Last call from HPC on east coast storm

[cycloneye]

OH VLY TO MID ATLC/SRN NEW ENGLAND...
SURFACE LOW AND ASSOCIATED UPPER TROF MOVES FROM THE OH VALLEY
EASTWARD ACROSS THE APPALACHIANS AND INTO THE MID-ATLANTIC.
SIGNIFICANT DIFFERENCES IN STRUCTURE...LOCATION AND STRENGTH
DEVELOP BETWEEN THE GFS AND THE NAM/ETA BY 23/00Z. REFER TO THE
HPC MODEL DIAGNOSTIC DISCUSSION FOR DETAILS. THESE DIFFERENCES
HAVE LARGE IMPACT ON PRECIPITATION FORECAST.

NEARLY ALL THE MODELS SUPPORT IDEA OF SNOW IN WARM
ADVECTION...ALONG WITH SOME FREEZING PRECIPITATION FROM THE
CENTRAL APPALACHIANS INTO THE MID-ATLANTIC AND SRN NEW ENGLAND.
AIRMASS SHOULD INITIALLY BE FAIRLY DRY...BUT PRECIPITABLE WATER
VALUES INCREASE AS H8 FLOW INCREASES TO BETWEEN 40 AND 50 KTS.

THE MODELS DIFFER ON HOW AMPLIFIED THE UPPER TROF BECOMES AND HOW
QUICKLY THE LOW MOVES OFF THE COAST BEFORE INTENSIFYING. THE GFS
TAKES THE LOW OFF THE MID-ATLANTIC COAST WHERE THE LOW DEEPENS AND
PULLS PRECIPITATION BACK TO THE COASTAL PLAIN AND SOUTHERN/CENTRAL
NEW ENGLAND. THE ETA...BEING FURTHER NORTH AND STRONGER WITH THE
UPPER TROF...BRINGS HIGHER QPF TO CNTRL/SOUTHERN NEW ENGLAND. THE
ETA WAS AN OUTLIER WITH REGARD TO ITS NORTHERN TRACK...WHILE THE
GFS HAD VARYING AMOUNT OF SUPPORT FROM THE MM5/ECMWF/SREF WITH A
MORE SOUTHERLY TRACK. HPC PREFERRED A BLEND OF THE MODELS WITH
SOMEWHAT HIGHER WEIGHTING GIVEN TO THE GFS. THIS PUTS A SWATH OF
HEAVY SNOW FROM PA/MD EASTWARD TO SOUTHERN NEW ENGLAND...WITH
ENOUGH WARM AIR ALOFT FOR ICE PELLETS AND A LOW RISK OF FREEZING
RAIN EAST OF THE MOUNTAINS IN PARTS OF VA/NC.

COMMA-HEAD PATTERN SHOWN BY THE GFS WOULD KEEP SNOW FALLING ALONG
THE MID-ATLANTIC COAST BEYOND 23/12Z...WHILE OTHER MODELS WOULD
SUPPORT PRECIPITATION ENDING BY 23/06Z.


Interesting reading this discussion by these folks and how thay analize all the scenarios for the east coast storm.