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000
FXUS10 KWNH 241702
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 PM EST SAT JAN 24 2015

VALID JAN 24/1200 UTC THRU JAN 28/0000 UTC

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

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


SHORTWAVE NEAR THE PACIFIC NORTHWEST TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GUIDANCE SHOWS REASONABLE AGREEMENT WITH THIS SYSTEM.


CLOSED LOW MOVING INTO THE WEST LATE MONDAY/TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE 12Z NAM IS THE STRONGEST WITH THIS SYSTEM ALOFT, WHICH IS ITS
TYPICAL BIAS.  PREFER A NON-NAM COMPROMISE WITH THIS SLOW-MOVING
AND RELATIVELY LARGE SYSTEM WITH ABOVE AVERAGE CONFIDENCE.


CLIPPER SYSTEM MOVING BY THE GREAT LAKES MON/TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CANADIAN COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GUIDANCE HAS OVERALL TRENDED EAST WITH THIS SYSTEM, MOSTLY DUE
TO A STRONGER/BROADER RIDGE ACROSS THE WEST, AND STRONGER AT THE
SURFACE DESPITE ITS WEAK APPEARANCE ALOFT.  THE 00Z CANADIAN IS A
QUICK OUTLIER WITH THIS SYSTEM ALOFT AND AT THE SURFACE, WHICH
ULTIMATELY CAUSES PROBLEMS DOWNSTREAM NEAR THE EAST COAST.


CLIPPER-TYPE SYSTEM EVOLVING INTO A NOR`EASTER MON/TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/ECMWF COMPROMISE (CLOSE TO THE UKMET)
CONFIDENCE: BELOW AVERAGE

THERE IS A BIT OF UNCERTAINTY WITH THIS SYSTEM, WITH SOME OF IT
INTRODUCED BY AN UPSTREAM SHORTWAVE STREAKING NEAR THE GREAT LAKES
AND SOME INTRODUCED BY ITS BURGEONING SIZE OF THE OVERALL SYSTEM
AS IT APPROACHES THE NORTHEAST/NEW ENGLAND.  THE 00Z CANADIAN IS
FARTHEST TO THE EAST/WEAKEST ALOFT WITH THIS SYSTEM DUE TO ITS
FASTER PROGRESSION WITH BOTH THIS AND AN UPSTREAM SHORTWAVE WHILE
THE 12Z GFS IS THE STRONGEST/MOST CONSOLIDATED ALOFT.  THE 00Z
ECMWF/12Z UKMET/12Z NAM/12Z GFS TAKE THE SURFACE LOW MUCH CLOSER
TO THE 40N 70W "BENCHMARK" (A RELIC TERM FROM THE OLD ACETATE DAYS
AT NMC).  WITH AT LEAST TWO NOTABLE SHORTWAVES MERGING TO CREATE
THIS LARGE SYSTEM, IT COULD TAKE A WHILE TO CONSOLIDATE ALOFT, SO
THE GFS IS PROBABLY TOO DEEP ALOFT.  THE TREND IN THE ECMWF IS
TOWARDS A MORE SOUTHERLY SYSTEM, WHILE THE ECMWF/GFS/UKMET HAVE
TRENDED STRONGER ALOFT OVER THEIR PAST DAY OF RUNS, WHICH HAS
FORCES A WESTWARD TREND AT THE SURFACE.  WITH THE STRENGTHENING
TREND ALOFT/WESTERLY SURFACE CYCLONE TRACK TREND, THE 00Z GLOBAL
ENSEMBLE GUIDANCE MAY HAVE LITTLE UTILITY TODAY.  A COMPROMISE OF
THE 12Z GFS/00Z ECMWF, CLOSE TO THE 12Z UKMET, AND IS PREFERRED
WITH BELOW AVERAGE CONFIDENCE DUE TO THE EVER-CHANGING
DETERMINISTIC GUIDANCE.


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

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

ROTH
$$




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