frd

I imagine this might be useful in winter, or anytime. Great resource material from Simon. Check it out.

As the GEFS trended warmer during the past 48 hours, and towards the earlier warmish Euro runs, the overnight EPS trends colder as the month nears an end, which looks very interesting. Possibly some wave breaking and influences from the tropical system. An interesting North Atlantic may be in the cards as well.

A good read - posted by bluewave yesterday from a recent study on the winter + NAO and the near record + IOD last November. < A recent study linked the very strong +NAO last winter to near record +IOD in November. The +IOD was associated with the standing wave in the MJO 1-2 which was observed as early as last October and November. Those October MJO phases were similar to the other La Niña and Niña-like below normal snowfall seasons in 19-20, 18-19, 11-12, and 07-08. They mention a stratospheric pathway linking the flat ridge north of Hawaii and the more +NAO in the Atlantic. The normal to above normal La Niña snowfall seasons since 2000 had stronger MJO 5 forcing in October. Those seasons were followed by intervals of -EPO and -NAO blocking. So this may potentially be how we saw the October to winter MJO relationship since 2000. But as always, there are no guarantees this relationship will work every season. https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/asl.1005 Predictability of European winter 2019/20: Indian Ocean dipole impacts on the NAO 3.3 Stratospheric pathway As alluded to in the previous section, the stratospheric teleconnection pathway of the IOD to the Atlantic involves the Aleutian cyclone, and is similar to that already documented for ENSO (Manzini et al., 2006; Ineson and Scaife, 2009). Demonstrated best by the IOD experiment in the month of December, Figure 3cshows a Rossby wave train emerging from the Indian Ocean that leads to poleward flow in the North Pacific near the dateline, and equatorward flow to the east of this. These two responses combine to give anomalously positive MSLP just south of Alaska and the Aleutian Islands. Figure 4a shows that this MSLP anomaly in DJF is in a very similar location to that due to ENSO (shown also in fig. 1 of Ineson and Scaife, 2009). For the single case of winter 2019/20, this signal is evident in early winter, as discussed below, and again in the DJF mean (Figure 3b) due to a particularly strong signal in January and February. As described in Ineson and Scaife (2009), the positive MSLP anomaly (Figure 4a) acts to reduce the strength of the climatological Aleutian cyclone and, thereby, reduces the amplitude of planetary waves propagating upwards into the stratosphere. Figure 4b demonstrates this reduction in planetary wavenumber 1 amplitude (diagnosed using geopotential height at 100 hPa, area averaged 40–80°N, and then Fourier decomposed; Hardiman et al., 2008) in the IOD experiment, and is consistent with fig. 10b of Fletcher and Cassou (2015). Reduced planetary wave driving in the stratosphere leads to an anomalously strong stratospheric polar vortex (defined by U(60°N, 10 hPa) in Figure 4c, and see also fig. 10 of Fletcher and Cassou, 2015). Anomalously strong vortex signals propagate downwards into the troposphere, resulting in a positive NAO at the surface approximately 1 month later (Baldwin and Dunkerton, 1999; Kidston et al., 2015). In fact, this positive MSLP anomaly in the Aleutian region occurs also in November, so reduced wave driving (Figure 4b) and an anomalously strong stratospheric polar vortex (Figure 4c) are already apparent in November. Indeed, the November polar vortex strength is anomalously positive in IOD composites, the IOD experiment, ERA‐5, and all forecast systems (not shown). Fig. 4 of Nie et al. (2019) demonstrated that an early winter preconditioning of the stratospheric polar vortex in November descends through the stratosphere and troposphere in the following winter months, projecting onto an anomalously positive NAO in DJF. The winter of 2019/20 was anomalously warm and wet across the UK and Northern Europe, due to a strongly positive NAO. The winter was well forecast by the C3S and the Met Office DP3 seasonal forecast systems. Even the details of individual months, such as the transition from the negative pressure anomaly west of the UK in December to a positive NAO in January/February, were well forecast by all seasonal systems. Such remarkable agreement amongst systems is suggestive of the positive NAO being strongly driven by global influences, and predictable in this case. In this paper, composite analysis and numerical experiments are used to identify the very strong positive IOD event at the start of the winter as the key driver. Two teleconnection pathways are identified using an experiment in which two ensemble forecasts, one with the observed November 2019 Indian Ocean SST anomalies, and one with the negative of these anomalies, are produced using DP3. The difference in the ensemble mean response, shows a Rossby wave train originating in the Indian Ocean and propagating across the Pacific and Atlantic Oceans. In the Atlantic, this wave train projects directly onto the observed Atlantic MSLP anomalies. In the Pacific, the wave train acts to reduce the amplitude of the Aleutian cyclone and therefore the amplitude of planetary waves propagating into the stratosphere. This results in an anomalously strong stratospheric polar vortex, projecting onto an anomalously positive NAO. This numerical experiment shows good agreement with both the ERA‐5 reanalysis data and the C3S multi‐model seasonal forecasts in terms of the details of both teleconnection pathways. Furthermore, both pathways are very similar to the well documented tropospheric and stratospheric teleconnection pathways whereby ENSO impacts the north Atlantic MSLP (Hardiman et al., 2019). The impact of the IOD on the Atlantic jet stream and associated precipitation anomalies is a northward shift in the jet latitude, a slight increase in the jet strength, and anomalously high precipitation over the UK and northern Europe, as shown in Figure 5. This is consistent with an anomalously positive NAO and agrees well with the features observed in winter 2019/20. There is a remarkable agreement between the IOD experiment and the C3S multi‐model mean forecast. The signal in the December observations is noisier (Figures 3a and 5a), but this is expected, being only a single realisation of a single month. A knowledge of the teleconnection pathways between the IOD and the North Atlantic gives greater confidence in the seasonal forecast skill they offer. The frequency of positive IOD events has doubled in the 20th century, and their intensity has also increased, with this trend projected to continue (Abram et al., 2020). It is likely, therefore, that such connections will become increasingly important for seasonal forecasting of European winters during the rest of the 21st century. >

Simon made this cool presentation. Also, looking from his site, there are some minor changes with regard to to the development of the early season PV. CFSv2 GEFS

Do you know if this tendency in a Nina carries to lower latitudes as well, such as the Northern Mid Atlantic ? I have always felt, and observed, during the past 40 years a snowy December exceeding 6 inches of snowfall in my area goes on to produce above normal snowfall in the ensuing winter ( in a Nino year ) . So far that indicator has done very well.

This has been ongoing the last several Fall seasons. I believe you posted something about the WAR and the Western periphery is where you will find many late record high temps, especially in Virginia down to Florida. The warm SSTs certainly are a factor along the immediate coastal plain and even further inland.

Models have been underestimating the WAR at times.

Weaker vortex early on might would support this outcome.

Taking advantage of the -NAO and - AO, along with other factors, this forecast from the GEFS makes sense with a cooler East and warmer West, at leasr for a couple weeks. But, notice how the deepest cold ( and highest HDD ) remains to our West during the next couple weeks. Looking at recent Octobers there seems to be a connection with the warmer Western Atlantic SSTs providing warmth near the coastal plain deeper into October. see here: courtesy Kris Karnauskas @OceansClimateCU Later into the month, the AO and NAO may start to trend positive. Meanwhile, ,according to the CFSv2 and the GEFS models ( bias correction not applied ) the PV looks to remain near seasonal norms moving ever so slightly up along the path of the ERA5 Mean.

For those interested in the prediction value of the GloSea5 model and the seasonal winter NAO phase, great post here by Grit. < The Met Office prides itself on its predictions of the NAO with its seasonal model. I looked at the NAO prediction from prior October seasonal model output back to Oct 2009 (this is the oldest date in the archive on the seasonal model site - https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/ens-mean). In looking at the charts, I would say that in 9 of the 11 years, the October prediction of the NAO on the model was a good one. The 2 misses were in Oct 2013 and 2015. Here was the Oct seasonal output from 2010 and 2011 - both quite good with the NAO prediction (-NAO in 2010-2011 / +NAO in 2011-2012), with both of those being La Nina winters. Finally, here is a chart from the Met Office showing hindcasts for their prediction of the NAO with the GloSea5 seasonal model for the winters of 1993 to 2012. The results are pretty good. Note: this is the NAO prediction from the Nov1 release each year - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GL059637 >

More battering surf for the South Jersey Shore . .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7am update...VAD wind profiles and surface obs across the region are indicating the low level jet is stronger than initially forecasted and thus I`ve increased the intensity of the winds and wind gusts across the region. This has lead to an upgrade from SCA to a Gale Warning for portions of the coastal waters as the low level jet should continue to increase in intensity over the next couple of hours. Widespread rain continues to fall over the region this morning and will continue through much of the day today. A strong easterly low level jet is pushing into the region which will continue to produce modest rainfall over the next couple of hours. Current accumulation totals are running around 1 to 1.5" across DelMarVa and southern NJ. Based on hires guidance I anticipate we`ll continue to see some 0.1-0.2" an hour rain rates over the next 3-6 hours hours across DelMarVa and southeastern NJ. Further north and west the impacts of high pressure seem to be winning out as rainfall totals are anticipated to be slightly lower than initial forecasted the past couple of days.

Seems as in past Octobers the warmer than average Western Alantic waters have induced a later freeze along the Eastern zones and coastal plain. Might even be responsible for stalling of cold fronts. Center of the country gets a taste of winter next weekend.

Without question our areas have been the target zone since back in June. However, we have been getting our share of Fall weather. Next weekend is a real prime Fall weekend. Better than a year ago.

Seems Delta may trigger chain of events leading to polar blocking and arctic intrusion.

interesting zonal wind forecast https://mobile.twitter.com/MattHugo81/status/1314440730534989824

Noticed the shorter days, and less solar heating, means it takes much longer to dry things out. Found out when looking at grass seedlings and checking soil moisture. It was still rather wet ad moist.

I am starting to like the idea of a mini front loaded winter , however, in our case/area that may simply mean normal temps with a minor event. Meanwhile trends with the PV at this time maintain a normal seasonal progression, along the line of the ERA5 mean. Along with a supported - AO. Even though recent Octobers have exhibited a - AO more so than in the heart of winter. Already spoken here is the possibility of a more so - NAO early in season . Although maybe more East based. And very interesting is this post, and the possible variations of the Nina and the effect on the NH

Looking for a last season beach trip, surf zone temps still in upper 60 s

Sounds DT- ish

Saw that this morning when the WPC made come changes that would effect my area. Not thrilled it is a weekend, but we will see. Mount Holly did not go into a lot of discussion about it with the AM AFD, as it is 6 days away. Meanwhile, parts of New England remain in an extreme drought.

Similar to last year, the Chukchi Sea presently has extremely low sea ice extent. . This my have some role in our late Fall weather. Another thing to look for regarding clues to the upcoming winter is what phase(s) the MJO mostly travels in during the month of October. As bluewave and Don S. have referenced there appears to be a connection to the following winter's EPO and AO state. From Don S. < In addition, from the larger pool of La Niña winters following El Niño winters, there were four cases where October saw the MJO in Phases 4-6 for 20 days or more: 1983-84, 1988-89, 1998-99, and 2016-17. All four cases featured an EPO+/AO+ winter. Three cases saw the MJO in Phases 4-6 for less than 20 days: 1995-96: 12 days, 2007-08: 6 days, and 2010-11: 6 days. Both 1995-96 and 2010-11 featured a predominantly negative AO. The latest ensemble guidance favors October 2020 falling into the former pool. Among that pool, October 1983 and 2016 featured above normal and near normal rainfall respectively. October 1988 and 1998 saw below normal and much below normal rainfall respectively. > Meanwhile the West Pac warm pool appears to be at near record temps. If you recall there was a study posted last winter https://www.nature.com/articles/s41586-019-1764-4 Here is a tidbit from the abstract. Here we show that rapid warming over the tropical oceans during 1981–2018 has warped the MJO life cycle, with its residence time decreasing over the Indian Ocean by 3–4 days, and increasing over the Indo-Pacific Maritime Continent by 5–6 days. We find that these changes in the MJO life cycle are associated with a twofold expansion of the Indo-Pacific warm pool, the largest expanse of the warmest ocean temperatures on Earth. The warm pool has been expanding on average by 2.3 × 105 km2 (the size of Washington State) per year during 1900–2018 and at an accelerated average rate of 4 × 105 km2 (the size of California) per year during 1981–2018.

Nina or Nino simply does not matter. As mentioned before the small area of cooler Pac waters is nothing compared to the HUGE global ocean impact specifically the Pacific. And the CFS sucks. Even the monthly CFS is horrible until you get to the 20 th of the present month for the next month's forecast.

I believe there are -NAO cycles or periods when winter blocking in the NAO domain continued for several winters in a row. Lately as you know the -NAO during the heart of winter has been lacking. The real game changer for us and for a large part of the country has been the fast Pac jet causing warmth to dominant and responsible for a lack of phasing storms ( think East Coast , and Miller A s ) and the breaking down of West Coast ridging.

I know it is early, but I go with 2015-2016

Are we not in a new era ? In my opinion winter analogs present little value currently, and there is a tendency for the warmer climate to our South to be nudging North. Saying we are due for an average winter, or there is no history of something is not a wise train of thought. We could go multiple years with a few inches of snow or a fluke blizzard may hit us.