The Seven Pillars Of October

[Rainshadow]

For this October beside just its PHL temperature (which really is the result, not the forcing mechanism), I wanted to follow other real forcing mechanisms as to how it will pertain to this upcoming winter. Some are in, some are not, so here we go.

1) October temps, you know the drill, if it ends in the top 33%, the chances of a warmer than normal winter is around 70% (failure last winter); if it ends in the bottom 33%, the chances of a colder than normal winter is around 65%. I use the long term median of 34.5F for PHL.

2) The QBO, will be negative, which should mean greater polar blocking or more instances than normal of polar blocking/ssw.

3) Eurasian snow cover by the end of October. Last two Octobers, were above normal, you know the rest. Hemispheric above normal snowfall by the end of October is a good sign.

4) The stength of the nina. Looks like most modeling is expecting another la nina winter. The PDF version of the CFS is now outlooking a moderate la nina. Most things being equal, the stronger the nina, the warmer and less snowier the winter.

5) The Newfoundland warm pool. Jack (we miss you) used to look at this for an NAO outlook. It averaged warm this predictive season which would mean a positive nao. It was neutral as a lead in to last winter. Of course the QBO is going to be negative which is a conflict. There used to be discussion of taking the opposite of the October NAO for the winter, but this has not worked well of late. After the last two winters, no one can deny the power of a negative NAO; it turned two normally warm and not snowy enso states into nirvana.

6) The number of tropical systems that have remained tropical north of 40N before dissipating. This is a paper Walt (Drag) showed me last fall and its a hemispheric result . The higher the number, the warmer the winter. BTW last winter most lost tropical characteristics south of 40N.

7) The PDO, more positive better. Tough though for it to be positive in a nina winter.

Let October begin....

[CoastalWx]

Nice breakdown Rainshadow. In reference to #6, is the reason behind the thought process of tropical systems not dissipating north of 40N the AMO? IIRC, there is some corelation to a +AMO and se ridging, so perhaps that is part of the reason. I'll have to see if I can dig up the paper.

[Rainshadow]

Nice breakdown Rainshadow. In reference to #6, is the reason behind the thought process of tropical systems not dissipating north of 40N the AMO? IIRC, there is some corelation to a +AMO and se ridging, so perhaps that is part of the reason. I'll have to see if I can dig up the paper.

I'll have to ask Walt or try to find the paper myself. Thank-you. I hope you visit us from time to time this winter. Your thoughts are spot on with many events.

[am19psu]

Nice breakdown Rainshadow. In reference to #6, is the reason behind the thought process of tropical systems not dissipating north of 40N the AMO? IIRC, there is some corelation to a +AMO and se ridging, so perhaps that is part of the reason. I'll have to see if I can dig up the paper.

Pretty sure this is a Bob Hart thing. The more recurving systems there are in the previous tropical season, the weaker the pole-to-equator temperature gradient in the winter due to heat transport from the tropical systems.

[CoastalWx]

I'll have to ask Walt or try to find the paper myself. Thank-you. I hope you visit us from time to time this winter. Your thoughts are spot on with many events.

Thank you for the kind words. I like to get the input from yourself and others during winter events, so yeah I'll be around. Hopefully we can get a nice episode or two of blocking and get redux of December 26th 2010..lol.

[CoastalWx]

Pretty sure this is a Bob Hart thing. The more recurving systems there are in the previous tropical season, the weaker the pole-to-equator temperature gradient in the winter due to heat transport from the tropical systems.

That's what I thought too, but the premise of systems remaining "tropical" north of 40N made me think that this was another theory.

But yeah I think you're right, that might be the paper. I have that saved somewhere..I'll have to take a peak.

[Grothar]

For this October beside just its PHL temperature (which really is the result, not the forcing mechanism), I wanted to follow other real forcing mechanisms as to how it will pertain to this upcoming winter. Some are in, some are not, so here we go.

1) October temps, you know the drill, if it ends in the top 33%, the chances of a warmer than normal winter is around 70% (failure last winter); if it ends in the bottom 33%, the chances of a colder than normal winter is around 65%. I use the long term median of 34.5F for PHL.

2) The QBO, will be negative, which should mean greater polar blocking or more instances than normal of polar blocking/ssw.

3) Eurasian snow cover by the end of October. Last two Octobers, were above normal, you know the rest. Hemispheric above normal snowfall by the end of October is a good sign.

4) The stength of the nina. Looks like most modeling is expecting another la nina winter. The PDF version of the CFS is now outlooking a moderate la nina. Most things being equal, the stronger the nina, the warmer and less snowier the winter.

5) The Newfoundland warm pool. Jack (we miss you) used to look at this for an NAO outlook. It averaged warm this predictive season which would mean a positive nao. It was neutral as a lead in to last winter. Of course the QBO is going to be negative which is a conflict. There used to be discussion of taking the opposite of the October NAO for the winter, but this has not worked well of late. After the last two winters, no one can deny the power of a negative NAO; it turned two normally warm and not snowy enso states into nirvana.

6) The number of tropical systems that have remained tropical north of 40N before dissipating. This is a paper Walt (Drag) showed me last fall and its a hemispheric result . The higher the number, the warmer the winter. BTW last winter most lost tropical characteristics south of 40N.

7) The PDO, more positive better. Tough though for it to be positive in a nina winter.

Let October begin....

Nice write up. Where does the location of the SE ridge play a part in this pillar after the tropical storm season departs? I always found that significant snowfall on the ground in the Rockys , Montana and into the Dakotas by Halloween lays the ground for us in December. Also the Gulf of Mexico has to be open for business in October with stalled fronts. Thanks

[Rainshadow]

Nice write up. Where does the location of the SE ridge play a part in this pillar after the tropical storm season departs? I always found that significant snowfall on the ground in the Rockys , Montana and into the Dakotas by Halloween lays the ground for us in December. Also the Gulf of Mexico has to be open for business in October with stalled fronts. Thanks

I don't know about the SE ridge. In general the higher NH snow cover by the end of October the better, but I think the Eurasian connection leads to patterns more conducive to -nao.

[NaoPos]

Your #4 was an epic fail last year lol. Of course, the was the exception, not the norm.

[WxUSAF]

Nice writeup! In reference to #5, the NAO state...did you look at all into the idea of long duration persistent NAO states? Many people have suggested that we are in a period with a predominant -NAO state and that this cycles on a period of several years to ~a decade.

[Rainshadow]

Nice writeup! In reference to #5, the NAO state...did you look at all into the idea of long duration persistent NAO states? Many people have suggested that we are in a period with a predominant -NAO state and that this cycles on a period of several years to ~a decade.

As far as the NF "pool", Jack gave me a list of failed warm Octobers, about half of them the "pool" was cool in the late spring/early summer. But I am unfortunately going to be hard pressed for time this fall because of Irene and Lee to cross reference what worked better when the NAO was in a predominate negative state.

For the NAO in general, yeah it does look like we are heading toward (or already in) a negative decade like the 60s, so this overall IMO adds more uncertainty to anyone is outlooking a mild winter and conversely a greater confidence if someone is outlooking a cold winter.

[Rainshadow]

Your #4 was an epic fail last year lol. Of course, the was the exception, not the norm.

Yeah it was on a number of levels, it was the snowiest moderate la nina on record in PHL.

[Rainshadow]

Pretty sure this is a Bob Hart thing. The more recurving systems there are in the previous tropical season, the weaker the pole-to-equator temperature gradient in the winter due to heat transport from the tropical systems.

Yup, that is it. Its a dozen or more northern hemispheric recurving tropical systems that make it as far north as 40N as the break point.

[tombo82685]

Yup, that is it. Its a dozen or more northern hemispheric recurving tropical systems that make it as far north as 40N as the break point.

what has this year been like so far?

[Rainshadow]

what has this year been like so far?

Looks like about 10 so far.

Edit: I can't read latitudes, make that about 7.

[tombo82685]

Looks like about 10 so far.

Edit: I can't read latitudes, make that about 7.

so that would basically be a half way point saying maybe some gradient between pole and equator?

[phlwx]

Looks like about 10 so far.

Edit: I can't read latitudes, make that about 7.

I count 4 or 5 depending on definition...I'm probably missing one or two though.

Cindy, Irene, Katia, and Maria.

(one could make a case on Franklin since its last advisory was at 39.7 but it had degenerated)

[am19psu]

I count 4 or 5 depending on definition...I'm probably missing one or two though.

Cindy, Irene, Katia, and Maria.

(one could make a case on Franklin since its last advisory was at 39.7 but it had degenerated)

WPAC, grasshoppa

[phlwx]

WPAC, grasshoppa

I misread hemispheric for Atlantic.

[Rainshadow]

so that would basically be a half way point saying maybe some gradient between pole and equator?

I'm speculating, but its probably the latitude that gave him the strongest correlation. The arctic sea ice has started recovering fairly early (compared to the past 10 years) and there is already snow on the ground in Siberia.

This is a departure from normal snow cover map, red negative, purplish positive.

[Quakertown needs snow]

Thanks Tony.

[Rainshadow]

Ok,

And October is off...

1) Cool start to October (tbd)

2) The QBO, will be negative, ( a plus)

3) Eurasian snow cover by the end of October (tbd)

4) The stength of the nina. weak to moderate outlooks (for now call it a wash)

5) The Newfoundland "warm" pool. ( a negative)

5a) The NAO for October (tbd)

6) The number of tropical systems that have remained tropical north of 40N before dissipating. About 8 now (12 magic number)

(a plus)

7) The PDO, is negative ( a negative)

[Rainshadow]

I just reread Bob Hart's article, forgot about the floor of 5 or less for colder. So right now we are in "equal chances".

[phlwx]

Tony, if you used the current 30 year norm for winter temps (35.3 or 35.5, whatever it is) instead of the long-term norm, how does the needle change on warm/cold October?

[Yes_Probably_Maybe_No]

Has anyone looked up a correlation for late october snow and winter snowfall....let's say, after the 20th of October? I'm thinking it would be similar to a cold october correlates to a colder winter. I don't want to get into the whole "correlation isn't causation" arguement here, I'm just curious about stats.

[Rainshadow]

Tony, if you used the current 30 year norm for winter temps (35.3 or 35.5, whatever it is) instead of the long-term norm, how does the needle change on warm/cold October?

Whoops just saw this now, would suspect it would weaken it. Before we dropped the 70s, the long term mean and the 30-year winter normal for PHL were within .3 of each other.

[Rainshadow]

Has anyone looked up a correlation for late october snow and winter snowfall....let's say, after the 20th of October? I'm thinking it would be similar to a cold october correlates to a colder winter. I don't want to get into the whole "correlation isn't causation" arguement here, I'm just curious about stats.

Subjectively I'd say its positive. Oct '72 and '79 (at least as far as winter snowfall went) get too much credit.

[phlwx]

61.8

+1.6 current norms through yesterday.

Probably get to 2.2 or so by Wednesday before we shave a bit off of that.

If next week's reality is as last night's GFS we should be in the "normal" third on temps for the month when all is said and done.

[phlwx]

61.1 +2.1 thru Saturday.

Still confident in the "middle third" call for the month given the chilly look later this week.

[Rainshadow]

I was reading more of Bob Hart's article about the recurving storms and the article that Jack based his Newfoundland Pool upon. The info Jack gave me was based on May-Aug departures, but I thought he personally told me not to include August because tropical systems would muddy the anomalies. The paper itself seemed to emphasize spring time temps, why when the UKMET used to put out (whether stopped at all or restricted) its NAO outlooks it was May anomaly based. Going through August might have given Jack the best results locally, not sure. May thru July looks close to "equal chances" or NAO neutral, if we include August it would be a negative NAO outlook.

Getting back to the recurving tropical systems, I see that Bob Hart has three categories, cold, "equal chances" and warm. The paper covers Jan thru Mar temp anomalies. Just speculating, maybe there is a lag or its the three month period it works the best, idk. Right now we are in "equal chances".

The bulk of the pillars of October as of today are in the "equal chances" or near normal range for temps, with one or two favoring cold, one favoring warm.

On ENSO alone I looked at JMA stats to try to increase the sample size and assuming a weak nina (at least) for this upcoming winter, the four "bounce back" (going from a mod nina or greater nina the prev winter to at least close to neutral if not pos enso in the summer) nina winters were 1917-8, 1943-4, 1974-5 & 2008-9.