frd

Pondering the Nina correlation to the ensuing winter's NAO and IOD, well.................

What once looked like a chilly air mass later this month has now turned into more of the same with cold fading and warmth returning. Some asked when this new era of less snowy winters and generally warmer weather started here, well this post by bluewave is an eye opener. I still feel that 2016 was a turning point. from bluewave < It has been the only cooler than average part of the US since the Super El Niño in 2016. >

Seems that Greenland ice melt effects ( has altered ) the Greenland ocean circulation/tripole that is used to forecast the winter's ensuing dominate NAO phase. Just started to research this and also read a few intriguing posts by HM. Some state the summer ice melt was not as bad in Greenland, but according to HM is still was not great when you target on his on his focus which is repairing the Greenland ocean circulation/tripole. As HM states, the ice melts throws a monkey wrench in the NAO forecasts of the upcoming winter. HM states it is better to look at the Spring's tripole for an indication of the ensuing winter's NAO versus the tropical season. Caveats apply though, in regards to Greenland ice melt and AGW. Some interesting things to consider here.

Mentioned we might get some interesting North Atlantic weather later in October, and it appears we may indeed get a deep bomb cyclone to form there near the 27 th., however, the exact outcome and lowest pressure are still uncertain. The 00Z GFS looks too extreme.

Looking ahead we go significantly above normal later this week. Anyone with flowers that did not have meaningful frost damage look to hang around deep into the month. Huge storm off the coast late week. but a phasing opportunity is lessening.

This was a surprise for my area, updated at 9:30 PM from MH AFD. With this update, have expanded the Frost Advisory to all counties where the growing season remains active, save for Philadelphia and Delaware Counties and the coastal strip. While the odds of frost will decrease closer to the urban corridor, there is enough potential in the more outlying areas to warrant an advisory throughout the CWA. Also, some areas within the advisory may get down to freezing, but not expecting it to be widespread enough to warrant a Freeze Warning in areas where the growing season remains active.

I have also scored relatively well with rainfall. Grass is green and lush. Tomorrow AM.looks like junior league Jebb walk weather. Looking forward to a walk with my greyhound trying on his new European sweater.

Appears that we go rain free for the next 7 days with moderating temperatures and beautiful weather for late October.

Nina results vary, but cool to see the various temp profiles going back to 1925.

From Met Walt Drag A fair amount of discussion about the 25th-26th... am considering a topic since it's amped with potential, but that this could still easily be a marine storm once past FL. I'd like to see more ensemble agreement on a storm up the coast, supported by 30% or greater prob for 2"+ along the E Coast. If that were to occur, it's probably a few days off but imo, little doubt (in my mind) the models are onto two more tropical systems 19th-26th in the W ATLC. One other thing...while most of the debate is about 1) whether a storm, and then 2) either out to sea or up the coast... I can visualize jet stream pattern adjustments that permit E GMEX and northward up the W side of Apps. Just very-very-very early. I think Epsilon may get named within 48 hrs. Am posting on tropical page a couple of graphics. It probably won't a direct influence on our area except for swells... however, its eventual development may strengthen the WAR, and provide an even more favorable flow pattern for the 25tth-26th? We'll see, Post goes up by 525PM, unless it's already done there by a tropics poster.

Looks like a black hole on the afternoon GFS.

Must be big axx squirrels !

Nina update

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.