Prognostic Meteorological Discussion
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FXUS10 KWNH 251657
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EST TUE NOV 25 2014

VALID NOV 25/1200 UTC THRU NOV 29/0000 UTC

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

12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

...SHORTWAVE TROUGH/LOW PRESSURE TRACKING FROM THE N. PLAINS TO
THE APPALACHIANS TODAY THROUGH WED...

PREFERENCE: GFS/00Z UKMET
CONFIDENCE: AVERAGE

OVERALL THE NAM/GFS HAVE SHOWN GOOD RUN-TO-RUN CONTINUITY.  IN
COMPARISON TO THE OVERNIGHT NON-NCEP RUNS...THE NAM IS A LITTLE
MORE AMPLIFIED IN THE BASE OF THE UPPER TROUGH AS IT MOVES FROM
THE MID MS VALLEY INTO THE TN VALLEY ON WED.  THE 00Z ECMWF MOVES
TO THE SLOWER SIDE OF THE GUIDANCE AS THE TROUGH MOVES ACROSS THE
LOWER OH/TN VALLEYS WED NIGHT.  OVERALL...THE 12Z GFS/00Z UKMET
FALL CLOSEST TO THE MIDST OF THE CURRENT MODEL SPREAD.

...LOW PRESSURE TRACKING UP THE EAST COAST TONIGHT THROUGH WED
NIGHT...

PREFERENCE: 12Z GFS/NAM AND 00Z ECMWF/UKMET COMPROMISE THROUGH 12Z
THU...FOLLOWED BY A NAM/ECMWF COMPROMISE THEREAFTER
CONFIDENCE: AVERAGE

WITH REGARDS TO THE SURFACE LOW TRACK...BOTH THE NAM/GFS HAVE
REMAINED GENERALLY CONSISTENT WITH THEIR 00Z RUNS.  ONE SUBTLE
DIFFERENCE OF NOTE IS THAT THE 12Z NAM IS A MILLIBAR OR TWO DEEPER
AND MAYBE A LITTLE SLOWER THAN ITS 00Z RUN AS THE LOW TRACKS ALONG
THE MID ATLANTIC COAST TONIGHT.  IN CONTRAST...THE 12Z GFS HAS
SHIFTED LITTLE WEAKER AND FASTER THAN ITS 00Z RUN DURING THAT SAME
TIME FRAME.

IN COMPARISON TO THE OVERNIGHT RUNS FROM THE NON-NCEP MODELS...THE
12Z GFS IS A LITTLE FASTER/WEAKER THAN THE OTHER MODELS...BUT
OVERALL THE 12Z NAM/GFS AND THE 00Z ECMWF/UKMET ARE ALL IN FAIRLY
GOOD AGREEMENT WITH THE SURFACE LOW TRACK THROUGH TOMORROW.  NOT
UNTIL THU MORNING AS THE LOW APPROACHES NOVA SCOTIA DO SOME
SIGNIFICANT DIFFERENCES BETWEEN THOSE FOUR MODELS START TO
EMERGE...WITH THE UKMET/ECMWF BECOMING NOTABLY SLOWER/DEEPER THAN
THE NCEP MODELS.  BY 12Z THU...THE MEAN OF THE ENSEMBLE SPREAD
SUGGESTS A POSITION THAT FALLS BETWEEN THE NAM AND 00Z ECMWF.  THE
ONLY TRUE OUTLIER PRIOR TO THAT IS THE 00Z CANADIAN GLOBAL WHICH
IS FASTER AND MOVES WELL EAST OF THE OTHER MODELS BY WED AFTERNOON.

...SHORTWAVE TROUGH BEGINNING TO INFLUENCE THE PACIFIC NORTHWEST
THURSDAY...

PREFERENCE: GFS/00Z ECMWF
CONFIDENCE: AVERAGE

12Z NAM/GFS HAVE NOT SHOWN ANY SIGNIFICANT CHANGES FROM THEIR 00Z
RUNS AND THEREFORE THE NAM REMAINS THE RELATIVE OUTLIER HERE...AS
IT SHIFTS A LARGE PORTION OF THE TROUGH ONSHORE MORE QUICKLY THAN
THE OTHER MODELS. GIVEN THE LACK OF SUPPORT FOR THE NAM FROM THE
OTHER DETERMINISTIC MODELS AND THE ENSEMBLE MEANS...INCLUDING THE
SREF...WILL RECOMMEND A COMPROMISE OF THE GFS/00Z ECWMF

...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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