Prognostic Meteorological Discussion
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FXUS10 KWNH 291851
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 PM EDT WED JUL 29 2015

VALID JUL 29/1200 UTC THRU AUG 02/0000 UTC

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

12Z MODEL EVALUATION WITH ANALYSIS AND FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ANY NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO AFFECT SHORT
TERM FORECAST ERRORS


WELL DEFINED UPPER LOW ACROSS WESTERN ONTARIO SETS UP OVER HUDSON
BAY BY FRIDAY WITH ATTENDANT COLD FRONT PROGRESSING EAST ACROSS
THE GREAT LAKES WED AND ALONG THE EASTERN SEABOARD BY FRIDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/NAM AND 12Z ECMWF CONSENSUS
CONFIDENCE: ABOVE AVERAGE

OVERALL MODEL AGREEMENT WAS GOOD WITH RESPECT TO THE
STRENGTH/TIMING OF THE UPPER LOW AND SURFACE COLD FRONT MOVING
EAST ACROSS THE REGION. THE ABOVE DETERMINISTIC GUIDANCE
PREFERENCE WAS ALSO IN GOOD AGREEMENT WITH THE ECMWF/GFS ENSEMBLE
MEANS...ADDING SOME CONFIDENCE TO THE EXPECTED EVOLUTION.


LOW-LEVEL SHEAR AXIS WITH EMBEDDED WEAK SURFACE LOWS ACROSS THE
GULF OF MEXICO INTO THE SARGASSO SEA AND ASSOCIATED WEAK UPPER
LOW/ELONGATED TROF
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL DETERMINISTIC MODEL CONSENSUS
CONFIDENCE: BELOW AVERAGE

MODELS START OFF IN GOOD AGREEMENT WITH THE TROUGH AXIS AND
GENERAL CORRIDOR OF VORTICITY MAXIMA THURSDAY INTO FRIDAY. SPREAD
AMONG THE GUIDANCE BEGINS TO EMERGE BY LATER FRIDAY INTO
SATURDAY...AS MODELS DIVERGE ON WHICH VORT AREAS BECOME DOMINANT
AND HOW MUCH OF THE ENERGY IS PUSHED NORTHEAST WITH THE LONG WAVE
UPPER TROUGH OVER THE EAST COAST...AND HOW MUCH IS LEFT BEHIND TO
PROGRESS WEST INTO THE GULF OF MEXICO. THE 12Z NAM/GFS ARE THE
MORE PROGRESSIVE SOLUTIONS...MOVING MOST OF THE ENERGY OFF TO THE
NORTHEAST...WITH THE 0Z ECMWF/UKMET/CMC HANGING MORE ENERGY BACK
NEAR FLORIDA. UNFORTUNATELY ENSEMBLE MEANS GENERALLY FOLLOW THEIR
DETERMINISTIC RUNS...THUS NOT OFFERING TOO MUCH IN THE WAY OF
HELP. ALSO THERE HAS NOT BEEN A RECENT TREND THAT HAS BEEN
CONSISTENT ENOUGH TO BE CONFIDENT WITH. THUS AT THIS TIME WPC
PREFERS A GENERAL CONSENSUS OF THE DETERMINISTIC GUIDANCE BUT AT
BELOW NORMAL CONFIDENCE IN THE EVENTUAL EVOLUTION FRIDAY INTO
SATURDAY ACROSS FLORIDA AND ADJACENT LOCATIONS.

THE NEW 12Z ECMWF HAS TRENDED MORE TOWARDS THE GFS/NAM IDEA OF
HAVING LESS ENERGY HANGING BACK ACROSS FLORIDA AND THE GULF OF
MEXICO. THIS MAY ADD SOME CONFIDENCE TO A SOLUTION MORE IN LINE
WITH THE GFS/NAM. HOWEVER RUN TO RUN CONSISTENCY HAS BEEN
LOW...AND IN GENERAL THE PATTERN FEATURES LOW PREDICTABILITY GIVEN
THE SUBTLE NATURE OF THE VORT MAXES IN PLAY. ALSO THE 12Z
UKMET/CMC HAVE STAYED CONSISTENT WITH THEIR FURTHER SOUTHWEST
SOLUTION. THUS AT THIS TIME NO CHANGE IN THE WPC GENERAL CONSENSUS
PREFERENCE.


ADDITIONAL SHORTWAVE ENERGY OVER BRITISH COLUMBIA ADVANCING INTO
THE GREAT LAKES DEEPENING THE LARGE SCALE TROF THU INTO SAT.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~
PREFERENCE: 12Z GFS/NAM/ECMWF
CONFIDENCE: AVERAGE

ON THURSDAY EVENING ONE SHORTWAVE IS EXPECTED TO MOVE ACROSS THE
GREAT LAKES AND PUSH NORTHEAST INTO NEW ENGLAND ON FRIDAY.
ADDITIONAL SHORTWAVE ENERGY WILL DIVE INTO THE GREAT LAKES FRIDAY
INTO SATURDAY ACTING TO DEEPEN THE LARGE SCALE TROUGH OVER THE
EASTERN PORTION OF THE COUNTRY.

WITH THE FIRST SHORTWAVE...THE 12Z GFS AND 0Z ECMWF SEEM TO HAVE
THE BEST HANDLE ON TIMING AND STRENGTH...MATCHING BEST WITH RECENT
TRENDS AND THEIR ENSEMBLE MEANS. THE 12Z NAM IS ON THE SLOWER SIDE
OF THE MODEL ENVELOPE AND THE 0Z UKMET ON THE FASTER SIDE...BOTH
CONSIDERED LESS LIKELY SOLUTIONS.

GUIDANCE BEGINS TO DIVERGE ON THEIR HANDLING OF THE ADDITIONAL
SHORTWAVE ENERGY THAT DIVES INTO THE GREAT LAKES FRIDAY INTO
SATURDAY. IN GENERAL THE 12Z GFS/NAM AND 09Z SREF MEAN ARE
STRONGER WITH THE ENERGY THAN THE 0Z ECMWF...WHICH RESULTS IN A
DEEPER LARGE SCALE TROUGH. THE 0Z UKMET IS AGAIN ON THE QUICKER
SIDE OF GUIDANCE...ITS USUAL BIAS. THUS THE UKMET SEEMED OUT OF
PHASE AND IS CONSIDERED A LESS LIKELY SOLUTION. THE ECMWF AND GEFS
ENSEMBLE MEANS SEEM TO OFFER A GOOD MIDDLE GROUND SOLUTION BETWEEN
THE WEAKER 0Z ECMWF AND STRONGER/DEEPER GFS/NAM SOLUTIONS. THE
TREND HAS IN GENERAL BEEN FOR A DEEPER EASTERN TROUGH BY
SATURDAY...THUS THE DEEPER 12Z NAM AND SREF ENSEMBLE MEAN CAN NOT
BE RULED OUT. GIVEN THIS TREND AND THE FACT THAT THE 0Z ECMWF
ENSEMBLE MEAN IS ACTUALLY DEEPER THAN THE DETERMINISTIC RUN...THE
0Z ECMWF WEAKER SOLUTION IS ALSO CONSIDERED A LESS LIKELY SOLUTION
AND THUS IS NOT PREFERRED AT THIS TIME.

THE NEW 12Z ECMWF HAS INDEED COME IN STRONGER WITH THE SHORTWAVE
AND THUS DEEPER WITH THE TROUGH COMPARED TO THE 0Z RUN. THIS COMES
MORE IN LINE WITH THE GFS/NAM SOLUTIONS. THUS THE ECMWF NOW
APPEARS TO BE A MORE VIABLE OPTION BY DAY 2/3 IN THIS REGION. THE
12Z UKMET STILL SEEMS A BIT QUICK...BUT IS NOW MORE IN LINE WITH
THE REMAINDER OF THE GUIDANCE. GIVEN THE TREND IN THE NEW
ECMWF...THE ONLY CHANGE IN THE MODEL PREFERENCE WAS TOO INCLUDE
THE NEW 12Z ECMWF INTO THE BLEND.



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

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

CHENARD/GALLINA


$$





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