Isotherm

@40/70 Benchmark - this is a great, highly detailed essay, and you did a very good job re explaining the various apposite factors. Our index forecasts are also quite similar, in fact, the only difference appears to be that I expect the positive geopotential height center to be centered more toward the NAO region rather than the north pole in the means but I am anticipating both a weakly neg AO and weak to mod neg NAO. Other indices are similar to yours as well. Earlier this month, there were actually some conflicting factors which IMO made this winter harder to call than most realized, but now, my confidence is fairly high on our forecasted outcomes.

@donsutherland1 - great work, and good luck with verification. There are plenty of commonalities between our forecasts, which is nice to see. I'm most interested to see the inter monthly progression, as I have thought and still do that a rather non-canonical progression is possible.

Thank you!

Very much appreciate that, Ray - thank you for the great compliment! It looks like you've produced an exceedingly fastidious disquisition there - I have not had an opportunity to read it yet, but will provide feedback after doing so. On first glance, it appears our conclusions are quite similar which is good to see. I believe strongly that the NAO will average negative for the first time in quite awhile. Latest data continues to give credence to the colder December.

Thank you both for the comments!

Thanks! Thank you very much, Don. I hope my NAO formula proves useful in the years ahead. Re snowfall, if I bust, I expect that it will be on the low side. The numbers may be slightly conservative.

Thanks very much for the nice compliment.

It seems we're weighting variables differently for analog purposes. You appear to assign significant weight to occurent weather similarities in the preceding autumn, which I do not. I'm much more interested in comparing global pattern drivers and indices, which in my view, will prove more salutary for prognostication purposes. Along that vein, 1963 checked more of my boxes as far as analoging than any other year since 1950.

Thanks, Nate. I compared the various years very strictly with respect to solar, QBO, ENSO, among many other variables. There were some differences with the years you mention that warranted exclusion from my perspective, such as descending easterly tendency or negative QBO, for example. 1969-70 was a second year Nino, which played a role in limiting its inclusion as well. Thank you! Thanks, Frd. It may be somewhat counter-intuitive, but the research I've read actually indicates that descending westerly QBO/low flux couplets aid in vortex stabilization in the upper levels. It's actually the least perturbed state insofar as technical sudden stratospheric warming events. However, like I delineated in the outlook, I don't think this should be of significant concern to anyone this particular year due to other factors which suggest tropospheric blocking. The still negative 50mb QBO, conducive wave driving, torque events, among other variables such as enhanced BDC/ozone transport, will keep the lower stratosphere + troposphere more perturbed this winter. Thank you. You seem to be making the assumption that analog = forecast, which isn't the case here. As I stated in the outlook, 1963 was the only year that met my threshold of sufficiently similarity for inclusion as an analog. However, that doesn't imply I'm projecting its sensible weather results directly onto this year's winter outlook. It's merely a guide. As one can see by my departure forecast, the temperature anomalies are MUCH more tempered compared to 1963, to account for the warmer globe, Agung, and expected less severe blocking in the NAO region. 1963-63 finished with departures of -3 to -4 for DJF in much of the Northeast. I have around -1 for NYC for DJF -- substantially warmer.

Knew I'd forget an image -- just a note -- I added the 500mb forecast map under "forecast and progression."

Any comments or inquiries are appreciated! http://www.lightinthestorm.com/ Prior Forecasts: Past years’ winter and summer outlooks are maintained on my website: http://www.lightinthestorm.com/ Since the outset in 2006, the verification has been 82%. Abstract: After multiple, successive winter seasons typified by negative ENSO conditions in the Pacific, a material alteration in the thermocline structure, walker-cells, and concomitant pressure pattern has occurred. The progression toward El Nino has been quite mercurial in that westerly wind bursts, surges of positive frictional torque, mountain torque, and angular momentum have generally been rapidly countervailed by diminutions in those values. This atmospheric warfare may persist to a certain extent, but eventually Nino-esque predilection will predominate. Global temperatures have cooled in comparison to prior years; although, anomalies are still modestly warmer than normal in the northern hemisphere. We continue our descent into the minimum of solar cycle 24, with a significantly reduced output of geomagnetic activity compared to the past few years; solar flux is suppressed quite low, and sunspot activity has been diminutive. The Atlantic sea surface temperature structure remains redolent of a warm Atlantic Multidecadal Oscillation, and the Pacific is likewise, in a warm phase. Going forward into the ensuing cold season, one of the most salient variables, invariably, will be the accurate prognostication of the tropospheric polar vortex intensity, proxies for which are the Northern Annular Mode / Arctic Oscillation and North Atlantic Oscillation. El Nino winters wherein the North Pacific and North Atlantic operate adjunctively with dual favorability feature much different sensible weather results than El Nino winters of only single domain favorability. Hence why it is highly salutary to accurately predict NAO behavior at longer lead times if possible, particularly in terms of Northeastern US winter weather. Contemporaneously, of course, it would be apocryphal to assert that the Pacific pattern is comparatively less important. It is axiomatic that the north Pacific atmospheric structure strongly modulates downstream weather, and weak-moderate El Nino north pacific patterns feature quite a bit of heterogeneity, historically. Specifically, Alaskan-low/British Columbian trough years induce largely warm CONUS patterns whereas Aleutian Low/E Alaskan ridge patterns produce the converse: colder CONUS. The discourse herein will expound upon these topics with the sensible weather prognostications thereupon. Methodology [Examination of Integral Factors] and Key Assumptions The genesis of a weak El Nino event has occurred, and accordingly, the sea surface temperature anomaly profile in the central Pacific is highly reflective of a positive/warm ENSO event. SOI values have been redolent of neutral ENSO, as the 30 day running SOI value is around 4.7, and October’s mean SOI value was 2.61, following September’s -8.5 (more indicative of El Nino). It is possible to have spasmodic SOI fluctuations such that some months are Nino-esque while others are not; however, the totality of the oscillations suggest very strongly that the ONI (Oceanic Nino Index) is unlikely to exceed low-end moderate El Nino status. I expect that the ONI peak will fall within the range of +0.8 to +1.0c, with low probability of exceeding +1.0c. The following is the IRI model output which accords with my postulated peak numbers. Atmospheric angular momentum (AAM) has generally been running on the negative side from late summer 2018 through mid-autumn 2018, suggestive of greater easterly wind stress in the atmosphere. While this is a La Nina signal typically, AAM can be negative through El Nino winters, wherefore, the resultant sensible weather patterns are quite different. However, westerly momentum has increased in recent weeks, in response to more frequent positive frictional and mountain torque event propagating poleward through the atmosphere. These westerly additions have begun to alter the hemispheric and global flows. Concordantly, an El Nino-esque z500 pattern will continue to develop down the road. It is also salient to note that many of the moderate to strongly negative AAM El Nino winters featured much colder Pacific SSTA (sea surface temperature anomalies), as negative/cold PDO (Pacific Decadal Oscillation) have been shown to retard westerly wind flows, concomitantly enhancing base state easterlies. Accordingly, a positive/warm PDO will aid in obviating persistent, deeply negative AAM periods over the coming months. Furthermore, the velocity potential z200 structure is redolent of a west based El Nino event. This will be one of the most west-based Nino events in database, not insofar as the putative “modoki” SST calculation, but pertaining to the actual walker cell orientation and concomitant uplift zones. Intermittent westerly wind bursts and attendant enhanced convergence near and west of the international dateline are likely over the coming months. There may also be significant off-equator forcing in the sub-tropical areas near/south of Hawaii, extending a bit eastward. The sub-tropical jet should be activated compared to normal. MJO cycling, as reflected by autumn analogs, sea surface temperature anomaly trends, and anticipated physical forcing, will produce conditions felicitous for MJO phases 7-8-1-2 in particular. The sea surface temperature structure; the precursor tropical forcing pattern; and British Columbian “correlate” as I term it, all indicate increased probability for higher than normal geopotential heights in British Columbia, eastern Gulf of Alaska, eastern Alaska and western Canada, in concert with an Aleutian Low feature, displaced slightly west of normal. Geopotential height patterns near British Columbia in late autumn have yielded approximately a 0.7 correlation with ensuing winter geopotential heights in that region. See the below image depicting z500 geopotential heights over the past few weeks. This pattern over W North America is likely to recur in the ensuing winter. It follows that my anticipation is for a largely negative East Pacific Oscillation, and positive Pacific North American Index. Turning to the Arctic and Atlantic, there are multifarious indicators under consideration. The Brewer-Dobson Circulation has been strengthening in recent days, as one can observe via cooling tropical stratospheric temperatures; this has shown to be an invaluable proxy which augurs polar stratospheric temperature increases as a consequence of heightened ozone concentration. Ozone has been running higher this autumn compared to the past few autumns. The Quasi-Biennial Oscillation (QBO) is now solidly positive at the 30mb atmospheric pressure level – estimating between +5 to +10 (the October value was slightly negative – but it is now solidly positive). However, the 50mb QBO value is still circa -10, and will remain negative through November, December, and January, with a probable flip positive sometime in February. The 50mb QBO modality reversal typically lags the 30mb alteration by 3 months. The vestiges of easterlies in this layer are an integral difference from other winters wherein 30mb through 50mb are moderate to strongly positive. Nevertheless, the increased westerly shear stress in the upper levels will tend to enhance zonal winds 60N/10hpa at times. Solar flux is running quite low, as we descend into the minimum of solar cycle 24 (which is still at least 1 year away). Flux values have generally hovered around 700 or slightly lower. Suppressed solar forcing in concert with increasingly westerly shear stress due to the positive QBO will act to stabilize the upper level stratospheric vortex, and destructively interfere with sudden stratospheric warming events. Geomagnetic activity is very low, with the 30-day running value around 7, indicative of a steep decline from previous autumns. Energetic electron precipitation is suppressed versus prior years, and will be below normal. Concordantly, ozone will be higher than normal in some parts of the Arctic Circle. Asian mountain torque activity will be higher than normal this winter, and coupled with other propitious tropospheric factors such as MJO cycling, will aid in increased vertical energy transfer. The Tamyra region, Barents-Kara Sea precursor geopotential height indicator is suggestive of a weaker than normal tropospheric vortex this winter. Higher than normal geopotential heights near this region in late autumn are indicative of heightened wave driving and negative northern Annular Mode / Arctic Oscillation approximately 70% of the time. See above z500 image for higher heights over the aforementioned region Oct 17-Nov 8; the coming weeks will feature a similar z500 pattern. My NAO, “Formula” which I developed several years ago and incorporates 4 main sub-components. Its retrospective success in forecasting the modality of the ensuing DJF NAO since 1950 has been 87%; and, since utilizing it prospectively, it has verified accurately in the past 4 winters as far as prognosticating the DJF NAO modality. The past several autumns, the NAO formula has strongly indicated a winter-time positive NAO. This year, for the first time since the beginning of this decade, the formula indicates that the NAO will average negative for the DJF winter season; not strongly so, but weakly negative to potentially moderately negative. Compared to the positive NAO dominance of the past several winters, it will be a material alteration. Aforementioned conducive variables, with favorable wave driving, tropospheric forcing, among other factors will produce a negative Arctic Oscillation (AO) for DJF, though not strongly so. There will be some destructive interference from attempted down-welling of a stronger than average upper stratospheric vortex. However, significant perturbation is expected from the mid/lower stratosphere through the troposphere. So while zonal winds at 60N/10hpa may run above normal, zonal winds at 70hpa may run near normal or below normal, and at 150hpa below normal. In light of the combination of factors discussed, tropospheric blocking will be greater than normal, but I anticipate that there will not be a technical sudden stratospheric warming event in the meteorological winter. However, this will be immaterial insofar as the impact on the tropospheric sensible weather pattern. Analogs were exceedingly sparse this year; the highly heterogeneous nature of this season’s indicators is such that sufficient commonalities were limited. The only analog that attains my threshold of featuring sufficiently high similarities is 1963-64, which is my primary and only analog for this winter. The AO average for DJF in 1963-64 was -0.46, and the NAO average was -1.43. The PNA averaged +1.06 and the EPO averaged +0.69. The primary disparity I anticipate here is a more negative EPO and a less negative NAO, compared to the 1963-64 values. The ridge/trough orientations in the mid-latitudes will be retrogressed westward somewhat compared to 1963. Teleconnection Index Forecasts ENSO: Weak to potentially low-end moderate El Nino (+0.8c to +1.0c trimonthly ONI peak) PDO: Near neutral (warmer than normal in the NE PAC) AMO: Positive (Warm) EPO: Negative (weak-moderately negative) PNA: Positive (moderate-strongly positive) AO: Negative (weakly negative) NAO: Negative (weakly to moderately negative) QBO: Positive/Descending westerly, +5 to +10 at 30mb, and strongly negative, -10, eventually neutralizing by the end of the winter at 50mb AAM: Near neutral; periods of negative and positive surges Analogs Forecast and Progression This will be my first winter outlook in 5 years (2014-15) since I forecasted colder than normal temperature anomalies in the Northeastern US. The indicators are suggesting very strongly that DJF temperature departures below the mean is a high probability event. While snowfall is much more difficult to prognosticate, a snowier than normal winter is likely for much of the Northeast corridor and Mid-Atlantic. There are a minority of indicators that may obviate the putative widespread “blockbuster” winter, but regardless, the majority of indicators are suggestive of a colder and snowier than average season in much of the East. As depicted in the 500mb anomaly forecast there are two principal keys to the success of this forecast: the verification of a trough-ridge couplet in the Aleutians and E GOA respectively; and, the verification of an east based negative NAO mean signal. The AO domain blocking will not be as significant. December The exogenous indicators will evolve such that lower than normal geopotential heights / trough becomes preeminent in the Aleutians region; higher than normal geopotential heights / ridge over E GOA and W Canada and the Western US; downstream, a trough should encompass much of the area from the N-Plains through the Northeast. The PNA (EPO) will be positive (negative) and the AO/NAO will be negative. Concordantly, for the first time in several years, a large percentage of the Eastern US should experience colder than average temperatures for the month. The walker-cell structure will be such that the mean ridge/trough action centers will be retrogressed a bit further west compared to the analog year (1963-64) and the putative “canonical” look for an El Nino; namely, cool anomalies should prevail from portions of the NW US eastward through the Northeast. The sub-tropical jet (STJ) should become active with wetter than normal and snowier than normal conditions. Most of the Northeast corridor will have the first real chance of a white Christmas in almost a decade. January The data analyzed suggests, quite incontrovertibly, that a relaxation in the synoptic pattern will occur, such that the poleward W-Canadian ridging reduces in magnitude. However, there may still be some vestiges of high latitude blocking that capture somewhat stale continental polar air, precluding locations in the southern/eastern part of the nation from experiencing blowtorch departures for the month. The STJ will continue to be enhanced with respect to normal. Temperatures should be warmer than normal across most of the Northern tier (though not blowtorch in the Northeast corridor: only slightly warmer than average), and cooler than normal across the South, wherein precipitation will be quite frequent. Snowfall will be near-normal in the Mid-Atlantic and portions of the Northeast, and above normal in interior/northern New England. February The data strongly suggests that February will be the snowiest month relative to normal. Whether it will be the coldest month relative to normal is more indeterminate; 1963-64, the primary analog year, featured its coldest departures relative to normal in December. The weight of other analogs indicated otherwise; however, the commonalities in those years were quite a bit less compared to 1963-64. In light of the indicators analyzed, it is quite possible that December turns out to be the coldest month relative to normal. I am not ruling that out as a possibility. Regardless, December and February should be colder than normal in the Northeast corridor. Snowfall and precipitation will be above normal in areas that normally receive snow in the East. This month (Feb) has the highest probability of a major or greater magnitude event. March (not included in the temperature outlook) The trough should retrogress into the W/Central US with normal to warmer than normal temperatures returning to the Eastern US. Blocking should begin to decrease adjunctively with lowering geopotential heights in Western North America. Snowfall should be below average in the Northeast corridor and Mid-Atlantic (much different than last winter) and above normal in northern New England, as the storm track retrogresses farther west. Thus, I am anticipating the majority of winter’s snowfall to occur within actual “meteorological winter” this year. The months of December and February should be the snowiest, and coldest with respect to normal. Outlook Specifics Outlook Temperatures For the Local New York City Region Dec-Jan-Feb Temperature Departure: Colder than normal; -0.6 to -1.6 Monthly Breakdown: December: -2 to -3 January: +1 to +2 February: -2 to -3 A colder than normal December is likely, followed by a warmer than normal January, and colder than normal February. The provenance of this outlook’s reasoning emanates from the factors delineated heretofore. Snowfall will be above normal in December. Prodigious amounts are not expected, but a major event cannot be ruled out. January will feature a more tepid atmospheric structure with lower-end snowfall potential. February is anticipated to feature the highest probability of a high-end snowfall event. The winter’s meaningful snowfall opportunities should dwindle rapidly following the end of February. The expectation is that this will be a winter with frequent Miller B events, and to a lesser extent Miller As. Concordantly, locations north of Philadelphia will be most favored with respect to maximum snowfall anomalies. Snowfall forecasting is inherently mercurial and lesser confidence than temperature forecasting. The ranges provided below are best, educated guesses given the expected physical forcing. The take-away message here should be a solidly snowier than normal winter, probably significantly so, for most of the Northeast corridor. Precipitation: Above normal Snowfall: Above normal Select snowfall amounts for various cities: Burlington, VT: 75-85” Boston, MA: 60-70” New York City, NY: 37-47” Philadelphia, PA: 25-35” Baltimore, MD: 22-32” Washington, DC: 18-28” Richmond, VA: 5-15” Raleigh, NC: 4-14”

Great, well-researched winter outlook as per usual, @griteater! Good luck with verification. I agree with some of your reasoning/conclusions and disagree with others; you'll see where those differences lie soon. Any thoughts regarding precipitation and snowfall departures? My only minor nit-pick is I prefer using the 1950-2010 as a base comparison period; I think the 1980-2010 base tends to overestimate cool anomalies somewhat. But very good job on your outlook last winter.

The most precise answer to the inquiry is that NYC is in the Northeast, and also Mid-Atlantic, which partially overlaps the Northeast (think of it as a Venn diagram). Every definition I have seen indicates PA and NJ northeastward are Northeast. However, states like DE, MD, and more often, Virginia, are sometimes not considered Northeast, but they are Mid-Atlantic. I've seen some classify VA as Southeast (if so, VA is Mid Atlantic and Southeast). Regardless, these are strictly geographical designations. Our region is both Mid-Atlantic (northern) and the Northeast, as the larger umbrella region.

Only once since 1950 has an ONI of that magnitude (+0.2c) or lower yielded an ENSO event stronger than weak El Nino. 1986-87 had a ONI value of +0.2c for JJA, and peaked circa +1.2c / low-end moderate el nino for the ensuing winter. All other examples were ensuing weak el ninos.

http://www.lightinthestorm.com/archives/1144 VERIFICATION See the following United States temperature and precipitation departure maps, respectively: Northeastern US temperature departures: Local temperature departures for June-July-August in the NJ-NY region included the following: Newark, NJ: +1.3 JFK, NY: +0.73 New York, NY: +1.4 LGA, NY: +2.6 Islip, NY: +1.8 Mean departure for those stations: +1.56 Thus, it is reasonable to state that, overall (for most locations) temperature departures for summer 2018 fell between approximately +1.0 and +2.0. My temperature departure map indicated +0.5 to +2 departures for the coastal Northeast, although specific numbers provided for NYC were 0 to +1. Therefore, while the warmer than idea verified, the heat was slightly greater in magnitude than anticipated. The progression for June and July verified very well: cool –> hot. However, August was the most aberrant deviation from the forecasted progression, although, higher dew points were correctly prognosticated throughout the summer. For the nation as a whole, temperature departures were mostly correct / within range, with the most robust warmth relative to normal in the SW US as expected. The primary flaw was the near-normal area forecasted in the Great Lakes/interior Northeast. Regarding precipitation, rainfall was above to well above normal in the Mid-Atlantic and Northeast, as anticipated. Most of the rest of the country was closer to normal or drier than normal, although, portions of the Mid-west/Ohio Valley were wetter than expected. Overall, nation-wide, this was a great forecast, and locally, a good to very good forecast, with the principal flaw being a slight underestimation in the magnitude of the heat, especially for the month of August. 90 degree days, forecasted to be 18-25, should have been forecasted as 20-30; however, the range will be close for most locations. In closing – in consideration of all the aforementioned factors: I conclude that this summer 2018 forecast verified with a grade of B.

The offical CPC AMO value was slightly positive for July. This is concordant with the warm WATL mediated mid level thermal feedback. The dichotomous SSTA structure in the ATL is an indicator that the diminution phase of the AMO is ongoing, but we will not transition consistently negative just yet. The enhanced ELY trades; the provenance of which is largely the atmospheric pressure circulation pattern in the South Pacific, has precluded the advance of el nino to date. Consequently, August is departing more so to the warm side than pre season indicators dictated. As such, this El Nino event should be weak and struggle to attain such status. Proxies suggest this event may be similar to ones that peaked circa 0.4 to 0.9c.

@Carvers Gap : The kind words are appreciated. I would not utilize the QBO as a correlate of blocking in and of itself (the correlation is minimal in a vacuum); however, its utility increases exponentially when employed adjunctively with other indices, most notably, proxies for solar status/activity. Further, the QBO trend; positive --> negative; negative transitioning toward positive, has proven somewhat informative as to the overall nature of the winter blocking. Again though, while yes, a(n) descending (ascending) QBO would implicate heightened (decreased) blocking probability, I don't place too much weight on QBO variation singularly. Further, there are other confounding variables that can contaminate this analysis, such as upstream tropical forcing, among other factors. Sudden stratospheric warming events occur with greater frequency in the negative QBO regime, but the sun modulates this probability as well. Going forward into this winter, the QBO will incontrovertibly be in an ascending phase; whether it converts technically positive during winter remains to be seen. However, we know, at the very least, it will be weak (either slightly negative or slightly positive most likely). Solar activity remains in a descending phase; so superficially, the probability appears somewhat heightened for potential -NAM, but there are other modulatory factors I examine in the autumn that I inject into my, "blocking equation" so we'll see how those shake out in a couple of months.

Thank you, denville. Yes, the urban corridor from New Brunswick-NYC was a local minimum as far as snowfall totals -- rapidly increased both to the east and west of there (and south).

http://www.lightinthestorm.com/nj-snowfall 2017-18's snowfall map for NJ has been completed. The polarity of totals, the highly heterogeneous nature of snowfall distribution, and the sheer frequency of events made this map one of the more arduous ones over the past decade. Questions and/or comments are welcome.

Pleased with how we're progressing thus far. As alluded to in the outlook, a significant, 1-2 week period of heat looks to overspread the Northeast for the first half of July. "Eventually, by the second half of June, more ridging will extend eastward, and the West Atlantic Ridge should retrograde later in June into July. July may feature at least 2 weeks of very hot weather in the Northeast, relative to normal, with a significant heat wave, as the ridges connect."

Thanks, Don.

Questions/Comments welcome, as always. A bit later than typical due to time constraints, but glad to have made it prior to the 31st deadline. http://www.lightinthestorm.com/ Snippet: The Outlook for the NYC local region stations Meteorological Summer JJA Temperature Departures: 0 to +1; Near normal to Slightly Warmer than Normal 90 Degree Days: 18-25 Across Most of the NJ-NYC-LI Area; 10-18 along the immediate coast Meteorological Summer JJA Precipitation Departures: Wet to Much Wetter than Normal; spatial distribution of summertime convection renders greater forecast specificity useless Hurricane Outlook: Named storms – around 10; Hurricanes – around 5; Major Hurricanes – 1 to 2; Impact – greater than normal potential in South Texas, Florida, and the Southeast US Coastline.

Moderately to strongly positive NAO winter, for meteorological winter DJF. My forecast of a +NAO winter verified. Another successful year for the indicators. 2017 0.88 2018 1.44 1.58

@IrishRob17 @40/70 Benchmark, That is correct, I am not advocating for the once per day observation -- which is much different than capturing the maximum snowfall for the 24 hour period. Ray, to be clear, I am merely presenting the guidelines as they currently stand, which states that non-airport measuring should be maximum snowfall for the 24 hour period. I am not advocating that the 6-hr clearing is necessarily a bad method. I just think congruence with historical records is important and we never should have added the option for 6hr clearing in the 1998-2012 period. Per my discussion with Matt who works with the NJ climatologist, there was extensive debate among the people on the panel for this 6hr - maximum snowfall issues. Interestingly enough, the person who pushed most for the 6-hr method was the same person who reversed his thinking and signed off on the return to the maximum snowfall method. Snow measuring is an inexact science; there are arguments for both methods.

I concur with this too, I think they should have maintained the maximum depth standard.