AO Winter Analogs When December Reaches +3.5

[usedtobe]

FWIW, the following is a scatter diagram showing KU snowstorms during La Niña, Neutral, and El Niño ENSO situations for AO+ and AO- situations:

The single La Niña KU snowstorm that commenced when the AO was positive was the January 24-26, 2000 storm.

Don, terrific graphic. Shows why a lot of us get excited when we have a nino and a neg ao or NAO.

[tornadojay]

Don, terrific graphic. Shows why a lot of us get excited when we have a nino and a neg ao or NAO.

Even in a -AO, it's interesting to see the drastic differences between a niño vs Nina situation

[donsutherland1]

This morning, the AO fell to -0.024. If that figure holds up when the final data is released, it will mark a temporary end to the AO+ regime that had lasted 36 days (SEE NOTE). Whether or not that stretch has ended, the guidance very strongly indicates that this is a temporary dip and that the AO will remain predominantly positive for the foreseeable future.

NOTE: The unoffocial data showed November 19 as -.989 in the midst of AO+ readings. That was sort of suspect. The final data for November showed +1.433 for November 19. Hence, if the stretch of positive AO readings ended today, the streak was 36 consecutive days (which would fit with the kind of AO+ regime that had been in place). There remains a distinct possibility that the final data will show a positive AO reading for today, as the guidance had not indicated a dip and it would have had to fall quite a bit from yesterday's figure.

[donsutherland1]

Don, terrific graphic. Shows why a lot of us get excited when we have a nino and a neg ao or NAO.

I agree, Wes. Hopefully, next winter will give us such opportunities. although I don't believe a 3rd consecutive La Niña can be ruled out at this time.

[OSUmetstud]

This morning, the AO fell to -0.024. If that figure holds up when the final data is released, it will mark a temporary end to the AO+ regime that had lasted 36 days (SEE NOTE). Whether or not that stretch has ended, the guidance very strongly indicates that this is a temporary dip and that the AO will remain predominantly positive for the foreseeable future.

NOTE: The unoffocial data showed November 19 as -.989 in the midst of AO+ readings. That was sort of suspect. The final data for November showed +1.433 for November 19. Hence, if the stretch of positive AO readings ended today, the streak was 36 consecutive days (which would fit with the kind of AO+ regime that had been in place). There remains a distinct possibility that the final data will show a positive AO reading for today, as the guidance had not indicated a dip and it would have had to fall quite a bit from yesterday's figure.

Don...I posted in the New England pattern change thread that there must be just enough ridging from the eastern side over the globe over the pole to throw the index slightly negative. The PV is still very strong and intact...so in some respect...a bit of a false reading.

[donsutherland1]

Don...I posted in the New England pattern change thread that there must be just enough ridging from the eastern side over the globe over the pole to throw the index slightly negative. The PV is still very strong and intact...so in some respect...a bit of a false reading.

OSUmetstud,

You might well be right. I see your point. I think it's definitely plausible, though a very close call. No matter what, even if it's negative, it will likely be just a brief aberration in a general stretch of positive readings.

[OSUmetstud]

OSUmetstud,

You might well be right. I see your point. I think it's definitely plausible, though a very close call. No matter what, even if it's negative, it will likely be just a brief aberration in a general stretch of positive readings.

[brad1551]

This slight dip in the AO is just a teaser, it looks like a mass of virgin cold air that does not want to go down onto the lower 48. Other areas in the central USA will get the blast but not my neck of the woods just yet.

[bluewave]

This looks like the strongest September to December +AO pattern that we have seen since 1950.

It's really the opposite of the pattern that we have experienced over the last decade. It's actually

closer to the 80's composite than anything that we have seen recently.

[blizzard1024]

The AO being this strongly positive during the darkest days in the Arctic allows for a very strong cold air source to be built. So when the AO finally goes negative, watch out! Though obviously we don't know when it actually will go negative. This concept was being discussed in one of the NYC subforum threads.

Actually, the heights are below normal but the surface temperatures have been normal to above normal. So there really isn't unusual cold air building up.

see: http://www.esrl.noaa.gov/psd/map/images/rnl/500z_07b.rnl.html for 500 mb height anomalies the last 7 days.

and

http://www.esrl.noaa.gov/psd/map/images/rnl/sfctmpmer_07b.rnl.html for surface temperature anomalies the last 7 days. Not much super cold air

and a very positive NAO....not good.

[Kevin Druff]

Actually, the heights are below normal but the surface temperatures have been normal to above normal. So there really isn't unusual cold air building up.

see: http://www.esrl.noaa...0z_07b.rnl.html for 500 mb height anomalies the last 7 days.

and

http://www.esrl.noaa...er_07b.rnl.html for surface temperature anomalies the last 7 days. Not much super cold air

and a very positive NAO....not good.

Someone correct me if I'm wrong, but... are not 500 MB height anomalies indicative of temperature anomalies above the surface, i.e. there's colder than average temperatures above 1000 MB, but not at the surface (i.e. ~1000 MB).

In other words, he's not wrong that the cold air is building, but to get it to his neck of the woods it needs to lower in altitude as well as latitude.

[Jonger]

Ya, I'm simply looking at the GFS progression and I don't see much hope to grab onto. It looks like the UP of Michigan could get into the clipper train, but everywhere else gets nothing.

This is probably going to be one of the worst winters we have ever experienced in most of our lifetimes.

[blizzard1024]

Someone correct me if I'm wrong, but... are not 500 MB height anomalies indicative of temperature anomalies above the surface, i.e. there's colder than average temperatures above 1000 MB, but not at the surface (i.e. ~1000 MB).

In other words, he's not wrong that the cold air is building, but to get it to his neck of the woods it needs to lower in altitude as well as latitude.

There is cold air at mid levels but not building at the surface. I believe it is related to the intense storminess in the North Atlantic Ocean...a la positive NAO. Hence,

there is more low pressure near the surface in the Arctic than normal and wind which keeps temperatures from falling in the high latitudes. Without low-level cold air, you get few arctic high

pressures to work southward. All the developing cold air in canada is being advected out to the north atlantic where it modifies and makes massive storms for

the UK. These storms also advect very mild air into the Arctic regions in northern Europe and the very high latitudes....look at the +15C anomalies north of Europe at the 00 hour initialiation!!!

see: http://www.policlima...raw_temp_c.html

I was around for the last very positive NAO patterns in the late 80s and very early 90s and winters were a joke...dismal in NY and PA. Snowless...hard to get anything but lake effect and some northern branch clippers. I hope this is just a one year thing...but I wonder....you never know what the atmosphere is going to do..