Prognostic Meteorological Discussion
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000
FXUS10 KWNH 261654
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1153 AM EST MON JAN 26 2015

VALID JAN 26/1200 UTC THRU JAN 30/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


EVOLVING COASTAL STORM ALONG THE NORTHERN MID ATLANTIC/NORTHEAST
MON-WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NAM/00Z ECMWF COMPROMISE
CONFIDENCE: AVERAGE TO BELOW AVERAGE

ONE OF THE MORE NOTABLE RUN-TO-RUN CHANGES BETWEEN THE 00/12Z NAM
OCCURS EARLY IN THE PERIOD.  THE 12Z RUN IS A LITTLE DEEPER WITH
THE SHORTWAVE LIFTING ALONG THE MID ATLANTIC COAST AND IS A FEW
HOURS FASTER TO CLOSE OFF A 500MB CENTER EARLY TUE.  THIS IS
REFLECTED AT THE SURFACE WITH A LOW THAT TRACKS A LITTLE CLOSER TO
THE COAST ON TUE.  THIS PLACES THE NAM SURFACE LOW TRACK ALONG THE
WESTERN EDGE OF THE DETERMINISTIC GUIDANCE FOR ABOUT A 12-HR
PERIOD FROM 06-18Z TUE.  FROM EARLY WED ONWARD...THE 12Z NAM IS A
LITTLE SLOWER AND LESS AMPLIFIED THAN ITS 00Z RUN AS THE SYSTEM
MOVES FROM OFF OF THE NEW ENGLAND COAST INTO THE CANADIAN
MARITIMES...BUT OVERALL...THE NAM HAS REMAINED FAIRLY CONSISTENT.
IN FURTHER COMPARISON TO THE LATEST MODEL RUNS...FROM 00Z WED
ONWARD...THAN NAM IS MORE PROGRESSIVE THAN THE 00Z ECMWF BUT BEARS
MORE IN COMMON WITH THE ECMWF THAN THE MORE PROGRESSIVE 00Z
UKMET/CMC GLOBAL AND THE 09Z SREF MEAN.

THE 12Z GFS IS A LITTLE DEEPER AND FASTER THAN ITS 00Z RUN AT 500
MB AS THE LOW CLOSES OFF AND THEN MOVES FROM THE NORTHERN MID
ATLANTIC TO THE SOUTHERN NEW ENGLAND COAST ON TUE.  OVERALL
HOWEVER...RUN-TO-RUN DIFFERENCES BETWEEN THE 00/06/12Z RUNS ARE
MINOR.  IN COMPARISON TO THE LATEST DETERMINISTIC RUNS...THE GFS
REMAINS BETTER CLUSTERED WITH THE 00Z UKMET/CANADIAN GLOBAL ALONG
THE EASTERN/PROGRESSIVE EDGE OF THE GUIDANCE.

CONFIDENCE IS TEMPERED BY THE LINGERING MODEL SPREAD...HOWEVER
GIVEN THE ORIENTATION OF THE SYSTEM (NEGATIVE TILT) AND A
SIGNIFICANT UPSTREAM RIDGE NOSING INTO THE CANADIAN MARITIMES...A
SLOWER AND MORE AMPLIFIED SOLUTION SIMILAR TO THE LATEST NAM/ECMWF
SEEMS MORE PLAUSIBLE THAN THE FASTER CAMP.

AS IS ALWAYS THE CASE WITH THESE BIG STORMS...SMALL DETAIL
DIFFERENCES RESULT IN LARGE IMPACT DIFFERENCES...ESPECIALLY WITH
PRECIPITATION. PREFERENCES LISTED HERE REFLECT MODEL POSITION AND
MASS FIELDS...BUT REFER TO WPC WINTER WEATHER AND QPF DESK
PRODUCTS FOR INFORMATION ON LIQUID EQUIVALENTS/SNOW.


WEAK CLIPPER PASSING THROUGH THE UPPER MISS VALLEY MON/TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: AVERAGE

THE GUIDANCE IS IN GOOD AGREEMENT HERE.


WEAKENING CLOSED LOW MOVING INTO CALIFORNIA EARLY TUESDAY
REMNANT SHORTWAVE PASSING THROUGH THE CENTRAL PLAINS INTO THE
MID MS AND OH VALLEYS WED NIGHT-THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/00Z UKMET AND ECMWF
CONFIDENCE: AVERAGE

THE 00/12Z NAM SHOW GOOD RUN-TO-RUN CONTINUITY UNTIL AROUND 18Z
WED WHEN THE 12Z NAM MAINTAINS A MORE AMPLIFIED SHORTWAVE MOVING
FROM WY/CO INTO THE PLAINS.  THIS IS WHEN THE NAM ALSO STARTS TO
BECOME A SLOW/AMPLIFIED OUTLIER IN COMPARISON TO THE 00Z
ECMWF/UKMET AND THE 09Z SREFMEAN.  OF THE LATEST DETERMINISTIC
RUNS...ONLY THE 00Z CMC GLOBAL IS SLOWER.

THE 12Z GFS IS A LITTLE SLOWER THAN ITS 00Z RUN AS THE SYSTEM
MOVES FROM THE MID MS INTO THE OH VALLEY THU MORNING...BUT IT IS
BETTER CLUSTERED WITH THE MORE PROGRESSIVE CAMP.  WHILE THE 00Z
ECMWF/UKMET SHOW THIS SYSTEM SHEARING OUT TO THE NORTHEAST AHEAD
OF A SHORTWAVE TROUGH DIGGING INTO THE GREAT LAKES...THE GFS SHOWS
A MORE DEFINED SYSTEM MOVING INTO THE UPPER OH VALLEY/NORTHERN MID
ATLANTIC ON THU...BUT IT REMAINS FASTER AND LESS AMPLIFIED THAN
THE NAM.


MID-LEVEL SHORTWAVE MOVING INTO BRITISH COLUMBIA MON NIGHT
SUBSEQUENT MOVEMENT INTO THE N-CENTRAL U.S./GREAT LAKES THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/00Z ECMWF
CONFIDENCE: AVERAGE TO BELOW AVERAGE

IN COMPARISON TO THEIR 00Z RUNS...BOTH THE 12Z NAM/GFS HAVE SLOWED
TO SOME DEGREE AS THE SYSTEM DIPS INTO THE NORTHERN PLAINS/UPPER
MIDWEST WED NIGHT/EARLY THU.  OVERALL...THE MODELS ARE IN FAIRLY
GOOD AGREEMENT WITH ONE ANOTHER INTO WED EVENING WHEN THE GFS
BECOMES A LITTLE FLATTER THAN THE MAJORITY OF THE GUIDANCE.  GIVEN
THE AFOREMENTIONED SHIFT IN THE GUIDANCE...THIS SOLUTION MAY BE
LESS PREFERRED. BY EARLY THU...THE 00Z ECMWF BECOMES MORE OF AN
OUTLIER...BECOMING MORE AMPLIFIED THAN THE OTHER DETERMINISTIC
RUNS AND ITS OWN ENSEMBLE MEAN.  AT THIS POINT...A COMPROMISE
BETWEEN THE GFS AND THE 00Z ECMWF MAY BE PREFERRED.

UPPER TROUGH MOVING INTO CALIFORNIA THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF
CONFIDENCE: AVERAGE

THE 12Z GFS IS A LITTLE SLOWER/DEEPER THAN ITS 00Z RUN AND IS
ALONG THE AMPLIFIED SIDE OF DETERMINISTIC GUIDANCE AS THE SYSTEM
DRIFTS ONSHORE LATE WED-EARLY THU.  IN CONTRAST...THE NAM IS LESS
AMPLIFIED THAN THE MAJORITY OF THE LATEST DETERMINISTIC RUNS.  THE
00Z CANADIAN IS A FLAT/PROGRESSIVE OUTLIER WITH THIS SYSTEM.  THE
00Z ECMWF APPEARS TO BEST FIT NEAR THE MIDST OF THE GUIDANCE
SOLUTIONS.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

PEREIRA

$$





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