NYC/PHL Dec 26-27 Potential - Part 5

[earthlight]

The NAM uses the GFS lateral boundary conditions but the errors on the GFS initialization were within the NAM domain over the midwest--this 18z run should have it's own data assimilated from the last 3 hours, drawn upon from the 06 hr forecast on the 12z NAM.

[Sundog]

It was called the 2008-2009 winter. Still sticks in my craw (craw?) .

You mean 07-08? That's the year they got over 50 inches while NYC barely cracked 10 inches and even less to the southwest. I really hated that winter.

[Snow_Miser]

.

s/w looks really healthy.

[stormman]

The NAM uses the GFS lateral boundary conditions but the errors on the GFS initialization were within the NAM domain over the midwest--this 18z run should have it's own data assimilated from the last 3 hours, drawn upon from the 06 hr forecast on the 12z NAM.

so shouldnt all this be pointed to maybe hey the 12gfs could be on to something, I mean, the gfs ensembles agree, now im hearing that the euro ensembles are also west of operational, and now the nam has shifted west?

[A-L-E-X]

You mean 07-08? That's the year they got over 50 inches while NYC barely cracked 10 inches and even less to the southwest. I really hated that winter.

Yeah, that was like 70-71. And some people were using 70-71 as an analog for us and saying thats a good thing because it was "cold." I would rather have a torch winter than a "cold" winter like 70-71

[MD Snow]

NAM at 78 hr prints out 1.5-2 " qpf for the coast of Maine, mass etc.

[Chris L]

Wow, people will really lose it if some people get hit hard while others get teased. This will get worse than 2/6 because of the time of year and the fact the pattern is going to shift for a bit after this storm.

I am not sure if its going to be a worse than Feb 6th.... We could have exceeded the blizzard of '96 if 2/6 came roaring up the coast; but on the other hand, it would be worse because of the pattern shift; that is another point entirely.

[_AR_]

Something we need to "nowcast" and observe is the strength of that low that forms in the GOM and bombs on the coast. The western solutions all bomb that low out fast. The more OTS solutions keep it weak until around DELMARVA latitude.

[Snow_Miser]

POPS have now been raised to 50% here.

[Edge Weather]

Yes, that is big time. Here is my take on this whole situation. HPC is in panic mode because they have a very serious forecast to make, one of the most important of the entire year, on the eve of Christmas with many people driving up and down the east coast on I-95 to and from Grandma's house. I for one know many people driving to and from Florida over the next couple of days. HPC has the GFS come in as the only model showing an all-out blizzard up and down the east coast of the United States. They tell someone in the model room to analyze the data and see if they can find a problem with the model run to explain why it is the only model showing this east coast blizzard. What a surprise they find a problem and throw out the run. The only problem is that if they scrutenized every model run this much, they would always find a problem with the run. Unfortunately, the JMA, the CRASS, the WRF NMM and ARW also show reason for concern, and now so does the NAM. Uh oh. Oh yes, and this happens to be not too far from what the EURO showed only a few runs ago and held onto for many runs.

Ouch! Look at that ensemble cluster around the benchmark. The operational is on the eastern edge of the ensemble mean.

This is probably more significant than anyone is willing to acknowledge.

[Kingwill]

Safe to say anyone making Final Calls right now would be foolish..The only safe call I would say right now is most of Strong Island is a "semi" lock for at least 6 Inches. GfS coming up will be interesting with all those earlier Data issues and tonights Runs will be huge. I wouldn't even put any final calls out if I were a weather man til after tomorrows 12Z runs..

[Ababa]

Yes, that is big time. Here is my take on this whole situation. HPC is in panic mode because they have a very serious forecast to make, one of the most important of the entire year, on the eve of Christmas with many people driving up and down the east coast on I-95 to and from Grandma's house. I for one know many people driving to and from Florida over the next couple of days. HPC has the GFS come in as the only model showing an all-out blizzard up and down the east coast of the United States. They tell someone in the model room to analyze the data and see if they can find a problem with the model run to explain why it is the only model showing this east coast blizzard. What a surprise they find a problem and throw out the run. The only problem is that if they scrutenized every model run this much, they would always find a problem with the run. Unfortunately, the JMA, the CRASS, the WRF NMM and ARW also show reason for concern, and now so does the NAM. Uh oh. Oh yes, and this happens to be not too far from what the EURO showed only a few runs ago and held onto for many runs.

Agree with this analysis. Not metro analysis but CYA analysis and actions that typically take place in large organizations. Good observations.

[Edge Weather]

Thank you. I thought much about this for the past couple of hours. I do believe we are experiencing a CYA situation and it is completely understandable, don't get me wrong. It is much easier to blame the models when you have only one model showing this solution than it is to go out on a limb and put up winter storm watches up and down the east coast and have to take it back if you are wrong. Hopefully the GFS was wrong for their sake, but I have my doubts.

Agree with this analysis. Not metro analysis but CYA analysis and actions that typically take place in large organizations. Good observations.

[WeatherFox]

1-2" is the NWS thinking now for the NYC area from what I read into their latest product. Of course it could be more or less. Just shows how challenging weather forecasting is in the short range let alone the long range. Anyway, that just might be enough for the kids to enjoy their new or old Christmas presents.

[_AR_]

So I guess forecasting without models is a no-no in this forum. LOL.

No, it's just the way you put it. It has been stated by several mets that this will come down to nowcasting the development of the surface low and how quickly it strengthens. Also the trough orientation.

[Snow_Miser]

Excellent post by WeatherMan Tyler on Accuwx forums

Right...you can't use the "initialization error" claim on the NAM...

WHY?

The 12z NAM and 18z NAM have significantly different solutions. (To those who point out that the 18z run uses 12z data)

[ARyan]

No, it's just the way you put it. It has been stated by several mets that this will come down to nowcasting the development of the surface low and how quickly it strengthens. Also the trough orientation.

I wasn't talking about nowcasting...I was talking about forecasting. But whatever. lol.

[A-L-E-X]

Meh lol-- I guess people can discount whichever solution they dont like. What's going to happen-- Yet to be determined and very much up in the air (literally maybe!)

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

355 PM EST FRI DEC 24 2010

VALID 00Z SAT DEC 25 2010 - 00Z TUE DEC 28 2010

DAYS 1-3...

...OH VLY/APLCHNS...

AREA OF SNOWFALL IN THE MIDWEST WILL CONTINUE EWD THRU THE OH VLY

THIS EVENING/OVERNIGHT AHEAD OF A DIGGING/DEVELOPING ERN CONUS

TROF. PVA/MID LVL FRONTOGENESIS/HT FALLS COMBINED WITH A MODEST

PLUME OF MSTR WILL SUSTAIN LIGHT SNOW EVENT FROM IL/IN TO THE

APLCHNS. MODELS HAVE COME TO GREAT AGREEMENT HERE MASS

FIELD-WISE... ALTHO THE NAM IS WETTER THAN THE CONSENSUS. BASED

ON OBSERVED SNOWFALL... A GENERAL 2-3 INCHES WILL BE ANTICIPATED

IN THE PLAINS/VLYS... BUT MORE IN THE FOOTHILLS/APLCHNS WITH

UPSLOPE ENHANCEMENT. ONCE THE WAVE SLIDES EAST... ALL BUT THE

TRRN WILL SEE PRECIP END. NW FLOW BEHIND THE WAVE COMBINED WITH

FLOW FROM DEVELOPING COASTAL STORM WILL PROMOTE A LONG-LIVED

UPSLOPE EVENT TO HIR TRRN OF KY/WV... ALTHO THE OVERALL MSTR WILL

BE LIMITED... SO ONLY 3-6 ADDITIONAL INCHES FCST LCLY.

...LWR MID-ATLC...

PRECIP WILL SPREAD INTO THE REGION LATE CHRISTMAS DAY AHEAD OF THE

APPROACHING DYNAMIC TROF... WHILE THE SFC FTR DEVELOPS IN THE ERN

GULF AND CROSSES FL. TRANSITION TO WET SNOW MIX SHOULD OCCUR

OVERNIGHT THEN CHANGE TO ALL SNOW AS CAA TAKES OVER ONCE THE LOW

ACCELERATES NWD OFF THE COAST. QUESTION REMAINS HOW MUCH PRECIP

WILL BE LEFT TO FALL ONCE THE THERMALS BECOME SUPPORTIVE OF SNOW.

CONSENSUS IS EMERGING DISCOUNTING THE 12Z GFS AND 18Z NAM... THAT

TAKES THE LOW FARTHER OFFSHORE AND BRINGS PERHAPS 1-2 INCHES TO

ERN/CNTRL NC AND EXTREME SE VA.

...NEW ENGLAND...

HPC CHOSE TO DEFER TO CONTINUITY HERE AFTER SEEING SPREAD OF 12Z

GUIDANCE. REGARDING SFC LOW OFF THE COAST... 12Z GFS/18Z NAM AND

SEVERAL GFS ENSEMBLE MEMBERS JUMPED WEST WHILE REMAINING HELD

SERVE OR TRENDED EAST. H5 EVOLUTION IS NEARLY AS

DISPARATELY-HANDLED AS AT THE SFC... WITH THE GFS AGAIN WRAPPING

IT TIGHTER AND FARTHER WEST. THERE WILL BE PLENTY OF DYNAMIC

ENERGY AS THE TROF GOES NEG TILT SUNDAY... AND THE DEEP LOW

OFFSHORE WILL PROMOTE A BURST OF HVY SNOWFALL TO PORTION OF NEW

ENG IN THE THE PREFERRED SCENARIO. STILL THINK CAPE COD AND NRN

COAST ME WILL SEE HEAVIEST AMTS WITH TIGHT ACCUM GRADIENT INLAND.

BLEND INCORPORATED 06Z GFS/00Z ECMWF REFLECTING PREFERENCE LOW

TRACK. STILL LOW CONFIDENCE HERE.

...WEST...

DEEP TROUGH IN THE ERN GULF OF ALASKA ROTATES A SIGNIFICANT

SHORTWAVE INLAND ALONG THE WEST COAST FROM NRN CALIF TO THE

CANADIAN BORDER ON SATURDAY/SUNDAY. WITH THE DEEP ONSHORE FLOW

DIRECTED PRIMARILY AT THE CASCADES AND SISKIYOUS...THE SYSTEM

SPLITS WITH SNOW LEVELS IN THE CASCADES FALLING TO 3000-4000FT MSL

AND SATURDAY AFTERNOON/EVENING THROUGH SUNDAY MORNING...THE SIERRA

AND WINDWARD FOOTHILLS RECEIVE ANOTHER ROUND OF MODERATE TO HEAVY

SNOWFALL AS CRITICAL TEMPERATURES FALL TO ELEVATIONS IN THE

5000-6000FT MSL RANGE. USED A BLEND OF THE EC/NAM/GFS THERMAL

PROFILES AND HPC QPFS ALONG THE WEST COAST...TO GENERATE THE

SIGNIFICANT SNOWFALL GRAPHICS.

[Snow_Miser]

Winter Storm Watches are already in effect for parts of North Carolina.

http://www.weather.gov/

[A-L-E-X]

Note that the above report I posted doesnt include our area.

[ag3]

Did RGEM have GFS data too? Lol.

Awesome sign to see new them way west and wound up.

[JTA66]

I just watched Hurricane on the 4 o'clock news. He referenced the differences in the foreign and US models. He also mentioned the initialization errors in the US models (yes, we've discussed them to death here). Anyway, it looks like he's siding w/the foreign models ATM, with a 60/40 chance of OTS as opposed to a hit.

[SnowGoose69]

I'd assume if the 18z GFS resembles 12Z its to be taken lightly given they said the 18Z NAM was out as well.

[tombo82685]

hr 12 looks like trof is a lil more amplified....also h5 is closed off over eastern tex

[stormman]

I'd assume if the 18z GFS resembles 12Z its to be taken lightly given they said the 18Z NAM was out as well.

thats funny, so in other words if the gfs is a hit, then throw it out, but if it shifts east, then its good???

[_AR_]

00Z cycle will make or break this. I'm sure of that. Although 50 miles one way or the other will TBD from nowcasting obs.

[bass28]

funny they said no issues on the 12z nam when the 18z comes and shows a hit its bad data come on already.

[Harbourton]

It's starting to tap the GOM.

[LVblizzard]

funny they said no issues on the 12z nam when the 18z comes and shows a hit its bad data come on already.

Who said to throw the 18z NAM out? I see nothing from the HPC.

[atownwxwatcher]

Who said to throw the 18z NAM out? I see nothing from the HPC.

HPC did under its heavy snow discussion