capitalweather Posted November 21, 2012 Share Posted November 21, 2012 I caught up with Judah Cohen... he sees strong potential for a big winter... See Q & A here: http://www.washingtonpost.com/blogs/capital-weather-gang/post/leading-forecaster-judah-cohen-favors-harsh-winter-for-washington-dc-east-coast/2012/11/21/ea5ff790-33e8-11e2-9cfa-e41bac906cc9_blog.html - Jason Link to comment Share on other sites More sharing options...
mappy Posted November 21, 2012 Share Posted November 21, 2012 Thank you for sharing, Jason! Have a wonderful holiday Link to comment Share on other sites More sharing options...
ravensrule Posted November 21, 2012 Share Posted November 21, 2012 Very good interview Jason. Link to comment Share on other sites More sharing options...
Deck Pic Posted November 21, 2012 Share Posted November 21, 2012 nicely done..Snowcover is not something I have given much weight to, but based on the Cohen research I threw it in there as an afterthought and combined with the -QBO, said it might help tend us toward a -NAO all other factors being equal (though there were other factors too) One thing I disagree with is his dismissal of the PDO....we have had a -PDO for 29 straight months now and we are also clearly in a -PDO decadal phase....even when we were in a positive phase (some say the neg phase started in 1999 but they are probably wrong), the winters of 2003-04 and 2004-05 with their weak Enso states had barely positive PDO's....even 2009-10's significant Nino wasn't able to achieve monster status though it was positive as it ran counter to the decadal phase...We still have a significant warm pool along 40N from the dateline west which may support an Aleutian high this winter....with such a weak enso state, I am very confident the PDO will be negative or neutral at best....I don't expect we will have a great PAC this winter, though it may be serviceable.... Link to comment Share on other sites More sharing options...
Ian Posted November 21, 2012 Share Posted November 21, 2012 Good read. I don't really know who he is but I see others seem to think he's legit. I'd generally take a local forecaster with knowledge over someone who forecasts for the whole country or a large region though. I think too often we get lumped in with the other 95 cities at a forecasters folly. We've seen plenty of good EC winters that were not great in DC. Hard not to lean toward a Matt type forecast personally rather than a snowier one. Is Siberian snowcover this year's stratrospheric warming? Link to comment Share on other sites More sharing options...
Deck Pic Posted November 21, 2012 Share Posted November 21, 2012 Good read. I don't really know who he is but I see others seem to think he's legit. I'd generally take a local forecaster with knowledge over someone who forecasts for the whole country or a large region though. I think too often we get lumped in with the other 95 cities at a forecasters folly. We've seen plenty of good EC winters that were not great in DC. Hard not to lean toward a Matt type forecast personally rather than a snowier one. Is Siberian snowcover this year's stratrospheric warming? yes...a winter like 2004-05 we both verify...I dont care if BOS is -2 or PHL gets 40" Link to comment Share on other sites More sharing options...
ThreeRedheads Posted November 21, 2012 Share Posted November 21, 2012 Interesting read! Link to comment Share on other sites More sharing options...
ORH_wxman Posted November 21, 2012 Share Posted November 21, 2012 yes...a winter like 2004-05 we both verify...I dont care if BOS is -2 or PHL gets 40" History and stats definitely favor your CWG type forecast for snowfall in DC. Also if something like '92-'93 or '04-'05 happens, DC is near normal with northeast of them being below normal. Link to comment Share on other sites More sharing options...
brad1551 Posted November 21, 2012 Share Posted November 21, 2012 What a wonderful article and Jason you did great on the interview. Judah defiantly knows his stuff but it doesn't always mean he is right. I work for HWPC as a Pro Forecaster and we have a winter forecast and there are so many others out there. I have read winter forecast that make me sick and angry that people really want to mislead people or they are just wishcasters. I disagree with Judah's forecast and agree more with CWG's forecast. Thanks again for the article and interview Jason. Happy Turkey Day Everyone!! Link to comment Share on other sites More sharing options...
radarman Posted November 21, 2012 Share Posted November 21, 2012 Judah's claim to fame is with respect to forecasting the AO based on the snowcover method. While the AO and the NAO are generally correlated, the latter is much more important to DC than the former. In fact in the overall means a negative AO features a trough position slightly west of the negative NAO position, which hurts DC with a bit of a SE ridge. Of course 09/10 didn't work out that way and his forecast was good for DC, but his papers clearly state the mechanism is with the AO, whereas forecasting the NAO is more of a challenge. Link to comment Share on other sites More sharing options...
ORH_wxman Posted November 21, 2012 Share Posted November 21, 2012 Judah's claim to fame is with respect to forecasting the AO based on the snowcover method. While the AO and the NAO are generally correlated, the latter is much more important to DC than the former. In fact in the overall means a negative AO features a trough position slightly west of the negative NAO position, which hurts DC with a bit of a SE ridge. Of course 09/10 didn't work out that way and his forecast was good for DC, but his papers clearly state the mechanism is with the AO, whereas forecasting the NAO is more of a challenge. The AO actually has a slightly better correlation to DC temps than the NAO...but they are close. Mostly because the CPC definition of the NAO covers some areas that traditionally might not be our "classic NAO"...also the AO shares domain space with the NAO. A -EPO is important for getting cold into the CONUS...the -NAO really helps drive it southeast instead of it hanging around within a couple hundred miles of the Canadian border. Link to comment Share on other sites More sharing options...
PhineasC Posted November 21, 2012 Share Posted November 21, 2012 Another log on the fire. A lot of spread in winter forecasts this year. I guess no one really has any clue. Always a safe bet to say winter will suck in the MA and really, truly suck in DC. Link to comment Share on other sites More sharing options...
usedtobe Posted November 21, 2012 Share Posted November 21, 2012 Judah's claim to fame is with respect to forecasting the AO based on the snowcover method. While the AO and the NAO are generally correlated, the latter is much more important to DC than the former. In fact in the overall means a negative AO features a trough position slightly west of the negative NAO position, which hurts DC with a bit of a SE ridge. Of course 09/10 didn't work out that way and his forecast was good for DC, but his papers clearly state the mechanism is with the AO, whereas forecasting the NAO is more of a challenge. Actually, that is not true. The ao more closely correlate with decent snow storms. I posted a CWG article with a plot that clearly showed that the AO was slightly more correlated with getting good storms than the NAO. Bob Chills stats pretty mcuh say the same thing. Link to comment Share on other sites More sharing options...
radarman Posted November 21, 2012 Share Posted November 21, 2012 Well I was referring to temps not snow, but WIll says in fact even temps are slightly better correlated to the AO than the NAO for DC. I'll defer to you guys on this but it goes against my memory of the literature from around 2000 shortly after Thompson and Wallace came out. Science has advanced a lot in that time obviously so I shouldn't have made claims without something firm in hand. Link to comment Share on other sites More sharing options...
Yeoman Posted November 21, 2012 Share Posted November 21, 2012 I'm waiting for KA's forecast before I pull the trigger on a 4" season. Link to comment Share on other sites More sharing options...
ORH_wxman Posted November 21, 2012 Share Posted November 21, 2012 Well I was referring to temps not snow, but WIll says in fact even temps are slightly better correlated to the AO than the NAO for DC. I'll defer to you guys on this but it goes against my memory of the literature from around 2000 shortly after Thompson and Wallace came out. Science has advanced a lot in that time obviously so I shouldn't have made claims without something firm in hand. Here are the correlation maps: AO: NAO: You can see is quite close, but AO is slightly more correlated...we're talking small amounts though. Link to comment Share on other sites More sharing options...
usedtobe Posted November 22, 2012 Share Posted November 22, 2012 Here's my response to DT who was extolling Cohen's work. I think his work shows promise but am not sure I'm yet ready to completely buy off on it. Dave I've read his articles and think his methodology may indeed have merit but for the longer of his two data sets, the correlation is .626 and if you square that you 0.39 as r squared so you are only expaining around 39% or the variance. not really enough to use alone as a forecast tool. If you use his shorter 20 year period then you explain around 70% which is high enough to use. The problem is knowing whether the shorter period with better data or the longer period with not quite as good data is the better representation of the actual correlations. Right now i don't think we know, I certainly don't/ Plus if the snow cover increase works through the stratosphere as Cohen postulates, we have to wait to see if the stronger than normal stratospheric polar vortex will weaken. Remember it also has a correlation to tthe AO though it's correlation is somewhere in the 40 to 50% range which is lower than those found by cohen. Right now to me neither correlation is high enough to have much faith in. If Cohens higher correlations hold as his data set increases, then I'll be more confident in thinking it is the answer. The trouble is, I can point out at least 4 nino events in the past 20 or so that had a negative ao that did not produce above normal snow. In essence, the AO helps but is no guarantee. Link to comment Share on other sites More sharing options...
usedtobe Posted November 22, 2012 Share Posted November 22, 2012 Well I was referring to temps not snow, but WIll says in fact even temps are slightly better correlated to the AO than the NAO for DC. I'll defer to you guys on this but it goes against my memory of the literature from around 2000 shortly after Thompson and Wallace came out. Science has advanced a lot in that time obviously so I shouldn't have made claims without something firm in hand. Here's a plot of the AO versus NOA for all 4 inch or greater events since 1950. Note how thre are more negative AO snowfall events than NAO ones. I've posted it here before several times and at least once on the CWG site. Link to comment Share on other sites More sharing options...
donsutherland1 Posted November 22, 2012 Share Posted November 22, 2012 I caught up with Judah Cohen... he sees strong potential for a big winter... See Q & A here: http://www.washingto...06cc9_blog.html - Jason Although I have not yet completed my winter thoughts, summer blockiness and recent trends in blocking suggest odds favor potentially abundant winter blocking (AO). If some of the ensemble members are accurate, there may be a signal associated with frequent, strong blocking perhaps along the lines of what one saw during 2002-03. The recent fading of the PDO-, enhances the probability of more frequent PNA+ regimes than might otherwise be the case. Link to comment Share on other sites More sharing options...
usedtobe Posted November 22, 2012 Share Posted November 22, 2012 Although I have not yet completed my winter thoughts, summer blockiness and recent trends in blocking suggest odds favor potentially abundant winter blocking (AO). If some of the ensemble members are accurate, there may be a signal associated with frequent, strong blocking perhaps along the lines of what one saw during 2002-03. The recent fading of the PDO-, enhances the probability of more frequent PNA+ regimes than might otherwise be the case. Don, if the AO goes strongly negative in early Dec and gets into the greater than 3 sd levels, I'll certainly be excited. I suspect that the AO will be more negative than positive this year but don't have much confidence about the call. Link to comment Share on other sites More sharing options...
donsutherland1 Posted November 22, 2012 Share Posted November 22, 2012 Don, if the AO goes strongly negative in early Dec and gets into the greater than 3 sd levels, I'll certainly be excited. I suspect that the AO will be more negative than positive this year but don't have much confidence about the call. I agree Wes. Hopefully, the AO will drop to or below -3 during the early part of December. Link to comment Share on other sites More sharing options...
PhineasC Posted November 22, 2012 Share Posted November 22, 2012 Here's my response to DT who was extolling Cohen's work. I think his work shows promise but am not sure I'm yet ready to completely buy off on it. Dave I've read his articles and think his methodology may indeed have merit but for the longer of his two data sets, the correlation is .626 and if you square that you 0.39 as r squared so you are only expaining around 39% or the variance. not really enough to use alone as a forecast tool. If you use his shorter 20 year period then you explain around 70% which is high enough to use. The problem is knowing whether the shorter period with better data or the longer period with not quite as good data is the better representation of the actual correlations. Right now i don't think we know, I certainly don't/ Plus if the snow cover increase works through the stratosphere as Cohen postulates, we have to wait to see if the stronger than normal stratospheric polar vortex will weaken. Remember it also has a correlation to tthe AO though it's correlation is somewhere in the 40 to 50% range which is lower than those found by cohen. Right now to me neither correlation is high enough to have much faith in. If Cohens higher correlations hold as his data set increases, then I'll be more confident in thinking it is the answer. The trouble is, I can point out at least 4 nino events in the past 20 or so that had a negative ao that did not produce above normal snow. In essence, the AO helps but is no guarantee. I bet DT's response was "fook you moran." Link to comment Share on other sites More sharing options...
usedtobe Posted November 22, 2012 Share Posted November 22, 2012 I bet DT's response was "fook you moran." No, he didn't respond and my response did have a typo as the correlation with the polar vortex and the northern annular mode is in the .40 to .50 range which explains somewhere between 16 and 25 percent of the variance. Link to comment Share on other sites More sharing options...
WinterWxLuvr Posted November 22, 2012 Share Posted November 22, 2012 Here's a plot of the AO versus NOA for all 4 inch or greater events since 1950. Note how thre are more negative AO snowfall events than NAO ones. I've posted it here before several times and at least once on the CWG site. If I'm reading that correctly, it would seem that IF the AO is positive, the last thing we want is a neg NAO. That seems to be the worst for DC snowstorms. I suppose that some of those storms that came during a double positive (surprising number of them) could have come later in the season when a freak snow is more likely to be of the heavy variety. Does the correlation of the indices to our weather here begin to change late in the winter? I would have thought a double pos would have been the worst. A further examination would confirm clearly that what you said is true, a neg AO is clearly much better, and it shows almost no correlation wrt the NAO. There are 34 storms with a pos NAO and 36 with a negative NAO. But that combo of pos AO and neg NAO looks awful. Link to comment Share on other sites More sharing options...
ORH_wxman Posted November 22, 2012 Share Posted November 22, 2012 If I'm reading that correctly, it would seem that IF the AO is positive, the last thing we want is a neg NAO. That seems to be the worst for DC snowstorms. I suppose that some of those storms that came during a double positive (surprising number of them) could have come later in the season when a freak snow is more likely to be of the heavy variety. Does the correlation of the indices to our weather here begin to change late in the winter? I would have thought a double pos would have been the worst. I think its more that it is very difficult to get a -NAO if the AO is positive. Its easier to get a -AO when the NAO is positive because the AO covers more of the NAO domain than the NAO covers of the AO domain. Link to comment Share on other sites More sharing options...
WinterWxLuvr Posted November 22, 2012 Share Posted November 22, 2012 I think its more that it is very difficult to get a -NAO if the AO is positive. Its easier to get a -AO when the NAO is positive because the AO covers more of the NAO domain than the NAO covers of the AO domain. . Oh, didn't think of that. You're saying that that combo is just so infrequent that there aren't as many possible times for a storm. Very reasonable. Thanks. Link to comment Share on other sites More sharing options...
usedtobe Posted November 22, 2012 Share Posted November 22, 2012 . Oh, didn't think of that. You're saying that that combo is just so infrequent that there aren't as many possible times for a storm. Very reasonable. Thanks. I think that partly true as the correlation is .68 or so they can differ. The other thing is the NAO is measure between Iceland and th azores so if the blocking is in northern Euro but extend only westward to iceland you still will have a negative NAO if the heights are low over Azores but that NAO is not favorable for us being that cold or snowy. Link to comment Share on other sites More sharing options...
Deck Pic Posted April 25, 2013 Share Posted April 25, 2013 nicely done..Snowcover is not something I have given much weight to, but based on the Cohen research I threw it in there as an afterthought and combined with the -QBO, said it might help tend us toward a -NAO all other factors being equal (though there were other factors too) One thing I disagree with is his dismissal of the PDO....we have had a -PDO for 29 straight months now and we are also clearly in a -PDO decadal phase....even when we were in a positive phase (some say the neg phase started in 1999 but they are probably wrong), the winters of 2003-04 and 2004-05 with their weak Enso states had barely positive PDO's....even 2009-10's significant Nino wasn't able to achieve monster status though it was positive as it ran counter to the decadal phase...We still have a significant warm pool along 40N from the dateline west which may support an Aleutian high this winter....with such a weak enso state, I am very confident the PDO will be negative or neutral at best....I don't expect we will have a great PAC this winter, though it may be serviceable.... yeah,....I was right.. Jason is absolutely blowing up Judah Cohen today, saying his verification made his jaw drop.....If I graded myself like that I would have given myself an A- and not a C+ EDIT - one thing though is Judah did not prep a DC specific forecast....so through no intention of his own he put a forecast out there because he was asked about DC....that said, his DC thoughts were bad...and his dismissal of PDO and ENSO were wrong... http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/04/25/aers-judah-cohen-produces-amazingly-accurate-winter-outlook/ Link to comment Share on other sites More sharing options...
Ian Posted April 25, 2013 Share Posted April 25, 2013 not sure my jaw has ever dropped -- must be a boring dude his forecast around here was crappy.. Link to comment Share on other sites More sharing options...
ORH_wxman Posted April 25, 2013 Share Posted April 25, 2013 AO was majorly negative but we didn't see the big cold departures in the east...they were all out in the western US (and into the upper plains if you include March). Pretty classic -PDO actually which does lend some credence to the idea that the PDO can't be ignored as just a minor piece. The snowfall did materialize for the northeast once you got north of Philly. Obv it was a bust for DC/BWI. Europe and Asia once again got the Lion's share of the frigid temperatures in the middle latitudes. 5H anomalies: sfc temp anomalies: Link to comment Share on other sites More sharing options...
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