NYC/PHL: December 24-27th Potential

[tornadojay]

updated discussion out of Binghamton, NY:

MAIN ATTENTION GRABBER ONCE AGAIN THIS AFTERNOON IS THE

POSSIBLE DEVELOPMENT OF A COASTAL STORM AFTER THE CHRISTMAS

HOLIDAY. BEFORE WE DIVE INTO THE DETAILS REGARDING THIS

FEATURE...HAVE BACKED OFF ON POPS ON SAT AS REGION WILL LARGELY

REMAIN TO THE EAST OF THE DEVELOPING STORM SYSTEM TO OUR WEST. THAT

SAID...UPPER FLOW PATTERN WILL BECOME HIGHLY AMPLIFIED BY LATE SAT

AS UPPER RIDGING BUILDS ACROSS THE NORTHERN ROCKIES/CANADIAN

PRAIRIE PROVINCES. AS THIS OCCURS...SOUTHERN STREAM ENERGY (THE

REMNANTS OF THE ONGOING WEST COAST WX MAKER) WILL BE UNDERCUTTING

THE DEVELOPING RIDGE BY SAT. THIS SOUTHERN STREAM ENERGY WILL THEN

CONTINUE WORKING EAST THROUGH THE GULF COAST STATES ON SAT/EARLY

SUN...WHICH WILL EVENTUALLY INGEST NORTHERN STEAM SHORTWAVE ENERGY

WORKING SOUTHEAST ALONG THE EASTERN PERIPHERY OF THE AMPLIFYING

RIDGE. THE KEY TO THE DEVELOPING STORM SYSTEM WILL BE JUST HOW

EASILY THE NORTHERN AND SOUTHERN STREAM ENERGY SOURCES PHASE.

AFTER THE PHASING...DEEP TROUGHING WILL THEN SETTLE ACROSS THE

EASTERN SEABOARD AS NORTHERN STREAM TROUGHING CONTINUES TO

DIG...WHICH WILL THEN RESULT IN A SOUTHERLY FLOW PATTERN ALONG THE

EASTERN SEABOARD AS THE WAVELENGTH BETWEEN THE DEVELOPING RIDGE AND

TROUGH INCREASES. AS IT STANDS RIGHT NOW...THE EASTERN SEABOARD

COULD BE DEALING WITH A SIGNIFICANT WINTER WX SITUATION AS EARLY

AS SUN.

CURRENT MODEL GUIDANCE CONTINUES TO HAVE DISAGREEMENTS THIS

AFTERNOON AS THE 12Z GFS IS NOW THE FARTHEST EAST SOLUTION.

MEANWHILE...THE 12Z CANADIAN GEM AND ECMWF MAINTAIN A MUCH MORE

AMPLIFIED FLOW PATTERN ACROSS THE EASTERN SEABOARD AND AS A

RESULT...A FURTHER WESTWARD POSITION WITH THE EXPECTED STORM

TRACK. BOTH MODELS PHASE THE NORTHERN AND SOUTHERN SHORTWAVES

ACROSS THE AMERICAN SOUTHEAST...WITH BOTH SUGGESTING RAPID

CYCLOGENESIS OFF THE NC COAST BY SUN AFTERNOON. BOTH ALSO CONTINUE

TO SLOW THE ARRIVAL OF THE MAIN PRECIP SHIELD ACROSS THE CWA WHICH

APPEARS PLAUSIBLE CONSIDERING THE AMPLIFIED NATURE OF THE EAST

COAST TROUGH. IN ANY EVENT...BOTH SOLUTIONS SHOW PRECIP ENTERING

SOUTHERN PORTIONS OF THE FORECAST AREA BY SUN AFTERNOON...WITH THE

MAIN SFC LOW THEN SLOWLY MOVING NORTHEAST ALONG THE COAST THROUGH

MON. THE 12Z GEM EVEN SUGGESTS THE SYSTEM WILL STALL SOUTH OF THE

CENTRAL LONG ISLAND COAST ON MON WHICH COULD LEAD TO EVEN HIGHER

SNOWFALL AMOUNTS IF REALIZED. WITH COLD AIR WELL IN PLACE THANKS

TO THE PERSISTENT BLOCKY PATTERN EXPERIENCED IN RECENT WEEKS...ALL

PRECIP IS EXPECTED TO FALL IN THE FORM OF SN.

STILL A LITTLE EARLY TO GET REALLY EXCITED HOWEVER CONSIDERING THE

AGREEMENT ON THE STORM TRACKS CURRENTLY BEING SUGGESTED BY THE

12Z ECMWF AND GEM SOLUTIONS...FELT PRUDENT TO INCREASE POPS ACROSS

THE BOARD BEGINNING SUN. WITH THIS SYSTEM HAVING ACCESS TO HIGH

AMOUNTS OF ATLANTIC MOISTURE AND ITS SLOW MOVEMENT...HEAVY

SNOWFALL ACCUMULATIONS MAY OCCUR ACROSS THE EASTERN SEABOARD. AND

CONSIDERING THAT WE/RE STILL 5 DAYS OUT...THERE/S STILL PLENTY OF

TIME FOR MODELS TO FLIP FLOP BACK AND FORTH.

SYSTEM TO THEN SLOWLY EXIT TOWARDS OUR NE ON TUE WHICH WILL THEN

BE FOLLOWED BY ANOTHER ROUND OF LAKE EFFECT SNOW AND CONTINUED

BELOW NORMAL TEMPS. STAY TUNED!-- End Changed Discussion --

[baroclinic_instability]

A met posted 72-120 was when it had the best verification scores compared to all the other models. I'm pretty sure, but I could be wrong.

Here are some height field verification stats from GEM.

http://www.weatherof...nthly_ts_e.html

[tornadojay]

Upton Update:

WEAK RIDGING ACROSS THE AREA FRIDAY NIGHT INTO SATURDAY MORNING.

MODELS STILL IN GENERAL AGREEMENT WITH A COASTAL LOW PRESSURE MOVING

UP THE EASTERN SEABOARD FOR THE CHRISTMAS WEEKEND. AT THIS TIME THE

EXACT EVOLUTION INCLUDING TIMING AND TRACK DETAILS OF THE STORM

SYSTEM REMAIN UNCERTAIN. THE GFS CONTINUES TO FLIP FLOP FROM PREVIOUS

RUNS. THE 12Z/GFS IS NOW FASTER...LESS AMPLIFIED AND OUTSIDE OF THE

70/40 BENCHMARK. THE 12Z/ECMWF...ALTHOUGH STILL INSIDE THE 70/40

BENCHMARK...IS MUCH SLOWER BRINGING PRECIP INTO THE AREA SUNDAY

NIGHT INTO MONDAY AFTERNOON TIMEFRAME.

PRECIPITATION...ATTM IT APPEARS THAT THE LOW WILL TRACK CLOSE ENOUGH

TO BRING PRECIP TO THE LOCAL AREA BUT ANY SHIFTS IN THE TRACK OF THE

COASTAL LOW WILL PRODUCE SIGNIFICANT CHANGES TO POTENTIAL SNOWFALL

AMOUNTS.

THEREFORE...WILL NOT DEVIATE MUCH FROM PREVIOUS FORECAST. WILL DELAY

SLIGHT CHANCE POPS TIL SATURDAY NIGHT...INCREASING TO CHANCE OVER

ALL BUT THE FAR EASTERN PORTION OF THE AREA BY LATE SATURDAY NIGHT.

THEN HAVE CHANCE POPS SUNDAY THROUGH EARLY MONDAY MORNING...WITH

CHANCE POPS W/SLIGHT CHANCE POPS WEST LATE MONDAY MORNING INTO

MONDAY AFTERNOON...THEN DRY MONDAY NIGHT.

[baroclinic_instability]

Here are some height field verificcation stats from GEM.

http://www.weatherof...nthly_ts_e.html

Here you can see error growth w.r.t. time for individual months.

http://www.weatheroffice.gc.ca/verification/error_growth_e.html

[tornadojay]

Mt Holly:

ALL EYES REMAIN FOCUSED ON AN EVENT FOR THE SECOND HALF OF THE

HOLIDAY WEEKEND.

SOME OF THE MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT, BUT

THERE REMAINS ENOUGH OF A SPREAD AND AT DAY 5, THIS STILL REMAINS

A LOWER THAN AVERAGE CONFIDENCE FCST.

ONE TREND THAT HAS DEVELOPED IS THAT VIRTUALLY ALL OF THE

GUIDANCE, WITH THE EXCEPTION OF THE GFS HAS TRENDED SLOWER WITH

THE UPCOMING STORM. AS A RESULT, CHRISTMAS DAY NOW LOOKS DRY,

DEPENDING ON THE ULTIMATE TIMING, SATURDAY NIGHT COULD END UP

MOSTLY DRY AS WELL.

VIRTUALLY ALL OF THE MDLS WANT TO BRING AT LEAST SOME PRECIP TO

THE AREA DURG THE SUNDAY INTO MONDAY TIME FRAME. THE MAIN

QUESTIONS REMAIN THE TIMING ULTIMATE PATH OF THE STORM WHICH WILL

AFFECT PRECIP AMTS (AND PSBLY PRECIP TYPE AS WELL).

THE 12Z GFS HAS A MUCH WEAKER SFC LOW, VIRTUALLY NO WELL DEFINED

VORT AND AS A RESULT IS MUCH MORE PROGRESSIVE WITH THE H5 PATN AND

KEEPS A MUCH WKR SFC LOW WELL TO OUR S AND E. THE 12Z GFS SOLN IS

AS CLOSE TO A NON-EVENT AS THE MDLS ARE SHOWING ATTM. HOWEVER, THE

GFS IS THE OUTLIER AND IS BEING DISCOUNTED ATTM.

THE 12Z UKMET HAS STUCK TO ITS GUNS ONCE AGAIN WITH A MORE ELY

SOLN, EVEN THOUGH IT HAS TRENDED WWD WITH ITS LATEST CYCLE. ITS

POSN AT 27/12Z IS WELL OFF THE NC CST. THE UKMET TENDS TO BE ONE

OF THE MORE RELIABLE MDLS, SO WHILE IT IS AN OUTLIER WITH THE

LATEST MDL CYCLE, IT REMAINS TO BE SEEN IF IT WILL CONTINUE TO BE

SO.

THE LATEST CMC HAS TRENDED A BIT SLOWER AND FURTHER E AT 12Z,

AFTER A MARKED WWD SHIFT LAST NIGHT. ON THE OTHER HAND, THE 12Z

ECMWF HAS TRENDED SLOWER BUT FURTHER W. BOTH THE CMC AND ECMWF

SOLNS WOULD BE A MORE SIGNIFICANT EVENT FOR THE REGION, WITH THE

ECMWF POSN ULTIMATELY BRINGING PRECIP TYPE INTO QUESTION

ESPECIALLY FOR SRN AND ERN SECTIONS.

THE LATEST NAEFS STILL INDICATES MORE OF A GLANCING BLOW FOR THE

REGION, WITH THE INDIVIDUAL MEMBERS PRESENTING ALL DIFFERENT

SCENARIOS.

SO, WHAT DOES THIS ALL MEAN? WELL, UNCERTAINTY PREVAILS, AS IT

SHOULD AT DAY 5, BUT INDICATIONS ARE THAT AT LEAST SOMETHING WILL

OCCUR IN THE SUNDAY/MONDAY TIME FRAME. AGAIN, THE UKMET WOULD AND

GFS WOULD INDICATE THE MOST MINIMAL EVENTS WITH THE CMC AND ECMWF

BEING MORE SIGNIFICANT. THE ULTIMATE TIMING, TRACK AND INTENSITY

OF THE LOW DETERMINE WHAT OCCURS AND THOSE DETAILS WILL HOPEFULLY

BE REFINED BY THE MDLS IN THE COMING DAYS. MDL POSNS VARY EXCEPT

FOR THE CMC AND ECMWF, WHERE THERE ARE TIMING DIFFS.

DEPENDING ON THE TIMING OF THE SYSTEM IT COULD BE OVER EARLY

MONDAY OR LINGER A BIT LONGER AS WELL, WITH IMPROVING CONDS. DRY

AND WINDY WX WILL BE IN STORE FOR TUESDAY WITH HIGH PRESSURE TO

THE W. IT WILL BE COLD THRU THE PD, WITH TEMPS AVERAGING 5-10

DEGREES BELOW NRML.-- End Changed Discussion --

[isnice]

Here are some height field verification stats from GEM.

http://www.weatherof...nthly_ts_e.html

When looking at the 5-day percent error, it seems as though the Euro pretty much dominates.

[LVblizzard]

Here you can see error growth w.r.t. time for individual months.

http://www.weatherof...r_growth_e.html

Thanks for the links! It's interesting that the JMA is the second best at hour 144 based on that graph.

[tornadojay]

Albany, NY update:

THE EXTENDED FCST FEATURES THE POTENTIAL OF A MAJOR EAST COAST

SNOWSTORM IMPACTING THE NORTHEAST ON THE SECOND HALF OF THE HOLIDAY

WEEKEND INTO MONDAY. CHRISTMAS AT THIS POINT LOOKS COLD WITH

PERHAPS SOME OVER RUNNING LIGHT SNOWFALL MOVING INTO LOCATIONS SOUTH

OF THE CAPITAL REGION LATE IN DAY INTO CHRISTMAS NIGHT. THE

QUESTION IS WHETHER OVER RUNNING PCPN QUICKLY DEVELOPS WELL NORTH OF

A DEVELOPING MILLER TYPE A CYCLONE EJECTING OUT OF THE DEEP

SOUTHEAST AND THE GULF OF MEXICO.

THERE CONTINUES TO MAJOR DIFFERENCES BETWEEN THE 12Z

ECMWF...CANADIAN GGEM...AND HPC VERSUS THE 12Z GFS AND GEFS. THE

INTERNATIONAL GUIDANCE FAVORS MAJOR CYCLOGENESIS OCCURRING ALONG THE

CAROLINA COASTLINE THE DAY AFTER CHRISTMAS. THE LATEST ECMWF HAS A

SUB-975 HPA LOW NEAR ERN NJ BY 12Z/MON.../THIS LOW DEEPENS TO 964

HPA SOUTH OF LONG ISLAND BY 18Z MON/. THE ECMWF SCENARIO WITH THE

H500 CIRCULATION CLOSING OFF OVER ERN PA AND NJ WOULD YIELD A

SIGNIFICANT SNOWFALL TO THE FCST AREA. THE GFS AND ITS ENSEMBLE

MEAN KICK THE WAVE OUT TO SEA QUICKLY WITH THE FCST AREA GETTING

MAINLY LIGHT SNOWFALL SUNDAY INTO MONDAY. THE CAN GGEM IS A DECENT

COMPROMISE AT THIS POINT WITH HPC MOVING SNOW IN SAT NIGHT INTO

SUNDAY MORNING. THE STEADIEST SNOW WOULD POTENTIALLY BE LATE SUNDAY

INTO MONDAY LATE MORNING BEFORE THE STORM MOVES NORTH AND EAST OF

CAPE COD. IT IS STILL WAY TOO EARLY TO BE CONFIDENT ENOUGH FOR

LIKELY POPS IN DAYS 5 AND 6. WE WILL MENTION HIGH CHANCE POPS

SATURDAY NIGHT THRU SUNDAY NIGHT. WE WILL CONTINUE TO HIGHLIGHT IN

THE HWO THE CHC OF A SIGNIFICANT SNOWSTORM.

[eduggs]

With such a wrapped up and early-deepening storm, the heaviest precip would likely fall west of the track from the lower mid-atlantic up through SEPa. NEPa, SENY, and SNE would likely see less precip as the surface low occludes and might also be slightly warmer. - esp aloft. This applies to the ECMWF and UKMET. Upslope areas further north would make up for the initial deficit with moisture wrapping around the stalled surface low. Regardless, the EC shows an historical snowstorm for many places up and down the coast!

Quick people at 18z NAM is also much improved at the end of its run.

[Stormlover74]

Saw this posted by HM on the homepage:

A quick update before I head out:

The MJO pulse described in the original post is turning out to be quite impressive, initiating the Atlantic invest and Pac storm. The upward motion has been completely weakened across the Indonesian sector based on the latest OLR/CHI anomalies. It has also become quite apparent that the 12/25-26 storm is legit and likely the Heather A. signal. The slower progression of the s/w from the Southwest and monster blocking has completely allowed for the potential of a monster coastal storm. I look forward to tracking this one with all of you.

I'll be back for another evening of 00z runs.

[LVblizzard]

18z DGEX misses the phase, way out to sea

[nevildev]

first post, figured I'd go with some poetry about the upcoming storm...

A poetic holiday weather forecast

December 21st, 2010 | Rich Woolley

Twas the days before Christmas, when all through the land

All the people were shopping, to find that right brand.

The shelves at the store were piled high with care,

In hopes that more shoppers soon would be there.

The stores were aglow with holiday gear,

While there were visions of more sales, especially year-on-year.

And Mam ma in her coat and I in my cap,

Dashed across the parking lot heading for the Gap.

When out on the West Coast arose such a clatter,

A mega snowstorm was slamming the Sierra Nevada.

Away to the radar I flew like a flash,

checked my forecast models and scratched my moustache.

There on the screen was a mega snowstorm

With snow and rain beyond what was norm.

When, what to my wondering eyes should appear,

A new storm was forming that would bring travelers fear.

With a strong little jet stream so lively and quick,

I knew in a moment that the snow could be thick.

More rapid than plows the storm's impact came,

And I whistled and shouted and called the states by name.

Now Kansas! Now Missouri! Now Illinois and Indy!

On Kentucky! On Virginia, On Maryland and Delaware!

To the Atlantic it shall move and then I do not know,

It could turn up the coast and New England could see snow.

The winds will be strong with a cold gusty blow,

Sending a frosty chill to states below.

So out come the shovels to do battle with the snow,

Rock salt and ice scrapers, will see their sales grow.

I spoke not a word but got to the store real quick,

Picked up eggs, bread, milk and a box of Bisquick.

Into the basket goes a fire log or two,

A sweater and mittens, there that will do.

The snow and the cold will bring traveling jeers this holiday season,

But retailers will smile as increased sales and higher margins will be the reason.

The storm will wind down at the start of the new week,

But cold weather will follow and is not for the meek.

A warm up is likely by the New Year,

Though another storm may foul up ringing in the cheer.

But as I shut down my computer and pondered the storm's plight,

I said Merry Christmas to all and it looks like it's going to be white!

www.wt360.com will update daily for storm updates. This guest post is by Rich Woolley, WTI's Chief Forecaster and VP Operations.

[eduggs]

18z DGEX misses the phase, way out to sea

You're joking, right?

18z crushes Baltimore to Boston

[earthlight]

You're joking, right?

18z crushes Baltimore to Boston

I think you're looking at yesterday's on PSU Ewall

[LVblizzard]

You're joking, right?

18z crushes Baltimore to Boston

You're looking at the old run on ewall. Check Allan's site.

[ParanormalWx]

Radio show tonight. The trend of radio shows killing snow chances needs to be stopped tonight!

[NortheastPAWx]

STORM CANCEL

Special Radio Show Tonight, 10:30 PM with Allan Huffman (Raleighwx) FoothillsNC, Dave Tolleris and possibly Will Schwartz (TBD).

[eduggs]

I think you're looking at yesterday's on PSU Ewall

Yes.

[eduggs]

18z DGEX misses the phase, way out to sea

Oh well. When the DGEX wraps up a monster - as it tends to do - we almost always miss. So this might be good for us.

[bluehens]

Radio show = OTS at 0z

[tombo82685]

alright 18z gfs time lol

[hazwoper]

Radio show = OTS at 0z

Thanks for your input.

18Z GFS rolling.

[SACRUS]

Oh well. When the DGEX wraps up a monster - as it tends to do - we almost always miss. So this might be good for us.

So was LV right or is it a hit?

[LVblizzard]

That 18z DGEX is yesterday's run, today's DGEX doesn't come out on ewall for at least another 10-15 minutes.

[Stormlover74]

Didn't we already decide this was yesterday's run and today is a miss?

yummy for the 18z dgex from balt to bos

[tombo82685]

Didn't we already decide this was yesterday's run and today is a miss?

whoops sorry

[Sn0waddict]

Yep that's yesterdays run. I remember because the bullseye at hour 150 is practically over my house.

[gkrangers]

Radio show = OTS at 0z

Guaran****ingteed.

[Blizzardo]

Tombo, a big for calling the runs like you do.

[Wonderdog]

Plus there is a date stamp on the graphic.

Yep that's yesterdays run. I remember because the bullseye at hour 150 is practically over my house.