Isotherm

Utilizing NOAA data, I did a couple of quick calculations. NYC-Central Park's mean snowfall for 1990-2020 is 30.1", and their median snowfall is about 27". The median, as you know, is a very indicative number, as it represents the relative frequency of above versus below normal snowfall winters. So, the 27" is fairly good, given the proximity to the mean, suggesting that there's an almost equal split of snowier than normal versus less snow than normal winters in NYC (I would guess probably 45% snowier than normal / 55% less snow than normal). The farther south one heads, the worse the median. For example, Washington DC sees much more below normal snowfall winters than above normal, so their mean snowfall is arguably inflated by a relatively small number of major winters. Conversely, I would guess Boston's median is almost identical to their mean.

One essential reason is that the mean climatological pattern favors a +AO and +NAO. It's a physical, meteorological fact that it is more difficult to induce and maintain, for protracted duration, a -AO/-NAO. The prevailing polar jet flow is westerly, so the +NAO/AO is effectively an enhancement of the the prevailing, "normal" regime. A -AO/-NAO is an interruption of the mean flow. The frequency of positive AO/NAO winters is higher, actually by quite a bit, when one utilizes a large sample size. There are decadal predilections wherein a -NAO/AO can dominate -- see the late 1950s through the early 1970s, but over the long term, the frequency of +AO/NAO is higher. I just did a rough calculation, and circa 36% of winters since 1950 have been -NAO mean for DJF. So, that's a majority +NAO by a statistically significant margin. I posted this chart the other day, but it's worth a re-post now, as one bit of good news derived from this persistent +AO/NAO regime is that Arctic Sea Ice Extent has officially touched the 2000-2010 mean line -- quite impressive given how poorly we were faring sea ice wise.

Thanks, Tim. I am happy re the outlook; and it would certainly be nice to see an areawide event prior to the end of the season. I still do believe there will be amelioration near the end of February into March, from hostile to more mediocre. I don't see any indications of a great pattern at this juncture, but all we would need is something serviceable to produce a plowable event in Feb 25-Mar 10, which is still favorable climatology. Post Mar 10 is when probabilities begin decreasing expeditiously.

For once, it appears the surface high pressure ridge crests with auspicious timing for near ideal/ideal radiational cooling Friday night. There may finally be a hard freeze in the single digits and teens.

Certainly -- agreed. It would remove some of the putative "bite" from minds regarding this winter, if we had at least one DCA-BOS snow event to track prior to season end.

Concur. I am very satisfied as well. My index forecasts [+NAO,-PNA,+EPO,-PDO] and hemispheric pattern hit well, as well as the warmth and snow anomalies for much of the country. My primary flaw to date was not going warm enough. As you mentioned, hitting high magnitude anomalies from advanced leads is extremely difficult. I did see some signals for a record type warmth winter -- so my only regret will be not going even warmer. Snowfall wise, the anomalies are doing well, and again, it has actually been a bit less than even I anticipated. However, I do still see *potential* for amelioration toward the end of February and March, i.e., transition from hostile to mediocre. But we shall see.

And interestingly, it is not so much an expansive spatial coverage of low geopotential heights, as one might expect with a classical strongly +AO. The absurdly high value is a function of the incredible pressure gradient / geopotential heigh differential between the North Atlantic and Azores region. The magnitude of the cyclone near Greenland in concert with the anomalous subtropical ridging near Azores is mediating this incredible AO spike. I have not, hitherto, seen such a gradient across the N ATL domain:

Any short term effect would be negligible; however, if the trend continues, it would permit a greater reservoir of colder air to the north. That said, a conducive pattern is still required to deliver the air. Note, this is merely an early observation as the trend could also reverse. But greater arctic sea ice in the long term would be salutary in terms of global temperature leveling.

One tangential benefit of the semi-persistent +NAM/AO mode this winter is the amelioration of ice growth across the Arctic spatial domain. The current Arctic sea ice extent is the "best" it has been since 2010; still far below the multi-decadal mean, but ahead of all of the past 10 years. Not far from the 2000-2010 average, either:

Underwhelming event here: 39 mph peak gust. Closest ASOS was also 39 mph.

If there is a material amelioration of the z500 from hostile to mediocre, it won't occur until very late in February and into March, as I've been delineating in my past couple of updates. So, I wouldn't expect to see anything too striking on the D10-15 EPS right now. I am still monitoring a few indicators [not related to the high frequency intraseasonal signal] which may improve near the end of February and beyond; however, that is not a guarantee. Until further notice, the RNA structure continues: cool NW US/Mid-west, warmer SE US.

Indeed -- a remarkably persistent regime. I also hope that the past couple of winters have rather debunked the notion that weak El Nino automatically translates to cold/snow for our region. Even with a more central-west based warm SST anomaly this winter, the z500 was quite the inverse of a typical weak Nino regime [not a surprise for either of us]. It will be interesting to see the ENSO vicissitudes of the coming year, as the subsurface presently "could" be indicative of an actual oceanic La Nina. However, as you know, the atmosphere will often behave in ways incongruous with the oceanic state. We'll have to see where we are post spring barrier.

The latest PDO value, unsurprisingly, is now strongly negative for January, reflective of the substantial SST cooling across the northern and eastern Pacific. The z500 pattern for February will be quite close to my analog package which featured the composite RNA structure, namely, lower heights toward the NW and higher heights in the SE US. 202001 -1.17

I certainly do not disagree with your comments, and it's much more complicated even than I alluded to in my highly simplified post. I went warmer than normal/less snow than normal this winter as well in my seasonal for numerous other reasons, too -- so that's interesting, potentially we are examining some of the same variables. Re, correlations to snowfall and 2m temperatures, the issue w/ meteorology, as I'm sure you know, is that many of these relationships are indirect and obfuscated by other contemporaneous signals, so finding the elusive direct correlation to snowfall might be quite difficult [although there are many indicators of high utility in my opinion]. I also disagree with any remarks pinning the blame solely on the IOD.

Very significant rise at New Brunswick. 1980-2010 had a mean January temperature of 30.4F, solidly in Dfa, and the 1990-2020 January mean is 31.7F, just barely within Dfa. Demonstrates the material warmth of the 2010-2020 period.

My final temperature departure here for January was +6.1, mean temperature of 37.0F. December was +1.1, so I am at +3.6 for the meteorological winter thus far. Snowfall: 5.2" (about the same number by this time last winter).

Solar activity and its attendant proxies have significant utility if one recognizes how to employ it. Those who argued solar minimum induced blocking for the present winter did so with incomplete knowledge. Solar forcing can modulate high latitude geopotential heights, but it must be analyzed in concert with other variables, such as the QBO for example. Thus, linear correlations between SSN and NAO values will be unimpressive because there are other variables masking and confounding. There is a false belief that low solar activity is both a necessary and sufficient condition for high latitude blocking, but that isn't veridical. It's a much more complex relationship. I did not think the suppressed solar activity would lead to a -NAO/AO this winter.

@frd -- thank you. Additionally, I wanted to provide my thoughts on something I saw posted regarding the IO interference and its attendant correlation to the NAO mode. While I am not asserting that the hypothesis should either be rejected or fail to be rejected, concurrently, I would caution [not you, the individual proposing the hypothesis] attempting to attribute a particular phenomenon to the perturbations of a multifactorial index like the NAO. As I've mentioned in previous posts, the NAO is forced via numerous pathways adjunctively, which is why it is more difficult to prognosticate (IMO) than other indices such as the PNA [much more modulated by Pacific based perturbations]. The Indian Ocean standing wave was certainly a factor, among many others, this winter. For example, another factor includes expanded Hadley Cells, driven in part by the SSTA structure, and the macro-scale propensity to intensify the mid-latitude jet in the West Pacific. The mode experienced was really the inverse of what is desired for the coastal Eastern US. Also, if interested, I posted an updated in my outlook thread which effectively rehashes the thoughts two weeks ago [no significant changes in thinking]. RNA structure February with potential / putative amelioration end of Feb-Mar.

Updated thoughts posted in my outlook thread [essentially a rehash / recapitulation of 2 weeks ago - no material changes in thinking]:

The recent MJO, FT/MT mediated momentum surge and concomitant high-GWO orbit should at least mediate the semi-persistent AK-GOAK low height anomaly --> wave 1 induction --> convergence/pressure onto the SPV. So, the material weakening of the SPV in mid February is likely more genuine than many of the GEFS plots have depicted this winter heretofore. As the stratospheric status begins to improve mid February onward, I am monitoring the next cycle of tropical wave propagation toward the Central Pacific as we reach the last week of February. At which time, better tropical--->stratospheric receptivity could mediate a more favorable pattern than we've seen to date, from approximately late February into March. Speculative/a priori, but as stated, there are signs that end of winter could feature an "improved pattern." Until late Feb, yes, I think RNA-type structure after a very marginal window in early Feb. As mentioned in my update a week or so ago, the pattern in Feb, while still favoring the interior (RNA structure) will probably offer more chances than Dec-Jan. Still watching late Feb-Mar [somewhat lower confidence speculation for now, but it's something to monitor].

This is a very confused communication of statistics. In statistics, a normal distribution includes 68% of the observations falling within 1 standard deviation of the mean. However, Bluewave was specifically employing the term, "climate normal" which signifies an average over a given time frame. https://scied.ucar.edu/blog/what’s-new-climate-normal The average snowfall for the given time period in question was as he stated. So, I fail to see the issue with his post.

@frd, I have read that research to which you refer, and believe it to hold value. There is a documented lagged-oceanic forcing, part of feedback cycle with the atmosphere. The interesting aspect about the NAO, as to why it is such a difficult 'beast' to forecast is its highly multifactorial nature. Unlike the PNA for example, which can be primarily forced by MJO or tropical Pacific disruptions, the NAO is forced by way of many disparate variables. That being said, there are propensities and correlations that can aid us in prognostication. Certainly, solar forcing is involved. As I believed I may have mentioned here before, there is a tendency for increased -NAO episodes immediately following the solar minimum point. Conversely, the years immediately preceding a solar minimum are often more +NAO slanted. This is not always the case but the tendency is quite noticeable. So, along those lines, yes, from a statistical and also physical forcing perspective, I think we will probably enter a period in which 2 or potentially 3 years out of the next 6 feature a -NAO in the means.

In the spirit of self-reflection/verification, I simply wanted to inject my two-cents, in that the primary issue here, AAM/MJO wise, is the partitioning of momentum predominantly into the S Hemisphere. I cited and broached this issue on January 3rd, in reference to last year's distorted MJO-7-8 response in late winter. As it turned out, this year's response wasn't too dissimilar. So it was very much foreseeable from my standpoint. Note on the MJO u-div and also the convection cross-section, the preponderance of the momentum is directed southward. Additionally, the anomalous AAM spike is a function, partially of the MJO-tropical component, but also the intense frictional and mountain torque production. But note the partitioning of that torque activity; again, principally in the southern hemisphere. This is therefore insufficient as it pertains to the induction of material stratospheric - and by extension - tropospheric vortex deceleration/diminution. As such, the resultant z500 is a distorted conglomeration of Nino-esque and Nina-esque features in the northern hemisphere.

And yes, I also agree with your point, @psuhoffman, regarding the altered base state, i.e., negative PDO structure, SSTA distortion in the WPAC, and this was certainly a variable in my winter outlook as well. When the waters are warmer in the macro-scale sense, the typical canonical weak Nino/neutral composites become much less meaningful. The jet flow is disrupted, hadley cells expand, among other things.

Thanks for the kind words re: my forecast. And Frd, that is correct. The window of opportunity would probably arise later February forward. As said, no guarantees, but certain variables may ameliorate by then. Re, the NAO. It now appears almost a lock that the Dec-Jan-Feb mean NAO modality will average positive [in fact, per CPC data, I don't believe we have had more than 1-3 -NAO days since December 1st]. This will bring my formula to 90% exactly as far as the success/verification rate utilizing the years 1950-2019. As I've said prior, the formula is multifactorial. And yes, to PSU's note, the AAM periodicity/fluctuations is certainly involved in the formula, along with other variables. I had contemplated publishing a paper on the formula, but I'd like several more years of observing its performance.