Interitus
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Posts posted by Interitus
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12 minutes ago, knocker said:
Interesting that it highlights the same Kamchatka high as my post above, however it's not set in stone and has gone on the next run. Whatever, further in the convo he adds -
This is interesting with regards to my post and downwards wave reflection. My speculation at the time ahead of the 2018 SSW was reflection acted to shift the heart of the troposphere vortex south towards northeast Canada (a known effect) with the centre of strat vortex attempting to follow and stretching, allowing the wave 2 to pinch it out or vis a vis his Scandinavia-Greenland dipole.
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On 28/01/2020 at 20:47, Singularity said:
I feel a good view of the situation is that the forcing toward relentlessly mobile weather patterns is relaxing toward or perhaps a little below average during 1st half Feb.
This being thanks to that big MJO wave which, while it didn’t make it far enough east across the Pacific to initiate HLB, did get far enough to seriously soup-up mid-latitude blocking (to record strength across the UK for example).
With that comes huge energy transfer into major mountain ranges, with wave deflection upward to assault the polar vortex via strat warming.
Now, the MJO looks to cycle back around to Indonesia. This suggests another round of MLB enhancement to come by mid-Feb. Potentially more strong wave breaking. So I can see where GFS is coming from with that second warming development.
In the meantime, we look to typical variation in jet meandering, to offer some most likely transitory cold snaps, which due to the Atlantic-side Arctic sea ice configuration may pack more of a punch than we’ve become used to this past decade. Main question is ‘direct hit, or glancing blow’. We know which one we tend to get...!
Did the MJO wave cause the UK high pressure? Easy conclusion to arrive at and it may be related but as well as a fairly short time lag, previous examples show that this was not the typical response. This graph shows three close analogues of MJO RMM1 over the 14 days to Jan 19th (x-axis day 0 - UK high pressure) -
These dates show a strengthened NAO with enhanced Azores high (your MLB?) and deepened Icelandic low, troughing to UK
One interesting feature they shared though appeared around 20 days later, with a significant negative EPO -
11/02/1986 -
19/02/1993 -
30/01/2007 -
They share not completely dissimilar features downstream also, though actual conditions varied for the UK. Various recent runs have been trying to replicate the 20 day -EPO this year also eg -
As well as battling a strong troposphere vortex, since looking at this a couple of days ago it is now being complicated by a possible wave 1 downward reflection event into the area, encouraging a strong high pressure in the Kamchatka area and the rejuvenation of the Siberian high -
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9 hours ago, Kirkcaldy Weather said:
P3 this time with a split, might as well post these for fun as there aint much else happening
Temporary split, vortex reforms, min zonal wind 13.1 ms at T228
Try 00z p15, not split but big displacement, min wind -15.1 ms and bearing in mind above post from Knocker, the window for a split may be quite small in the short term -
Actually the latest GFS runs are ramping up the vortex later on as they're giving no coherent signal for other than transient wave 1 even, with the angular phase shifting in longitude all over the place.
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3 hours ago, Kirkcaldy Weather said:
If only we could get something like p8 from the gefs
though I think we will need a miracle for that unfortunately.
No reversal - zonal wind 2.1 ms at T294 -
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Just had to rescue a rather drowsy bumblebee off a pavement, bit early to be out yet!
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Despite the recent GFS runs in long range, from the analogues there is actually a decent chance of a SSW before the end of February, maybe 30-50% at a guess.
As an aside, interesting split forming on the 12z, probably won't be it, but is popping out at relatively short range so the FI is definitely not certain.
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Last night the GFS was so wrong. Now they all are
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22 hours ago, Singularity said:
I feel a good view of the situation is that the forcing toward relentlessly mobile weather patterns is relaxing toward or perhaps a little below average during 1st half Feb.
Whoa!
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Don't worry, one of the CFS members has the strongest reversal/early final warming on record
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Well the GFS has backed down from a SSW quite a bit, here are the 1mb zonal winds on the runs since the last negative values on yesterday's 06z -
The x-axis represents the 3 hourly forecast intervals and the minimum on today's 06z of 17.5 ms at T219 - day 9 - fairly accurate at that range. It's not unlikely that it could flip back beyond this, though at the moment it is looking increasingly like perhaps a first bite of the cherry. The GEOS out to T240 (one run per day) still has the 1mb wind down to 8.9 ms at the last timeslice, will be interesting to see its direction on the 28/01 00z.
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10 hours ago, Nick L said:
Bit harsh. He's a meteorology graduate.
More than a bit harsh, he has completed his masters and is half way to his PhD and is a published researcher alongside well known meteorologists (with particular regard to the stratosphere) such as Amy Butler, Andrew Charlton-Perez and Jason Furtado, and has a paper currently in review co-authored by sometime contributor to the strat thread Zac Lawrence (curator of stratobserve.com). His tweets are some of the more interesting out there and a world apart from some of the popular uninformed drivel which frequently graces these forums!
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14 minutes ago, Paul_1978 said:
I’m still concerned that he also said a couple of days ago that the effect on the UK would be “enhanced westerlies”. Just our luck.
You might be more concerned whether a SSW is going to happen at all!
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18 minutes ago, Dennis said:
These are interesting charts, but look at the verification scores on the right hand side.
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4 hours ago, Mike Poole said:
Trying to get there on the 12z, T 384:
Not exactly the same as the 0z or 6. All within the envelope of what exactly? Well I think it has all the hallmarks of a SSW that isn't too far away being picked up slowly by all models...so that's all good.
Actually the 12z backed away from an SSW, 1mb minimum wind of 11.7 ms at T261 recovering to 29.8 ms at the end. 10mb ends on 16.5 ms which is higher than the previous 3 runs.
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1 hour ago, Mike Poole said:
6z GFS follows the 0z with the split, gathering momentum now, here T348, T384:
If the split occurs it will be important how big the two daughter vortexes are and where they go, 6z is a rather uneven split with one piece much bigger than the other.
Trying to split on 00z -
Not split on 06z -
Maybe tries to nip the end off, despite perhaps a better split at the higher levels, the 30 mb temperature gradient is not conducive to a 10 mb reversal on the 06z but reversal likely on the 00z. Perhaps most significantly, whilst 1mb reversals are still at the end of the forecast periods, the last three runs start to bring reductions in 1mb zonal wind closer to the reliable at 9 days rather than stuck beyond 10 days +
edit: Note the strongest 1mb reversal forecast was still that from the 18th 00z (not shown)
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On 17/01/2020 at 09:46, Interitus said:
Roughly half-way through winter, taking the daily CET data from December and estimated values to January 15th, how mild has it been?
This winter is 13th mildest (out of 245) with 2015/6 unsurprisingly top after the incredible December, but there are some short memories, last year was a tad milder to this point and of recent years 2006/7 is also ahead. Close behind are 2013/4 and 2011/2 in the top 20 -
An alternative view is the absence of cold to this point, seen from the lowest daily CET. By this measure 2019/20 is joint 12th with a coldest day of 1.5°C, albeit right at the start of December. However 2013/4 is top with the coldest day a barely below average 3.5°C -
A week on, winter 2019/20 has slipped to 16th mildest. Of recent years it has passed last winter, but has in turn been overtaken by 2013/14 and is still behind 2015/6 and 2006/7 -
For lack of cold this winter is now 9th, but 2013/14 still rules the roost with basically no cold to this point whatsoever -
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On 18/01/2020 at 10:12, bluearmy said:
Definitely reversed at the top
looked like it wasn’t quite below 2hpa
To update, this 18/01 00z is a bit of an outlier at the moment, there hasn't been a reversal in the 24 runs since, clustering of the windspeed graph shows that reductions are struggling to get inside the 10-12 day reliable timeframe -
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1 hour ago, Mucka said:
Rate of change.
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6 hours ago, bluearmy said:
the wider view not without interest either .....
T375 on the 12z was the lowest 10mb 60N zonal wind of any GFS op run since before the start of November at 8.3 ms. Gone on the 18z, lowest 23.3 ms.
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5 hours ago, damianslaw said:
How can the cold blob turning into a warm one then?
This graph shows the average May/June SST for the arbitrary central north Atlantic region from 1950-2019 -
Clearly, there has been a downward trend counter to warming elsewhere, which represents the 'cold blob'. But the decrease is not monotonic and displays much interannual/interdecadal fluctuation. Primarily the temperatures are a response to atmospheric conditions, precipitation, evaporation, insolation etc which vary with the NAO. On top of this there is infeed of currents of varying temperature and salinity into the sub-polar gyre and levels of winter deep convection overturning the static stability. To show the contrasts in temperature compare the coldest year 2015 at 9.568°C leading to the record December CET - just five years earlier the cold December was preceded by the 5th warmest SST in the series at 11.0475°C.
Here is an interesting paper comparing the winters 2009/10 and 2010/11 and highlighting the probable importance of SST anomalies in the latter -
QuoteNorth Atlantic SST Anomalies and the Cold North European Weather Events of Winter 2009/10 and December 2010
Abstract
Northern Europe experienced consecutive periods of extreme cold weather in the winter of 2009/10 and in late 2010. These periods were characterized by a tripole pattern in North Atlantic sea surface temperature (SST) anomalies and exceptionally negative phases of the North Atlantic Oscillation (NAO). A global ocean–atmosphere general circulation model (OAGCM) is used to investigate the ocean’s role in influencing North Atlantic and European climate. Observed SST anomalies are used to force the atmospheric model and the resultant changes in atmospheric conditions over northern Europe are examined. Different atmospheric responses occur in the winter of 2009/10 and the early winter of 2010. These experiments suggest that North Atlantic SST anomalies did not significantly affect the development of the negative NAO phase in the cold winter of 2009/10. However, in November and December 2010 the large-scale North Atlantic SST anomaly pattern leads to a significant shift in the atmospheric circulation over the North Atlantic toward a NAO negative phase. Therefore, these results indicate that SST anomalies in November/December 2010 were particularly conducive to the development of a negative NAO phase, which culminated in the extreme cold weather conditions experienced over northern Europe in December 2010.
https://journals.ametsoc.org/doi/full/10.1175/MWR-D-13-00104.1
For reference, the 2009 May/June SST was cooler than average at 10.16°C which should have tended towards a warmer December.
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On 18/01/2020 at 10:43, Blessed Weather said:
Hope not - a strongly positive IOD seems to be a winter killer for the UK (if cold/snow is your preference). Here's the index since 1982 showing 3 previous strong events in 1994, 1997 and 2006.
Source: https://stateoftheocean.osmc.noaa.gov/sur/ind/dmi.php
And the weather in the winters that followed?
1994/95 - Very mild with a 3-month winter average CET of 5.9C. The summer of 1995 saw a record breaking heatwave.
1997/98 - Very mild with a 3-month winter average CET of 6.1C. Record breaking winter warmth for the UK and Europe.
2006/07 - Very mild with all 3 winter months CET above long term average. This article from Philip Eden:
Very interesting, but it can also tie into this other post -
On 20/01/2020 at 18:05, Kirkcaldy Weather said:A couple of years back after speculation that the 'cold blob' would increase risk of early frosts and a colder winter for 2018, a rough analysis suggested that a negative May/June SST anomaly for an arbitrary 45-60°N, 10-50°W actually leads to a milder November and December, similar to the Atlantic tripole findings of Rodwell and Folland et al -
The source area was not optimised for correlation and also ignored any wider tripole which may explain that the cooler the blob area, the more pronounced the effect and milder the December. For the 12 coldest May/June average blob temperatures since 1950, there was only one colder than average December, 1976 (not 2009 as wrongly stated originally).
A simple 2nd order polynomial fit for the SST data 1950-2017 gives a CET prediction of 6.0°C for Dec 2018 (actual 6.9) and 5.76°C for Dec 2019 (actual 5.8) so that's only 1 colder than average December from the 14 coldest 'blobs' and 8 of these are 6+ degC.
At the extreme, the second coldest blob gave the second warmest December, 1974, and the coldest gave the warmest, 2015....which brings us back to the positive IOD years. 1994 fits the pattern well with its 6.4°C December following the 4th coldest blob. 1997 and 2006 however are very much in the 'warm blob' territory. A fuller analysis taking into account patterns of SST and detrending temperatures may give better results, but there do appear to be reasonable predictions available at 6/7 months in advance.
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6 hours ago, Daniel* said:
There is “support” for +ve heights in that region a Canadian warming. NAO trending less positive...
Not really, the warming normally occurs over over troughing - the steeper the geopotential gradient of the trough below the particular vortex level, the stronger the warming, strongest of all when the geopotential contours of the two levels are perpendicular. In the corresponding 500mb charts to the animation the low heights can be seen over northern Canada and Greenland. If the EPS shows increased heights in this area later on, the warming will fade away.
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On 16/12/2019 at 00:35, Sunny76 said:
This will be the year of another poor summer, and probably the poorest overall since 2012.
January : A slightly colder than average month overall, after a mild and damp start. From the 5th until 20th a cold spell will set in, but turning bitterly cold around the 15th to 18th with frequent heavy snowfall, and becoming more widespread between the 16th-18th. Some areas will record record levels. Windchill and low overnight temps will affect the most vulnerable.
Not the best of starts! Better luck with the rest.
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Might be a bit cynical to point out that both locations mentioned that reached 1050+ are above 300 metres altitude thus needing a bigger pressure adjustment to sea-level.
Model tweets
in Forecast Model Discussion
Posted
Ironically, if Helsinki became drastically colder, there would be the same trend on the chart. Of course that's not happening / going to happen.