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Vendor Forecast Discussion

am19psu

By am19psu,
in Philadelphia Region

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Parsley

Parsley

Posted
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Well since we technically fall in the "vendor" forecasts being an accredited LLC in the state of PA, here is the Eastern PA Weather Authority call that encompasses (1) the frontal passage tomorrow morning + Lake effect tomorrow. Issue yesterday morning, no change today.

That's a good looking map IMO, atleast in eastern PA/NJ where we're focused. Definetely see the Poconos squeezing out 1-3" before all is said and done. South of there not much.

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ChescoWx

ChescoWx

Posted
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Latest Tweets from JB at WB

"White Christmas likely 40n all the way to NJ from the "Festivus Miracle" storm US models did not even see 3 days ago"

"Post Christmas Noreaster with heavy inland snows - big cities in battle ground snow/ice/rain - snow to I40 in south - Winter taking over!"

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ChescoWx

ChescoWx

Posted
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Some paraphrased thoughts from Steve D over at NJ PA weather -

He mentions with the position of the upper level low this morning and the way the 500 MB pattern is locking in disturbances that approaches the Philadelphia and New York City metropolitan areas (Christmas eve) will likely feature a track from the Ohio River Valley to the Delmarva or the SJ coast. Monday night the storm will start to interact with the Atlantic Ocean leading to a rapid expansion of the precip which will spread into both Philly and NYC. He is waiting till tomorrow for a snow map but the further N the track less for NYC and Philly. Regarding his early thoughts - a swath of 2 to 4 or 3 to 6 inch snowfall between late Monday night into Tuesday morning with temps more than cold enough to support accumulating snowfall to the north of the low pressure system track. The other wild card Steve mentions is the potential for rapid intensification as the surface low comes into interaction with the warm waters of the Atlantic and if the storm track is towards the Delmarva it could create an enhancement in lifting to the northwest of the low pressure system and produce a moderate to heavy band of snow. He expects a strong agreement on the model guidance by tonight's Oz runs.

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ChescoWx

ChescoWx

Posted
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Latest from JB after the Warm 12z runs Euro/GFS

"JMA UKMET Canadian all big city heavier options - GFS , EC west - has to do with energy transfer timing and feedback no changes from me"

"Very confident about track to OH - jump to coast - Should mean fight on I95 - Models tend to overdue warm advection/feedback"

"Hint on EC/GFS is less than norm deepening once past 35N so much of model warmth is feedback - probably overestimating warm advection"

"Conversely JMA etc may be underestimating and a bit far east - So I like the blend which is where my idea has been and will remain"

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ChescoWx

ChescoWx

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JB thoughts paraphrased from his evening thoughts...

He mentions he did not expect to see the west look of the GFS and ECMWF - while he won't dismiss them or trash them. He sees three options

1)major low to the lakes 25% chance

2)JMA, UKMET, Canadian idea ( The Canadian ensembles are very far southeast) have a 25% chance

3) In between where he stands with a low to Ohio secondary on the mid atlantic coast to Cape Cod he gives a 50% chance

He sees the more progressive nature of the pattern leading to redevelopment to the east.

He thinks the models taking this up to the west are jumping all over the idea that the system pulls very warm air out of the gulf, feeds back and once the spin up proccess is started sends the low level jet up the west side of the Appalachians even as the natural area of warming with downsloping occurs on the south or southeast wind - he says he has always allowed for that hence his forecast of the primary up west of the mountains with a secondary on the coast.

He says both of these are valid options, but he remains in the middle here - his other problem.. as we get closer to the time that this is all supposed to happen there is more low level cold air around. This is harder to lift and get out of the way. The model suddenly realizes this and flips back. One aspect of the GFS/Euro alliance besides the obvious fact he disagrees is that this system is going to be moving east aloft. There is low level cold air damming into the area that this forces the low to jump to Va rather than offshore he has seen that....but not with highs over Montreal. So for now he holds with both his Christmas eve and 26th forecasts.

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ChescoWx

ChescoWx

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Latest tweet from Steve D at NJ PA Weather

For starters, in the warmer model guidance, the upper low basically collapses and is replaced with an upper low over Ontario. Is this possible? Sure, and I think this is going to happen, but the question is how fast. You see, what we have here are lower heights developing over the northwestern Atlantic and lower heights developing over central Canada. We can thank our changing stratosphere pictured to the left for the cause of this insanity. As you can see, there are warming heights over the northwestern Atlantic and over northwestern Canada pushing our changing weather pattern along. These changes force an upper low to develop towards Ontario and another towards the Canadian Maritimes. As such, there much be building heights over Quebec. This process SHOULD lead to stronger high pressure at the surface around Maine and Quebec due to convergence and confluence, but the warmer models don’t see this. The process though in the colder and much snowier 12Z CMC or Canadian model guidance is slower, keeping the low pressure track for Christmas further south and thus snowier for the northern Mid Atlantic followed by a storm track further east on 12/27 as the blocking is stronger over the Canadian Maritimes as oppose to the upper low over Ontario.

So in short this forecast comes down to which upper level low is strong to drive this weather pattern. If the upper level low is stronger towards Ontario and Manitoba, than the storm track is over the coastal plain and into New England. However, if the upper low over the Canadian Maritimes is strong like seen in the ECMWF Ensembles and CMC guidance this morning, than the track is further south and east.

These question is why I warned not to get into details just yet for Christmas and for the storms that follow and it is why I am not putting out a snow map yet. These unresolved issues stuck out like a soar thumb yesterday and they continue to create high volatility now. We’ll get a lot of information on how this evolves in tonight’s model runs. By then I will have a fair strong handle on the set up for Christmas with a snow map out tomorrow morning, maybe a video too. Then once that storm is handled, everything else through the last week of 2012 will fall into line. Patience is the key. Don’t get worked up right now with snow or no snow at this point. After all, this is the winter. This is what I expected. Each storm will be determined by the interaction of these disturbances. For snow lovers, sometimes you lose and sometime you win big.

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ChescoWx

ChescoWx

Posted
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JB 12/23 AM tweets

"Huge 850 mb temp disagreement with post Christmas storm"

"My take is GFS is overloading feedback and sending too much up west of Apps - storm jumps to VA coast quicker and heads for Cape Cod"

"GFS notorious for model feedback usually OFF east coast but problem is it jumps on first source of warm air - EC snow agrees with us"

"Transfer should occur faster, also front runner should not fall apart as fast. Model focusing on what's behind - Still like Christmas idea"

"Have seen this before, let's see if it holds or GFS scores coup! remember it is the WARMEST of the EC,UKMET, Canadian and JMA so test is there"

"Model problem is estimation of gradient - If it is overwarmed in front it jumps low up. Runs out to seas, it warms too late u see it do this - in any case great pattern - Next storm starts in plains on 28th and reaches East Coast by 30th"

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snowwors2

snowwors2

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JB 12/23 AM tweets

"Huge 850 mb temp disagreement with post Christmas storm"

"My take is GFS is overloading feedback and sending too much up west of Apps - storm jumps to VA coast quicker and heads for Cape Cod"

"GFS notorious for model feedback usually OFF east coast but problem is it jumps on first source of warm air - EC snow agrees with us"

"Transfer should occur faster, also front runner should not fall apart as fast. Model focusing on what's behind - Still like Christmas idea"

"Have seen this before, let's see if it holds or GFS scores coup! remember it is the WARMEST of the EC,UKMET, Canadian and JMA so test is there"

"Model problem is estimation of gradient - If it is overwarmed in front it jumps low up. Runs out to seas, it warms too late u see it do this - in any case great pattern - Next storm starts in plains on 28th and reaches East Coast by 30th"

What, no updates from JB in the past 8 hours?

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ChescoWx

ChescoWx

Posted
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Parapharased Musings from Mr Bastardi this fine Christmas Eve morn...

He likes a widespread 1-2 inch snow amounts tonight ....hard pressed to kick out a 4. He mentions how he is happy he does not jump with each model run and stood his ground on his long forecasted Christmas Festivus miracle snow - doesn't mean he is right but he still thinks modeling is wrong with the snow tonight as he finds it hard to believe it does not snow this afternoon and tonight with wet bulbs in most of the area below 32, light winds and sub 0 5k temps..

With the 26th /27th storm he needs to shift the heaviest snows have EAST and there is more snow back - he still likes the idea of the double barrelled storm, with the primary only reaching to where the true cold boundary from the north gets too and not running north into the lakes - The secondary develops east, but it may use the coastal front to move along, which he admits could mean the track is 75-100 miles west of what he described to his loyal readers at the start of last week. He still sees the snow/ice/rain battle line is close to the big cities of I95 so why change his forecast now? "No reason to jump around. Why not figure things out... call the play , and then wait to see what the defense looks like before changing it?"

He can see why the models like a Chesapeake bay jump, rather then to the VA capes so that would take the storm more AC to BOS. Also of note he talks how each storm is spreading snow further and further south so the southern edge of 1 inch with this storm could be the axis of heaviest snow with the next!

He goes on to say he likes the pattern, and dont let the indexes get you all upset. The NAO has been major league negative the past 3 weeks where did that get the US as far as cold?

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ChescoWx

ChescoWx

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Latest paraphrase from JB regarding the problems with the US Model and the upcoming system

He thinks last night was a wake up call if you looked at forecasts based on US models you could understand why a day before there was very little mention of snow outside of mixed here and there, and well north of where the heaviest was...however it ended up snowing south of DC yesterday....He says you may may say...big deal it all melted but the reason the forecast the day before was not saying it would snow was due to modling being warmer than what occurred...this points to one of JBs pet peeves the failure of the GFS to recognize how critical the source regions of air masses are to a strong forecast. He says if a model determines temperature without the rather subjective idea of source region it may fail to understand the distribution of temperature within the layer it's looking at. In an unstable air mass it is colder relative to height the higher up you go....what could be happening in the case of the US models is that the model estimates temp based on a computed thickness within a certain layer....but what if the its colder relative to the layer closer to the surface. Suppose the average temperatures 0 to 10 thousand feet is -5 celsius but it gets that way by being below freezing - but just barely the whole way. The snowflake doesn't melt. Now suppose the model thinks it is -5, but for some reason is raising the temperature in one level because it is not correctly estimating the stability of the air. The air is more unstable, more likely to rise, with lower pressure where there is convergence near a warm source not inland. So the model that can see that will hit that. Unfortunately what is happening, you see it in Texas where this low is near Houston...not quite southwest of Dallas as it was forecasted a couple of days ago - so it started snowing in an area where forecasts based on US models had no idea it was going to do that a day before. In his looking at the surface track and 700 mb low he asks - how does it get so warm so far nw on the US models - so his advice/forecast remains the same.. unless the GFS some how agrees with the non US models - he insists it is likely wrong - which means his map from Friday is still valid - He thinks it will be interesting to see when the snow breaks out tomorrow...where this change over will get to

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