Thanksgiving Week Nor'easter Discussion

[96blizz]

Yet again... (GFS + Euro) / 2 = FTW!

[IsentropicLift]

That lead vort on the GFS actually makes a lot of sense if it's legit and explains some of the reasons why the non-phased solutions have been showing multiple lows. That lead vort then blows up and kicks everything east.

[WeatherFox]

That lead vort on the GFS actually makes a lot of sense if it's legit and explains some of the reasons why the non-phased solutions have been showing multiple lows. That lead vort then blows up and kicks everything east.

For the record, NWS Forecast 9:40 AM Nov 22, 2013:

 

WEDNESDAY...CLOUDY. A CHANCE OF RAIN AND SNOW IN THE MORNING...THEN

A CHANCE OF RAIN IN THE AFTERNOON. BREEZY WITH HIGHS IN THE MID 40S.

CHANCE OF PRECIPITATION 50 PERCENT.

WEDNESDAY NIGHT...MOSTLY CLOUDY. A CHANCE OF RAIN AND SNOW IN THE

EVENING...THEN A CHANCE OF SNOW AFTER MIDNIGHT. WINDY WITH LOWS IN

THE UPPER 20S. CHANCE OF PRECIPITATION 40 PERCENT.

 

Snow showers and temps in the upper 20's could give us a dusting!

[eduggs]

because the pattern is progressive like i've been saying for the past two days

I think "progressive pattern" is one of the most overused and meaningless phrases that gets repeated to death on these boards.  Even the concept of a pattern is misunderstood.  Weather in the mid latitudes is always progressive.  Though it varies by degree or rate of progression. Storms form and intensify all the time in regimes that lack "blocking" to impede longitudinal flow progression.

 

I favor a suppressed solution because that's what the majority of model guidance has suggested over the past few days.  And because of the modeled orientation of the polar jet with multiple s/w's imbedded in the flow - which creates a higher than normal likelihood of wave interference problems.  Not because of some hasty interpretation of the "pattern"... which itself could change as a result of a particular storm.  Models interpret synoptic scale meteorology much better than humans.  If the GFS or Euro or GEM shows a particular solution, it could probably physically happen.  Storms have wrapped up into the Lakes region numerous times in similar patterns.

[Weathergun]

The 12z GGEM appears to be inland runner. 992mb low over NNE

 

[eduggs]

The 12z operational GFS is certainly a lot less interesting than the previous two runs.  Despite being much further east, it's only marginally cooler near 850mb and maybe even warmer at the surface.

 

But we expect this to happen.  Semi consensus from last night's midrange guidance was something of a fluke.  There will likely continue to be large inter and intra model differences.  I'd rather see guidance offshore than into the lakes at this point.

[KEITH L.I]

As much as I think Forky is a troll, he is right in this case. The pattern is very progressive and it's going to make a snowy solution very difficult. Especially for the I-95 crew east.

GFS ensembles are tucked in near the coast..rain verbatim on the coast,but I think there will be a storm with heavy precip amounts

[Wxoutlooksblog]

I think "progressive pattern" is one of the most overused and meaningless phrases that gets repeated to death on these boards.  Even the concept of a pattern is misunderstood.  Weather in the mid latitudes is always progressive.  Though it varies by degree or rate of progression. Storms form and intensify all the time in regimes that lack "blocking" to impede longitudinal flow progression.

 

I favor a suppressed solution because that's what the majority of model guidance has suggested over the past few days.  And because of the modeled orientation of the polar jet with multiple s/w's imbedded in the flow - which creates a higher than normal likelihood of wave interference problems.  Not because of some hasty interpretation of the "pattern"... which itself could change as a result of a particular storm.  Models interpret synoptic scale meteorology much better than humans.  If the GFS or Euro or GEM shows a particular solution, it could probably physically happen.  Storms have wrapped up into the Lakes region numerous times in similar patterns.

I think you're completely wrong. I think the overall pattern dictates the eventual outcome more than what ANY model guidance suggests. If you understand the pattern you are in, you understand where the players on the maps will most likely end up. The models can digest the data and spit out solutions, but if anything, ANY data, is even slightly different by the time the model spits out a subsequent solution, it will throw the solution off entirely usually correcting it toward the result the overall pattern would yield.

WX/PT

[eduggs]

The 12z GGEM appears to be inland runner. 992mb low over NNE

 

Yeah, sure is.  Hits SYR, western Adks and up into Montreal pretty hard with snow.  Big rain producer.

 

Blows up a polar s/w and then phrases a lot of it with the cutoff.  I'd rather see coastal grazer solutions at this stage, but if anything is going to over-wrap a low, I'd rather it be the CMC.  GGEM west and GFS east seems to be a natural historical fit.  Both are easily within the multi guidance ensemble spread.  Full suite of options available.

[Wxoutlooksblog]

I think you're completely wrong. I think the overall pattern dictates the eventual outcome more than what ANY model guidance suggests. If you understand the pattern you are in, you understand where the players on the maps will most likely end up. The models can digest the data and spit out solutions, but if anything, ANY data, is even slightly different by the time the model spits out a subsequent solution, it will throw the solution off entirely usually correcting it toward the result the overall pattern would yield.

WX/PT

And further, if you understand this pattern and climo, you understand the probability of a perfect track that would yield snow at the coast, acccumlating snow at the coast, is highly unlikely. Firstly, in order for this storm to climb the coast, the flow of cold air into the area has to be shut off. You have a pattern in which, if you get the right track, you lose the cold air, if you get the cold air, you lose the right track.

WX/PT

[Wxoutlooksblog]

Yeah, sure is.  Hits SYR, western Adks and up into Montreal pretty hard with snow.  Big rain producer.

 

Blows up a polar s/w and then phrases a lot of it with the cutoff.  I'd rather see coastal grazer solutions at this stage, but if anything is going to over-wrap a low, I'd rather it be the CMC.  GGEM west and GFS east seems to be a natural historical fit.  Both are easily within the multi guidance ensemble spread.  Full suite of options available.

I think an inland runner is more likely than a track that would bring accumulating snow here. I still favor the OTS track above all other solutions, but not by that much over the inland runner idea.

WX/PT

[Weathergun]

12z UKMET has a partial phase and coastal hugger:

 

[eduggs]

I think you're completely wrong. I think the overall pattern dictates the eventual outcome more than what ANY model guidance suggests. If you understand the pattern you are in, you understand where the players on the maps will most likely end up. The models can digest the data and spit out solutions, but if anything, ANY data, is even slightly different by the time the model spits out a subsequent solution, it will throw the solution off entirely usually correcting it toward the result the overall pattern would yield.

WX/PT

I see where you are coming from and I respectfully disagree.

 

I think you have the causal relationship backwards.  I don't believe patterns dictate weather outcomes.  Rather, weather outcomes (or a collection of numerical values tabulated from physical parameters) define patterns. 

 

The progression of weather is driven by physics.  The models "know" this physics - at least as well as can be approximated with equations and encoded in software.  The characteristic state of the atmosphere (pattern) today and the state of the atmosphere next week are correlated.  I think that's why so many people have come to believe that patterns drive the weather.  But one does not cause the other.  They are correlated because they are part of the same sequence, driven by external forces.  Without modeling the physics somehow,  we would just be blindly guessing how we get from the first state to the second.  Patterns are just descriptions.  They can change.  And without models, we wouldn't be able to see how and when a pattern might change.

[uncle W]

the ice storm predicted for Dallas reminds me of a football game on TV from Dallas in late November with ice and rain...that was in 1993...plenty of low level cold air back then and this year is starting out the same way...

[Wxoutlooksblog]

12z UKMET has a partial phase and coastal hugger:

 

This is also a possibility that would bring little or no accumulation of snow to the coastal areas and big cities. But still looks like we will eventually go all one way or the other to me, OTS or on the coast/inland of the coast.

WX/PT

[Wxoutlooksblog]

I see where you are coming from and I respectfully disagree.

 

I think you have the causal relationship backwards.  I don't believe patterns dictate weather outcomes.  Rather, weather outcomes (or a collection of numerical values tabulated from physical parameters) define patterns. 

 

The progression of weather is driven by physics.  The models "know" this physics - at least as well as can be approximated with equations and encoded in software.  The characteristic state of the atmosphere (pattern) today and the state of the atmosphere next week are correlated.  I think that's why so many people have come to believe that patterns drive the weather.  But one does not cause the other.  They are correlated because they are part of the same sequence, driven by external forces.  Without modeling the physics somehow,  we would just be blindly guessing how we get from the first state to the second.  Patterns are just descriptions.  They can change.  And without models, we wouldn't be able to see how and when a pattern might change.

Of course they can change and of course they effect each other. But a long term pattern is extremely difficult to break and you really have to see the larger overall pattern change. The maps the models generate will pick up on the large-scale changes. The key is this, usually when it happens, it happens over time, not overnight. And, usually when it is on the verge of happening, which I think it is, and I have stated that, the models will usually go too far initially, and then correct toward backing off of it at least partially as you ease into the change over time.

WX/PT

[eduggs]

And further, if you understand this pattern and climo, you understand the probability of a perfect track that would yield snow at the coast, acccumlating snow at the coast, is highly unlikely. Firstly, in order for this storm to climb the coast, the flow of cold air into the area has to be shut off. You have a pattern in which, if you get the right track, you lose the cold air, if you get the cold air, you lose the right track.

WX/PT

I think accumulating snowfall to the coast is unlikely.  I've stated in numerous times since Wed.  But reading the "pattern" tea leaves does not lead me to this conclusion. 

 

Coastal snowfall is generally unlikely even in the heart of winter.  A perfect track is almost always needed.  Deep antecedent cold air helps a lot, but even in these scenarios, the coast usually mixes or changes over in the bigger nor'easters.  It's basic NYC climo.

 

But I fully believe that accumulating snow is POSSIBLE all the way to the coast, regardless of the pattern progression, or lack of blocking, or NAO state or whatever else you want to use to define the pattern.  I believe it because a few operational runs as well as a respectable minority of ensemble runs have shown accumulating snowfall scenarios.  It's plausible.  Yes, the h5 pattern would have to evolve delicately to lock in enough cold air while wrapping in enough moisture.  But at least as the low center reaches our latitude we could have a chance to change over to snow, even if most falls as rain.  I don't expect it, but I would certainly not call it impossible.

[Wxoutlooksblog]

I think accumulating snowfall to the coast is unlikely.  I've stated in numerous times since Wed.  But reading the "pattern" tea leaves does not lead me to this conclusion. 

 

Coastal snowfall is generally unlikely even in the heart of winter.  A perfect track is almost always needed.  Deep antecedent cold air helps a lot, but even in these scenarios, the coast usually mixes or changes over in the bigger nor'easters.  It's basic NYC climo.

 

But I fully believe that accumulating snow is POSSIBLE all the way to the coast, regardless of the pattern progression, or lack of blocking, or NAO state or whatever else you want to use to define the pattern.  I believe it because a few operational runs as well as a respectable minority of ensemble runs have shown accumulating snowfall scenarios.  It's plausible.  Yes, the h5 pattern would have to evolve delicately to lock in enough cold air while wrapping in enough moisture.  But at least as the low center reaches our latitude we could have a chance to change over to snow, even if most falls as rain.  I don't expect it, but I would certainly not call it impossible.

I never said it was "impossible".

WX/PT

[jm1220]

I actually disagree. If you take the 12z gfs solution but bomb the low or phase faster and bring it further west, then even the coast would be in play for some snow. It's not like there is no cold air in place where we sometimes see coastals in January fail to produce snow even in higher elevations. 

What mechanism though is going to force the faster phase? There is no block, which would buckle the northern jet and force it to dive south, and there isn't that huge of a PNA ridge. Therefore, the northern stream is kept north and flatter. The storm we are seeing now is driven completely by the southern stream. As such, it could generate a lot of rain because it's juicy, but the only way there is a lot of snow available is if the northern stream dives in faster. And for that even, we have to hope the ridge over the Atlantic is sharp enough to force a left turn. If not, it will be a fish storm. If it does phase quicker, there's the risk of a sharp inland turn and a bigger snow event for the Appalachians but just a warmer rain here.

 

I just don't see (for us) what there is to get excited about besides some needed rain if the sharp ridge works out.

[Weathergun]

Can't post it here. 12z GEFS mean has a 1000mb low just south of Eastern LI, over 40N at 126hr. Well west of the op GFS.

 

GEFS control member has 985mb low east DE then a 976mb low over the Gulf of Maine. Likely why the GEFS is so amped.

[eduggs]

I think an inland runner is more likely than a track that would bring accumulating snow here. I still favor the OTS track above all other solutions, but not by that much over the inland runner idea.

WX/PT

I'm in complete agreement here.  Said almost the same last night.  Slightly favor OTS, but if not, I would expect something further west than last night's consensus.  An ideal snow track is much lower on my list of likely general outcomes.

[SnoSki14]

Ultimately it'll be probably be in the upper 30s with a cold rain for us. Pattern continues to look interesting heading forward though.

[Wxoutlooksblog]

I'm in complete agreement here.  Said almost the same last night.  Slightly favor OTS, but if not, I would expect something further west than last night's consensus.  An ideal snow track is much lower on my list of likely general outcomes.

An ideal snow track in this case would probably not bring much if any snow to the coast and NYC, that's the problem for snowlovers. Yes, that track is lowest on my likely general outcomes, but the other problem is that the source of cold air is exiting into the Atlantic and being cut off while the new cold airmass is not in the ideal position being way too far to the west.

WX/PT

[eduggs]

Of course they can change and of course they effect each other. But a long term pattern is extremely difficult to break and you really have to see the larger overall pattern change. The maps the models generate will pick up on the large-scale changes. The key is this, usually when it happens, it happens over time, not overnight. And, usually when it is on the verge of happening, which I think it is, and I have stated that, the models will usually go too far initially, and then correct toward backing off of it at least partially as you ease into the change over time.

WX/PT

Well said, but I have a different philosophy.  I think the commercial forecasters have infected the masses and younger Met students with misleading terminology and partial understanding.  Starting with Gary Grey, and on to DT and the crazies at Accuweather.  Personally, I think you are a good forecaster, and I'm not trying to lump you in with them.  But concepts like snowstorms can't happen without a 50/50 low are ludicrous and just spread confusion.  I've been digesting models and following the weather for 20 years and I can't count how many times a forecaster said a particular outcome could not happen because the pattern didn't support it... only to have it happen.  To me it's kind of maddening to hear people say they can interpret the future implication of a pattern by looking at a few charts or reading a few numerical indices off a scream, better than supercomputers that compute billions of calculations a second.  We are just not that good at interpreting synoptic patterns.  It's WAY too complicated for simple definitions.  What "pattern" are we even in.  Just makes me shake my head.  I believe the meteorologist still has an important role to play in the understanding of regional and local weather climo.  But when we try to out-forecast the global models or make long term forecasts, we usually just look stupid.

 

Regardless, despite our philosophical differences, I think we have come to the same conclusions with regard to outcome likelihoods for next week.  I suspect we are seeing the same things and making similar conclusions but describing the reasoning with different terms.

[snywx]

I never said it was "impossible".

WX/PT

I think it has been stated numerous times already that this isn't a threat for NYC & points east.  Anyone 30+ miles NW of NYC should be monitoring this.

[96blizz]

Question for the mets / more experienced crew.  If the GEFS and other Ensembles like the Euro are the mean of a lot of different runs, why is it that we look so hard at the operational runs?  Is there something about the operational that makes it 'better' than the ensembles, or is it just that it comes out first? 

 

Thanks, in advance. 

[bluewave]

Euro west of GFS through 102.

[eduggs]

An ideal snow track in this case would probably not bring much if any snow to the coast and NYC, that's the problem for snowlovers. Yes, that track is lowest on my likely general outcomes, but the other problem is that the source of cold air is exiting into the Atlantic and being cut off while the new cold airmass is not in the ideal position being way too far to the west.

WX/PT

It's not a perfect setup, but it almost never is.

Just looking at the 12z  GFS temp profiles.  KNYC at hour 120 has a wet bulb temp below 1000mb.  That would be snow.  Surface temps don't look to increase much during the day with a north wind and limited solar heating.  850mb and esp just above is marginal... but I believe supportive of snow from nyc metro north and west.  Rough est from the charts would be about .1 - .6 liquid eq. west to east across the area.  I don't love the GFS solution, but I think it depicts accumulating snow for many.  And that's pretty exciting for the day before Thanksgiving.

 

I think we could get a closer track without a warmer profile.  The cold air is not locked too far to the west.  It is not ideally located either.  I just don't think this is as hopeless as you seem to describe.  Maybe I just have low expectations for snow in general, and so I consider any trackable snow threat kind of exciting.  To me, this is a legit threat.  I would put probs of >1" of snow for the metro region at somewhere between 10 and 25%.

[snywx]

Upton:

 

ALL EYES TURN TOWARD THE GULF STATES AS LOW PRESSURE
TRACKS TOWARD THE SOUTHEASTERN UNITED STATES MONDAY NIGHT AND
TUESDAY AHEAD OF SOUTHERN STREAM TROUGH. A COLD FRONT TO THE WEST
APPROACHES AS WELL...ASSOCIATED WITH NORTHERN STREAM TROUGH. THE
SOUTHERN LOW MOVES NORTHEAST...WITH TIMING...POSITIONAL AND STRENGTH
DIFFERENCES NOTED. HOWEVER..G J.IT DOES APPEAR THAT THIS SYSTEM WILL

HAVE SOME IMPACT ON THE LOCAL AREA...LIKELY TRACKINUST SOUTH AND
EAST OF THE AREA.

AS FOR SENSIBLE WEATHER...A FEW SNOW SHOWERS OR FLURRIES ARE
POSSIBLE SAT NIGHT AND INTO SUNDAY. LIMITED MOISTURE WITH THE
FRONT/UPPER TROUGH THOUGH...SO NOT MUCH PRECIP EXPECTED WITH THIS.

DRY WEATHER SUNDAY NIGHT THROUGH MONDAY NIGHT AS HIGH PRESSURE
BUILDS.

THEN CHANCES FOR PRECIP INCREASE TUESDAY THROUGH WEDNESDAY...WITH
THE HIGHEST CHANCE WEDNESDAY AND WEDNESDAY NIGHT.

OVERALL...RAIN/SNOW OR SNOW NW ZONES...WITH MAINLY RAIN CLOSER TO
THE COAST TUESDAY AND TUESDAY NIGHT...IF ANY PRECIP DOES INDEED
OCCUR.

THEN A NW TO SE RAIN TO SNOW TRANSITION WOULD LIKELY OCCUR WEDNESDAY
AND WEDNESDAY NIGHT AS COLDER AIR MOVES IN ON NORTH FLOW. STAY
TUNED...BUT WOULD GENERALLY EXPECT RAIN TO SNOW AS THE DAY
PROGRESSES WEDNESDAY AND INTO WEDNESDAY NIGHT.

AGAIN...PLENTY OF TIME TO FINE TUNE DETAILS THOUGH.

[Dsnowx53]

Well said, but I have a different philosophy.  I think the commercial forecasters have infected the masses and younger Met students with misleading terminology and partial understanding.  Starting with Gary Grey, and on to DT and the crazies at Accuweather.  Personally, I think you are a good forecaster, and I'm not trying to lump you in with them.  But concepts like snowstorms can't happen without a 50/50 low are ludicrous and just spread confusion.  I've been digesting models and following the weather for 20 years and I can't count how many times a forecaster said a particular outcome could not happen because the pattern didn't support it... only to have it happen.  To me it's kind of maddening to hear people say they can interpret the future implication of a pattern by looking at a few charts or reading a few numerical indices off a scream, better than supercomputers that compute billions of calculations a second.  We are just not that good at interpreting synoptic patterns.  It's WAY too complicated for simple definitions.  What "pattern" are we even in.  Just makes me shake my head.  I believe the meteorologist still has an important role to play in the understanding of regional and local weather climo.  But when we try to out-forecast the global models or make long term forecasts, we usually just look stupid.

 

Regardless, despite our philosophical differences, I think we have come to the same conclusions with regard to outcome likelihoods for next week.  I suspect we are seeing the same things and making similar conclusions but describing the reasoning with different terms.

 

 

I think you make a lot of good points. 

 

However, I think it makes much more sense that in a medium-range forecast, computer model guidance will be much better at predicting what is going on in the larger scales of things. It is easier for a computer to predict a fast flow because all that needs to happen for one is ridging getting into Canada, and low heights poleward of that, creating an intense gradient. That is a lot easier for a computer to nail down than say the nuances and intricacies of wave interference and exact positioning of shortwave troughs.

 

Based on this, we can make some assumptions about the medium-range pattern going forward, and that any shortwave trough that does form should be in a pretty fast flow.