Long Range Discussion 22.0

sroc4 wrote:This is always fun to do.  Below is the long range ensemble forecasts for both GEFS and Euro ENS depicting the mean 500mb height anomalies, valid 00z November 17th(15days from now)  Notice the most prominent feature on both maps is the dark blues south of the Aleutian Islands.  IF true this would lead to ridging along the West coast of NA; in turn troughing would be favored in the east.  This would def lead to BN air masses and early snow chances; esp for the interior....if true.    

Now make sure we keep expectations in check as this is 15days out, and as I pointed out above, if the MJO forecasts come to fruition there will be resistance in the atmosphere.  It will be interesting to see how it evolves.  Ill try and post updated snap shots of the evolution as we go along.  

GEFS




Euro ENS

UPDATE:  See above for latest images.  First images was the one I posted  from 00z 11/02, and the second was 00z 11/06.  As you can see both GEFS and Euro Ens cont to feature a trough south of the Aleutians.  That is key.  The euro ensembles are now showing a stronger signal for a +PNA and -EPO.  Both of which would mean a pretty significant cold shot into the NE ala a deep trough of Polar and perhaps even arctic origin.  The GEFS on the other hand are not quite as robust on this, at least in this snap shot.  On the GEFS image above the black arrow points out that little area of white in between the EPO and PNA regions indicating the possibility of pieces of energy breaking off the mean trough south of the Aleutians resulting in a decrease in the amplitude of the ridging along the west coast; particularly the PNA region.  This could result in some Pac air mixing with our polar air mass, and the depth and amplitude of the trough into the NE would be diminished somewhat; the full extent unclear at this point.

The takeaway:  It is becoming more and more clear that a significant trough looks likely south of the Aleutian islands; the result of which means troughing into the east.  The 7-10day time frame seems to be the transition from a brief N to AN temp period(about a week) to a period of N to BN temps.  Given the time of year and climatology I am def gaining confidence that at the very least our friends to the N&W of NYC, esp those with elevation, will get some good chances at seeing some measurable white gold after about the 13th-15th time frame.  There are still some questions about the PNA and EPO regions and the duration of which these features are around, but confidence is gaining on a +PNA, -EPO couplet is on the horizon.  As an FYI the AO and NAO appear to hover around neutral to slight negative as we head beyond the 7-10day timeframe.  It does appear there is at least some staying power to the BN to N temp regime in the NE, but time will tell.  Another update some time this week if possible.

amugs wrote:Weakening




From 33 n Rain

They are calling that weakening over at 33&rain Mugs? That looks like strengthening for the next week; then relatively maintained thereafter.

Update on the snap shots Ive been posting about for the 17th time frame coming later today or tomorrow. Like Frank mentions above not nearly as favorable as prev indicated in the modeling.

Frank_Wx wrote:Looks like region 3.4 in the ENSO is forecasted to warm a bit, which is good considering we did not want La Nina to overly dominate our pattern. This nicely corresponds to what the avg of stat models are predicting.



So, probably looking at a weak-moderate Nina this winter. Not too bad.

Frank don’t be so sure about that. A mod-strong is still on the table. That map you posted looks like it was from Sept.

algae888 wrote:Right now we have a coupled LA Nina with the atmosphere unlike last year which is good news considering LA nina's are often Fast starts to Winter.  Also if we peak early enough it may prevent The usually warm 2nd half of winters during LA Nina's.  Some good signs today a lot of mixed signals going forward and we will need the help in the North Atlantic this Winter

Al Im not sure why the SSTA animation map isn't working for you but I hope it works for me.  I def see what your saying.  Here is the Animation (hoping it works) for all to see.  In addition is the last 4 month subsurface temp anomaly still frames on avg for the month.  The black arrow in Oct and Nov is showing the area that has warmed more recently.  This can be clearly seen happening over time on the animation.  




But be careful with that.  There is one particular met that I have seen a couple of times since this summer have to back track his thoughts because he underestimated the on coming La Nina.  He currently is doing the same, calling for weak La Nina conditions, but it would not surprise me if he were to need to back track yet again because I think there will be another surge through the end of the year.  

Al you are def correct in that the atmosphere is def in that Base state La nina, unlike last year around this same time.  Take a look at the graph below.  You can see that this year very abruptly the SOI shot up and went from a neutral state to a strong positive state between June and July and remained ever since; whereas, last year it was a much more modest and slow increase starting from a modest neg state early on before reaching moderate status later on.   I think the rapid transition the beginning of the summer has allowed the La Nina more time to establish itself in the base state of the atmosphere.  Meaning when other drivers are neutral the La Nina base state takes back over. driving the pattern.  The stronger the base state of ENSO, the harder time other drivers will have influencing the pattern...in general.  



In general when the SOI is in the positive state its considered La Nina conditions, and when its in the negative state its considered in the El Nino conditions, but more accurately stated when the 30 and 60 day avg is greater than or equal to +8 it is considered La Nina, and less than or equal to -8 its considered El Nino conditions; with values between -8 to +8 its considered La Nada or a neutral ENSO state.

Take a look at the next graph.  Look at the time between Oct 20th - Nov 2nd.  Notice the Daily contribution between these dates is mostly negative or neutral.  The result is both the 30 day and 60 day avg dropped.  But also notice the daily values have spiked again into the 20's and the 60 day avg has gone back up above the 8 threshold and the 30day avg is close. 


So why is the SOI Important?  The SOI value is calculated based on the relative mean surface pressure between Darwin Australia and Tahiti.  When Darwin's pressure is lower relative to Tahiti then the SOI value increases.  The closer Darwin's pressure comes to Tahiti's pressure the smaller the number becomes, and when Darwin's pressure becomes greater than Tahiti the number goes negative.  Again why is that important?  

Look at the images below.  As we all know air tends to move from areas of HP to areas of LP.  So you can picture in your mind that the mean flow of air wants to be westerly or to the west.  This is the case when you have a base state in a La Nina.  




Now use your imaginations and pretend that the trop Pacific is like a big bathtub filled with water only the temps of the water differ depending on which side of the bath tub (see the image below) or at what depth you are at(see the first two images/animation posted above).  You can clearly see that the water to the north of Australia is very warm, and it slowly gets cooler as head east.  Now image a giant fan located in the eastern Trop Pac is blowing along the surface.  One would imagine that the longer and harder the fan blew to the west the more the relatively cooler waters in the eastern pac might get pushed or displace to the west into areas with relatively warmer waters mixing cooling them relative to normal.  You could also just as easily image the opposite effect if the fan was in the west, N of Australia, pushing the relatively warmer waters easterly mixing with the relatively cooler waters in to the east making them warming relative to normal.  

One also might imagine that if you were pushing the water on the surface to the west the water that gets displaced from immediately in front of the fan would need to be replaced.  So imagine the water beneath the surface(upwelling) rises to replace the displaced water on the surface.   So with this visualization it makes sense and one may expect to see colder than normal SSTA develop over time when the fan blows consistently from east to west as in La Nina years, and warmer sea surface temps if the fan blowing west to east during El Nino years.  THIS is why and how you use the SOI index as an indicator of the base state of ENSO.  



Now see the image below.  This is the graph for ENSO region 3.4.  You can see at the end of it we get a little rise in the SSTA.  Refer back to the SOI index above.  It no coincidence that with a flip in the SOI index going neutral to negative during this time frame that we got a surge in SSTA.  Why?  Image the fan again.  Its been blowing fairly steadily at a mod speed for awhile from the east to the west.  We have pushed a fair amount of water to the western side of the bath tub and the resistance from the fan has kept it there.  What happens if you turn the fan down or off temporarily?  You get a reflexively rebound of the water you pushed into the western side of the tub.  A wave of warmer waters, relatively speaking, sloshes back, if you will, to the east because the resistance from the blowing fan is reduced.  As you can see by the SOI daily contributions above from Nov 3rd through today the values have drastically gone back up strongly positive.  The resulting 30day and 90day avg have both gone back up again.  The short and md term forecast cont to show the MSLP  in Tahit and Darwn to support the more positive SOI values.  If we get a few more days of positive values you will see the trend on the graph below go back down pretty quickly.  




Now to bring this all home, I really do still think we see predominately positive SOI values for the next 1.5-2 months.  And even though there have been some warming in the sub-surfaces and its pushed a little east these areas are very deep and aren't ready to influence the ENSO status just yet.  And I think the upwelling that occurs when the fan is blowing westerly, SOI is in a mod to strong positive state, will cont to cool the surface in the ENSO region to reach at least moderate La Nina status.  Obv I dont know this for sure, but this is what my Spidey senses tell me.  We shall see.

What had looked like a fairly promising pattern to end Nov and start Dec is looking more like bleh.

algae888 wrote:I should also add GEFS has below normal 850's day 9 thru the end of the run

Al id take anything you see beyond day 7-10 with a huge grain of salt.  Remember the evolution we were follwoing for Nov 17th?  What happened to the trough S of the Alutian islands that seemed likely, and what happened to the possible +PNA/-EPO couplet....transient:

GEFS




Euro ENS



There are still some questions about the PNA and EPO regions and the duration of which these features are around, but confidence is gaining on a +PNA, -EPO couplet is on the horizon.  As an FYI the AO and NAO appear to hover around neutral to slight negative as we head beyond the 7-10 day time frame.  It does appear there is at least some staying power to the BN to N temp regime in the NE, but time will tell.  




Well here is the current GEFS Ens(Euro is the same) for 00z Nov 17th.  As you can see there is a deep negative now over the WC of Canada and the north west CONUS.  The trough coming on the heals of tomorrows rain for next week has no staying power.  It gets booted by that energy crashing the coast and the result if the SE ridge immediately flexing 24hrs later.






Here is the next snap shot to follow.  So long as there is a negative showing up along the WC of Canada and NW CONUS the cold will be transient. 2-4 days then out. The question will be as the next cold shot swings through can we get a storm track that brings in the cold first vs the SE ridge means warm out ahead and the cold only on the heals of the frontal boundary. If we can lay down some snow pack into NE over the next few weeks hopefully the cold air masses become more dense and diff to scour out.  

Al I think Im the glass empty guy and your the half full guy. Between the two of us we have a full glass...lol I dont mean to be going against the grain here but I was thinking about writing up these thoughts anyway.