40/70 Benchmark

December update....no changes. https://easternmassweather.blogspot.com/2025/11/wintry-december-forecast-remains-on.html

Wintry December Forecast Remains On Track: First Winter Storm Possible Late Tuesday Strong Consensus Converging on December Analog Composite Here is the Eastern Mass Weather December 500mb Analog Composite as a point of reference: Note that while the CFS and CANSIPS appear to have lower heights displaced east due to a more +PNA, the consensus matches the analog composite remarkably well. It is highly likely that the CFS and CANSIPS are in error in this regard, an assumption that the extended ECMWF corroborates. This is the reason that the western CONUS is not anticipated to be as mild as it was in the Maritime continent forcing deviation analogs of 2017 and 2024, which more closely resembles the aforementioned CFS and CANSIPS guidance, thus December 2025 is not expected to be a cold as December 2017 throughout the forecast area. December 2017-January 2018: December 2024-January 2025: The common theme is, of course, poleward Aleutian ridging, as indicated by a myriad of different methods in the Winter Outlook. Here is the December composite data versus the latest CFS temperature anomaly forecast, which matches up strikingly well despite the apparent inconsistency within the PNA domain, thus further buttressing the notion that it's 500mb depiction is somewhat astray: The month of December is forecast to average near normal, anywhere from -1F to +1F, except near normal to +2F across the middle Atlantic. The Climate Prediction Center has recently settled on a similar solution, which yields an active storm track running through the area, between the southeast ridge, and the cold reservoir in southeastern Canada. This colder anomalies over southeastern Canada was the other high confidence portion of the seasonal forecast, in addition to the poleward Aleutian ridging. It is this cold pool that not only provides amply opportunity for storminess in conjunction with the southeast ridge, but also ensures an ample supply of antecedent cold over New England even when approaching storm systems take what would otherwise be a relatively hostile track. Active Start to December Possible Although an official SSW as defined by the reversal of the mean H85mb zonal westerly winds remains unlikely, and a faster than currently modeled recovery is still expected to ensue, that does not preclude wintry weather from taking place given the cold in place to the north. Indeed, the first of what is likely to be several SWFE and overrunning events is a distinct possibility Tuesday afternoon and evening, as a system approaches from the southwest. Note the similarity of the pattern depicted to the December 2008 analog. It is important to remain mindful of the fact that this is still several days away, and there remains a distinct possibility that the region's first winter storm will occur during the second week of the month, as per the 2008 analog. However, the potential for a significant snowfall, especially north of the Mass pike and inland from the immediate coast, is growing. There are likely to be more opportunities behind this system until a potential moderation beyond mid month. Look Ahead to latter December & the Holiday Period Given the active, seasonably cold pattern that is expected to ensue and last for at least half of the month, the probability for a White Christmas is above climatological levels, but it remains somewhat dubious for the coastal plane given a possible milder turn prior to the holidays. In fact, the proverbial "Grinch Storm", which occurred in both the 2007 and 2008 analogs, is a distinct possibility. The MJO is currently entering phase 7, which will constructively interfere to reinforce the gradient pattern (se Canada cold/se US ridge) to begin the month. Although it is technically forecast to edge into phase 8, it is very dubious whether or not it will truly make it. First of all, the wave is expected to dissipate just about the time it is expected to enter phase 8 mid month. Failure of the MJO to materialize in phase 8 would not at all be a surprise given the proclivity for guidance to erroneously due to over the past 10-15 years, presumably due to the emergence of the western Pacific warm pool. Should the wave enter phase 8 at a reasonably amplitude, it is likely to carry over the active, SWFE laden regime of the first half of the month into the holiday period. However, it either fails to make it, or does so at a very low amplitude, the pattern is likely to turn milder owed to a consolidating polar vortex in conjunction with the development of a Pacific trough pattern. As per Lee et al (2019), the arctic high regime is favored for less than 20 days following a weak PV, which in this case is occurring in latter November. This time frame is also consistent with the onset of a reflection event on December 21,1981, which occurred just over two weeks after the December 4th SSW. This would imply a pattern change just beyond mid-month. Stay tuned for updates on the potential storm system for Tuesday, as First Call will be issued Saturday if necessary.

https://easternmassweather.blogspot.com/2025/11/wintry-december-forecast-remains-on.html First Call Saturday if necessary.

If you are looking for a jackpot, yes, but not for a plowable event. I NNE will rule the month....don't sweat that. We should do fine, though.

H85 looks to track just south of Boston, H7 is up over S NH.

Pretty much dead-nuts on 18z. I'm inclined to toss the EURO, as the GFS, GEM and UK better fit my analog seasons.

Sell that faster than a dozen donuts in a Brooklyn precinct.

Anyone have the link of the CIPS analog site?

12" line is probably non-existent, but not the point.

I expect to do very well this month relative to most of SNE....should be a slump-buster.

I'd hit it-

Gonna have to dive into this soon....probably going to get something out, along with my December preview, either late tonight or tomorrow night.

Yes, you did. The person that MJO took that graphic from on Twitter is.