bluewave

Updated for November 2020. 11....2020...EWR....4...NYC...1....LGA....1...JFK...4...BDR...5....ISP....4

I was pointing out back in the October and early November threads how the atmosphere wasn’t showing the canonical La Niña patterns. We have been experiencing these more Niño-like +AAM spikes since the fall. So I mentioned that we may not follow a typical La Niña November. This is much like the last few years with mismatched Niño and Niño-like influences at the same time. This is due to all the competing record equatorial and off equatorial SST warmth from the Indian Ocean into the Pacific.

Those long range strat forecasts for change are very uncertain given how strong the PV has been.

The OP GFS longer range has had less of a cold bias than the ensembles over SE Canada. Sometimes, the lower resolution ensembles smooth out the ridge near the near the Northeast too much. Where the OP runs don’t.

The Euro is really struggling with the split flow. Notice how much different the GFS and CMC are at day 10. Remember, the errors at day 7-10 often build into the day 11-15.

Longer range, we need to watch for the ridge east of New England verifying stronger than forecast. This has been the pattern for a while now. Today is just the most recent case. 7 day Forecast Verification

The 7-8th will depend on the evolution of the storm threat for the 5th. If the storm on the 5th is more amped, then the 7-8th could get suppressed like the CMC shows. Have to see which model gets the evolution on the 5th correct. The Euro may be struggling with hanging too much energy back to the SW again on the 4-5th.

Plenty of spread between the model guidance at 12z. UKMET and CMC are west while GFS and Euro east. Euro may be struggling with holding back too much energy to the SW again.

It has been an ongoing issue for the GEFS. I can’t wait until machine learning brings us bias corrected model guidance maps. Maybe someday we can look at day 11-15 bias corrected maps which will take long range forecasting to the next level. But that will probably require quite a bit more computer power.

The first week of December will start out milder in the Northeast than some of the guidance was indicating a week ago. New run Old run

2016 to 2018 featured great snowstorms that melted a few days later in many cases. 2014 to 2015 had long lasting snow cover but the storms weren’t as impressive in my area as 2016 to 2018. 2010-2011 was the rarest of them all with great snowstorms and long lasting snow cover. I can still remember the snow mountains from the road crews piled high near the LB Boardwalk into the spring.

I don’t really mind if the snow melts a few days later. Our snowy 15-16, 16-17, and 17-18 winters featured big warm ups following most snowstorms. Kind of like spring in the Rockies. But it isn’t the greatest if you run a ski resort and have to put up with the sloppy conditions.

The cutter and hugger storm tracks can really produce for the areas around the Great Lakes. But all the warmth gets tired during the summer when people go north to cool off. Last several summers you had to go up into Canada to escape the heat.

You usually have to be north of I-80 to cash in on gradient snowfall patterns. EWR to ISP finished last December in the 2-4” range. The one exception was the cold 93-94 gradient. But even that one hit diminishing returns the closer you got to Philly.

3-21-18 was my last 10” event. It was also my 2nd favorite late season snowstorm behind 4-6-82. https://www.weather.gov/okx/storm03212018

The duration of multiyear below normal snowfall regimes can be uncertain. But it usually takes a 10.0”+ event to get the ball rolling back in the right direction. Great pattern breaking snowstorms like 1-20-78, 3-13-93, and 12-30-00 come to mind.

This month the very strong IO MJO combined with a near record polar vortex for November record warmth. So it really enhanced the upper ridge over the area. The closest MJO composite match for November was a phase 3. You can see the dominant VP anomalies focused near that part of the IO.

Discuss...

Great post. The quick reversal from -AO in October to +AO in November is something that we normally see during an El Niño. This may be related to lingering neutral to positive IOD which is also more Niño-like. The IO standing wave the models have for November was implicated in the very strong PV and +NAO +AO last winter. The current +PMM with near record SST warmth north of such a strong La Niña cold tongue is also a first for a La Niña. A very warm November has also been associated with El Niño’s in the past. Several times this warm November during an El Niño carried over into December. So such an occurrence this year would be different than the typical front loaded La Niña winter progression. There have also been several very warm La Niña Novembers followed by warm Decembers. On the other hand, a warmer PMM was present for our most recent La Niña warm November in 2016. That was a near record warm winter. But it may have been the +PMM allowing occasional poleward extensions of the North Pacific Ridge into Alaska. Those were also accompanied by short -NAO -AO episodes for respectable seasonal snowfall despite the record warmth. There are many factors this year which could interact. We may just have to wait and see how things look in another month or so. But even beyond the specific ENSO conditions and interactions, we have just seen the warmest 5 winter stretch on record. Predictability of European winter 2019/20: Indian Ocean dipole impacts on the NAO https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/asl.1005

Don recently posted a very informative paper on the topic. https://www.nature.com/articles/s41598-020-71945-4 Extreme weather events in Asia have been occurring with increasing frequency as the globe warms in response to rising concentrations of greenhouse gases. Many of these events arise from weather regimes that persist over a region for days or even weeks, resulting in disruptive heatwaves, droughts, flooding, snowfalls, and cold spells. We investigate changes in the persistence of large-scale weather systems through a pattern-recognition approach based on daily 500 hPa geopotential height anomalies over the Asian continent. By tracking consecutive days that the atmosphere resides in a particular pattern, we identify long-duration events (LDEs), defined as lasting longer than three days, and measure their frequency of occurrence over time in each pattern. We find that regimes featuring positive height anomalies in high latitudes are occurring more often as the Arctic warms faster than mid-latitudes, both in the recent past and in model projections for the twenty-first century assuming unabated greenhouse gas emissions. The increased dominance of these patterns corresponds to a higher likelihood of LDEs, suggesting that persistent weather conditions will occur more frequently. By mapping observed temperature and precipitation extremes onto each atmospheric regime, we gain insight into the types of disruptive weather events that will become more prevalent as particular patterns become more common Over Siberia they found a significant increase in the frequency and duration of warm spells and wet days, while central Asia saw more cold spells and wet days, and east Asia experienced more long wet spells. These results are consistent with an increased (decreased) prevalence of the pattern in node #1 (#12). They also found that warm, wet, and dry spells predominantly lengthened in most parts of Asia, suggesting a general increase in persistence. Another study14 analyzed output from several atmosphere-only models forced by sea-ice and ocean-temperature conditions consistent with a 2 °C warmer world. Similar to our results, they found significantly increased persistence of warm spells over northern and central Asia, as well as wet spells over northern and eastern Asia. In addition to supporting previous findings, our study demonstrates an increasing frequency of persistent large-scale circulation regimes and associated extreme weather events, especially since the mid-1990s when AAW emerged as a clear signal. As greenhouse gases continue to accumulate in the atmosphere owing to ongoing human activities, we find that patterns characterized by warming in high latitudes will occur more frequently while cold-Arctic patterns will decline. A higher percentage of days/year in any one pattern will increase the likelihood of multiple consecutive days occurring in that pattern, leading to more frequent persistent conditions. Moreover, we demonstrate that the predominant warm-Arctic pattern also exhibits a higher probability of long LDEs occurring relative to days belonging in a node, thus further augmenting the likelihood of persistent weather events. Three of the climate models participating in CMIP5 agree that warm-Arctic patterns will increase several-fold by the end of the century at the expense of cold-Arctic patterns, suggesting a substantial rise in the frequency of persistent circulation regimes and their associated extreme weather. The connections with changes in jet-stream characteristics, such as blocking and other cut-off circulation features, will be addressed in future work.

New record lowest October average extent. There have been 10 new monthly lowest average extent records set since 2016. The only remaining monthly records are August and September 2012.

While the record cold around the Rockies and Plains has been impressive, it’s focused over a very small geographic region of the planet. The coverage of the record cold is much smaller than the areas and magnitude of record warmth as the world warms. It’s no coincidence that the record October cold near Montana is occurring in an isolated pocket relative to the overall extent of the global temperature increases. Montana represents a portion of the only 17 out of 2,844 stations with under 6 months of warming over the last 30 years.