The Winter 2010-11 NYC/PHL Medium Range Thread

[Sundog]

IDEAL is rare, I think the point I was trying to make is we don't need ideal to get snow, even at the end of November.

Certainly as you get deeper into the winter less than ideal works more times than not, a good example, Feb 06. NAO just got enough west based with a just barely good enough 50/50. Most certainly that setup would NOT work earlier in the winter.

I am NAO'ed out....LOL.

Just wondering, who were you before on Eastern? Btw I love the name and sig lol. One of the best characters ever.

[am19psu]

My major concern regarding the post-Thanksgiving cold flip is the persistence of the SE ridge. Even with a blocked up Atlantic, Philly southward will stay at or above normal if the ridge remains robust off the SE Coast. It may be different now that we are dealing with stronger temperature gradients (and therefore more baroclinic forcing), but all summer, the models were too quick to break down the SE ridge.

I'm still forecasting the cold after Thanksgiving, but I'm far less confident tonight than I was three days ago.

Oh, and tombo, I posted the D8/D10 verifications a few pages back

[tombo82685]

My major concern regarding the post-Thanksgiving cold flip is the persistence of the SE ridge. Even with a blocked up Atlantic, Philly southward will stay at or above normal if the ridge remains robust off the SE Coast. It may be different now that we are dealing with stronger temperature gradients (and therefore more baroclinic forcing), but all summer, the models were too quick to break down the SE ridge.

I'm still forecasting the cold after Thanksgiving, but I'm far less confident tonight than I was three days ago.

Oh, and tombo, I posted the D8/D10 verifications a few pages back

thanks....what causes the se ridge to be so pronounced?

[A-L-E-X]

For whatever reason the last 5 years or so the NAO when its been negative has had a pronounced tendency to be east based vs. west....I'm not sure why this has been occurring but its been a notable trend for sure.

Is there any site that catalogs west vs east based NAO?  This would seem to be such an easy thing to keep track of-- I dont know why they dont it automatically.

Ive heard that an east based neg nao is worse than a positive nao.

Question, if an east based neg nao is bad, does that mean that an east based pos nao is good?

[Guest Kramer]

timberrrr on both indices. Something tells me its going to be like pulling teeth to get that pna pos this winter.

While the PNA isn't "red" there, its still going from deeply negative to almost neutral which works for east coast cyclogensis.

[jrodd321]

While the PNA isn't "red" there, its still going from deeply negative to almost neutral which works for east coast cyclogensis.

Yep, which is clearly shown with that storm both models are depicting around the 26/27 timeframe.

[am19psu]

thanks....what causes the se ridge to be so pronounced?

This isn't my area of expertise, but I've always rationalized the SE ridge associated with La Nina to be associated with the lack of a subtropical jet. When there is no subtropical jet forced by the SST pattern (i.e. there is a weaker temperature gradient between the tropics and subtropics in the East Pac), cutoff lows/-PNA patterns are more likely over the West. The resulting warm advection then pumps up the ridge over the Southeast/SW Atlantic. Once forming, the ridges are relatively steady state until shortwave activity riding over top the ridge advects cold air southward, weakening the ridge.

[A-L-E-X]

This isn't my area of expertise, but I've always rationalized the SE ridge associated with La Nina to be associated with the lack of a subtropical jet. When there is no subtropical jet forced by the SST pattern (i.e. there is a weaker temperature gradient between the tropics and subtropics in the East Pac), cutoff lows/-PNA patterns are more likely over the West. The resulting warm advection then pumps up the ridge over the Southeast/SW Atlantic. Once forming, the ridges are relatively steady state until shortwave activity riding over top the ridge advects cold air southward, weakening the ridge.

Youd like Rob Guarino's forecast-- he has it staying mild through Thanksgiving and the first part of December-- said December will be a tease and January will be a torch but the big snow and cold month will be February.

[A-L-E-X]

This isn't my area of expertise, but I've always rationalized the SE ridge associated with La Nina to be associated with the lack of a subtropical jet. When there is no subtropical jet forced by the SST pattern (i.e. there is a weaker temperature gradient between the tropics and subtropics in the East Pac), cutoff lows/-PNA patterns are more likely over the West. The resulting warm advection then pumps up the ridge over the Southeast/SW Atlantic. Once forming, the ridges are relatively steady state until shortwave activity riding over top the ridge advects cold air southward, weakening the ridge.

east based neg nao also amplifies any south east ridge.... the reinforcement from both the pacific and the atlantic makes it a stable pattern.

[am19psu]

Youd like Rob Guarino's forecast-- he has it staying mild through Thanksgiving and the first part of December-- said December will be a tease and January will be a torch but the big snow and cold month will be February.

Where I've been at for the last week or so is warm until Thanksgiving, cold through Nov 30, then AOA normal through the first week in December as the +EPO sets up forced by the MJO moving into P3-P4. But I'm far from a good medium range synoptic forecaster and the better guys like HM, Wes, Gibbs, et al. are all talking about the cold after Thanksgiving lingering through Dec 10 or so. Like I said earlier, I'd trust their word over mine.

Plus, I'm not entirely sure how to deal with a +EPO/-NAO pattern with the potential for ridging in the Southeast. If there is less ridging, the -NAO might set the mean longwave trough over the Great Lakes, which would keep us cold and wet, but not snowy. All it would take is one negatively tilted, strong shortwave for a Miller B to set up - which reading between the lines sounds a lot like what the medium range crew is talking about in the main forum.

[am19psu]

east based neg nao also amplifies any south east ridge.... the reinforcement from both the pacific and the atlantic makes it a stable pattern.

I'd argue you have the causation backwards, but otherwise I agree.

[tombo82685]

Where I've been at for the last week or so is warm until Thanksgiving, cold through Nov 30, then AOA normal through the first week in December as the +EPO sets up forced by the MJO moving into P3-P4. But I'm far from a good medium range synoptic forecaster and the better guys like HM, Wes, Gibbs, et al. are all talking about the cold after Thanksgiving lingering through Dec 10 or so. Like I said earlier, I'd trust their word over mine.

Plus, I'm not entirely sure how to deal with a +EPO/-NAO pattern with the potential for ridging in the Southeast. If there is less ridging, the -NAO might set the mean longwave trough over the Great Lakes, which would keep us cold and wet, but not snowy. All it would take is one negatively tilted, strong shortwave for a Miller B to set up - which reading between the lines sounds a lot like what the medium range crew is talking about in the main forum.

lol ugh, this could be a long winter.

[SnowGoose69]

This isn't my area of expertise, but I've always rationalized the SE ridge associated with La Nina to be associated with the lack of a subtropical jet. When there is no subtropical jet forced by the SST pattern (i.e. there is a weaker temperature gradient between the tropics and subtropics in the East Pac), cutoff lows/-PNA patterns are more likely over the West. The resulting warm advection then pumps up the ridge over the Southeast/SW Atlantic. Once forming, the ridges are relatively steady state until shortwave activity riding over top the ridge advects cold air southward, weakening the ridge.

Those classic ridges all tend to be hard to displace once they get locked in...the +PNA pattern though with the ridge over the Western US is often a much tougher pattern to get rid of than is the SE ridge....generally if you see that western ridge set in during late November and early December it seems to be very hard to get rid of it the rest of the winter.

[tombo82685]

Those classic ridges all tend to be hard to displace once they get locked in...the +PNA pattern though with the ridge over the Western US is often a much tougher pattern to get rid of than is the SE ridge....generally if you see that western ridge set in during late November and early December it seems to be very hard to get rid of it the rest of the winter.

is it the same for a -pna pattern?

[Chris L]

Just wondering, who were you before on Eastern? Btw I love the name and sig lol. One of the best characters ever.

George Costanza is funnier than Kramer (No Offense Kramer)

If I were to rank....

1.George

2.Kramer

3.Jerry

4.Elaine.

[Sundog]

George Costanza is funnier than Kramer (No Offense Kramer)

If I were to rank....

1.George

2.Kramer

3.Jerry

4.Elaine.

To me George and Kramer are basically tied for 1st place. Then Jerry, then Elaine.

[Alpha5]

Its all in the PNA

The GFS had a great MECS at 12z while the Euro had a GLC....look at the pacific and the +PNA trying to develop on the GFS which funnels the cold air down into the central/east us, while the euro shows a strongly -PNA and a SE ridge as well

Both models have a very strong -NAO (looks like it might be west based) block, both models are showing the block over the Aleutians, there main disagreement is with the PNA

[tombo82685]

Its all in the PNA

The GFS had a great MECS at 12z while the Euro had a GLC....look at the pacific and the +PNA trying to develop on the GFS which funnels the cold air down into the central/east us, while the euro shows a strongly -PNA and a SE ridge as well

Both models have a very strong -NAO (looks like it might be west based) block, both models are showing the block over the Aleutians, there main disagreement is with the PNA

if we can hold onto the -nao through the winter we could be ok even if its a -pna. Will posted in the general forum that atleast in the northeast, not sure about down here that years with a -nao and -pna were cold and snowy up there. Again, someone would have to dig up years with a -pna and -ano and see how they faired down here.

[tombo82685]

if we can hold onto the -nao through the winter we could be ok even if its a -pna. Will posted in the general forum that atleast in the northeast, not sure about down here that years with a -nao and -pna were cold and snowy up there. Again, someone would have to dig up years with a -pna and -ano and see how they faired down here.

will made a list of the yrs since 1980 with a -nao and -pna

84-85

08-09

81-82 (was close, but the nao was smidge pos for the winter)

snowfall for philly those years:

84-85 16.5

08-09 22.8

81-82 25.4

basically its right around avg maybe a smidge abv

for abe

84-85 24.2

08-09 24.1

81-82 43.9

[A-L-E-X]

I'd argue you have the causation backwards, but otherwise I agree.

so the se ridge causes the east based nao?

I figured the pacific caused the east based nao and the two together cause the se ridge to amplify, but Im probably off lol.

[ORH_wxman]

will made a list of the yrs since 1980 with a -nao and -pna

84-85

08-09

81-82 (was close, but the nao was smidge pos for the winter)

snowfall for philly those years:

84-85 16.5

08-09 22.8

81-82 25.4

basically its right around avg maybe a smidge abv

for abe

84-85 24.2

08-09 24.1

81-82 43.9

The full list since 1950 (if you include the borderline '81-'82 year) is:

1955-1956

1961-1962

1964-1965

1965-1966

1967-1968

1968-1969

1970-1971

1978-1979

1981-1982

1984-1985

2008-2009

[A-L-E-X]

Where I've been at for the last week or so is warm until Thanksgiving, cold through Nov 30, then AOA normal through the first week in December as the +EPO sets up forced by the MJO moving into P3-P4. But I'm far from a good medium range synoptic forecaster and the better guys like HM, Wes, Gibbs, et al. are all talking about the cold after Thanksgiving lingering through Dec 10 or so. Like I said earlier, I'd trust their word over mine.

Plus, I'm not entirely sure how to deal with a +EPO/-NAO pattern with the potential for ridging in the Southeast. If there is less ridging, the -NAO might set the mean longwave trough over the Great Lakes, which would keep us cold and wet, but not snowy. All it would take is one negatively tilted, strong shortwave for a Miller B to set up - which reading between the lines sounds a lot like what the medium range crew is talking about in the main forum.

Hmmmm, it makes me wonder if they might be talking about a storm similar to what we had in early Nov-- that kind of retrograding storm is extremely hard to model.

[tombo82685]

The full list since 1950 (if you include the borderline '81-'82 year) is:

1955-1956

1961-1962

1964-1965

1965-1966

1967-1968

1968-1969

1970-1971

1978-1979

1981-1982

1984-1985

2008-2009

thanks Will, do you know any place where i can get snowfall data for philly going back to the 50s?

[phlwx]

0z euro goes cool/cold after Turkey day similar to the GFS...we'll see if the shift becomes a trend

[tombo82685]

looks like the euro gave in. 0z euro brings the cold air in thanksgiving day. At day 10 of the euro, it still has a decent west based -nao but it may be a little displaced to the north, also a nice ridge trying to build just off the west coast. Big difference between the 12z run and this 0z run is the pacific. The euro builds the a healthy ridge out west like the gfs was showing allowing for a deep trof to come into the east..

[phlwx]

looks like the euro gave in. 0z euro brings the cold air in thanksgiving day. At day 10 of the euro, it still has a decent west based -nao but it may be a little displaced to the north, also a nice ridge trying to build just off the west coast. Big difference between the 12z run and this 0z run is the pacific. The euro builds the a healthy ridge out west like the gfs was showing allowing for a deep trof to come into the east..

Looks like 40's from NYC on south for highs after Thursday...30's in the mountains, perhaps a day of around 40 in the cities on Black Friday. Nothing historic but a decent early season cold shot if this is right.

[Quakertown needs snow]

nice to see to euro bringing back the chill.

its a start.

[am19psu]

so the se ridge causes the east based nao?

Yeah. The NWrly flow/cold advection on the eastern side of the ridge leads to a trough in the Central Atlantic, which then pumps a ridge up over the E Atlantic. At least that's the way I always envision the cause/effect.

[Quakertown needs snow]

for what its worth, JB mentions this am COLDEST ENDING TO NOVEMBER SINCE 1996.

[earthlight]

Man, the 00z Euro was an absolute beauty. Absolutely tremendous above average anomalies (+50dm!!) over Greenland (albeit a bit further north than one might ideally want), some ridging over the west coast, which hints at a neutral or positive PNA, and a well timed Aleutian trough, all leading to a broad mean trough over the East. The likely result would be the development of much colder air on our side of the pole feeding into Southeast Canada and the Northeast..with the potential increasing for frozen precipitation near Day 10+. The GFS isn't far off either, but the Pacific has a slightly different tune with a big ridge still just west of the Aleutians in the Central Pacific. This could still bring us a favorable longwave pattern given the NAO and North Atlantic setup. The problem with the ECMWF solution, as it is, could be the duration of the cold air supply...as the downstream ridge over the Central/West US is propagating east pretty fast--and given how fast the Pacific has been recently, this may suggest a quick end to the cold air and -/+ PNA regime.