Prognostic Meteorological Discussion
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000
FXUS10 KWNH 261854
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
153 PM 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...

FINAL 12Z MODEL EVALUATION WITH 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 AND 12Z 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 12Z TUE
ONWARD...THAN NAM BEARS MORE IN COMMON WITH THE LAST TWO RUNS OF
THE ECMWF THAN THE MORE PROGRESSIVE 12Z UKMET/CMC GLOBAL/GEFS MEAN
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 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 ALOFT (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...EVEN 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/UKMET/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 LATEST
DETERMINISTIC RUNS AND THE 09Z SREF MEAN.

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
ECMWF/UKMET SHOW THIS SYSTEM SHEARING OUT MORE TO THE NORTHEAST
AHEAD OF A SHORTWAVE TROUGH DIGGING INTO THE GREAT LAKES...THE GFS
SHOWS A BETTER 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/ECMWF/UKMET
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 ECMWF BECOMES MORE OF AN
OUTLIER...BECOMING MORE AMPLIFIED THAN THE OTHER DETERMINISTIC
RUNS AND ITS OWN ENSEMBLE MEAN AS THIS SYSTEM MOVES FROM THE UPPER
MS VALLEY INTO THE UPPER GREAT LAKES REGION.  AT THIS POINT...A
COMPROMISE BETWEEN THE GFS..ECMWF AND UKMET MAY BE PREFERRED.

UPPER TROUGH MOVING INTO CALIFORNIA THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/ECMWF/UKMET
CONFIDENCE: AVERAGE

TO VARYING DEGREES...THE GFS..ECMWF..UKMET..CMC GLOBAL HAVE ALL
SHIFTED TOWARD A SLOWER/MORE AMPLIFIED TROUGH AS THE SYSTEM DRIFTS
ONSHORE LATE WED-EARLY THU.  THE NAM/CMC GLOBAL FALL ALONG THE
LESS AMPLIFIED SIDE OF GUIDANCE.  GIVEN THE TRENDS...WILL
RECOMMEND LEANING TOWARD THE MORE AMPLIFIED SET OF 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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