I Have Questions

[CCPSUSuperstorm2010]

I have a few questions that have been itching at me the last few days:

1.) How does one process the Index values that the CPC provides into a negative, neutral and positive values? Are the values separated by -0.5 to +0.5 and anything below or above falls into the positive or negative phase of the index? How does that work?

2.) What is the most favorable pattern one can see developing, for a HECS? I mean does the Aleutian RIdge need to be positioned over the western Aleutian islands so that the GOA trough can be more so positioned south of Alaska or over western Alaska so enough ridging can build into the western US to allow for a steady troughing pattern to evolve over the eastern US so we can get one great snowstorm?

3.) So how does one find historical records on snowstorms before 1997 here in SNE? I have seen the Taunton NWS snowfall information PNSs already, but I need some records from before then.

4.) What is the historically worst Ocean Effect Snowstorm to hit Cape Cod, MA in history? So far there have been 2-4" events, but I am talking about something like 6"+ in the past. There has to be records for these things.

Those are the questions on my mind for now.

[Tropopause_Fold]

I have a few questions that have been itching at me the last few days:

1.) How does one process the Index values that the CPC provides into a negative, neutral and positive values? Are the values separated by -0.5 to +0.5 and anything below or above falls into the positive or negative phase of the index? How does that work?

2.) What is the most favorable pattern one can see developing, for a HECS? I mean does the Aleutian RIdge need to be positioned over the western Aleutian islands so that the GOA trough can be more so positioned south of Alaska or over western Alaska so enough ridging can build into the western US to allow for a steady troughing pattern to evolve over the eastern US so we can get one great snowstorm?

3.) So how does one find historical records on snowstorms before 1997 here in SNE? I have seen the Taunton NWS snowfall information PNSs already, but I need some records from before then.

4.) What is the historically worst Ocean Effect Snowstorm to hit Cape Cod, MA in history? So far there have been 2-4" events, but I am talking about something like 6"+ in the past. There has to be records for these things.

Those are the questions on my mind for now.

James,

Question 1: not sure exactly what you are asking.

You should snag the Kocin books. You'll thoroughly enjoy them and they will help with some of these things here in generalizations.

also, re: OES - we've definitely had some >6" events. i'll see if i can snag some of the dates. sometimes it's tough to differentiate the pure OES from some larger synoptic things though.

[CCPSUSuperstorm2010]

Thanks Phil.

The first question I am asking this, you know how the values are in the negative through positive values, like for instance a -0.456 for the AO index lets say. Is there a system in place to help differentiate whether or not this is part of the negative or neutral AO index?

So is the value +0.456 a neutral or positive value?

So is the value +0.567 a positive or neutral value?

So is the value 0.054 a neutral or positive value?

Do you see what I mean, looking at the CPC daily archived values for the AO, NAO or PNA indices?

Thanks again Phil for the help. I saw the Kocin/Uccelini books I have them, but they don't specify the overall Northern Hemispheric pattern, they just focus on the North Atlantic Ocean.

[Tropopause_Fold]

Thanks Phil.

The first question I am asking this, you know how the values are in the negative through positive values, like for instance a -0.456 for the AO index lets say. Is there a system in place to help differentiate whether or not this is part of the negative or neutral AO index?

So is the value +0.456 a neutral or positive value?

So is the value +0.567 a positive or neutral value?

So is the value 0.054 a neutral or positive value?

Do you see what I mean, looking at the CPC daily archived values for the AO, NAO or PNA indices?

Thanks again Phil for the help. I saw the Kocin/Uccelini books I have them, but they don't specify the overall Northern Hemispheric pattern, they just focus on the North Atlantic Ocean.

Gotcha. that makes more sense.

some of it is subjective. i always think of anything less than . 4 or .5 as a fairly weak signal. when you get down to your example with ".054" i call that neutral and would expect that other forcings could/would be more at play. for me (and maybe Will, Ryan or Scott feel differently - they can probably chime in with their thoughts) anything over say .75 in the positive or negative direction is a pretty decent signal...borderline weak / moderate, imo. you get up over 1.5 and you are looking at a strong index.

the other thing is, it depends on the variable at work. some of them are less important for our geographic area...so despite it being strongly positive or negative (for example) it may have little bearing on our neck of the woods if some other mechanism is at play.

[CoastalWx]

Thanks Phil.

The first question I am asking this, you know how the values are in the negative through positive values, like for instance a -0.456 for the AO index lets say. Is there a system in place to help differentiate whether or not this is part of the negative or neutral AO index?

So is the value +0.456 a neutral or positive value?

So is the value +0.567 a positive or neutral value?

So is the value 0.054 a neutral or positive value?

Do you see what I mean, looking at the CPC daily archived values for the AO, NAO or PNA indices?

Thanks again Phil for the help. I saw the Kocin/Uccelini books I have them, but they don't specify the overall Northern Hemispheric pattern, they just focus on the North Atlantic Ocean.

In addition to what Phil says, there is some variation to the indices because of the methods used to calculate the index. Some methods use sea level pressure difference between Greenland and the Azores, while others you the H5 heights. The result could be that one index may be a result like 0.4 for instance. However, the other method works out to be -0.2. Most of the time, I don't think the difference is that large, and chances are whether it is slightly + or -..it falls under the neutral category.

[CCPSUSuperstorm2010]

Thanks Scot. Yeah I agree with your assessments Phil, I would say anything of a .5 to -.5 is neutral and anything above 0.5 is positive. That does pretty well when you are talking about certain indices like the three main ones, of the AO, NAO and PNA.

[Tropopause_Fold]

for the historical snowfall record, my advice is just use Will

the BOX page does have older data on it, but it is kind of crappy and for locations outside of the 4 major climo sites it is particularly weak in areas.

you can also use the ncdc site and look through the coop sites and the dailies. but again, for the cape, the data is hit or miss. i know of several dates where sizable events went unlisted.

[CoastalWx]

for the historical snowfall record, my advice is just use Will

the BOX page does have older data on it, but it is kind of crappy and for locations outside of the 4 major climo sites it is particularly weak in areas.

you can also use the ncdc site and look through the coop sites and the dailies. but again, for the cape, the data is hit or miss. i know of several dates where sizable events went unlisted.

I wish the Cape had better data.

[CCPSUSuperstorm2010]

I wish the Cape had better data.

yeah Scot, I do to, given that we have a much different climo then BOS, PVD or ORH. Cape Cod, MA snowstorms need a particular pattern in order to develop and occur in a fashion to favor the area for snow instead or a mixed storm system. We need a 40/70 BM track at least for snowfall.

[OKpowdah]

When is the snow coming?

[Tropopause_Fold]

When is the snow coming?

[Tropopause_Fold]

I wish the Cape had better data.

yeah it's pretty awful. i get mad at myself for not following the advice of people who used to tell me to write everything down...when i was like 5 yrs. old. everyone said to start writing down my observations everyday and i'd be really happy i'd done it. all those other people FTW...me FTL.

[CoastalWx]

yeah it's pretty awful. i get mad at myself for not following the advice of people who used to tell me to write everything down...when i was like 5 yrs. old. everyone said to start writing down my observations everyday and i'd be really happy i'd done it. all those other people FTW...me FTL.

I used to have a weather log book in 3rd grade. I even updated it in school....lol. Unfortunately, I was stupid and stopped logging obs after a year or so.

[weatherwiz]

What I basically do is this:

Values between -0.500 and + 0.500 I categorize as neutral

Values >0.500 I categorize as positive

Values <-0.500 I categorize as negative

The NAO can be a bit tougher to do though since there are different methods of it's calculation. Like Scott said, some methods are used by the 500mb height differences and some use the SLP differences.

Basically what I have done for the NAO is make a list for each of the methods (CPC, Hurrell, Hurrell PC Based, and Osborne). I have a list of neutral values for CPC, Hurrell, Hurrell PC Based, Osborne, as well as negative values and positive values.

I also try to look at 500mb heigh anomalies and SLP differences more as well as zonal wind anomalies as looking at the maps can give you a much better idea as well.

[alex]

OK so I have a question... 2008, if I remember correctly, was also La Nina. In December of that year, we had lake cutter after lake cutter which redeveloped on the coast. The result - we (on the CP) had a bunch of snow to drizzle to a few hours of 39F to back below freezing situations... and little by little, as sloppy as the storms were, we built an awesome snowpack - definitely the deepest I've seen in the 3 years I've been in Winchester. Why is that not the case this year?

[Tropopause_Fold]

OK so I have a question... 2008, if I remember correctly, was also La Nina. In December of that year, we had lake cutter after lake cutter which redeveloped on the coast. The result - we (on the CP) had a bunch of snow to drizzle to a few hours of 39F to back below freezing situations... and little by little, as sloppy as the storms were, we built an awesome snowpack - definitely the deepest I've seen in the 3 years I've been in Winchester. Why is that not the case this year?

thankfully, nothing says for certain that it won't be. it was later in the season than it is right now.

but, every year/winter is different. think of the multitude of factors going on in the atmosphere governing a given pattern.

[alex]

thankfully, nothing says for certain that it won't be. it was later in the season than it is right now.

but, every year/winter is different. think of the multitude of factors going on in the atmosphere governing a given pattern.

True. I'll keep my fingers crossed, though it was a really stressful pattern in a way - every storm was forecasted to be mostly rain - and then every storm would end up adding 5-8" to the snowpack. Nail biting, but so exciting.

[CCPSUSuperstorm2010]

Yeah I kind of wish I had a weather log, at least back in middle school or high school where we had some awesome winters. Second best winter at least since 97 was 2003 where we got around 52" of snow. Unfortunately I don't remember when we had like 6" of snow out of nowhere and had school closed for that one day back in middle school, sometime in the late 90s I believe. Now I know it was OES because of the suddeness of it all. It quickly melted though do to the high snow ratios.

[ORH_wxman]

I wish the Cape had better data.

The Cape data is the worst in SNE bar none. Its too bad because there's some interesting winters down there that might have been more unnoticed in the rest of the region.

1988-1989 is one that goes under the radar a bit. I specifically remembering a couple spots down there getting 20" in the Feb 24-25, 1989 storm. They also had an OES event that gave someone over 6" (I think it was fairly close to CHH). I know 1998-1999 was a sneaky good winter down there too...though that is recent enough that we have people like Phil that remember a lot of the events from that winter. There's spots that probably had as much snow as my area did in '98-'99 despite averaging over 30" less.

February 1952 had one of the worst blizzards down there that probably rivaled Jan 2005. I doubt it actually beat it, but it wasn't horribly far off. That storm was a little further offshore though and didn't hit the rest of SNE nearly as hard. But there were spots on the Cape that had over 30" of snow from it and extreme winds. Less than a week later, the Cape got hit again with another 12"+ storm....probably making Feb 1952 one of the snowiest months on record there. (probably only behind Jan 2005)

[nzucker]

2.) What is the most favorable pattern one can see developing, for a HECS? I mean does the Aleutian RIdge need to be positioned over the western Aleutian islands so that the GOA trough can be more so positioned south of Alaska or over western Alaska so enough ridging can build into the western US to allow for a steady troughing pattern to evolve over the eastern US so we can get one great snowstorm?

You don't really want an Aleutian ridge for a HECS because that causes a trough to amplify in the GoA and Pacific Northwest, which in turn pumps up heights ahead of it and makes it harder for the East Coast to see a snowstorm. Most HECS events occurred in El Niño years, which tend to feature an Aleutian low. This causes higher pressures over the GoA and West which brings cold air down from the Arctic and allows shortwaves to amplify further south. The most notable feature for the HECS composite 500mb maps is the strong west-based -NAO, however, not the Pacific features.

OK so I have a question... 2008, if I remember correctly, was also La Nina. In December of that year, we had lake cutter after lake cutter which redeveloped on the coast. The result - we (on the CP) had a bunch of snow to drizzle to a few hours of 39F to back below freezing situations... and little by little, as sloppy as the storms were, we built an awesome snowpack - definitely the deepest I've seen in the 3 years I've been in Winchester. Why is that not the case this year?

2008-2009, if that's the winter you're referring to, was a very weak Niña. It was borderline neutral in terms of ENSO status. This allowed the winter to feature a variety of patterns, some of which were more typical of the Pacific regime you'd see in an El Niño. January 2009, which had a huge arctic outbreak around the 16th and multiple snowstorms, had some El Niño like features over the Pacific with strong blocking in Alaska. This is a very strong La Niña, which means you'll probably see less variety in the pattern and more tendency for the typical trough out west and ridge in the East.

[nzucker]

The Cape data is the worst in SNE bar none. Its too bad because there's some interesting winters down there that might have been more unnoticed in the rest of the region.

1988-1989 is one that goes under the radar a bit. I specifically remembering a couple spots down there getting 20" in the Feb 24-25, 1989 storm. They also had an OES event that gave someone over 6" (I think it was fairly close to CHH). I know 1998-1999 was a sneaky good winter down there too...though that is recent enough that we have people like Phil that remember a lot of the events from that winter. There's spots that probably had as much snow as my area did in '98-'99 despite averaging over 30" less.

February 1952 had one of the worst blizzards down there that probably rivaled Jan 2005. I doubt it actually beat it, but it wasn't horribly far off. That storm was a little further offshore though and didn't hit the rest of SNE nearly as hard. But there were spots on the Cape that had over 30" of snow from it and extreme winds. Less than a week later, the Cape got hit again with another 12"+ storm....probably making Feb 1952 one of the snowiest months on record there. (probably only behind Jan 2005)

Was the February 25, 1989 storm the same one that pounded the extreme Mid-Atlantic coast and Delmarva, Will?

[ORH_wxman]

Was the February 25, 1989 storm the same one that pounded the extreme Mid-Atlantic coast and Delmarva, Will?

Yes it hit the Delmarva peninsula and extreme SE NJ near ACY...then it hammered Cape Cod. We only got about 4" here. 1-2 feet was forecasted the day before.

I didn't know it at the time, but I actually lucked out with 4", apparently NYC to PHL was supposed to also see 1-2 feet, but they got nothing at all but overcast skies.

[CCPSUSuperstorm2010]

The Cape data is the worst in SNE bar none. Its too bad because there's some interesting winters down there that might have been more unnoticed in the rest of the region.

1988-1989 is one that goes under the radar a bit. I specifically remembering a couple spots down there getting 20" in the Feb 24-25, 1989 storm. They also had an OES event that gave someone over 6" (I think it was fairly close to CHH). I know 1998-1999 was a sneaky good winter down there too...though that is recent enough that we have people like Phil that remember a lot of the events from that winter. There's spots that probably had as much snow as my area did in '98-'99 despite averaging over 30" less.

February 1952 had one of the worst blizzards down there that probably rivaled Jan 2005. I doubt it actually beat it, but it wasn't horribly far off. That storm was a little further offshore though and didn't hit the rest of SNE nearly as hard. But there were spots on the Cape that had over 30" of snow from it and extreme winds. Less than a week later, the Cape got hit again with another 12"+ storm....probably making Feb 1952 one of the snowiest months on record there. (probably only behind Jan 2005)

Wow, thanks Will. Very informative. how do you find the records for winter storms back then?

You don't really want an Aleutian ridge for a HECS because that causes a trough to amplify in the GoA and Pacific Northwest, which in turn pumps up heights ahead of it and makes it harder for the East Coast to see a snowstorm. Most HECS events occurred in El Niño years, which tend to feature an Aleutian low. This causes higher pressures over the GoA and West which brings cold air down from the Arctic and allows shortwaves to amplify further south. The most notable feature for the HECS composite 500mb maps is the strong west-based -NAO, however, not the Pacific features.

2008-2009, if that's the winter you're referring to, was a very weak Niña. It was borderline neutral in terms of ENSO status. This allowed the winter to feature a variety of patterns, some of which were more typical of the Pacific regime you'd see in an El Niño. January 2009, which had a huge arctic outbreak around the 16th and multiple snowstorms, had some El Niño like features over the Pacific with strong blocking in Alaska. This is a very strong La Niña, which means you'll probably see less variety in the pattern and more tendency for the typical trough out west and ridge in the East.

Thanks zucker, yeah I found that out just about yesterday looking at the major snowstorms on the NESIS scales looking at the 500mb NHEM maps. They all have a common PAC theme, an Aleutian trough.

[weatherwiz]

I'm a little confused as how to classify this NAO.

The 500mb height anomaly kind of looks negative I guess with the positive height anomalies just east of Greenland:

SLP anomaly has a very weak positive NAO look...although I suppose this could be more of a neutral look:

Zonal wind anomalies look more like a +NAO...although I suppose it could be a -NAO b/c I'm not sure which are the westerlies here:

[ORH_wxman]

That's a weak negative NAO...but its pretty displaced to the southeast. So it certainly wouldn't be your typical/classic -NAO. Being weak and poorly placed, it gets dominated by that monster vortex in the PNA region and we all torch.

[weatherwiz]

That's a weak negative NAO...but its pretty displaced to the southeast. So it certainly wouldn't be your typical/classic -NAO. Being weak and poorly placed, it gets dominated by that monster vortex in the PNA region and we all torch.

Thanks!

Man, compiling this list is going to take me forever.

Considering there are 52 weeks in a year and 60 years for the dataset that's 3,120 weeks to classify!

Just started on 1953.

[ORH_wxman]

Thanks!

Man, compiling this list is going to take me forever.

Considering there are 52 weeks in a year and 60 years for the dataset that's 3,120 weeks to classify!

Just started on 1953.

CPC method has it as a positive NAO but SLP would have it as a negative NAO...either way, its pretty pathetic looking.

[mahk_webstah]

Yes it hit the Delmarva peninsula and extreme SE NJ near ACY...then it hammered Cape Cod. We only got about 4" here. 1-2 feet was forecasted the day before.

I didn't know it at the time, but I actually lucked out with 4", apparently NYC to PHL was supposed to also see 1-2 feet, but they got nothing at all but overcast skies.

I lived in Center City Philly at the time. Oh the horror! Watching these bands spin 30 miles to my east and seeing the vid from Atlantic City of a blizzard. Happened a couple of times that winter. Didn't chase because it was supposed to be snowing heavily in the city. I kept having radarluccinations thinking that it was pushing back west. We all know that sickening feeling....had it 3 times just last season.

That being said there were some good winters in the late 80s in Philly, where snow cover stayed around even in the city.

[HoarfrostHubb]

I hope this is like an "Ask a Met" thing: what does Archambault mean?

I assume some type of setup named for whoever first quantified it?

Thanks in advance

[OKpowdah]

I hope this is like an "Ask a Met" thing: what does Archambault mean?

I assume some type of setup named for whoever first quantified it?

Thanks in advance

This observational study investigates statistical and synoptic–dynamic relationships between regime transitions, defined as a North Atlantic Oscillation (NAO) or Pacific–North American pattern (PNA) index change from at least a 1 standard deviation anomaly to at least a 1 standard deviation anomaly of opposite sign within 7 days, and cool-season (November–April) northeastern U.S. (NE) precipitation. A statistical analysis is performed of daily cool-season NE precipitation during all NAO and PNA transitions for 1948–2003, and a composite analysis and case study of a major cool-season NE precipitation event occurring during a positive-to-negative NAO transition are conducted. Datasets used are the 0.25° NCEP Unified Precipitation Dataset, the 2.5° NCEP–NCAR reanalysis, and the 1.125° 40-yr ECMWF Re-Analysis (ERA-40).

Results of the statistical analysis suggest that cool-season NE precipitation tends to be enhanced during positive-to-negative NAO and negative-to-positive PNA transitions, and suppressed during negative-to-positive NAO and positive-to-negative PNA transitions. Of the four types of regime transitions, only the positive-to-negative NAO transition is associated with substantially more frequent major cool-season NE precipitation events compared to climatology. Results of the composite analysis and case study indicate that a surface cyclone and cyclonic wave breaking associated with the major NE precipitation event can help produce a high-latitude blocking pattern over the North Atlantic characteristic of a negative NAO pattern via thermal advection, potential vorticity transport, and diabatic processes.

http://journals.amet...5/2010MWR3362.1