The following winter is a difficult forecast. I understand that many forecasters say this every year and that is simply not the case....09/10, 13/14, 14/15 were easy and last year and 12/13 were fairly straightforward with 12/13 and certainly 10/11 the tougher of the last recent years. Anyone who got the easy ones wrong missed something plain and simple. This year features a a QBO that has undergone a never before seen anomaly, an oncoming La Niña that is nowhere near strong and follows a super Niño, the effects of which are still being seen atmospherically even now. Now these post El Niño atmospheric effects are expected and enhance the chances of snowfall comparative to a La Niña or neutral after Niña/neutral. Meaning that poleward heat flux/jet enhancement/mountain tourque events...and the fact that all of these lead to such a long feedback loop from the oceans to the stratosphere mean that the lag in the El Niño's effects will continue to make its presence felt for some time.
Does enhanced chances for snowfall for the mid-Atlantic and northeast comparative to the other years objectively mean more? No. It simply means the odds are higher compared to what they'd be if we were currently following an ENSO neutral/cold cycle.
The state of the stratospheric polar vortex is that it is weaker than normal, something that is quite unusual as it is normally ramping up in intensity rapidly this time of year. This reversal in climatological behavior means a few things, first...the strat PV will reinitensify at some point as is the case when it is attacked by wave 1/2 and warms...second, there will already be deflected upward wave pressure via wave 1 and 2s that are caused by processes closer to earth that are related to and enhanced by poleward heat flux/Hadley cell activity and oceanic-atmospheric feedback.
The long and short of it is that the stratospheric polar vortex will continue to be barraged until it splits very early this cold season and though it will reintensify, the surface and tropospheric processes at that time will cause it to weaken once again.
The theory that there is a totally inverse relationship to the current strat PV state and winter state is plausable but too much of a blanket statement for me, and I feel that it doesn't apply this winter due to the surface/solar/geomagnetic/lack of real volcanism activity.
There is this thinking the a "blob" in one ocean and a "blob" in another means "X" is happening. This is not the case. There is a warm pool in the northeast Pacific and a cold pool in the North Atlantic, true...however both have been there for years and have come and gone with time and will again...So what does it mean for this winter?....
Well, the PDO has taken a big hit and many of the other pros have said that it will at least maintain and go back positive this winter, as it has all of the last times it has dived to neutral or negative over the past few years.....this is either unscientific assumption or "persistence forecasting"....either way, they're wrong.
Expect the PDO to not come back in any real way anytime soon and the warm pool in the northeast Pacific to take its hits but hang on. The result of this will be a higher propensity for a +PNA but for it to be displaced East of where it traditionally would be in a +PDO. I expect a bootlegged -EPO to show up, meaning I think we see a similar height field but through different processes and slightly displaced. Overall it likely ends up neutral.
I am forecasting the NAO to average negative early this winter and then go positive for the rest, (mid winter onward).
I am forecasting the AO to average negative this winter.
Due to the location and movement of the arrival of air masses that will cause the most change this winter, I expect that New York City's farther north and colder average compared with Philadelphia's farther west and lack of strong oceanic influence to 2M temp will offset and that changing the numbers to either city's forecast temp departures would amount to unnecessary "finessing" with little chance of being any more accurate, for the right reasons, so the departures for both cities are the same and as follows:
DEC: -2.5 to + 0.5 JAN: -2.0 to +1 FEB: -0.5 to +2 MAR: +1 to +4
The snowfall forecast for PHL:
The NYC forecast:
-----More than half of seasonal snow at both stations in the first half of winter.
-----Near misses with coastal storms that hit New England and Canada strongly will happen.
-----Significant coastal storm effects still add a good amount to the numbers but in totality most snowfall comes from overunnning events and Alberta clippers, of which there will be many.
-----There will be two severe cold outbreaks, both before mid winter and then a rapid "snap" to spring with a mild late winter.
----There is the potential to significant icing events to occur a couple of times with overrunning events from the southwest....especially inland.
Thanks for reading,
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But after reaching phase 1, then it goes to COD. So the cold pattern doesn't last long after that. There is no evidence to show that there will be blocking earlier this winter. -NAO trend has ended already since El Niño weakened and is now in weak La Niña. The pattern change was supposed to happen in mid-November and is clearly not going to happen. Models will tease and will keep pushing back for a cold pattern in the long range until January which likely occurs. Nothing is accurate going past 7 days. So I have a hard time believing on this fast start to the winter. Anyone predicting cold December is hyping up like JB at weatherbell who just changes thoughts constantly especially with December being cold.
Phillyweather, indeed this year does not have any one dominating driver, no super El Niño etc.
Mustufa, the thinking behind a cooler than average December is the barrage of hits that stratospheric polar vortex is taking and that more are coming and this at a time when it is normally strengthening. This is increasing the propensity for high latitude blocking and the North Pacific warm pool aiding a +pna along with an MJO heading through phases 7/8/1 is why. I hope this helps.
"Difficult" is the nice way to sum up the winter forecast.With a weak La Nina and a volatile QBO among other factors, this winter will give everyone a headache with forecasts unless you are N&W of I-95. I will end up detailing that in my forecast when i put that out, but I too think that this will be a difficult winter with regards to forecasting.
Why do you think December will be a cold month? Just because November turns cold does not always mean the following month is colder. Can you explain this to me why you think that and what is influencing a fast start to the winter. The trend has always been a mild December here which seems like the new normal. Cold Decembers that are front-loaded continue to be rare instead of backloaded winters which are more typical in the Mid-Atlantic.