Winter 2020

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Sebastiaan
Berichten: 5703
Lid geworden op: 01-01-1978

Re: Winter 2020

Bericht door Sebastiaan » 07-11-2019 13:22

EC seizoensverwachting laat positieve NAO zien.

Andere verwachting: http://www.lightinthestorm.com/
Voor Ted ;) Hij verwacht een zachte eerste helft van de winter en meer blokkades in de tweede helft.

Abstract

Historical accuracy has been 80% since inception of long-range forecasting in 2006. The dynamic interaction between the atmosphere and ocean will – to a certain extent – be congruous with the preceding cool season, though certain variables will derogate from that putative status quo. Background forcing is redolent of a continued diminution in solar activity, surrogates of which are sunspot number and solar flux; however, geomagnetic activity has not yet reached a minimum in solar cycle 24. Another exogenous forcing mechanism, the QBO, is in a transitional phase with descending, downward propagating easterly shear stress, but juxtapositions between the present pace and 10-30mb temperature analysis and other QBO phase vicissitudes indicate that the descent into negative will be modestly protracted. Although the QBO, adjunctively with suppressed solar forcing, will be more felicitous than the prior cold season, the descending QBO will not have a significant effect on mediating blocking genesis for much of the winter season. Walker and Hadley Cell proxies, atmospheric angular momentum transport and tendencies, Pacific oceanic signaling, my NAO formula, among other considerations, evince that the winter will be dominated by z500 mid-level ridging in the sub-tropical latitude belts, redolent of a Nina-esque structure. Spasmodic poleward ridging is likely in the North Pacific, though much less than multifarious, notable years of poleward ridging. The Atlantic will generally feature a stronger than normal mid-latitude jet with lower than normal geopotential heights near Greenland, though a one-month period of higher than normal heights is possible, if not more probable than not. The themes of the winter sensible weather wise will include plentiful snows across the Rockies, Northern Plains, Upper Mid-west, and potentially into the Eastern Lakes and Northern New England. Elsewhere, snow will be near or below normal. The temperature paradigm will project strongly on the climatological La Nina regime, with colder than normal anomalies in the Rockies and Plains, and warmer than normal in most other areas. Herein, the veridical data will be examined; apocryphal notions will be refuted; and, the overall anticipated patterns delineated.

Methods

One of the principal index forecasting techniques employed is my NAO formula, developed several years ago. It has a success rate of 89%; namely, for the period 1950-2018, the formula correctly prognosticated the ensuing NAO modality for DJF 89% of the time. This is a formula underpinned by significant research; the formula accounts for the multifactorial nature of the NAO via inclusion of several, heterogeneous proxies. Other methods for prognostication include data collated on sea surface temperatures, ENSO status, SOI, IOD, the PDO, AMO, geopotential height patterns and trends in the Arctic during the autumn, diagnosis of atmospheric angular momentum distribution, trends, and likely prospective transports, torques, the GWO, tropical forcing, QBO direction/magnitude, solar forcing (including solar flux, sunspot number, and geomagnetic activity), analysis of Walker and Hadley Cell structure/behavior; and, apposite analogs, that is, years which comport with the present day paradigm.

Results

Prognosticated Teleconnection Index Modalities are as Follows [Note: these forecasts are for the mean values for DJF]:

NAO: Positive

AO: Near neutral, Slightly Negative to Slightly Positive [via significant shifts during the winter]

EPO: Positive

WPO: Negative

ENSO: Near-neutral

PNA: Negative

PDO: Negative

A more descriptive disquisition of the above index results follows.

Discussion

The atmosphere constantly strives to attain a balance it can never achieve. The periodicity of the ENSO cycle is an exemplar of this. A particular snapshot of several years may be dominated by cold ENSO conditions, but a macro-scale view of several decades reveals an increased spectrum of warm and cold ENSO. Thermodynamic disequilibrium drives weather. Ultimately, equilibration would cause energy available for work to approach zero. It is therefore axiomatic that disarray is a centerpiece of meteorology. One atmospheric pattern may be pleiotropic, in that it has a ripple effect of impacts.

This autumn, there are several integral variables to note. The atmospheric angular momentum budget has tended below parity, redolent of more easterly momentum deposits in the Earth system than average. The GWO, a proxy of total torque, tropical/extratropical wind-flow additions and subtractions, demonstrates that the atmosphere is behaving more like a La Nina than El Nino, via circuits through octants 1-2-3, nearing 4. While momentum has increased over recent weeks due to extratropical torque forcing, that forcing is insufficiently powerful to induce a surplus of angular momentum in the system. Moreover, the transport and distribution of this momentum throughout the hemisphere is unpropitious for the initiation and maintenance of protracted, anomalous blocking action centers.

The atmospheric pattern in November 2019 is responding to an interlude of intra-seasonal forcing via the MJO, much like November 2018, which operates to produce an ephemeral mask on the background, base state. Indubitably, the MJO forcing will yield a transient diminution in the Northern Annular Mode (NAM) and NAO values. Again, note that the MJO circuits this autumn are concordant with the circuits of 2018 – amplifying in coherence through phases 6-7, then declining subsequently.

The latest Pacific Decadal Oscillation (PDO) value for October 2019 is -0.81, indicative of an increasingly inauspicious regime for Southeastern US mean troughing. Warmer than normal water temperatures in the Western Pacific, the off-equator portions of the Pacific, and west of the West Coast USA, will act adjunctively and feedback with the neutral to negative AAM regime, favoring a retracted jet, and low-latitude Aleutian ridging. ENSO-QBO interplay and Hadley Cell modulation will permit occasional poleward proclivities to this Aleutian ridging, however, these episodes will increase polar transport into the northern tier of the CONUS.

Dovetailing from the aforementioned expectations, the eastern EPO domain will be dominated, often, by lower than normal geopotential heights. The Walker, Hadley Cell behavior will favor ridging in the North Pacific with concomitant trough in the West/Rockies of the United States. Prior years that featured extensive negative EPO patterns and potent mid-level ridging in the Northeast Pacific are generally distinguishable from the present year, either by way of GWO/AAM tendencies, sea surface temperature anomalies, and/or Walker/Hadley structure and behavior. Note that QBO-ENSO dynamical forcing plays a significant role, too, and La Nina seasons of modest to strong westerly shear stress may force more robust Pacific ridging. Some hints of those factors are present this year, which is precisely why I favor spasmodic poleward ridging, but the factors extant this season do not support a continuance/persistence of poleward ridge of the magnitude recorded in 2013-14, or 2014-15, for example.

The QBO easterly shear stress will eventually down-well to z30; however, the pace of descent as evinced by the slope, and the temperature profile, suggests that there could be a multi-month period of weak positives or near 0 values, prior to the full transition into negative. Concordantly, the true negative phase should not effectuate tropospheric vicissitudes until the second half of winter, particularly February and March. At which time, it is more likely that the NAM/AO tends on the negative side, countermanding the more positive NAM/AO of the first half of winter. It is – additionally – critical to cognize that the likelihood of the stratospheric polar vortex reaching zonal winds of 40 m/s at the 10hpa/60N level in November is very high. Since that event is relatively anomalous, analogs may provide a further hint insofar as auguring the ensuing mean stratospheric (and tropospheric) vortex state. The vast majority of the cases wherein zonal winds reached 40 m/s continued to feature stronger than normal vortices during the winter. Often, reversals occurred in late winter (late January onward). In this particular winter, I anticipate that the stratospheric vortex will weaken significantly in late January, potentially leading to more tropospheric blocking in February. Whether this results in a technical stratospheric warming event is indeterminate.

As noted hitherto, the provenance of the NAO forecast is a combination of disparate proxies that account for its multifactorial nature. The NAO is also an index of persistence and cyclic propensities. Although solar conditions are weak and purportedly near optimal, that is often a necessary but not sufficient condition for extensive NAO domain blocking. There are other factors forcing the mode as well. Furthermore, as a general and practical matter, the descent of the solar cycle tends to force a greater frequency of positive NAO periods. My NAO formula suggests that the mean will be positive for DJF. This is not a deviation from most winters of the past decade.

To recapitulate, the winter will be characterized by retracted jet propensities; neutral to negative AAM; null to 1-2-3, Nina attractor phase GWO orbits; a negative PDO/PNA, a variable AO via less blocking early-mid winter and more late winter; a generally positive NAO, though one month could be negative (favoring February); a neutral ENSO; a warm AMO; and, a QBO/solar combination, though seemingly not very unpropitious, that will tend to underwhelm in terms of its relative inability to induce significant, protracted tropospheric blocking.

Outlook and Progression

December

The month will be characterized by hemispheric forcing agents highly inimical to the development and persistence of high latitude blocking structures. The northern Hemisphere should feature sub-tropical ridging throughout the 30N latitude belt, and concomitant positive momentum deposits in the 60N latitude belts. This should create an overall lower than normal geopotential height anomaly in the Arctic/NAO domain, thus, teleconnecting to mid-latitude zonal westerlies.

The ramifications for sensible weather include a fairly benign pattern, in the context of normal winter conditions, across much of the United States, and likely Western Europe. There should be aperiodic injections of polar/arctic air into the Rockies and Northern Plains. Snowfall should be below to well below normal in the Eastern, coastal regions, and closer to normal the farther north one goes. Across the Lakes and Northern New England, snowfall departures are more correlated to precipitation vicissitudes than temperature anomalies, so for these areas, it is unlikely that snowfall will be below normal. Temperatures, a fortiori, given the z500, will be warmer than normal for most of the South and East.

January

Alterations should begin to initiate across the Arctic domain as the month progresses onward, due in part to downward propagating easterly shear stress via the transitioning QBO. Poleward Pacific ridging tendencies are possible, and, a priori, these ridges may connect with developing Arctic geopotential heights to facilitate a stronger transport of polar/arctic air into the Rockies and Northern Plains. However, the momentum backdrop should be neutral to negative, and its distribution continuing to promote sub-tropical ridging.

The resultant sensible weather should near to colder than normal temperatures in the N Rockies/N Plains/Upper Mid-west, and generally warmer than normal in the East/South. Snowfall departures, accordingly, should be below normal for most of the East outside of Northern New England. Central New England may see closer to normal snowfall in January due to increased jet suppression via spasmodic Pacific poleward ridging. Precipitation will be above normal in the OH Valley, interior Northeast, and Lakes, via an active SW-NE storm track.

February

Of the three meteorological winter months, February will differ most from the mean pattern. It is in this month that easterly shear stress will have a more significant effect on the AO and NAO domain, though mediated in significant part by anticipated, enhanced tropospheric receptivity to the genesis of blocking action centers. Higher than normal geopotential heights should dominate the Arctic domain, in concert with some North Pacific ridging. However, there will still be some persistence of SE US ridging via the angular momentum tendencies and backdrop. This should otherwise obviate would could have been very cold and snowy month on the East Coast. Nonetheless, the month should be the coldest and snowiest of the winter, compared to December and January. Still, the expectation is that these conditions will not be sufficient for many of the East Coast cities to reach their average snowfall for the season. Temperatures will be colder than normal across the northern tier and warmer than normal across the South, and near normal elsewhere. Snowfall will be near or above normal across most of the Lakes, OH Valley, Northeast and Northern Mid-Atlantic. There may still be a gradient across the Mid-Atlantic due to SE US ridging, thereby preventing much snowfall south of Washington DC.

Jaap
Berichten: 1547
Lid geworden op: 01-01-2007

Re: Winter 2020

Bericht door Jaap » 09-11-2019 23:49

Was aan het eind van de middag een mooi verhaal aan het schrijven met mijn jaarlijkse wintervoorspelling, is de site ineens onbereikbaar. Na vernieuwen wel weer, maar het stuk was weg. Balen.
Daarom nu in telegramstijl. Ik kom er graag op terug als er vragen of opmerkingen zijn.
Ik doe dit al sinds 1987 ongeveer en heb met terugwerkende kracht ook eerdere jaren bekeken. 65% redelijk goed, 35 % kwam niet uit. De professionals en de Enkhuizer Almanak scoren ook zo hoog.
Theorie: de luchtdrukontwikkeling tussen 5 okt. en 5 nov. staat ruwweg model voor de drie wintermaanden daarna.
1. Het lijkt een depressie-winter te worden.
2. Temperatuur normaal tot bovennormaal, afhankelijk van de koers en de ligging van de drukgebieden.
3 Grote kans op een natte winter, waarbij af en toe een pak sneeuw kan vallen.
4. Misschien een paar korte perioden met stralingsvorst. De Tocht zal wederom niet verreden worden.
5. Grotere kans op sneeuw tijdens Kerst of Oud en Nieuw.
6. De randen van de winter kunnen licht winters zijn, dus rond Sinterklaas of eind februari.


Jaap
Berichten: 1547
Lid geworden op: 01-01-2007

Re: Winter 2020

Bericht door Jaap » 10-11-2019 22:02

Ik volg het wel, die beschrijvingen van NOA, SSW, El Nino enz., maar voor een simpele weer-amateur-historicus is het nogal ingewikkeld. Bovendien gaat het over wereldwijde weerkunde, met toch wel veel nadruk op bijv. Noord-Amerika. Ik zie de directe invloed van globale zaken op het Nederlandse weer niet zo, maar ik volg op een afstandje de wetenschappers die de verbanden willen aantonen.
Mijn woorden over de professionals en de Enkhuizer Almanak klinken aanmatigend, maar zijn niet zo bedoeld. Ik toon alleen aan, dat seizoensverwachtingen maken voor Nederland een zeer moeilijke en hachelijke materie is. Grote namen uit verleden en heden kwamen bij mijn weten niet verder dan sporadische treffers en zelden of nooit twee achter elkaar. En dan doel ik op iets gedetailleerder dan een ruwe schets van een paar regels.
Voor ons gebied is een tiendaagse verwachting al heel lastig, laat staan een heel seizoen.

Hans
Berichten: 688
Lid geworden op: 01-01-1998

Re: Winter 2020

Bericht door Hans » 10-11-2019 23:39

Ik ben heel benieuwd Jaap!

Sebastiaan
Berichten: 5703
Lid geworden op: 01-01-1978

Re: Winter 2020

Bericht door Sebastiaan » 12-11-2019 10:42

Laatste Glosea5 toont wederom positieve AO/ NAO deze winter.

Paul
Berichten: 510
Lid geworden op: 01-01-1980

Re: Winter 2020

Bericht door Paul » 12-11-2019 18:45

Sebastiaan schreef:
12-11-2019 10:42
Laatste Glosea5 toont wederom positieve AO/ NAO deze winter.

Inderdaad.
Knipsel.PNG
Weer een waardeloze winter :cry:

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Hans
Berichten: 688
Lid geworden op: 01-01-1998

Re: Winter 2020

Bericht door Hans » 12-11-2019 23:23

Doe er toch niet zoveel op uit!! Laat je verrassen...!

Paul
Berichten: 510
Lid geworden op: 01-01-1980

Re: Winter 2020

Bericht door Paul » 13-11-2019 08:49

Hans schreef:
12-11-2019 23:23
Doe er toch niet zoveel op uit!! Laat je verrassen...!
Je hebt helemaal gelijk, Glosea5 is ook maar seizoensverwachting ;) .
Knipsel.PNG
Knipsel2.PNG
En zit er geregeld ook behoorlijk naast.
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Ko
Berichten: 3627
Lid geworden op: 08-06-2013

Re: Winter 2020

Bericht door Ko » 13-11-2019 09:27

Alle termijn verwachtingen voorzien toch een zachte winter? Kun je je toch maar beter voorstellen op weinig tot niets. Die ecmwf bijvoorbeeld ook en die zat er zelden naast in verleden. Sterker nog, vaak viel de winter nog zachter uit dan zij voorzagen.

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