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00z Model Discussion | January 2-3 Winter storm


user13

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I'm wondering if we see a Boxing Day type trend with the models by tomorrow or Wednesday because the setup really doesn't look bad. I'm surprised the models are so far east with this. The block in the Davis Strait looks solid, there are hints at a negatively tilted trough, and the pattern is quite amplified with nice ridging out west, but we'll see I guess. 

 

I guess that could happen. Crazier things have happened. 

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00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

==================================================

NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO

SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.

==================================================

...BROAD PROGRESSIVE CYCLONE TO AFFECT THE CENTRAL AND EASTERN

U.S...

...ASSOCIATED LOWER OHIO SURFACE LOW PASSING OFF TO A MID ATLANTIC

COASTAL LOW...

PREFERENCE: 18Z GFS...SUPPORTED BY THE 12Z ECMWF ENSEMBLE MEAN

THIS FORECAST IS VERY SENSITIVE TO THE STRENGTH OF A SHORTWAVE

THAT WAS OFFSHORE OF BRITISH COLUMBIA AT 00Z...AND WHICH WILL DIVE

INTO THE SOUTHERN PLAINS ON DAY 2. THIS SENSITIVITY WAS EVIDENCED

NOT ONLY BY THE SPREAD IN OPERATIONAL GUIDANCE...BUT ALSO BY AN

UNUSUAL AMOUNT OF SPREAD AMONG THE 18Z GEFS MEMBERS. IN VIEWING

THE SOLUTION OFFSHORE OF THE MID ATLANTIC/NORTHEAST AT THE END OF

THE SHORT RANGE...03/12Z...THE GEFS MEMBERS WERE LOOSELY SCATTERED

RATHER THAN SHOWING THEIR TYPICAL TIGHT SUPPORT FOR THE

OPERATIONAL GFS.

THE GEFS MEAN AND ECMWF ENSEMBLE MEAN FEATURE VERY SIMILAR

SOLUTIONS ASIDE FROM THE GFS BEING MORE PROGRESSIVE. WITH THE GFS

SYSTEM BEING SOMEWHAT SYSTEMATICALLY PROGRESSIVE...ONE WOULD TEND

TO LEAN TOWARD THE SLOWER ECMWF ENSEMBLE MEAN. IN LOOKING TO

CHOOSE AN OPERATIONAL MODEL AS THE BASIS FOR FORECAST

PRODUCTS...THE 12Z AND 18Z GFS APPEAR USEFUL...AS THEY WERE

SLOWER...MORE AMPLIFIED AND DEEPER THAN THE GEFS MEAN...BUT NOT SO

EXTREME IN THOSE RESPECTS AS THE PAST TWO RUNS OF THE ECMWF.

WHAT IS EVIDENT FROM VIEWING SEVERAL CYCLES OF ENSEMBLE SPAGHETTI

PLOTS...IS THAT THE ECMWF ENSEMBLE MEAN DEEPENED WITH THE 30/00Z

CYCLE AND THEN STEADIED OUT...AND THAT THE OPERATIONAL UKMET AND

ECMWF HAVE BEEN ON THE SLOW/DEEP SIDE OF THE MEAN. THESE DEEPER

AND MORE AMPLIFIED SOLUTIONS ARE SUPPORTED BY ABOUT 20 PERCENT OF

THE THE ECMWF ENSEMBLE MEMBERS AND A FEW GEFS MEMBERS. WE

NOTE...HOWEVER...THAT IN RECENT WEEKS THE OPERATIONAL ECMWF HAS

ERRED ON THE DEEP SIDE BEFORE MOVING BACK TOWARD THE MEAN...AND

THE UKMET HAS NOT DONE WELL HANDLING THE SPEED OR AMPLITUDE OF THE

NORTHERN STREAM FLOW. WE CONTINUE TO TAKE A CONSERVATIVE APPROACH

BY FAVORING THE MIDDLE-GROUND 18Z GFS. THE 00Z GFS WAS SLIGHTLY

FASTER...PARTICULARLY ALONG THE EAST COAST...BUT IT WAS CONSISTENT

WITH OUR PREFERENCE THROUGH DAY 2

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