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And we begin

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Am I the only one rooting for low and slow snow cover this year? After the last 3 years it seems that we probably have a better chance at blocking if it goes down like that. 

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On 9/14/2017 at 6:26 PM, Bob Chill said:

Am I the only one rooting for low and slow snow cover this year? After the last 3 years it seems that we probably have a better chance at blocking if it goes down like that. 

No, you are not..

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2 hours ago, nzucker said:

I don't see the map auto-updating. I stilll see the image from 9/12. How does it look now?

 

It won't update, I hard saved it for baseline.  Snooze to mid October imho.

 

however, since you asked...

 

 

 

IMG_0049.GIF

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My last post was mostly in jest but this one is serious. The last 3 years obviously didn't pan out and that's fine because no long lead signal is perfect. We're a long ways away from getting there. However, one thing that I would like to see is minimal gains in Sept. Don't remember which year it was but one of the recent ones has large gains in Sept. Have no idea if that means much but if we are going to have big gains this year I would like to see them happen during the prime window and then let the chips fall. 

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Cohen posted the graph below last November with the red line indicating the October SAI.  I manually added the blue and black squares to indicate the corresponding winter AO Index value, and whether the SAI performed well (blue) or poorly (black).  After a promising start, the SAI has performed poorly in each of the last 4 years.

78LYTY8.gif

Rather than drawing a link between snow cover advance and the AO, 3 years ago in this snow cover thread, met poster “millwx” discussed the link between snow cover extent (SCE) at week 42 (mid to late Oct) to population-weighted U.S. winter temperatures.  So, winter temperatures for the U.S., but with added weight given to the population centers in the NE quadrant of the country.  He noted that neither the SAI to AO correlation <NOR> the SCE in Week 42 to population-weighted U.S. temperature correlation were strong, but that he preferred using the latter for inclusion into seasonal predictions.  More info here:

https://www.americanwx.com/bb/topic/44473-and-we-begin/?do=findComment&comment=3066907

 

I put together the charts below to show this correlation using the top/bottom 20th percentile in each case…snow cover extent data goes back to 1966.

Here are the Top 10 Oct SCE cases.  6 of 10 had below normal temperatures.

qxKdiSt.gif

 

Here are the Bottom 10 Oct SCE cases. 5 of 10 had above normal temperatures.

cPLxxfa.gif

 

I was curious as to whether this correlation performed better/worse when including ENSO.

Here are the Top 4 Oct SCE / +ENSO cases (Positive Neutral or El Nino).  3 of 4 had below normal temperatures.

Qu8jxZw.gif

 

Here are the Bottom 4 Oct SCE / +ENSO cases.  3 of 4 had above normal temperatures.

R2J2qbw.gif

 

Here are the Top 6 Oct SCE / -ENSO cases (Negative Neutral or La Nina).  4 of 6 had below normal temperatures.  With -ENSO, one thing I noticed was that Oct SCE tended to be lower as the -ENSO strength increased (i.e. strong La Ninas tended to have lower Oct SCE compared to weak La Ninas).  I didn’t see this type of tendency with +ENSO years.

DvAjTP4.gif

 

Here are the Bottom 6 Oct SCE / -ENSO cases.  4 of 6 had above normal temperatures.

9oKmkwa.gif

 

Finally, here is a chart showing trends in fall Eurasian snow cover extent.

0EqCvsz.gif

 

Summary: After a promising start, the SAI has performed poorly over the past 4 winters.  When using top/bottom 20th percentile data, a correlation exists between Oct SCE at week 42 and population-weighted U.S. winter temperatures.  The correlation isn’t super strong, but one that can possibly be used to enhance winter season prediction ideas regardless of the ENSO phase.

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4 hours ago, griteater said:

Here are the Top 6 Oct SCE / -ENSO cases (Negative Neutral or La Nina).  4 of 6 had below normal temperatures.  With -ENSO, one thing I noticed was that Oct SCE tended to be lower as the -ENSO strength increased (i.e. strong La Ninas tended to have lower Oct SCE compared to weak La Ninas).  I didn’t see this type of tendency with +ENSO years.

DvAjTP4.gif

A strong La Nina tends to correlate with above normal temperatures in Siberia/Eurasia, which is where the vast majority of the snow cover area is located. This would make sense because -ENSO tends to induce a stronger Aleutian/Kamchatka ridge which forces cold air into North America and away from Eurasia. On the other hand, El Nino tends to create a strong Gulf of Alaska low (+EPO), which would have cold air behind it in Siberia, and warmer air in front of it in North America. Remember 2009-2010 was a very warm fall and winter globally, but there was a small area of extremely below normal temperatures in Siberia where the PV resided that cold season.

The PV tends to favor North America in La Ninas and Siberia in El Ninos, at least from what I've seen. 95-96 and 83-84 were two La Nina years that had significant PV intrusions into the United States..early February '96 had -60F temperatures in northern Minnesota, and Christmas 1983 is a very well known arctic outbreak. All of the stronger El Ninos have had very limited PV intrusions...82-83 and 97-98 had none at all, 15-16 had one very brief PV outbreak around Valentine's Day when NYC hit -1F.

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