bluewave

Certain types of patterns have become more common over the last decade. So it’s not cherry picking pointing out the obvious. The bias being discussed involves the models.

That was our last month with an average temperature below freezing and above normal snowfall thanks to the MJO 8.

Yeah, it could be related to the warmest departures setting up just to the west of the main ridge axis near Minnesota and the Dakotas where the cold bias was. It’s also possible the drought enhanced the radiational cooling over the Northeast with so much high pressure and light winds. So the Euro could have missed that. Most other times over the years we had a cold bias on those charts when the ridge was in the East with higher dew points.

You missed the broader context of my analysis which is why you incorrectly used the term cherry pick.

It was probably due to the ridge axis setting up over the Upper Midwest and Canada. So the models underestimated the temperatures under the strongest ridging. The ridge most other times has been located further east. So this has been where the typical cold bias has been. Unfortunately, DTN only posts the 90 day averages. So we don’t get to see the biases for specific patterns which produce a ridge in the East. Pattern dependent biases is the next level but they may not have the computer tech to pull off such specific data. I have noticed when the ridge sets up over the East this is when the cold biases occur. Shift it back to the upper Midwest and this is where the cold biases occur. But the northeast when averaged out over the last 10 years shows a consistent longer range bias beyond the what the shorter 90 day average shows. Most recent 10 year 500 mb height anomaly stronger in East which is a reversal from previous 10 year period

This is one of the reasons that the last 9 winters here have had an average temperature the equivalent of what Northern Virginia used to have from 1981-2010.

If you go back in these various threads including the ones in the NYC Metro forum you will see me positing model biases all the time. This is how I have been able to identity where the potential errors were to the forecasts going back years in these threads. I apply these corrections manually. If you can train the models with AI to adjust for these biases, then my guess is that the forecasts for weeks 2 and 3 would greatly improve. This could also lead to better seasonal forecasts beyond the 1 month range.

The ridge in the East has been one of the most under-forecast features beyond 7 days going back to December 2015 which leads to warmer temperatures than originally forecast. My guess is that this has something to do with the models underestimating long range convection near the Maritime Continent. Since forcing in that region leads to higher 500mb heights and temperatures in the East. 11-15 EPS forecast significantly underestimated Maritime Continent forcing Verification much stronger forcing

This has been the repeating theme over the last 9 winters. Longer range models underestimate the forcing in the MJO 4-7 regions. So they start out too cold for our area and then shift warmer the closer we get to the forecast period. New run stronger forcing near the Maritime Continent Old run was underestimating the forcing there

Your colder example is the exception to the rule which will eventually happen from time to time. But most of the time the models adjust warmer as we get closer we get to the forecast period. The colder pattern than originally forecast around the start of December was the result of the models adjusting to the +AAM rise. But at the same time they underestimated the forcing currently in MJO 4 going over +2.00. Stronger forcing in that part of the world accelerates the Pacific Jet and weakens the -EPO. So you had one event strengthening the -EPO and another weakening it. The height falls showing up near Alaska around the 7th with a faster jet than forecast weren’t there previously when the models were underestimating the forcing near the Maritime Continent. This process lead to the quick change in the week 2 forecast to much warmer than previous runs. This is why I was mention earlier back in this thread that the EPS was probably underestimating the Pacific Jet.

This has been one of the bigger reversals from cold to warm that we have seen from the EPS weeklies during this time of the year. https://charts.ecmwf.int/products/extended-anomaly-2t?base_time=202412020000&projection=opencharts_north_america&valid_time=202412160000 Dec 9-16 new run Dec 9-16 old run

Our last +4 east based El Niño during the winter was 97-98. https://www.cpc.ncep.noaa.gov/data/indices/ersst5.nino.mth.91-20.ascii

A recent paper is trying to figure out why the EPAC hasn’t warmed like the rest of the Pacific and whether it will continue. It will be interesting to see if the record EPAC WWB and warming in the spring of 2023 was the beginning of a shift. Plus we just had the near record EPAC WWB back in November with the +AAM. It’s also possible that the big jump in global temperatures which wasn’t forecast last few years is somehow related.

We will probably need to see more Nino 1+2 warming in order to try and shift the Pacific cold phase. But even if we do a potential warm phase will still have to compete with the WPAC warm pool near the equator. In the age of marine heatwaves any cold pool east of Japan would pale in comparison to the marine heatwaves across other parts of the Pacific which would be different from our last +PDO era. Another wild card could be that we could actually see an east based El Niño like 97-98 should 1+2 really take off. But the actual 500 mb pattern could be different due to a stronger WPAC warm pool.

My guess is that will need a solid MJO 8 in January like in 2022 to see more than a brief 10 day window of cold.

January 2022 was the last time my area had a real winter month with the average temperature below freezing and heavy snows.

These brief windows in recent years have favored the Great Lakes with the record lake warmth and the dominant northern branch of the Pacific Jet.

Thursday looks like a potentially impressive wind and snow squall day. Near record surface to 700mb lapse rates for early December. Could see some gusts over 50mph with scattered snow squalls. The record warm lakes are really going to modify the air mass below 850mb. This is one of the larger temperature spreads between 850 mb and the surface we have see in early December. So the wind chills will be more impressive than the actual temperatures.

The RONI seems to work better with La Ninas since the WPAC warm pool enhances the La Niña effect. But it doesn’t work the greatest with a very strong El Niños like last winter. The record Niño 4s extending west of the Dateline served to enhance the El Niño effect of the ridge in Canada which was on par with super El Niño events. The much weaker Aleutian low and Eastern Trough than past very strong El Niño events may have been a better use of RONI. But even then the numerical value wasn’t that much of a help in describing the actual pattern.

That is correct in terms of the La Niña background pattern. The pattern from mid to late December is more a reflection of the record WPAC pool forcing. Not necessarily the weak La Niña SSTs which are still neutral.

Will be interesting to see if extended GEFS is correct and we can get the forcing east of the Dateline in January and have the warmer Maritime Continent influence begin to weaken by then.

Maybe some snow squalls can make it to the coast later this week with wind gusts over 50 mph due to the very steep low level lapse rates and tight gradient.

All we know is that we were able to get a brief +AAM influenced period between the record warmth this fall and warmer pattern beginning to emerge next week. So maybe we can get a few more of these going forward after December. Our next modeling clue may have to wait until later December into early January.

Do you have the EPS and GEFS AAM forecasts? The CFS hasn’t been very reliable. If we could indeed see another +AAM influenced interval then maybe we can see alternating patterns this winter at times.

After the briefly cooler start to December, the models are shifting back to warmer winter pattern which has been in place since 15-16. We can see the familiar Aleutian Ridge and -PNA trough in the West. This leads to a warmer Southeast Ridge pattern for us by mid to late December.