) it was heading towards +ve territory and is probably already there.  +ve FT really assists with the tropical forcing (caused by the stresses created by tropical convection and changes in AAM).  It should help with the strat/trop coupling down there which may well see this El Nino event finally get over the line with a sustained period of Nino conditions as well as contributing to the overall poleward push of momentum.

 

So, it looks like all this is finally occurring with a much greater degree of harmony.  The AO (Arctic oscillation) is already going -ve and should go more strongly -ve next week with HP showing up near the pole.  The PNA (Pacific North American oscillation) is also going +ve with the Aleutian LP setting up.  The down stream pattern of ridges and blocks then develops in conjunction with the forced extensive HLB from the Arctic.  The Canadian PV should weaken and be pushed further south.  HP is likely to rise in the Greenland area.  Siberian, Arctic and Scandinavian HPs should all be seen at stages and the NAO (North Atlantic oscillation) should at last go -ve.  For Europe and the UK an extended period of north easterlies or easterlies are favoured.  The current LPs with increasingly polar maritime and Arctic incursions in it should be forced southwards or south eastwards.  Given the long SSW event in the strat,, we can expect these surface conditions to dominate for much of February and perhaps well into March too.  Eastern CONUS and Canada should see even more extensive and prolonged cold.  Just how much snow any of us see will be decided closer to the events but all of us should see a fair amount of it.

 

So, once again, I've been very bullish.  I do hope that we do not see another "curve ball" - but this time it does look like our patience will be fully rewarded.  Those with model fatigue need to recharge their batteries. We can expect the models to pick up on these imminent changes increasingly during the next few runs.  In fact therehas already been a shift.  UKMO looks to be the most progressive with D6 Arctic blocking (and consistent with their extended outlook).  Exciting times ahead.  David   

[Bristawl Si]

Interesting and contrasting views there, from Catacol and David.

[knocker]

Following last evening's post the ext EPS this morning is not indicating any decisive move, Upstream low pressure in the Arctic and an east Pacific ridge/west north America trough  Still a strong upper flow exiting the eastern seaboard across the Atlantic where it diverges to some extent around the Scandinavian/Iceland ridge but as the European trough is virtually no more, continuation of a weak westerly flow over the UK.This would portend changeable weather without extremes with temps a little below average.Any really cold air is a long way east

Edited January 27, 2019 by knocker

[phil nw.]

2 hours ago, knocker said:

Following last evening's post the ext EPS this morning is not indicating any decisive move, Upstream low pressure in the Arctic and an east Pacific ridge/west north America trough  Still a strong upper flow exiting the eastern seaboard across the Atlantic where it diverges to some extent around the Scandinavian/Iceland ridge but as the European trough is virtually no more, continuation of a weak westerly flow over the UK.This would portend changeable weather without extremes with temps a little below average.Any really cold air is a long way east

At last signs of the Canadian vortex relenting with those +ve ht.anomalies spreading across to our north.
The Scandinavian ridging continues to tease and the T360hrs eps clusterings show it is the larger option with developing into a block 

 

 

Edited January 27, 2019 by phil nw.

[Singularity]

Nice update from @Bring Back1962-63 earlier.

The absence of an east based -ve NAO remains a peculiar feature of the modelling in the 8-16 day range, as it implies no effect from the crossing of the Pacific by the MJO in the coming days, which allowing for lag should start forcing quite widespread high-lat height rises by around D10 and with a focus on the neg NAO pattern soon emerging... yet the models are suggesting either a positive NAO or a west-based negative NAO which is more of a fit to the MJO moving right through P8 this coming week. Little sign of that in the RMM plots or even the VP200 ones so... who knows, model mishaps or missing information on our part? 

Edited January 27, 2019 by Singularity
16 not 26!

[bluearmy]

28 minutes ago, Singularity said:

Nice update from @Bring Back1962-63 earlier.

The absence of an east based -ve NAO remains a peculiar feature of the modelling in the 8-16 day range, as it implies no effect from the crossing of the Pacific by the MJO in the coming days, which allowing for lag should start forcing quite widespread high-lat height rises by around D10 and with a focus on the neg NAO pattern soon emerging... yet the models are suggesting either a positive NAO or a west-based negative NAO which is more of a fit to the MJO moving right through P8 this coming week. Little sign of that in the RMM plots or even the VP200 ones so... who knows, model mishaps or missing information on our part? 

I’m not sold on the MJO this winter ....whilst the wave can’t be denied, I don’t see the analogues as having worked out so well. Whether that reflects the fact we had a Nino with Nina type atmospheric repsonse for a while or that the ssw forcing a flushing down of westerlies,  I wouldn’t know but for over a month now I haven’t trusted the MJO analogues.

[snowice]

Ukmo96

[knocker]

According to the gfs the rather elongated trough arrives west of Ireland at midday on Thursday with the front roughly N. Ireland and the south west.It then comes under pressure and realigns as high pressure amplifies to the west and east. This results in the front tracking north east over a quite cold surface which at this stage wise to just say a likely rain/snow event. The trough then moves only slowly east so a cold and unsettled two or three days

 

[Singularity]

2 hours ago, bluearmy said:

I’m not sold on the MJO this winter ....whilst the wave can’t be denied, I don’t see the analogues as having worked out so well. Whether that reflects the fact we had a Nino with Nina type atmospheric repsonse for a while or that the ssw forcing a flushing down of westerlies,  I wouldn’t know but for over a month now I haven’t trusted the MJO analogues.

Nina-like interference from upper divergence over the Maritime Continent has been distorting the patterns away from the analogues for over a month now, so more or less as you suspect - but that divergence is dissipating now, so in theory a more typical MJO response, perhaps even with a Nino edge to it, should become possible again.

Looking at the 12z runs so far, I wonder if the models are just being slow to respond to the changing situation over the MC - but it's too soon to be at all sure about this. Should the HLB signal continue to grow in what's currently the D7-D10 range over the coming couple of days, then some greater confidence in seeing the MJO P7 response come through becomes reasonable to gain.

[bluearmy]

1 hour ago, Singularity said:

Nina-like interference from upper divergence over the Maritime Continent has been distorting the patterns away from the analogues for over a month now, so more or less as you suspect - but that divergence is dissipating now, so in theory a more typical MJO response, perhaps even with a Nino edge to it, should become possible again.

Looking at the 12z runs so far, I wonder if the models are just being slow to respond to the changing situation over the MC - but it's too soon to be at all sure about this. Should the HLB signal continue to grow in what's currently the D7-D10 range over the coming couple of days, then some greater confidence in seeing the MJO P7 response come through becomes reasonable to gain.

As we are at months end, how do you resolve the jan/feb analogue differences ... they don’t simply switch as the month ends ! (Assuming the predicted phase has monthly jan/feb diffs  )

[Singularity]

15 minutes ago, bluearmy said:

As we are at months end, how do you resolve the jan/feb analogue differences ... they don’t simply switch as the month ends ! (Assuming the predicted phase has monthly jan/feb diffs  )

Figure out if it will blend and then do the best you can .

Serious hat on - usually there's enough continuity between months that a middle ground is a reasonable approach. Between Jan and Feb we see the MJO become more conducive to HLB in useful places in P6 and P8, though P8 can be risky as it also opens the door to a west-based negative NAO depending on where the GWO is in its related, but foten not entirely harmonious cycle... if it wasn't for the importance of the extratropical factors captured by the GWO, mid-long range forecasting would be much easier going! As it is, we just have to put up with it .

Edited January 27, 2019 by Singularity

[Weather-history]

Synoptic experts may have an answer to this.

How can a cold front (one crossing central Britain) turn into an occlusion when no warm front appears to be evident preceding it?

[knocker]

Looking at the GEFs ext mean anomaly this evening one would have to say it's inclining towards blocking in the Greenland area ( a hint from the det run as well) with a much more benign outlook for the eastern Atlantic. The colder air is over Asia and Russia  but the correct pressure distribution could create advection pathways/

Edited January 27, 2019 by knocker

[sebastiaan1973]

4 hours ago, Singularity said:

Nice update from @Bring Back1962-63 earlier.

The absence of an east based -ve NAO remains a peculiar feature of the modelling in the 8-16 day range, as it implies no effect from the crossing of the Pacific by the MJO in the coming days, which allowing for lag should start forcing quite widespread high-lat height rises by around D10 and with a focus on the neg NAO pattern soon emerging... yet the models are suggesting either a positive NAO or a west-based negative NAO which is more of a fit to the MJO moving right through P8 this coming week. Little sign of that in the RMM plots or even the VP200 ones so... who knows, model mishaps or missing information on our part? 

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjoupdate.pdf

According to NOAA there is no influence of MJO in the coming weeks. 

"MJO activity appears unlikely to influence the extratropical circulation in the coming weeks. For North America, the negative phase of the AO is likely tied to the response of the signal crossing the Pacific over the last two weeks, and appears “locked in” for the near future. This is likely to negate any building ridging across the Great Lakes that would typically be the lagged response to the MJO crossing the Maritime Continent. "

[phil nw.]

The height anomalies continue to build over the polar regions in the ens/clusters.I think the modeling is now factoring in the down welling of the reversal in the zonal winds as they reach the trop level.

wrt MJO forecasts they  continue to vary within different models.Phase 6 is the current position which pretty much matches this weeks NWP profile but no real agreement for a meaningful phase 7 spell yet with differing forecasts

The American forecasts favouring phase 7 but the others less keen.

 

Edited January 27, 2019 by phil nw.

[Singularity]

1 hour ago, sebastiaan1973 said:

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjoupdate.pdf

According to NOAA there is no influence of MJO in the coming weeks. 

"MJO activity appears unlikely to influence the extratropical circulation in the coming weeks. For North America, the negative phase of the AO is likely tied to the response of the signal crossing the Pacific over the last two weeks, and appears “locked in” for the near future. This is likely to negate any building ridging across the Great Lakes that would typically be the lagged response to the MJO crossing the Maritime Continent. "

I read this but that was back on Mon before GEFS started to amp a lot in P6 and go for a P7 move. Also they favour EPS despite it proving erroneous in also predicting a stall in P6 last tropical cycle... so I’m not convinced they’ve made the right call there, especially with the sliding lows into Europe MJO P6 pattern having shown it’s hand after all for the coming week.

[Man With Beard]

An early look at D10 - D15 prospects on the individual ensembles. The means won't be representative (again). There's a real mix of options during the period. In fact, I'd say if there is to be a decent block to the north, it's more likely to be in place at D10 rather than D15. It really is a "rule out nothing" period, and certainly don't pin your hopes on blocking winning out at any point. 

[bluearmy]

I quite like the clusters .....loads of options and not really a favoured one but most are singing systems undercutting a block or sliding against one 

[Nick F]

50 minutes ago, bluearmy said:

I quite like the clusters .....loads of options and not really a favoured one but most are singing systems undercutting a block or sliding against one 

I think a brief mild period of a few days to a week starting Mon/Tues week before we could see lows starting to pull under a burgeoning blocking high to the NE - that's what the EPS seem to suggest for now. The wait for the HLB goes on ...