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1/17-1/18 Southern Special


phlwx

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Mount holly

 

 

 

FORECAST WILL POST AT 330 PM SIMILAR TO OUR 11AM UPDATED SNOW AMTS ETC.
I DID UP AMOUNTS A BIT AT 330 PM DEADLINE IN DE AND SE NJ BASED ON THE
205 PM RECEIPT OF THE ECMWF AND THE 18Z NAM.

CONFIDENCE IN SNOW AMOUNTS IS BELOW AVERAGE FOR A NUMBER OF REASONS.
WE ARE MUCH HIGHER THAN HPC. WE STILL NEED PHASE CHANGE AS OF THIS
330 PM WRITING. WE NEED TEMPS TO DROP TO 33-34F TO ACCUMULATE AT
NIGHT. AND THERE ARE MODE UNCERTAINTIES.

MY FCST AMTS HAVE BEEN A BIT VARIABLE IN DE AND COASTAL NJ...LOWERED
A BIT AT 11 AM AND INCREASED A BIT AT 330 PM PER THE OMINOUS 12Z
EC AND 18Z NAM.

SLEET HAS BEEN OCCURRING IN PARTS OF CAPE MAY COUNTY AND NOW SUSSEX
COUNTY DE. ITS SNOW NOW IN S CENTRAL VA AND A RAPID TRANSITION WILL
OCCUR IN PORTIONS OF OUR FCST AREA THIS EVENING AS THE STRONG UVM
MOVES TO THE SRN EDGE OF OUR AREA.

WE COLLABORATED WITH HPC ON THE NEWLY ROBUST ECMWF. THE EC
RECENTLY HAS BEEN AS INCONSISTENT AS THE NAM AND BEHIND THE NCEP
MODELS ON FLAGGING EVENTS. SO WE ARE NOT CONFIDENT IN ITS SOLN.

THIS HAZARD ISSUANCE LEANS HEAVILY ON PUBLIC IMPACT RATHER THAN
PURE CRITERIA AMOUNTS...ESPECIALLY SINCE WE`VE HAD SO LITTLE SNOW
THIS WINTER... INCLUDING KACY 2.5" SO FAR. I ADDED A CHC OF S- TO
NE NJ LATE TONIGHT PER MULTIPLE MODEL SUGGESTIONS.

MELTING WILL REDUCE SNOW TOTALS IN THE S PART OF OUR FCST AREA LATE
THIS AFTN BUT I STILL THINK ITS GOING TO BE ROUGH GO FOR SEVERAL HOURS
BETWEEN 5 AND 10 PM INCLUSIVE OF A VERY SHORT PERIOD OF NEARLY 1"/HR
SNOW ACC IN 1/2SM MDT SNOW.

THE NOTABLE ENE-WSW ORIENTED COLD FRONT MOVING S FROM NYS WILL HAVE
ITS OWN CONVERGENT FIELD AND LOWER CLOUDS AND FLURRIES ARE GRIDDED
FOR PTNS OF NE PA AND W NJ DURING THE NIGHT. THIS CF...CHANGES OUR
AIRMASS AND WE ARE MUCH CLOSER TO NORMAL ON FRIDAY.

YOU`LL NOTICE THIS CFP WITH A BRIEF GUSTY NNE WIND SHIFT FM N TO
S DURING TO NIGHT ...AN HOUR OR SO OF NNE GUSTS 15 TO 22 KTS AND
TEMPS FALLING BRIEFLY BUT ABRUPTLY.

RAIN SHOULD CHANGE TO BIG WET FLAKES AND DRILL THE SFC TEMPS DOWN
TO 33-34F ...BUT NOT MUCH MORE THAN THAT THIS EVENING.

THATS A WET CLINGY SNOW...ESPECIALLY AFTER SUNSET...THAT IF IT
ACCUMULATES TO NEAR 5 INCHES IN EXTREME S SUSSEX COUNTY DE...WOULD
CAUSE POWER OUTAGE PROBLEMS. THE COLD AIR ARRIVES IN THE WARNING
AREA AFTER THE SNOW ENDS AND SO ITS UNLIKELY SFC TEMPS WILL BE MUCH
LOWER THAN 32F IN THE SNOW OF DE/MD TONIGHT.

IN THE ADVY AREA...SFC TEMPS MAY BE A TAD WARMER HELPING MELT THE
FALLING SNOW AND DELAYING THE CHANGE TO SNOW TIL AFTER THE AREA TO
THE SOUTH CHANGES! THIS IS AN UNUSUAL EXPECTATION AND ITS NOT
GUARANTEED BUT THATS WHAT WE SEE IN THE TSECTIONS INCLUDING THE BL
TEMP.

 

http://forecast.weather.gov/product.php?site=NWS&issuedby=PHI&product=AFD&format=CI&version=1&glossary=1&highlight=on

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Nope. The southern wave doesn't have enough latitude to trend significantly far north and the Hudson Bay PV is too strong. Small details will cause the deformation zone to shift run to run but basically you are out of the game at this point if you are north. If the models are missing some feature associated with the PV that trends stronger, there could actually be a suppressive trend just before storm time.  

nice call!

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fwiw the euro is even further nw than the 0z yesterday, it gets .25 past philly now

 

This had to be by far one of the worst Euros run in a long time.  Not only was the qpf way off, but its forcing was practically in the same areas as the GFS, its mid level frontogenetic forcing axis was in Sussex County Delaware and its mid level trowal was offshore.  That whole run was bizarre, took Friday's clipper practically to James Bay.

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