Prognostic Meteorological Discussion
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000
FXUS10 KWNH 260442
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1141 PM EST SUN JAN 25 2015

VALID JAN 26/0000 UTC THRU JAN 29/1200 UTC

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

00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


MID-LEVEL SHORTWAVE MOVING INTO BRITISH COLUMBIA MON NIGHT
SUBSEQUENT MOVEMENT INTO THE N-CNTRL U.S. EARLY THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS...12Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE 00Z GFS AND 12Z ECMWF REPRESENT THE MIDDLE OF THE LATEST
DETERMINISTIC/ENSEMBLE SPREAD WITH A MID-LEVEL SHORTWAVE FORECAST
TO CROSS INTO SWRN CANADA TUE MORNING. THE 00Z NAM AND 12Z CMC ARE
FLATTER...WHILE THE 12Z UKMET IS ON THE STRONGER/DEEPER SIDE OF
THE AVAILABLE GUIDANCE.


WEAKENING CLOSED LOW MOVING INTO CALIFORNIA EARLY TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE THROUGH 12Z/28
    70% 12Z ECMWF / 30% GFS BLEND
CONFIDENCE: AVERAGE

THE GUIDANCE IS IN GOOD AGREEMENT HERE THROUGH 12Z/28 AT WHICH
POINT THE 12Z ECMWF HOLDS MORE SHORTWAVE ENERGY BACK TO THE WEST
ACROSS THE GREAT BASIN WHILE THE GFS FOCUSES MORE TOWARD THE FRONT
END OF THE SHORTWAVE TROUGH PROGRESSING ACROSS THE WEST. THE
ECMWF/NAM/CMC HAVE TRENDED TOWARD THE 12Z ECMWF IDEA COMPARED TO
PREVIOUS CYCLES...BUT THE GFS HOLDS GOOD CONTINUITY FROM 00Z/25.
THE ENSEMBLE MEANS ARE SPLIT ON THIS IDEA...BUT GIVEN THE
TRENDS...WILL LEAN MORE TOWARD THE ECMWF.


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

THE GUIDANCE IS IN GOOD AGREEMENT HERE.


CLIPPER-TYPE SYSTEM EVOLVING INTO A NOR`EASTER MON/TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM / 12Z ECMWF COMPROMISE
CONFIDENCE: AVERAGE

THE MODELS HAVE CONVERGED TOWARD A COMMON SOLUTION BUT 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.

THROUGH 12Z/27...THE 00Z NAM...00Z GFS AND 12Z ECMWF SHOW FAIRLY
GOOD AGREEMENT IN POSITION AND STRENGTH REGARDING THE SURFACE AND
MID-LEVEL LOWS BUT THE GFS IS SLIGHTLY WEAKER BY TUE MORNING.
ENSEMBLE TRENDS AND THE LATEST ENSEMBLE MEANS...INITIALIZED
12Z/25...SUPPORT THE NAM/GFS/ECMWF COMBO.

BEYOND 12Z/27...A BLEND OF THE 00Z NAM AND 12Z ECMWF APPEARS BEST
AS THE GFS LIFTS THE PRIMARY SURFACE LOW TO THE NORTH...QUICKER
THAN PREFERRED. HOWEVER...THE 21Z SREF MEAN...12Z EC MEAN AND 00Z
NAM ARE IN GOOD AGREEMENT AND SUPPORT A TRACK THAT IS FASTER TO
DEPART THE PRIMARY SURFACE LOW COMPARED TO THE 12Z ECMWF.
THEREFORE REGARDING POSITION/STRENGTH...A BLEND OF THE 00Z NAM AND
12Z ECMWF IS PREFERRED. BOTH THE 12Z UKMET/CMC APPEAR EITHER
UNSUPPORTED IN POSITION OR STRENGTH.


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

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

OTTO

$$




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