bluewave

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.

https://nsidc.org/arcticseaicenews/faq/#area_extent What is the difference between sea ice area and extent? Area and extent are different measures and give scientists slightly different information. Some organizations, including Cryosphere Today, report ice area; NSIDC primarily reports ice extent. Extent is always a larger number than area, and there are pros and cons associated with each method. A simplified way to think of extent versus area is to imagine a slice of swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. That is why if you compare extent and area in the same time period, extent is always bigger. A more precise explanation of extent versus area gets more complicated. Extent defines a region as “ice-covered” or “not ice-covered.” For each satellite data cell, the cell is said to either have ice or to have no ice, based on a threshold. The most common threshold (and the one NSIDC uses) is 15 percent, meaning that if the data cell has greater than 15 percent ice concentration, the cell is considered ice covered; less than that and it is said to be ice free. Example: Let’s say you have three 25 kilometer (km) x 25 km (16 miles x 16 miles) grid cells covered by 16% ice, 2% ice, and 90% ice. Two of the three cells would be considered “ice covered,” or 100% ice. Multiply the grid cell area by 100% sea ice and you would get a total extent of 1,250 square km (482 square miles). Area takes the percentages of sea ice within data cells and adds them up to report how much of the Arctic is covered by ice; area typically uses a threshold of 15%. So in the same example, with three 25 km x 25 km (16 miles x 16 miles) grid cells of 16% ice, 2% ice, and 90% ice, multiply the grid cell areas that are over the 15% threshold by the percent of sea ice in those grid cells, and add it up. You would have a total area of 662 square km (255.8 square miles). Scientists at NSIDC report extent because they are cautious about summertime values of ice concentration and area taken from satellite sensors. To the sensor, surface melt appears to be open water rather than water on top of sea ice. So, while reliable for measuring area most of the year, the microwave sensor is prone to underestimating the actual ice concentration and area when the surface is melting. To account for that potential inaccuracy, NSIDC scientists rely primarily on extent when analyzing melt-season conditions and reporting them to the public. That said, analyzing ice area is still quite valuable. Given the right circumstances, background knowledge, and scientific information on current conditions, it can provide an excellent sense of how much ice there really is “on the ground

The last few days set the new all-time extent anomaly record.

All the extra ocean heat on the Siberian side is really slowing the freeze-up this October. So the the extent is currently the lowest on record for this time of year well below 2012. The Siberian heatwave this year was one of the most extreme events we have seen.