Interitus
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Posts posted by Interitus
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14 hours ago, Kirkcaldy Weather said:
The wave 1 modifies the vortex enough to bring values closer to the range where a SSW has occurred. Taking the GEOS forecast from 15/1 for 24/1, the earliest an SSW has happened from the 10mb zonal wind is 6 days (30th Jan), 10% by 14 days (7th Feb), 20% 17 days (10th Feb)
From 30mb wind earliest 7 days (31st Jan), 10% 10 days (3rd Feb), 20% 21 days.(14th Feb)
From 30mb polar cap temperature earliest 6 days (30th Jan), 10% 7 days (31st Jan), 20% 17 days (10th Feb)
From 50mb polar cap temperature earliest 6 days (30th Jan), 10% 13 days (6th Feb), 20% 19 days (12th Feb)
Note the percentages are not quite absolute chance as not all SSW were immediately preceded by the forecast values forecast for 24/1, it is the percentage of all SSW that were.
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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 -
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15 minutes ago, northwestsnow said:
Cohen tweeting about strong PV coupling and postitve AO into Feb.
Fat lady clearing her throat?
Have to see the effect of the Euro/UK/North Atlantic high giving spike in wave 1. Vortex displacement again (as is the norm) but probably no quick change from the strat.
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10 minutes ago, Glacier Point said:
RMM plots are something of a blunt tool - and will not capture neither lagged influence of poleward westerly momentum transports nor low frequency influences. The suggestion is that the MJO may appear to be weaken during late January, but other measures may be far more instructive.
Without knowledge of the exact dates used, the MJO - 500mb anomaly composites are an even blunter tool.
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16 hours ago, carinthian said:
As promised , some pictures sent by my son out in Vancouver. Heaviest snowfall and coldest spell for some years.
C
Well, since last February anyway.
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17 minutes ago, jules216 said:
@Glacier Point can the MJO trail the extratropical pattern rather then lead it? One would think that if its going to phase 6 now with lag of 10 days it would be reasonable to assume MJO is leading the way with Scandi through and mid atlantic/western EU ridge. Also would it be reasonable to assume teh Scandi trough will be here for a while looking at strat vortex displacement and EL Nino Jan/Feb climo? thanks in advance for answers
Yes it can, if you have time for example read this link posted by @knocker
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15 hours ago, Daniel* said:
This cold looks to entrench and I foresee it doing wonders, you would expect Barents Sea to freeze 100%
No, you really wouldn't!
14 hours ago, Northwest NI said:When was last time Svalbard to North Scandinavia open water was frozen. I am new to this so if it’s a ridiculous question, let me know.
30th March 8000 B.C.
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On 12/01/2020 at 13:38, damianslaw said:
Not sure if anyone has any stats on strength of PV in say last 20 years winters, how it is measured not sure.. and corresponding ENSO state, QBO state. Just be interesting to see correlation between various factors and reasons why some winters see a rampant PV, and others note so. The other main player is state of Strat and when SSW have occurred.
A good indicator I guess is the AO measurement.
The cold winters of 08/09, 09/10, 10/11 and 12/13 all saw a generally weak PV, SSW's featured in three of these winters, not 09/10 I think - the state of El Nino was the overriding factor I feel.
ENSO and strat profile appear to be the main influencing factors.
Another omi-present feature of the past 5 winters, scuppering any sustained cold appears to the PDO, and propensity for an aluetian ridge thanks to warm SST's..
No simple answer really. With regards to the years mentioned however, 2008/9 featured a roaring vortex at record strength from 4-8th Jan before the SSW. 2009/10 did have an SSW but on February 9th after the main cold spell. 2010/11 had no SSW and a generally stronger than normal strat vortex.
Somewhat puzzling that while conditions are considered in remote influences such the Tropics and Pacific, Atlantic SSTs on the other hand rarely get a mention (indeed didn't feature in the Netweather winter forecast) when they have long been known to directly affect synoptic patterns for the UK and western Europe.
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1 hour ago, bluearmy said:
We can’t be far from a record strong spv status around day 3 ......
Tomorrow about 67 ms, about the same as 1981 but less than 1989 for that day of the year.
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7 minutes ago, Kirkcaldy Weather said:
Can see where he's going with the MJO plot but the 500s?? They look nothing alike and in any case similarity should be of interest after a similar MJO i.e. at the end of the MJO forecast period, surely?
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OK, a quick look at something interesting from the analogues. The 30 day 10mb wave 1 heights from the GEOS analysis and forecast to 17/1/20 shows two very similar years, 2006 and 2013 -
Day 31 corresponds to 17/1/20, 11/1/13 and 25/1/06. all dates are preceded by a similar peak in wave 1. This year it is currently easing off with an increase in zonal wind in the near term, but in 2013 and 2006 this reduced wave 1 was for a very different reason as can be seen in the wind chart -
Both years had SSW on exactly the same dates from the corresponding wave 1 data, which would be 12/1 this year.
What could cause the difference, MJO perhaps?
The RMM plots show that 2006 and 2013 were almost identical -
But get this, the amplitudes were generally low, only reaching 2 in both cases just 1 day before SSW (day 26)
And the phases 7-8-1 don't feature at all in the previous fortnight -
Clearly the similarities would suggest that there is some relation between the MJO and SSW in these instances but it would appear that the SSW or cause of it was affecting the MJO rather than the other way round.
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41 minutes ago, booferking said:
All this warmth and record heat Greenland just records it's all time record low
Read the rest of that twitter thread.
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Statistical Characteristics of Major Sudden Stratospheric Warming Events in CESM1-WACCM: A Comparison with the JRA55 and NCEP/NCAR Reanalyses
Abstract:
Using the historical simulation from the CESM1-WACCM coupled model and based on the JRA55 and NCEP/NCAR reanalyses, the general statistical characteristics of the major sudden stratospheric warmings (SSWs) in this stratosphere-resolving model are assessed. The statistical and diagnostic results show that CESM1-WACCM can successfully reproduce the frequency of SSW events. As in the JRA55 and NCEP/NCAR reanalyses, five or six SSW events, on average, occur in a model decade. The seasonal distribution of SSWs is also well simulated with the highest frequency in January (35%). The unprecedented low SSW frequency observed in 1990s from the two reanalyses is also identified in a model decade (1930s). In addition, the overestimated duration of SSW events in the earlier WACCM version is not identified in CESM1-WACCM when compared with the two reanalyses. The model can well reproduce the downward propagation of the stratospheric anomaly signals (i.e., zonal wind, height, temperature) following SSWs. Both the modelling and observational evidences indicate that SSWs are proceeded by the positive Pacific–North America (PNA) and negative Western Pacific (WP) pattern. The negative North Atlantic Oscillation (NAO) develops throughout the SSW life cycle, which is successfully modeled. A cold Eurasian continent–warm North American continent pattern is observed before SSWs at 850 h Pa, while the two continents are anomalously cold after SSWs in both the reanalyses and the model.
Obviously a large degree of uncertainty is involved, but what may be of particular interest in this paper is the inclusion of SSW dates in reanalysis going back to 1850!
https://www.mdpi.com/2073-4433/10/9/519/htm
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47 minutes ago, feb1991blizzard said:
But he is saying the EPS are backing them, what else should we use then?
With respect to him, how well have Michael Ventrice's composites performed based upon these in tweets posted on here? All the resources should be used, but the point is as said none of them are set in stone beyond the deterministic limit. It's relying on tentative long range trop predictions then supposing that the strat is merely passive in response (it's not, its state matters) so...maybe, maybe not.
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Just now, feb1991blizzard said:
He means the GEFS suite.
We know how good they are.
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5 hours ago, Glacier Point said:
The way end of week 2 EPS and GFS look, wave 2 bottom up splits could be in play.
Maybe....maybe not -
2 hours ago, DiagonalRedLine said:Not sure whether WeatherOnline expect some kind of split, weakening or displacement to the Troposphere/Stratosphere Polar Vortex’s later into the month to make their 30 day outlook possible. Northern blocking I don’t think is impossible without some kind of Stratospheric Warming and Vortex disruption events. Suppose these events (particularly the Sudden Stratospheric Warming ones) do help, and allow for any blocking to the North of the UK to sustain itself.
As shown many times, northern blocking is as likely to lead to a SSW as be caused by one.
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1 hour ago, seaside 60 said:
Is that the same mega warm temps as has been forecast for over the last week, yes it got to 16c in Scotland but generally its been no higher than 8c down here and def not feeling mild.
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On 31/12/2019 at 15:15, Blessed Weather said:
Indian Ocean Dipole (IOD)
The IOD has continued its sharp decline during December with a latest reported value from the Australian Met (BOM) for w/e 29th December of +0.3C, bringing the index into the 'neutral' zone (-0.4 to +0.4C). Although strangely their narrative suggests a latest value of +0.6C and anticipated drop to neutral in January, contradicting their chart which clearly states +0.3C:
Source: http://www.bom.gov.au/climate/enso/indices.shtml?bookmark=iod
The 0.6C figure was for the most recent weekly data prior to the Dec 24th Climate Model Summary update, the 0.3C value was the latest weekly value on Dec 29th.
Interestingly, given the association of a postive IOD with Indonesian drought, severe flooding has hit the capital Jakarta - 377.4 mm was reported in 24 hours on New Year's day at Halim Perdanakusuma airport in the southeast of the city, the highest one day total on record.
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On 31/12/2019 at 12:28, Interitus said:
Obviously the ECM HRES doesn't go out to 10/1/2020 at this point so there is no way to compare. The GFS chart above has since updated and toned down that vortex disturbance, but at that range beyond the accurate deterministic limit, a SSW is likely to appear quite suddenly if one occurs (along with numerous false alarms).
To illustrate this, the 31/12 GFS 00z had a large wave break cleave a large chunk off the vortex at the 1mb level -
source: instantweathermaps.com
1mb 60°N mean zonal wind 15.2 ms in the above 348 hr charts falling to 7.7 ms at 377 hr.
But by the 31/12 18z run and subsequently there has been virtually no wave propagation and dartboard charts like today's 06z -
1mb zonal wind up to 82 ms, If these were to verify it would likely guarantee no SSW in January such is the timescale for one to develop.
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3 hours ago, Kirkcaldy Weather said:
For tropopause defined by lapse rate the 500mb level is in the stratosphere and the GFS analysis 2PVU pressure gave a dynamic tropopause pressure of about 629mb. Interestingly though the actual GFS tropopause pressure value was 490mb, not sure how that's calculated, and at these low altitudes relative humidity is much higher than typical stratospheric air which can be seen with the dew point depression above 250mb.
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1 hour ago, Redbull165 said:
GFS showing a gradual weakening of zonal winds at the top of the stratosfere after 10.1. The problem is its just GFS, I prefer the ECMWF model every day of the week.
Obviously the ECM HRES doesn't go out to 10/1/2020 at this point so there is no way to compare. The GFS chart above has since updated and toned down that vortex disturbance, but at that range beyond the accurate deterministic limit, a SSW is likely to appear quite suddenly if one occurs (along with numerous false alarms).
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2 hours ago, knocker said:
See Ryan Maue's tweet
Just for context, most parts of Alaska display a continental temperature range such that difference between the average monthly minimum and daily mean minimum is typically quite a bit more than we are used to in the UK - (for December) varying from 11.5 degrees C for Anchorage in the south with more Pacific influence, to 13.5C for Bethel and Fairbanks and 16.2C for Bettles further north in the cold interior. So these anomalies typically appear annually on average and are a long way from December records (Anchorage -34, Bethel -42, Fairbanks -52, Bettles -51).
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On 20/12/2019 at 17:01, Kirkcaldy Weather said:
Was going well, then he invoked the CFS.....here various members are simultaneously forecasting for February a SSW and record u1060 for the time of year.....well it's going to be somewhere between these, all bases covered!
source: weatheriscool.com
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1 hour ago, bluearmy said:
Did any model come out of this strong uptick with any merit ???
This chart shows GFS day 8 vs GEFS day 5 since 7th November. Over the whole period they have a similar RMSE, but while the GFS got the recent peak fairly accurately eight days in advance, the ensembles didn't even 3 days later.
Indeed the GEFS only showed a mean >50ms for the first time at 3 days prior to the peak whilst when the GFS cottoned on it showed >50ms at day 10 -
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Stratosphere and Polar Vortex Watch
in Spring Weather Discussion
Posted
Good estimates, -10.6 min at 1mb, 0.6 at 2mb.
Compared to 21.9 ms and 27.3 on the 06z mind you.