Prognostic Meteorological Discussion
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000
FXUS10 KWNH 301714
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
113 PM EDT SAT MAY 30 2015

VALID MAY 30/1200 UTC THRU JUN 03/0000 UTC

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

12Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY PREFERENCES


SURFACE WAVE TRACKING INTO THE NRN MID-ATLANTIC REGION SUN NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE 00Z UKMET IS QUICKEST WITH THE SURFACE LOW / COLD FRONT INTO
THE NRN MID-ATLANTIC THROUGH SUN NIGHT...AND IS NOT WITHIN THE
LATEST ENSEMBLE LOW CLUSTERING. ALTHOUGH THE 12Z NAM/GFS SHOW GOOD
AGREEMENT WITH A SLOWER TRACK...THE 00Z ECMWF/CMC ARE ALSO SIMILAR
WITH THEIR FASTER PROGRESSION OF THE LOW. A BLEND OF THE GFS/ECMWF
APPEARS MOST LIKELY WITH THIS FEATURE GIVEN THEIR AGREEMENT WITH A
BLEND OF THE LATEST ENSEMBLE MEANS.


NORTHERN STREAM TROUGH CROSSING THE GREAT LAKES MON AND TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM / 00Z ECMWF BLEND
CONFIDENCE: AVERAGE

REGARDING THE UPPER TROUGH FORECAST TO INTENSITY OVER THE GREAT
LAKES REGION AND TRACK TOWARD NEW ENGLAND FOR LATE TUE...THE GFS
IS WEAKER AND A BIT FASTER THAN THE CONSENSUS...WITH THE 00Z ECMWF
STRONGER AND SLOWER. THE ENSEMBLE MEANS SUPPORT A STRONGER SYSTEM
THAN DEPICTED BY THE 12Z GFS...AND ALSO A SLOWER EVOLUTION. THE
00Z ECMWF AND 12Z NAM APPEAR TO MATCH SLOWING TRENDS SEEN IN THE
ENSEMBLE GUIDANCE BEST AT THIS TIME.


MCV AND ATTENDANT SURFACE LOW OVER THE MIDDLE MS VALLEY
MID-UPPER LEVEL TROUGH CROSSING THE GULF COAST THROUGH TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM...12Z GFS THROUGH 12Z/01
            1/3 WEIGHT EACH OF THE 12Z NAM...12Z GFS...00Z EC MEAN
              BETWEEN 12Z/01 AND 00Z/03
CONFIDENCE: AVERAGE

THE 12Z NAM/GFS ARE MUCH BETTER INITIALIZED WITH AN MCV NEAR THE
DALLAS-FORT WORTH METROPLEX THIS MORNING...COMPARED TO THE 00Z
ECMWF/UKMET/CMC WHICH DO NOT RESOLVE THE FEATURE WELL. THE NAM/GFS
TAKE THE REMNANTS OF THE MCV TOWARD THE LOWER-MIDDLE MISSISSIPPI
VALLEY BY 12Z/31 WHILE ALSO TRANSLATING AN UPPER
TROUGH...CURRENTLY MOVING INTO KANSAS/OKLAHOMA...TOWARD THIS AREA
AS WELL. THE NAM/GFS FORECAST A SLOWER PROGRESSION OF THE
SHORTWAVE CURRENTLY OVER THE KANSAS/OKLAHOMA BORDER THAN THE 00Z
ECMWF/UKMET/CMC...WITH SOME FLIP FLOPPING OF FASTER/SLOWER NOTED
IN THE UKMET/CMC.

THE RESULT IS A DEEPER AND SLOWER 500 MB TROUGH OVER THE LOWER
MISSISSIPPI VALLEY BY 00Z/01 IN THE 12Z NAM/GFS...AND THIS IS
BETTER SUPPORTED BY THE SREF/GEFS ENSEMBLE MEANS WITH THE 00Z
ECMWF ENSEMBLE MEAN A LITTLE SLOWER THAN THE 00Z ECMWF. AFTER
12Z/01...THE 12Z GFS IS SLOWEST WITH THE TRACK OF THE UPPER TROUGH
EWD ALONG THE GULF COAST FOR MON AND TUE...BUT THE 00Z ECMWF MEAN
COULD BE A BIT TOO QUICK BASED ON THE LATEST SREF/GEFS ENSEMBLE
MEANS.

THEREFORE...A NAM/GFS BLEND APPEARS REASONABLE GIVEN BETTER
HANDLING OF THE TEXAS MCV THROUGH 12Z/01...BUT A BLEND OF THE
NAM/GFS WITH THE FASTER 00Z ECMWF MEAN APPEARS BEST AFTER 12Z/01
THROUGH 00Z/03.


UPPER TROUGHING ACROSS THE NORTHWEST THROUGH TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM...12Z GFS...00Z ECMWF
CONFIDENCE: AVERAGE

THERE ARE MULTIPLE SHORTWAVES EMBEDDED WITHIN A BROADER SCALE
UPPER TROUGH TO IMPACT THE NORTHWESTERN U.S. THROUGH THE MIDDLE OF
THE WEEK. OVERALL...THE MODELS SHOW SOME RELATIVELY MINOR
DIFFERENCES WITH THE SYNOPTIC SCALE DETAILS OF THE UPPER TROUGH
FOR MON/TUE...WITH THE 00Z UKMET FASTEST OF THE DETERMINISTIC
GUIDANCE AND TOWARD THE FASTER END OF THE LATEST 564 DM ENSEMBLE
SPAGHETTI 500 MB HEIGHTS. NO SIGNIFICANT TREND IN TIMING HAS BEEN
NOTED IN OVER THE PAST 4 CYCLES OF ENSEMBLE SPAGHETTI HEIGHTS BUT
BETTER CLUSTERING EXISTS TOWARD THE DEPTH/TIMING OF THE 00Z EC
MEAN...BEST MATCHED BY THE 12Z NAM...12Z GFS AND 00Z ECMWF.


...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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