The Seasonal Forecast Thread

[Blessed Weather]

Meteo-France MSLP Anomaly forecast for Dec/Jan/Feb (issued Oct 2019). Yet another model going for a positive NAO.

"This month's Météo-France model forecast for DJF shows a stronger ridge near SW Europe than the other models. If correct, this would not be good news for longstanding rainfall deficits in (ironically) France."

Source: Twitter @WorldClimateSvc

[Don]

41 minutes ago, Blessed Weather said:

Meteo-France MSLP Anomaly forecast for Dec/Jan/Feb (issued Oct 2019). Yet another model going for a positive NAO.

"This month's Météo-France model forecast for DJF shows a stronger ridge near SW Europe than the other models. If correct, this would not be good news for longstanding rainfall deficits in (ironically) France."

Source: Twitter @WorldClimateSvc

Well, it wouldn’t want to feel left out?!  Hope the models are reading off the wrong sheet.

[knocker]

 

[bluearmy]

4 hours ago, knocker said:

 

Not sure that a three month mean tells us a lot ...... the movement from the previous issue is towards a more ridgy Atlantic/ Nw Europe with scrussian troughing ...... however, notable how low anomoly across the arctic stays solid 

 

[feb1991blizzard]

Its a shift North of the ridge, you can bet your bottom dollar that late winter is fairly blocked on that run and December hugely zonal.

[Frost HoIIow]

10 hours ago, feb1991blizzard said:

Its a shift North of the ridge, you can bet your bottom dollar that late winter is fairly blocked on that run and December hugely zonal.

I'd take that if we got beasts like Feb & March 2018. Just a pity we don't get snow around Christmas these days. Some on here will moan about travel chaos or the economy taking a hit but it's been 9 years since the last one! 

[feb1991blizzard]

Just now, Frost HoIIow said:

I'd take that if we got beasts like Feb & March 2018. Just a pity we don't get snow around Christmas these days. Some on here will moan about travel chaos or the economy taking a hit but it's been 9 years since the last one! 

See i would like December but early December, but the problem is you rarely get the really brutal uppers to tap into, i prefer just after xmas - like Jan 10th ish - while the North Sea is warm enough still to create massive convection but while it is still possible to get the -18c uppers in on a gale force Easterly - you want it in afternoon rush hour for maximum impact!

[Catacol]

Copied across from the speculation thread to where this should probably be. Seem to have lost the charts though. Oh well - text only. Long post coming….

OK – here’s my winter forecast for 2019/20. My rationale is simple – I want it to be accessible in plain speak but technical enough to tweak some interest. I’m a snow hunter so have written it largely from a snowfall perspective (and make no apologies for that purpose). Finally I do see 2 quite clear possible routes, with the potential direction of travel hinging on the extent of vortex disruption in early January. I am not using any analogs. If you want to see forecasts hinging on analogs there are plenty on sites over in the US at 33andrain. I have become less and less convinced by the relevance of analogs, though acknowledge they make for interesting reading and pattern matching.

 

Drivers

Both via observation and technical paper reading there are clearly core drivers that impact the pattern over the UK. In some kind of approximate hierarchy these are:

1.       ENSO forcing that impacts global momentum budgets and, as a result, likely pressure patterns. Central to this in winter is the extent to which the sub tropical high pressure belt is supported in a northerly direction by circulation at the pacific equator (including convection patterns mapped via the MJO), but also the extent to which surges in momentum can create blocking at higher latitude. The UK sits right on the boundary between the sub tropical (Azores) High and the polar jet, and torque events either over North America or East Asia can have a significant downstream impact on the ridge/trough pattern that leaves us either on the warm or cold side of the flow.

2.       Vortex strength from the top down, but also the extent to which impacts from the bottom up can either disrupt the vortex or alternatively encourage a coupling of the upper and lower layers. Once coupled the vortex is a tough beast to break. The tropospheric vortex naturally strengthens through November and into December before beginning a slow decline through January and more especially through February, and this is an important precondition to keep in mind.

3.       Sea Surface temperature anomalies in the North Atlantic and the extent to which the jet can be affected by this.

4.       Snow cover, ice extent and the issue of arctic variability which can impact on the Siberian High in particular. Perhaps also impacts the vortex in terms of tropospheric ridges in the arctic causing disruption.

5.       Solar variability. Much disagreement here amongst forecasters and interpreters, but the balance of the argument suggests that times of low solar activity encourage higher than average ozone levels in the stratosphere with a greater chance of vortex disruption, but also reduces the overall strength of the jet, encouraging more “wobble”, often described as a more meridional pattern.

6.       Finally its worth acknowledging the natural waxing and waning of the wave pattern, and therefore shifts of wavelength and movements in the peak/trough pattern are inevitable.       Observationally I have come to see these as working in thirds of months, with occasionally a standing wave situation creating less movement. We are in one such standing wave situation now with the trough fixed over the UK for, I would think, two thirds of the month. With such a neutral ENSO background state I wouldn't be surprised to see static periods of wave activity repeat.

 

The Driver Context in 2019/20

1.       ENSO impacts are expected to be minimal this season, with an essentially neutral position currently. The MetOffice forecast sees the weak Nino focused in the central pacific

but a context further to the west of a very positive IOD and cooler waters which, in theory, promotes more of a Nina pattern. Much further to the east the pacific is cool, once again suggestive of Nina impacts. This “Nino Sandwich” is a tricky one to call, but the signature is so close to neutral that impacts will probably not be substantive. However – and this is important – the global atmospheric momentum signature is rising and has been rising for several weeks.

This is indicative of Nino forcing in the pattern (as well as nature's desire to try and return momentum budgets to zero....), and so it looks possible that the tropical cycle through the winter may become more of a factor later on, particularly if GLAAM hits positive values as it rebounds. Given the elastic nature of GLAAM the upwards trend looks likely to continue for at least a few more weeks with a likely peak in January. Whether the upwards trend continues beyond that is a tough call – but more Nino style impacts increase the chances for stronger late winter blocking patterns. More commentary later on this in the monthly descriptors.

2.       The stratospheric vortex is currently strong, but just beginning to feel the impacts of a well known tropospheric combination of low pressure over the Aleutians and High Pressure over Eastern Europe and Scandinavia which encourages warm to be fired into the upper vortex from opposite sides of the globe. This is providing early stress on the vortex, helping prevent the upper and lower layers from properly coupling, and this is a process that may be being enhanced by the background low solar context. Given expected lag times, the impact of this wave 2 attack may take up to 4 weeks to see real tropospheric change given any stretch/split/displacement needs to work its way through the layers (assuming the atmosphere is receptive to frictional downwelling…and we all know that last year it wasn’t…) meaning end of December or early January for maximum downwelling effect. As we move towards December the signs of vortex stress in the modelling are increasing, though these values vary a bit from day to day and model to model. There is broad agreement, however, on an unusual trend towards a weak vortex by end of November and probably beyond.

3.       Sea Surface anomalies currently favour a slightly south of normal jet projection. Warmer than average water around Greenland, if maintained, may help to further support any anomalous ridging in that area, and a jet firing beneath weak heights to the north, and over cooler waters, is a tendency we have already seen this season and one which ocean temperatures suggest may continue. Low solar may also strengthen this signal.

The CFS forecast going forward for the season sees warmer waters to the north, and cooler do the west. To me this strengthen the possible undercut signature with favourable conditions, especially late season, for continental high pressure to nudge west.

4.       Snow cover is high, and ice regrowth on the atlantic and Siberian side has been robust, much more so than around Alaska in the pacific sector. This may well help create a very strong Siberian anomaly for this coming season, and this is a consideration for the second half of winter when atlantic firepower starts to drain away.

5.       The sun is quiet, and looks set to remain quiet. No pepping up of a flat jet is a decent bet for the coming season, and indeed already I think the seasonal models have been blindsided by the angle of the jet as encouraged by the more meridional flow than expected. This is a context that will be with us all season.

 

Monthly specifics

December 

Current patterns have demonstrated a very resilient Scandy/East Euro block that has acted as a solid barrier that any amount of atlantic fury has failed to crack. Watching the first 2 weeks of November carefully has been instructive in this, and for snow lovers the sight of atlantic lows hitting this block is mana from heaven in terms of adding weight to vortex disruption. The MJO pattern through late November is also supportive of blocks at higher latitude. As a result a trough has remained as a semi permanent feature over western Europe, unable to move, dropping copious amounts of rain in England (less so Scotland with the southerly displaced jet) and temperatures have undercut model predictions. However, this pattern looks set to fade. The MJO will reenter the Indian Ocean shortly. In addition, the tropospheric vortex continues to be on an upwards curve seasonally, reinforced in all probability by growing cyclogenesis caused by colder than average temperatures in the US, and into early December a flatter pattern looks likely. A neutral ENSO signature overall is not going to significantly disrupt this seasonal trend. In this scenario the vortex disconnect will remain in force, as tropospheric impacts on the stratosphere disrupt the stratosphere while at the same time the atlantic becomes more dominant tropospherically. +NAO setup will be the end product for the first two thirds with an increasingly +AO in attendance. However, by month’s end downwelling impacts of vortex distress, and possibly even vortex disintegration, will begin to be felt, and the next ENSO cycle will bring the MJO back close to phase 7-8-1 and more support for blocking. A wet first two thirds, with temperatures average to slightly above average will be replaced by a drier final third, greater presence of frost and a pattern shifting towards less mobility.

 

January

Timings tough to pin down here, but two possibilities broadly. Possibility No 1 rests on major vortex distress and a downwelling that impacts significantly. If GLAAM continues in an upwards direction, elastically turning positive on the current upwards curve, then torque events may enhance this phase. Lag time, and likely MJO cycle and associated torque increases, suggests mid month for any potential reversal pattern as the AO drops swiftly, and much will depend on where residual shards of the vortex may land. With the axis of attack sitting between Alaska and Siberia we may expect energy displaced to east Asia and Canada, so a burst of atlantic energy initially via a +NAO followed by a swift reduction and a reversed pattern with a -NAO taking over. Best guess here therefore is for greatest cold impacts mid month, maybe final third. Blocked, cold and snow potential at that point.

Possibility No 2 rests on the vortex resisting the predicted assault, stretching and reforming. This may be assisted by a transition back to a lower GWO (low GLAAM state) as the ENSO signature fades and the MJO returns to the Indian Ocean. In this circumstance again a stormy first third to January, perhaps with a Scandy High in attendance due to vortex stretch, and a slight relaxation into a default westerly regime by mid to late month. A close but no cigar event for snow hunters. Southerly jet predisposition may keep temperatures around average, perhaps marginally below, with rainfall above average. The angle of the jet wont totally rule out snow at times, but widespread and durable cover difficult in this scenario.

 

February

Being honest, if the vortex collapses in January then I think February could turn out very cold. Shortening seasonal wavelengths, as the tropospheric vortex continues its slow decline, encourages retrogression of the wave pattern, and the generally cold and blocked January could lead to a period of significant continental influence as the Siberian High edges west. It is beyond my gift to predict with any reasonable accuracy the likely progress of the month from start to end, but years of observation would suggest that, as the month ends, any cold pattern would begin to relax. First two thirds very cold, final third relaxation as inevitably a degree of late season vortex reforming returns. However the likely passage of the MJO later in the month may help to sustain the blocking throughout, and any relaxation would be relative. Dry overall, with temperatures below average.

If the vortex reforms its shape in January then a second opportunity for cold blocking arrives in the latter half of February as the troposphere makes one final stab at vortex stability. January mobility will produce more wave breaking and another assault on a much weakened vortex, and the knock out blow may arrive with the final ENSO pacific cycle of the season towards the end of February. Chance of late season cold in this scenario – but no guarantee. A non descript first two thirds, certainly drier than January, with temperatures perhaps above average as the Azores High makes an appearance initially, before a colder final third as blocking appears to the north, and intrusion of further cold into March. Temperatures overall around average as the cold end cancels out the relatively mild beginning.

So – there it is. I’m going to plump optimistically for possibility No 1 through January (though possibility 2 definitely remains on the table), and summarise my overall spread as:

December: Broadly +NAO, wet, average temperatures but more blocked final third.

January: Stormy first third under renewed +NAO, then strongly negative -NAO mid to end of month and continental influence. Widespread snow potential. Temperatures overall slightly below average, rainfall overall average.

February: Largely -NAO regime, especially first two thirds. Temperatures below average throughout, relatively dry.

I hope this reads coherently. Bear in mind we all have limits to skill levels, and the truth behind most forecasts is that they are as much hopecasts and guesses as anything else. However I'm interested to see how the season works out in relation to the level of understanding that has created this moment of crystal ball gazing, and ultimately I post for enjoyment more than anything in looking for cold weather patterns. If we get a cold December with snow, and a mild January/February with no ice in sight I won't mind one bit - a cold December would cancel out any disappointment at inaccuracy and, in any case, we are all learning all the time. I'll do a review in Mid March once the winter has lost its edge.

[damianslaw]

I'm no expert and find backing up my seasonal thoughts on evidence very difficult. I tend to think the base state for the season doesn't tend to set in until nearly a third into the new season, and at 3 weeks or so ahead of where you are when making the call, too far out to have any ideas how things might happen from using the model output at the time.

Not explaining it well, I'm saying winter base state for rest of winter including well into March often sets in around christmas, likewise summer, around June solstice - i.e. northern hemispheric state develops into a groove around then. The opening to each season has a lag effect, and consequently often feels like the season just gone. 

When it comes to winter in particular, I often write off the first fortnight of December in terms of expectations for cold an snow and begin to look for clues around middle of the month as to what the season might hold overall.

One thing I look out for is the behaviour of the jet through November and into December as this can offer insights into what it might do through winter proper.. I'll give some general thoughts for what its worth at the end of the month.

Edited November 16, 2019 by damianslaw

[BLAST FROM THE PAST]

Document 2019.docx

[Catacol]

deleted

Edited November 17, 2019 by Catacol

[BLAST FROM THE PAST]

Deleted

Edited November 17, 2019 by BLAST FROM THE PAST

[Catacol]

1 minute ago, BLAST FROM THE PAST said:

It’s my issue, I HATE technology....its crap! 

Hehe - no worries....I fixed it.

[BLAST FROM THE PAST]

WINTER 2019/20 

 

What may this winter bring.  As you know I base my forecasts on the primary solar forcing of the cycles of the sun, the magnetic field effect modulated by the lunar gravitational pull.   

In 2009/10 and 2010/11 winters we saw incredible cold and snowy spells.  This was at Schwabe solar minima between cycle 23 and 24.  Sunspot count was as follows 

2007 – 152 spotless days 

2008 – 268 spotless days 

2009 – 260 spotless days 

2008/9 winter was not a cold one 

As cycles are generally 11 years long I think we are at the position of 2008.  Current sunspot run in this minima between cycles 24 and 25 

2018 – 221 spotless days 

2019 – currently at 238 spotless days and the sun is currently blank with 46 days still to go.  Will we exceed 268?  It’s up for grabs that is for sure....time will tell.  I might be wrong and we might be at the same spot now as 2009 and not 2008.   If so then this minima isn’t looking as deep so we’d have to include 2017 which ran at 104 spotless days.  So my comparison looks like this 

2007 – 152 v 2018 – 221 

2008 – 268 v 2019 currently at 238 and counting 

If we are at same place as 2008 then this is the comparison 

2007 – 152 v 2017 – 104 

2008 –268 v 2018 – 221 

2009 – 260 v 2019 currently 238 and counting 

 

Factors I’m looking at 

So, could this be important?  It could be and as we know the deep minimas do appear to bring northen blocking, a meridional and a southerly tracking jetstream.  Already Nov is nicely below average with a very meridional jetstream.   

We have now seen that October was 5th in snow cover league which was some going considering the rapid expanse in the last week.  Added, Nov now the snowiest on record. 

Arctic ice was very very low in relation to the ‘recorded’ mean but as highlighted by MIA on the appropriate thread we have had a very notable, sit up and look rapid refreeze up there. Also the lack of refreeze in Chukchi Sea may support ridging in that region.  MIA also made a point re SSTs this side of the NH.  Cold blob to our west and cold going up Norway round Lapland and Finland to our N and NE.  This would make any northerly or NE’ly have much more bite with less moderation of uppers.  We have seen incredible (at times) record cold surges being recorded with early snowfall being recorded widely.   

We still have a disconnect between strat and Trop and are descending towards eQBO 

 

So is this the winter to be a 20th century Great matcher, (in 2018 I touted one of the next 3 2018/9, 2019/20, 2020/21 will be).  It wasn’t last winter so it has to be this year or next winter for me to be correct.   

So here we go, this winter has a real chance.  November has behaved very well to my thoughts and indeed is looking to be cooler than I thought with the jet digging further south.  My concern has been re December that I’ll looking for pM and at times aM air to be the main feature (basically a lot of northerly winds with a displaced PV over Scandinavia.  The issue in past is how far south the cold will push and how much mixing out of the cold will there be it being maritime air.  Well the SSTs imo favour that the cold should be quite punchy.  

Rest of November, another southerly tracking LP to come before we see HP have greater influence/build over us from the Atlantic cross us to the north and to likely to slip away east with a less cold period last week of the month before we see what I think will develop for Dec at months end. 

 

December – The way Nov has and is panning out I am now edging towards cold and at times snowy conditions for whole of UK and Ireland and not just far North Scotland and NI. 

From very end of Nov I think we’ll see a PV displacement to set up shop to our NE driving down at times arctic air over the whole of the UK.  The cold will be of significance with at times secondary LPs coming at us on NW/SW axis off the Atlantic bumping in to very cold air.  I’m anticipating a very snowy at times December with Northerly Quadrant flow generally dominating for the month.  Periods for me of potential note for disruptive weather 2nd week up to midmonth and last week of December.  If it’s cold then snow and gales likely issue, if not cold enough then very heavy rain and gales.... hedging bets as I know how disappointing northerly flow can be for southern parts. 

However, we could be looking at a month here of memory with potential of memorable cold and snow periods 

January – I’m really up in the air on this.  Initially I think first week continues the theme of December, another very disruptive week of (hopfully) snow but disruption through precip and wind.  However, I think HP will then develop and dominate most of the month.  Its where it positions itself will be all important.  I’m currently of the thought it will be over us ie mid lat blocking and we’ll see cold nights but with daytime temps gradually rising.  However, slight adjustments could see real cold easterlies or a drab and not very cold S to SE’ly flow. 

 

February – Continues HP them with potential cold easterly and southerly tracking LP during 2nd week but more norm temps if not mild at times....stubborn HP in wrong place. 

 

Alternative to this is the HP being bang on in right place and bitterly cold.......but for me a front loaded winter and a disappointing last half.....but very much open to change as that is on a fine edge. 

 

BFTP 

Edited November 17, 2019 by BLAST FROM THE PAST

[Yarmy]

8 hours ago, BLAST FROM THE PAST said:

As cycles are generally 11 years long I think we are at the position of 2008

11 years is just the average. Cycles can vary in length from 9 to 13 years. SC23 lasted 12 years and 4 months, SC22 9 years and 11 months:

Cycles durations | SILSO

SIDC.OMA.BE

---

Table of minima, maxima and cycle durations Cycle Minimum Maximum Duration in Nb Year Month SN Year Month SN Years + Months 01 1755 02 14.0 1761 06 144.1 11 04 02 1766 06 18.6 1769 09...

Also, the cycle could begin at any point in a given year. For these two reasons, it is meaningless to compare the spotless totals of individual calendar years.

 Jan Janssens at STCE uses the following definition for the start of solar min: the month in which the 10th spotless day appears. That's somewhat arbitrary too, but it gives a much better view of the solar cycle progress.

 

[BLAST FROM THE PAST]

7 minutes ago, Yarmy said:

11 years is just the average. Cycles can vary in length from 9 to 13 years. SC23 lasted 12 years and 4 months, SC22 9 years and 11 months:

Cycles durations | SILSO

SIDC.OMA.BE

---

Table of minima, maxima and cycle durations Cycle Minimum Maximum Duration in Nb Year Month SN Year Month SN Years + Months 01 1755 02 14.0 1761 06 144.1 11 04 02 1766 06 18.6 1769 09...

Also, the cycle could begin at any point in a given year. For these two reasons, it is meaningless to compare the spotless totals of individual calendar years.

 Jan Janssens at STCE uses the following definition for the start of solar min: the month in which the 10th spotless day appears. That's somewhat arbitrary too, but it gives a much better view of the solar cycle progress.

 

I know that Hence why I said generally Yarmy?  I’m just trying to show that if this minima is to br deeper than the last then the position we are at will be equivalent to 2008.   If we are not and cycle 25 fires up next year then we are not as deep.  That’s all

Indeed there is even discussion that 25 could peak at 2023........which would be odd

BFTP

Edited November 18, 2019 by BLAST FROM THE PAST

[Sceptical]

BFTP,

"So is this the winter to be a 20th century Great matcher"

Are you suggesting that this winter could rival 1947 or 1963/63?

Edited November 18, 2019 by Sceptical

[Yarmy]

16 minutes ago, BLAST FROM THE PAST said:

I know that Hence why I said generally Yarmy?

The average height of a man in the UK is 5 foot 9 inches. That does not mean that men in the UK are generally 5 foot 9 inches tall.

But anyway, it's meaningless to compare spotless day counts by calendar year, which is the point. Moreover, nobody should be using spotless day counts anyway, as the record is not homogeneous over time. The International sunspot number should be used as that is adjusted to account for differing number of observers in different time periods and the rest.

[Methuselah]

I'd be interested to see a plot of # of sunspot-free days/year versus the following winter's CET.

[Weather-history]

Winter 2008-09 not a cold one? 

Hmmm well put it this way the cold spells outweighed the mild ones resulting in the coldest winter since 1995-96 and with a CET  that was 0.5C below the 1961-90 winter average.

Edited November 18, 2019 by Weather-history

[Weather-history]

1 hour ago, Sceptical said:

BFTP,

"So is this the winter to be a 20th century Great matcher"

Are you suggesting that this winter could rival 1947 or 1963/63?

The funny thing is, is that 4 of the great winters of the 20th century, (below 2.0C for the CET),  were near or around solar maxima

[ArHu3]

1 hour ago, Ed Stone said:

I'd be interested to see a plot of # of sunspot-free days/year versus the following winter's CET.

There is more chance of high latitude blocking in the ascending phase of the solar cycle and more chance of a positive AO in the descending phase 

 

I'm busy but if you look around on the forum someone posted a Finnish paper on this correlation 

[Sceptical]

53 minutes ago, Weather-history said:

The funny thing is, is that 4 of the great winters of the 20th century, (below 2.0C for the CET),  were near or around solar maxima

Slightly inconvenient for the solar minimum/colder winter working theory.

[ArHu3]

6 minutes ago, Sceptical said:

Slightly inconvenient for the solar minimum/colder winter working theory.

It is generally colder in the mornings just after dawn than midnight, same principle could apply for solar cycles, the earth needs time to cool off and the sun needs time to warm up the earth 

[Methuselah]

3 minutes ago, ArHu3 said:

It is generally colder in the mornings just after dawn than midnight, same principle could apply for solar cycles, the earth needs time to cool off and the sun needs time to warm up the earth 

In which case, wouldn't there be a clearly discernible 11-year oscillation in global temperature?