Abstract

Long range forecast accuracy, inclusive of summer and winter outlooks, has been 81% since inception in 2006. Last winter’s forecast verified pursuant to pre-season expectations. The etiological factors underpinning this season’s progression are multifarious and will be adumbrated herein. The globe, overall, continues to run well above normal in terms of temperatures, with an asymmetric skewing of the warmth toward the Northern Hemisphere. Oceanic heat content remains much higher than the baseline average, again, especially in the Atlantic and Pacific Oceans. 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 deceleration in the diminution in solar activity, and likely plateauing, surrogates of which are sunspot number, solar flux, and geomagnetic activity. However, we are effectively within the minimum of this present solar cycle. The QBO proxies are indicative of westerly shear stress extant throughout the integral atmospheric layers, z30 through z60. This predilection toward another westerly QBO winter is rather novel in the record, aside from the 2016 QBO reversal. The QBO will operate adjunctively with solar activity, and to a degree, the ENSO paradigm, to extirpate protracted attempts at high latitude blocking structures. Walker, Ferrel, and Hadley Cell assessment / proxies, atmospheric angular momentum 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 – yet again – of a Nina-esque structure. Vicissitudes in this predominant structure will largely be a function of interruptions in the mean angular momentum, ENSO, and tropical forcing signaling. When juxtaposed with the preceding winter season(s), possibly the most notable difference should be the propensity for a less negative PNA regime. In fact, a positive modality is anticipated most of the meteorological winter, barring February, and a fortiori, the sensible temperature composites will not entirely project upon/align with the past two winter seasons. Nevertheless, an otherwise hostile polar domain, will operate to frequently countervail attempts at sustained troughing in the CONUS. Spasmodic poleward ridging is likely, but this winter will mostly be incongruous with composites of the northward displaced Pacific ridge in +QBO La Nina seasons. It follows that Alaska is expected to be near or colder than normal. Herein, the veridical data will be examined, apocryphal notions will be refuted; and, the overall anticipated patterns delineated seriatim.

Methods

One of the principal index forecasting techniques employed is my NAO formula. It has a success rate of 89%; namely, for the period 1950-2020, the formula correctly prognosticated the ensuing NAO modality for DJF 89% of the time. This is a formula underpinned by significant research; the formula attempts to account for the rather multifactorial nature of the NAO via inclusion of certain, heterogeneous proxies. Other methods employed in developing the winter’s 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, torques, the GWO, tropical forcing, QBO direction/magnitude, solar forcing (including solar flux, sunspot number, and geomagnetic activity), analysis of Walker, Ferrel and Hadley Cell structure/behavior; and, apposite analogs, that is, years which comport with the present day paradigm. However, it should be noted that my analog technique is to identify only a few (in this case, mostly one, and to a lesser degree two) years which comport with the present on as many fronts as possible.

Results

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

NAO: Positive (note***=January has the highest probability of negative, otherwise, DJF overall will be positive)
AO: Positive (note***=January has the highest probability of negative, otherwise, DJF overall will be positive)
EPO: Positive
ENSO: Strong La Nina Conditions
PNA: Positive (note***=via a positive PNA December and January, and negative PNA February)
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.

Ab initio, 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. However, recently, there has been an ephemeral circulation above parity, and mildly toward El Nino attractor octants, due in part to the tropical portion of the budget. The MJO/intra-seasonal passage through phases 6-7-8-1, although of descending magnitude, has aided in this transient rise in the momentum budget. Nonetheless, as the upper divergence signal continues propagating into the Eastern Hemisphere, the atmosphere will pass the veritable precipice and a diminution in momentum will follow. Overall, the winter season will feature repeated iterations of the GWO circulation through the La Nina attractor octants, 1-2-3, with potentially spasmodic ascent into near neutral territory. Angular momentum will be antithetical to protracted high latitude blocking structures, much like the past two winter seasons.

The latest Pacific Decadal Oscillation (PDO) value for October 2020 is -0.58. 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 mostly low-latitude Aleutian ridging. ENSO-QBO interplay and Hadley Cell modulation will permit occasional poleward proclivities to this Aleutian ridging, however, my indicators suggest that persistent poleward ridging (i.e., the typical scenario for +QBO z50 La Nina winters) will not be a staple of the ensuing winter. Rather, the likely, mean, structure will be +EPO, +AO, +NAO in the means, in concert with +PNA predilection for the first 2/3 of the winter season.

As noted hitherto, the NAO is an index of persistence and cyclic propensities. That much is axiomatic. Although solar conditions are weak and purportedly near optimal, that is often an insufficient 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. Nevertheless, there is an opportunity for an interruption in the mean positive NAO signaling mid-winter – targeting January – with near neutral values (or potentially slightly negative). This signal may ephemerally operative adjunctively with a neutral to positive PNA mode to permit increased polar air transport, particularly into the Lakes and Northeastern US.

This winter will continue the decade long stretch of almost entirely positive NAO winters. Concomitantly, the AO will feature similar propensities – predominately positive throughout DJF.

In terms of ENSO, the globe has transitioned from a neutral/warm ENSO mode to moderate to strongly cold ENSO. The La Nina event should peak at a level of “strong” as ascertained by trimonthly values in region 3.4 of -1.5c or colder. The event, as is not disharmonious with climatology, tend to weaken post January into late winter. Nevertheless, the modulatory impact on the winter season will have been accomplished by the point at which the La Nina weakens significantly.

Key Highlights

• This outlook represents the fourth time in the past five years with my forecast of predominantly warmer than normal for most of the United States; this will be a warm to potentially very warm winter overall, in most areas of the country.
• Canada will have a normal to colder than normal winter across much of their regions; it follows, that there will be a fairly significant equatorward-poleward thermal gradient in temperatures, frequently, as one approaches the US-Canadian border.
• The z500 paradigm overall will permit the highest opportunity to secure a colder than normal winter in the state of Maine, and potentially northern New England. Elsewhere, it is unlikely to find any colder than normal anomalies for the DJF mean period.
• The warmest anomalies relative to normal for DJF should be from the Central US into the Mid-South and portions of the Southeastern US
• Precipitation, overall for DJF, will be drier than normal in the Mid-Atlantic, Southeast, and Southwest, wetter than normal in the far Pacific Northwest, portions of the Lakes region, and northern/central New England. This is not inconsistent with the canonical strong La Nina paradigm.
• Above normal snowfall is likely over the higher elevations of the Pacific Northwest, the Northern Lakes, portions of the northern Appalachians, and the northern half of New England. The most wintry location when coupling both cold and snow will be Maine. Snowfall will be near or below normal in all other areas that typically receive snow. For most of the I-95 corridor, this winter will not be remembered as one which produces supererogatory snowfall totals. However, there will be a window of opportunity for meaningful snowfall in mid-winter.
• Opportunities for significant snowfall events will be limited in the Eastern US from coastal Southern New England southward, however, the best window for such potential is in the month of January. The likelihood of a historic (18”+) or major (12”+) snowstorm is lower than normal this winter for most of the I-95 corridor.
Progression

• December: z500 structure = +EPO/+AO/+NAO/+PNA; this is a month which will feature predominantly warmer to much warmer than normal temperatures across most of the United States. Northern/Eastern New England will be closer to normal temperature wise. Snowfall will be above normal in the Lakes and northern New England, and below normal elsewhere.
• January: z500 structure = neutral or +EPO/Near neutral AO/Near neutral or negative NAO/+PNA: this month, while still warmer than normal for most of the United States, will provide the highest opportunity for winter conditions in the coastal Northeast and Mid-Atlantic. Temperatures will be colder than normal across the Lakes and New England, near normal into the northern Mid-Atlantic, and warmer than normal elsewhere in the country. Snowfall will be above normal in the Lakes, New England, and near normal in the Mid-Atlantic.
• February: z500 structure = +EPO/+AO/+NAO/-PNA: this month will feature the most inimical paradigm for wintry prospects in the Eastern US, with the possibility of a top 10 warmest February across much of the Eastern US. Conversely, the canonical strong Nina z500 will project upon the pattern with colder than normal conditions, and snowier than normal, in the Northwestern US. Snowfall will be below normal from central New England southwestward.
• March: low confidence is expressed for this month, but the expectation is a paradigm congruous with February – generally hostile for cold and snow in the Eastern US, particularly south of northern New England. The overall structure of +EPO/+AO/+NAO/-PNA should persist in the means.

Outlook Specifics: Temperature, Precipitation, Snowfall
NYC Metro Region

Temperature Departures, DJF: Warmer than normal: +1.67 to +2.67
Monthly Breakdown

December: +1.5 to +2.5, solidly warmer than normal
January: 0 to -1.0, near normal to potentially slightly colder than normal
February: +4.5 to +5.5, anomalously warmer than normal

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Snowfall Overall: Below normal
December: Less snow than normal
January: Near normal to potentially above normal snowfall
February: Less snow than normal
March: Less snow than normal
Total Snowfall Projections for Select Cities:
NYC (Central Park): 16-24”
Philadelphia, PA: 10-18”
Baltimore, MD: 5-13”
Washington DC: 2-10”
Boston, MA: 40-48”
Burlington, VT: 87-95”
Richmond, VA: < 5”
Raleigh, NC: < 5”

Detroit, MI: 47-55”

Forecast Maps – Note*** – analog 500mb projections do not represent, exactly, what my forecast will be – however – it should be fairly similar in terms of the major features.

***Note: one can assume, for the purpose of the monthly temperature maps, that the legend is the same as the DJF map.

Near normal = -0.5 to +0.5

Slightly warmer than normal: +0.5 to +1.5

Solidly warmer than normal: +1.5 to +2.5

Much warmer than normal: +2.5 to +3.5

Anomalously warmer than normal: > +3.5
Slightly colder than normal: -0.5 to -1.5
Solidly colder than normal: -1.5 to -2.5

December Analog, z500:

January analog, z500:

February analog, z500:

December to February analog, z500:

Winter Outlook Temperature Departures:

December Temperature Outlook:

January Temperature Outlook:

February Temperature Outlook:

Snowfall Anomalies:

VERIFICATION:

Verification is broken down into: temperature departures locally (highest weight), temperature departures nationally (second highest weight), snowfall and z500 pattern.

National temperature departures: C+

NYC metro area temperature departures for DJF, meteorological winter:

NYC: +0.933

LGA: +2.1

Overall winter outlook grade: