chionomaniac Posted December 20, 2011 Share Posted December 20, 2011 In the long-range, one is seeing a shrinking of the area of warm anomalies and deepening cold ones. That could be an indication of a lack of blocking in the long-range. If the long-range forecast plays out, the polar vortex would strengthen anew and a strong AO+ regime would reassert itself. That would increase prospects for warmth in the East, especially if a PNA- setup is in place. I don't think that is a foregone conclusion by any stretch, Don. So far we have seen a forecast increase in wavenumber 1 activity which is about to set off a warming within the stratosphere. The stratosphere has been very cold so far this autumn and winter which has led to stronger than average vortex conditions driven right through into the troposphere. But I suspect a slow change is on the way. Firstly, if we look at the zonal mean wind anomalies for November and December we see that the period of greatly increased zonal wind anomalies is already showing signs of subsiding even prior to the forecast warming. This may be linked to the slowly increasing ozone content or greater influence from the easterly QBO at the mid stratospheric level. I have added lines to indicated the downwelling seen from the zonal winds already witnessed in the troposphere and also I have indicated what is likely to possibly occur in the future. Even without a SSW we see a drop in the mean zonal winds which are likely to hit the troposphere in the first half of January. My guess is that we will see a reduction in the zonal tropospheric conditions during that period with the chance of blocking becoming more likely. Any SSW will only add to that likelihood. Link to comment Share on other sites More sharing options...
okie333 Posted December 20, 2011 Share Posted December 20, 2011 Models are definitely trending warmer with this (12Z GFS shows 38C at 1mb BEFORE 192h)... yet still the PV doesn't split... Link to comment Share on other sites More sharing options...
donsutherland1 Posted December 21, 2011 Share Posted December 21, 2011 That last map was from 10mb not 1mb. Big difference. I only posted it to show that the warming actually downwells as opposed to staying up at 1mb. Thanks. I hadn't noticed that it was 10 mb. Link to comment Share on other sites More sharing options...
donsutherland1 Posted December 21, 2011 Share Posted December 21, 2011 I don't think that is a foregone conclusion by any stretch, Don. It isn't. I had looked quickly and didn't notice that the last map was 10 mb. I had assumed they were all 1 mb maps. Link to comment Share on other sites More sharing options...
HM Posted December 21, 2011 Share Posted December 21, 2011 Models are definitely trending warmer with this (12Z GFS shows 38C at 1mb BEFORE 192h)... yet still the PV doesn't split... The ECMWF is just beginning to show a more poleward EP vector solution at the end of the run. I think once the wave crests and then another becomes modeled, the models will begin to show more interference. I am starting to like the idea of full blown MMW this January. Link to comment Share on other sites More sharing options...
Alpha5 Posted December 21, 2011 Share Posted December 21, 2011 The ECMWF is just beginning to show a more poleward EP vector solution at the end of the run. I think once the wave crests and then another becomes modeled, the models will begin to show more interference. I am starting to like the idea of full blown MMW this January. Pardon my ignorance, but what is a MMW? Link to comment Share on other sites More sharing options...
WxMidwest Posted December 21, 2011 Share Posted December 21, 2011 MMW = Major Mid-Winter Warming (as it relates to the stratospheric temps)....... Link to comment Share on other sites More sharing options...
okie333 Posted December 21, 2011 Share Posted December 21, 2011 Pardon my ignorance, but what is a MMW? It means the mean zonal wind at 10mb 60N is negative. More practically, it usually means that the polar vortex has been either split or displaced south of 60N. Link to comment Share on other sites More sharing options...
Absolute Humidity Posted December 21, 2011 Share Posted December 21, 2011 Major Mid-winter Warming - Link to comment Share on other sites More sharing options...
Hailstorm Posted December 21, 2011 Share Posted December 21, 2011 It means the mean zonal wind at 10mb 60N is negative. More practically, it usually means that the polar vortex has been either split or displaced south of 60N. Does a MMW event lower the AO as much as a SSW event does? Link to comment Share on other sites More sharing options...
Alpha5 Posted December 21, 2011 Share Posted December 21, 2011 It means the mean zonal wind at 10mb 60N is negative. More practically, it usually means that the polar vortex has been either split or displaced south of 60N. Ah, ok. And is that usually induced by a SSW event? Or are there other means of displacing the vortex Link to comment Share on other sites More sharing options...
okie333 Posted December 21, 2011 Share Posted December 21, 2011 An MMW is a major SSW... the definition of "major" is based off the zonal winds though. Link to comment Share on other sites More sharing options...
wxmx Posted December 21, 2011 Share Posted December 21, 2011 MMW===SSW Link to comment Share on other sites More sharing options...
Hailstorm Posted December 21, 2011 Share Posted December 21, 2011 An MMW is a major SSW... the definition of "major" is based off the zonal winds though. Okay, thanks for your analysis. Link to comment Share on other sites More sharing options...
okie333 Posted December 21, 2011 Share Posted December 21, 2011 00Z goes crazy... still no MMW just yet though. Link to comment Share on other sites More sharing options...
Amped Posted December 21, 2011 Share Posted December 21, 2011 Link to comment Share on other sites More sharing options...
Weathergun Posted December 21, 2011 Share Posted December 21, 2011 By 240hr, 12z/20 ECMWF has a huge temp spike up at 10mb. Zonal winds at 1mb are decreasing rapidly. as well. But from what I gathered from previous posts here, the EP vectors just shifting upward, means it might take a few more weeks to fully propagate down: Link to comment Share on other sites More sharing options...
usedtobe Posted December 21, 2011 Share Posted December 21, 2011 By 240hr, 12z/20 ECMWF has a huge temp spike up at 10mb. Zonal winds at 1mb are decreasing rapidly. as well. But from what I gathered from previous posts here, the EP vectors just shifting upward, means it might take a few more weeks to fully propagate down: If it propagates down, the graphs you show are the first ones that really are interesting and hopefully will start propagating down. Not all SSW events do. Link to comment Share on other sites More sharing options...
dtk Posted December 21, 2011 Share Posted December 21, 2011 If it propagates down, the graphs you show are the first ones that really are interesting and hopefully will start propagating down. Not all SSW events do. Plus this discussion still revolves around 240 hour nwp forecasts...... Link to comment Share on other sites More sharing options...
usedtobe Posted December 21, 2011 Share Posted December 21, 2011 Plus this discussion still revolves around 240 hour nwp forecasts...... Very true. Link to comment Share on other sites More sharing options...
donsutherland1 Posted December 21, 2011 Share Posted December 21, 2011 By 240hr, 12z/20 ECMWF has a huge temp spike up at 10mb. Zonal winds at 1mb are decreasing rapidly. as well. But from what I gathered from previous posts here, the EP vectors just shifting upward, means it might take a few more weeks to fully propagate down: That's the best things have looked for awhile. Hopefully, the modeling won't back down as the possible warming draws nearer. Also, it should be noted that not every SSW has led to strong, sustained blocking. The December 15, 1998 SSW event led to some blockiness, but the AO+ was still predominant until a February 1999 SSW induced strong, sustained blocking culminating in a cold March in the eastern half of the U.S. (except northern New England, which was impacted by the above normal height anomalies associated with the blocking). Since 1958, there have been three SSWs that have occurred during predominant strong AO+ regimes and AO+ months: January 31, 1973, February 21, 1989, and December 15, 1998. The SSWs did not lead to strong, sustained blocking. However, the AO Index was lower, overall, during the succeeding month. The sample size is small, but might suggest that an SSW might weaken but not reverse the current regime of predominant AO+ values. If so, January could wind up closer to normal in terms of temperature anomalies than December in the East, even if readings are still milder than normal. That would be consistent with some of the AO analogs that saw January wind up the coolest month relative to normal during the winter. At present, it remains to be seen if an SSW will unfold. Many winters don't see them. If there is an SSW, it will be interesting to see the impact especially if the AO spikes as is currently indicated on the GFS ensembles. In any case, the mild pattern in the East looks likely to continue into the New Year. Link to comment Share on other sites More sharing options...
Weathergun Posted December 21, 2011 Share Posted December 21, 2011 Plus this discussion still revolves around 240 hour nwp forecasts...... Yes, that's always the elephant in the room. Link to comment Share on other sites More sharing options...
packbacker Posted December 21, 2011 Share Posted December 21, 2011 I believe January 2009 had a SSW, it was a "weak" La Nina, January average moderate AO and than February the AO averaged negative. Not sure what this December AO is going to average but it probably will be stronger than Jan 2009, but at least there is some hope. Link to comment Share on other sites More sharing options...
donsutherland1 Posted December 21, 2011 Share Posted December 21, 2011 I believe January 2009 had a SSW, it was a "weak" La Nina, January average moderate AO and than February the AO averaged negative. Not sure what this December AO is going to average but it probably will be stronger than Jan 2009, but at least there is some hope. The AO has averaged around +1.7 this month. The monthly average will probably finish between +1.5 and +2.0 if the current guidance is reasonably accurate. Since 1950, 11/12 (91.7%) cases that saw the December AO average +1 or above had a January AO > 0. 1979-80 was the single exception. In January 2009, the AO averaged +0.800. Link to comment Share on other sites More sharing options...
Jaguars Posted December 21, 2011 Share Posted December 21, 2011 The AO has averaged around +1.7 this month. The monthly average will probably finish between +1.5 and +2.0 if the current guidance is reasonably accurate. Since 1950, 11/12 (91.7%) cases that saw the December AO average +1 or above had a January AO > 0. 1979-80 was the single exception. In January 2009, the AO averaged +0.800. amazing, albeit daunting stat there Link to comment Share on other sites More sharing options...
usedtobe Posted December 21, 2011 Share Posted December 21, 2011 amazing, albeit daunting stat there Bob Chill broadened the sample size by going to Plus 0.8 and got 15 years. 14 of the 15 averaged having a positive AO in January. The only good thing is that some of those years had one week to 10 day negative ao periods embedded within all the positive periods. Link to comment Share on other sites More sharing options...
wxmx Posted December 21, 2011 Share Posted December 21, 2011 EP flux vectors are still mostly equatorward, although a not as strong as the first 10 days of Dec. One thing to note is that the upward flux is very strong now, which means that planetary waves are reaching the stratosphere and doing it's dirty work there...which current observations confirm. If EP flux vectors slowly change to a more poleward direction in the next 15-20 days, then probabilities of a strat->tropo propagation will be good Link to comment Share on other sites More sharing options...
okie333 Posted December 21, 2011 Share Posted December 21, 2011 43C at 1mb 240h on yesterday's 12Z Euro... also zonal wind reversal at that level. Link to comment Share on other sites More sharing options...
wxmx Posted December 21, 2011 Share Posted December 21, 2011 Plus this discussion still revolves around 240 hour nwp forecasts...... True, although the warming mechanisms are already in motion, which gives us some certainty... we are just about to see the magnitude of the warming we are going to deal with. Link to comment Share on other sites More sharing options...
wxmx Posted December 21, 2011 Share Posted December 21, 2011 43C at 1mb 240h on yesterday's 12Z Euro... also zonal wind reversal at that level. For people learning about SSWs...we want to see blues around 60N/10mb in the above graph. Blues in the upper stratosphere from 50N-poleward are depicting the first stages of a stratospheric warming. Link to comment Share on other sites More sharing options...
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