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Fall 2017 Model Mehham

Go Kart Mozart

By Go Kart Mozart,
in New England

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Typhoon Tip

Typhoon Tip

Posted
Posted

That depiction may belie the actually state of the NAO out in time.

Unsure ... but that "look" is exceptionally flat compared to what the nightly index value from CPC have been indicating; which that agency employs the 500 mb geopontial anomaly in the EOF (empirical orthogonal funciton derivatives - hence why I use them for that comparison). As of last night, continues to drill the index into the -1 to -2 SD range.  Those sort of numbers are a-priori akin to better actual "curved" blocking features over the N and NW Atlantic Basin, and in that product, we're only seeing modest positive anomalies and not much indication of blocking at all - looks almost zonal through there. 

Nevertheless, there are enough individual GEFs members that are far and a way much more coherent with a structure that takes on those sort of appeals..  I would caution that the NAO is probably the most stochastic/erratic behaved index domain spaces. Models notoriously over(under) predict the emergence of blocking era's there, sometimes at even < than single week time spans. Keep that in mind as this decent really gets underway...

nao11122017.jpg.376985128ba6c4922cd44accc339fcf5.jpg

Despite my own admission regarding the vagarious nature of this index and the intrinsic unpredictability there in ... this is a multi-day signal demonstrating outstanding continuity. That's a (sort of) long way of saying ... that downward "cupping" at the right hand side of the annotation above, has been here for a long time.  For the lay-person, forecasting 101, you want that consistency to 'feel confident' ... 

So, my thinking here is that is a pretty strong single there? ...reasonable to above normal confidence..  It's quite coherent with albeit some, but less "splaying" of individual members around a general theme of -SD values - particularly considering that is between week 1 and week 2 at the nadir of that curve there.

How all this relates to practical matter: 

I am not entirely convinced that deep layer amplitude that all guidance core out over the eastern Lakes, won't end up farther E and/or S of that position as the D7 becomes D6 ... D3 and nears.  In other words, that may correct in that direction, in time.  The changing NAO index times are not just problematic in the general sense, it is also hugely unclear how all that uncertainly will then exactly relate/instruct the backlogged flow down into the Lake/upper OV/ NE regions/ eastern Canada.  I mean...we are compounding uncertainties there...  Timing both related to both spacing and intensities?  Good luck!  Obviously prone to significant error. 

There are three possibilities there -- which is also in part my personal thinking just based-upon the 'tenor' of present atmospheric cadence... 

1 ... We could be sitting here looking at a time-bomb for a historic event and not even know it, simply because the guidance does not in-fact show a major event ... and the imagination isn't working. Heh. 

2 ... The models are exactly right, as is...and the mid and U/A features intensely deepen closer to 90W/50N, ...sending a "southwest flow event" up our way, that probably features cold rain given to climo...etc.  This is a troubling prospect in my mind, because ... diving NAOs reenters the uncertainties described above, and, -NAO in general does not correlate to that position so well. If the NAO ended up weakly negative ... like the operational runs, that does open the door for less resistance to such an evolution (statistically, but there are synoptic conceptual reasons why that is true).  So, ... I'm willing to wait that out a bit to see what yields, while keeping in mind that anomalies relative to anomalies also sometimes do take place and oy!

3 ... The whole system ends up weaker anyway.  A weaker system arriving into the northeast under a -NAO ...  initially, your not likely to see a system turn left that aggressively if it is weaker, in a -NAO that is evolving stronger in time. 

 

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CoastalWx

CoastalWx

Posted
Posted
9 minutes ago, Typhoon Tip said:

That depiction may belie the actually state of the NAO out in time.

Unsure ... but that "look" is exceptionally flat compared to what the nightly index value from CPC have been indicating; which that agency employs the 500 mb geopontial anomaly in the EOF (empirical orthogonal funciton derivatives - hence why I use them for that comparison). As of last night, continues to drill the index into the -1 to -2 SD range.  Those sort of numbers are a-priori akin to better actual "curved" blocking features over the N and NW Atlantic Basin, and in that product, we're only seeing modest positive anomalies and not much indication of blocking at all - looks almost zonal through there. 

Nevertheless, there are enough individual GEFs members that are far and a way much more coherent with a structure that takes on those sort of appeals..  I would caution that the NAO is probably the most stochastic/erratic behaved index domain spaces. Models notoriously over(under) predict the emergence of blocking era's there, sometimes at even < than single week time spans. Keep that in mind as this decent really gets underway...

nao11122017.jpg.376985128ba6c4922cd44accc339fcf5.jpg

Despite my own admission regarding the vagarious nature of this index and the intrinsic unpredictability there in ... this is a multi-day signal demonstrating outstanding continuity. That's a (sort of) long way of saying ... that downward "cupping" at the right hand side of the annotation above, has been here for a long time.  For the lay-person, forecasting 101, you want that consistency to 'feel confident' ... 

So, my thinking here is that is a pretty strong single there? ...reasonable to above normal confidence..  It's quite coherent with albeit some, but less "splaying" of individual members around a general theme of -SD values - particularly considering that is between week 1 and week 2 at the nadir of that curve there.

How all this relates to practical matter: 

I am not entirely convinced that deep layer amplitude that all guidance core out over the eastern Lakes, won't end up farther E and/or S of that position as the D7 becomes D6 ... D3 and nears.  In other words, that may correct in that direction, in time.  The changing NAO index times are not just problematic in the general sense, it is also hugely unclear how all that uncertainly will then exactly relate/instruct the backlogged flow down into the Lake/upper OV/ NE regions/ eastern Canada.  I mean...we are compounding uncertainties there...  Timing both related to both spacing and intensities?  Good luck!  Obviously prone to significant error. 

There are three possibilities there -- which is also in part my personal thinking just based-upon the 'tenor' of present atmospheric cadence... 

1 ... We could be sitting here looking at a time-bomb for a historic event and not even know it, simply because the guidance does not in-fact show a major event ... and the imagination isn't working. Heh. 

2 ... The models are exactly right, as is...and the mid and U/A features intensely deepen closer to 90W/50N, ...sending a "southwest flow event" up our way, that probably features cold rain given to climo...etc.  This is a troubling prospect in my mind, because ... diving NAOs reenters the uncertainties described above, and, -NAO in general does not correlate to that position so well. If the NAO ended up weakly negative ... like the operational runs, that does open the door for less resistance to such an evolution (statistically, but there are synoptic conceptual reasons why that is true).  So, ... I'm willing to wait that out a bit to see what yields, while keeping in mind that anomalies relative to anomalies also sometimes do take place and oy!

3 ... The whole system ends up weaker anyway.  A weaker system arriving into the northeast under a -NAO ...  initially, your not likely to see a system turn left that aggressively if it is weaker, in a -NAO that is evolving stronger in time. 

 

Yeah I agree. If one were to just look at the big picture, the 6z GFS makes sense to me, next weekend. Perhaps nothing special here, but that is a wintry look from the Lakes Region on north and east regarding snow and mixed precip. It also depends on how strong that s/w is digging into the Plains. If that s/w decides to go fracking...it won't matter and end up cutting west anyways. 

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WinterWolf

WinterWolf

Posted
Posted
27 minutes ago, Typhoon Tip said:

That depiction may belie the actually state of the NAO out in time.

Unsure ... but that "look" is exceptionally flat compared to what the nightly index value from CPC have been indicating; which that agency employs the 500 mb geopontial anomaly in the EOF (empirical orthogonal funciton derivatives - hence why I use them for that comparison). As of last night, continues to drill the index into the -1 to -2 SD range.  Those sort of numbers are a-priori akin to better actual "curved" blocking features over the N and NW Atlantic Basin, and in that product, we're only seeing modest positive anomalies and not much indication of blocking at all - looks almost zonal through there. 

Nevertheless, there are enough individual GEFs members that are far and a way much more coherent with a structure that takes on those sort of appeals..  I would caution that the NAO is probably the most stochastic/erratic behaved index domain spaces. Models notoriously over(under) predict the emergence of blocking era's there, sometimes at even < than single week time spans. Keep that in mind as this decent really gets underway...

nao11122017.jpg.376985128ba6c4922cd44accc339fcf5.jpg

Despite my own admission regarding the vagarious nature of this index and the intrinsic unpredictability there in ... this is a multi-day signal demonstrating outstanding continuity. That's a (sort of) long way of saying ... that downward "cupping" at the right hand side of the annotation above, has been here for a long time.  For the lay-person, forecasting 101, you want that consistency to 'feel confident' ... 

So, my thinking here is that is a pretty strong single there? ...reasonable to above normal confidence..  It's quite coherent with albeit some, but less "splaying" of individual members around a general theme of -SD values - particularly considering that is between week 1 and week 2 at the nadir of that curve there.

How all this relates to practical matter: 

I am not entirely convinced that deep layer amplitude that all guidance core out over the eastern Lakes, won't end up farther E and/or S of that position as the D7 becomes D6 ... D3 and nears.  In other words, that may correct in that direction, in time.  The changing NAO index times are not just problematic in the general sense, it is also hugely unclear how all that uncertainly will then exactly relate/instruct the backlogged flow down into the Lake/upper OV/ NE regions/ eastern Canada.  I mean...we are compounding uncertainties there...  Timing both related to both spacing and intensities?  Good luck!  Obviously prone to significant error. 

There are three possibilities there -- which is also in part my personal thinking just based-upon the 'tenor' of present atmospheric cadence... 

1 ... We could be sitting here looking at a time-bomb for a historic event and not even know it, simply because the guidance does not in-fact show a major event ... and the imagination isn't working. Heh. 

2 ... The models are exactly right, as is...and the mid and U/A features intensely deepen closer to 90W/50N, ...sending a "southwest flow event" up our way, that probably features cold rain given to climo...etc.  This is a troubling prospect in my mind, because ... diving NAOs reenters the uncertainties described above, and, -NAO in general does not correlate to that position so well. If the NAO ended up weakly negative ... like the operational runs, that does open the door for less resistance to such an evolution (statistically, but there are synoptic conceptual reasons why that is true).  So, ... I'm willing to wait that out a bit to see what yields, while keeping in mind that anomalies relative to anomalies also sometimes do take place and oy!

3 ... The whole system ends up weaker anyway.  A weaker system arriving into the northeast under a -NAO ...  initially, your not likely to see a system turn left that aggressively if it is weaker, in a -NAO that is evolving stronger in time. 

 

Nice post, and explanation.  

That post should make some of the peeps that are already backing off the "White Thanksgiving," and wintry December some decent insight.  

 

We've all seen decent/good patterns that just don't produce much in the way of wintry weather..happens quite a bit actually.  And being quite early, and among other reasons this could certainly be the case here.  That's why it's so important to keep expectations and the weenie talk in check as many who are in the know here have advised ...which is truly "Legit."   

However, as you pointed out, there is Potential there,  but things are very uncertain at best. 

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