Prognostic Meteorological Discussion
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000
FXUS10 KWNH 011737
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
136 PM EDT SAT AUG 01 2015

VALID AUG 01/1200 UTC THRU AUG 05/0000 UTC

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

12Z NAM/GFS MODEL GUIDANCE EVALUATION INCLUDING ANALYSIS AND
PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SHORTWAVE ENERGY ROUNDING THE WESTERN AND NORTHERN PERIPHERY OF
THE SOUTHWEST U.S. RIDGE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  BLEND OF 12Z NAM/00Z ECMWF BEFORE 04/12Z ... 00Z
ECMWF AFTER.
CONFIDENCE:  SLIGHTLY BELOW AVERAGE

MODEL AGREEMENT CONTINUES STRONG THROUGH 00Z MONDAY WHEN
INFLUENCES FROM UPSTREAM CLOSED PACIFIC LOW BEGINS TO INFLUENCE
THE NORTHWEST EDGE OF THE SHORTWAVE AS IT ELONGATES/SHEARS ACROSS
THE NORTHERN SIDE OF THE SOUTHWEST U.S. UPPER LEVEL RIDGE.  THE
12Z GFS APPEARS MOST HEAVILY INFLUENCED PLACING MUCH OF THE ENERGY
IN THE NORTHWEST PORTION OF THE SHEAR AXIS...BEGINNING TO INTERACT
WITH THE LOW REMAINING NORTH AND TRACKING ACROSS THE MT/WY LINE BY
THE END OF THE PERIOD WITH WEAKER SHEAR LOBES INTO THE LOWER
MISSOURI AND LOWER OHIO RIVER VALLEYS.   ON THE OTHER SIDE OF THE
SPECTRUM THE 00Z CMC RESOLVES THE LEAST ENERGY BUT CENTERED OVER
KANSAS BY 00Z WED....BUT HAS VERY LITTLE SUPPORT.   THE ECMWF IS
CENTRAL TO THE SUITE SUPPORTED BY ECMWF ENSEMBLE MEMBERS.  THE 12Z
NAM IS A GOOD COMPROMISE TO THE GFS/ECMWF SOLUTION...AND GIVEN
UPSTREAM TREND (SEE BELOW) SOME 12Z GFS/06 GEFS SUPPORT MAY BE
WARRANTED GIVEN RUN TO RUN TRENDS IN THE ENSEMBLE SUITE.  AS SUCH
A 12Z NAM/00Z ECMWF BLEND IS PREFERRED BUT WITH SLIGHTLY BELOW
AVERAGE CONFIDENCE.  OF NOTE: THE 12Z NAM HAS A SIGNIFICANT
CONVECTIVE FEEDBACK THAT NEGATIVELY AFFECTS MASS FIELDS COMPARED
TO THE ECMWF AFTER 12Z ON THE 4TH (TUESDAY).


CLOSED LOW AFFECTING THE PACIFIC NORTHWEST BY TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  BLEND OF 12Z GFS & 00Z ECMWF/UKMET
CONFIDENCE:  AVERAGE

THE 12Z GFS REMAINS IN CLOSE PROXIMITY AND EVOLUTION TO THE 00Z
ECMWF THOUGH SHIFTS A BIT SOUTH AND EAST UNDER SOME INTERACTION
WITH ENERGY ROUNDING THE TOP OF THE RIDGE (DESCRIBED ABOVE)...BUT
WITH GOOD ENSEMBLE AGREEMENT SUPPORT FROM THE 00Z ECMWF ENSEMBLE
AND 06 GEFS SUPPORTS A CONTINUED BLEND OF THE 12Z GFS AND 00Z
ECMWF. THE 12Z NAM IS A BIT TOO FAST AND THE 00Z CMC IS A BIT TOO
FAR WEST...TO BE INCLUDED AT THIS TIME.  THE 00Z UKMET IS ALSO IN
DESCENT ENOUGH AGREEMENT FOR INCLUSION AT THIS TIME AT AVERAGE
CONFIDENCE.


SHORTWAVE TROUGH AND ASSOCIATED SURFACE LOW CROSSING THE GREAT
LAKES/OH VALLEY MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: AVERAGE

THE TIMING OF THE SHORTWAVE AND ASSOCIATED FRONTAL ZONE ARE IN
QUITE GOOD AGREEMENT THROUGH THE GUIDANCE SUITE...WITH LARGEST
DIFFERENCES GENERALLY IN DEPTH OF THE TROF AND PLACEMENT OF THE
SECONDARY SURFACE LOW/TRIPLE POINT NORTH/SOUTH ALONG THE WELL
TIMED FRONTAL ZONE AS IT CROSSES THE GREAT LAKES. THE 12Z NAM
REMAINS THE DEEPEST WITH THE SHORTWAVE RELOADING THE BASE OF THE
LARGE SCALE TROF PARTICULARLY BY THE END OF MONDAY INTO TUESDAY
WHEN IS IT IS A CLEAR OUTLIER OVER THE EAST COAST.  THE 12Z GFS IS
ALSO ON THE DEEPER SIDE OF THE ENSEMBLE SUITE BUT NOT SO MUCH SO
TO NOT HAVE SOME WEIGHTING.  THE 00Z UKMET IS A SHADE FAST...ITS
NORMAL BIAS...BUT LIKEWISE IS NOT TOO BAD.  ECMWF HAS BEST RUN TO
RUN CONTINUITY AND SOLIDLY WITHIN STRONGER ENSEMBLE MEMBER SUPPORT
TO BE WEIGHTED MORE HEAVILY.  ALL THINGS CONSIDERED...A NON-NAM
BLEND IS PREFERRED AT AVERAGE CONFIDENCE.


FRONTAL BOUNDARY ACROSS THE SOUTHEAST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  BLEND OF 12Z GFS/00Z ECMWF
CONFIDENCE:  SLIGHTLY BELOW AVERAGE

THE 12Z GFS MUCH LIKE ITS PRIOR RUNS IS IN GOOD AGREEMENT WITH THE
ECMWF SOLUTION OF BEING A BIT WEAKER AND LESS CONSOLIDATED WITH
INDIVIDUAL SHORTWAVES/VORT LOBES ALONG THE SHEAR AXIS ALOFT AND A
BIT WEAKER WITH SURFACE INFLECTIONS ALONG THE FRONTAL BOUNDARY
ACROSS THE ENTIRE GULF ACROSS FL AND UP THE CAROLINA COAST.
SLIGHT DIFFERENCES EXIST WITH THE INTERACTION WITH TUTT CELL
COMING OUT OF THE BAHAMAS ON MONDAY BUT GENERALLY GOOD AGREEMENT
EXISTS TO CONTINUE A BLEND OF THE 12Z GFS/00Z ECMWF... THOUGH
OVERALL ORIENTATION IS GOOD...INTERNAL DETAILS REMAIN INCONSISTENT
ENOUGH TO HAVE SLIGHTLY BELOW AVERAGE CONFIDENCE.    THE 12 NAM
WAS IN BETTER AGREEMENT WITH THE 12Z GFS/00Z ECMWF BLEND...BUT
REMAINS TO CONSOLIDATED WITH THE VORT FEATURES (PARTICULARLY OVER
THE WESTERN GULF) AND OVER DEEPENS THE SURFACE LOWS A BIT FURTHER
NORTH THAN OTHER GUIDANCE.   00Z UKMET AND CMC APPEARED TO BE TOO
STRONG WITH SURFACE LOWS ALONG THE FRONTAL ZONE AWAY FROM THE MORE
CONSISTENT/PREFERRED BLEND WHICH HAS ENSEMBLE SUPPORT.

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

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

GALLINA


$$





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