Prognostic Meteorological Discussion
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000
FXUS10 KWNH 011856
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 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 GFS/ECMWF/NAM BEFORE 04/12Z ... 12Z
GFS/ECMWF AFTER.
CONFIDENCE:  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.  THE 12Z NAM WAS A GOOD
COMPROMISE TO THE GFS/00Z ECMWF SOLUTION...GIVEN UPSTREAM TREND
(SEE BELOW) SOME 12Z GFS/06 GEFS SUPPORT MAY BE WARRANTED GIVEN
RUN TO RUN TRENDS IN THE ENSEMBLE SUITE.  THIS WAS FURTHER
SUPPORTED WITH THE 12Z ECMWF TRENDING MUCH CLOSER TO THE 12Z
GFS/NAM...PROVIDING STRONGER CONFIDENCE IN THIS TREND.   AS SUCH A
12Z GFS/NAM/ECMWF BLEND IS PREFERRED AT 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/ECMWF/UKMET
CONFIDENCE:  AVERAGE

THE 12Z GFS AND ECMWF REMAINS IN CLOSE PROXIMITY AND EVOLUTION TO
EACH OTHER...THOUGH THE GFS  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 THIS CONTINUED BLEND.
THE 12Z NAM IS A BIT TOO FAST AND THE 12Z CMC REMAINS A BIT TOO
FAR WEST...TO BE INCLUDED AT THIS TIME.  THE 12Z UKMET LIKE ITS
00Z RUN IS IN 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 PARTICULARLY OVER
SOUTHERN CANADA ALOFT AND BEING THE FURTHEST SOUTH WITH SURFACE
LOW OVER QUEBEC...THOUGH DIFFERENCES ARE NOT SIGNIFICANT ENOUGH TO
ELIMINATE IT FROM THE BLEND COMPLETELY.  THE 00Z UKMET WAS A SHADE
FAST...ITS NORMAL BIAS...BUT THE 12Z RUN WAS IS BETTER AGREEMENT
WITH OTHER BLEND SUPPORTED MEMBERS.  THE  ECMWF CONTINUES GOOD
RUN TO RUN CONTINUITY AND SOLID ENSEMBLE 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/ECMWF
CONFIDENCE:  AVERAGE

THE 12Z GFS MUCH LIKE ITS PRIOR RUNS IS IN GOOD AGREEMENT WITH THE
ECMWF SOLUTION 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.  THE
12Z RUNS OF THE GFS/ECMWF HAVE INCREASED AGREEMENT THROUGH MUCH OF
THE FORECAST PERIOD INCLUDING INTERACTION WITH TUTT CELL MOVING
OUT OF THE BAHAMAS.  THIS IS INCREASES CONFIDENCE IN THIS BLEND TO
AVERAGE BUT DUE.

THE 12Z 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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