Prognostic Meteorological Discussion
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FXUS10 KWNH 311838
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT FRI JUL 31 2015

VALID JUL 31/1200 UTC THRU AUG 04/0000 UTC

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

FINAL 12Z MODEL EVALUATION AND PREFERENCES

UPPER HIGH EXTENDING FROM OREGON INTO TEXAS...
SHORTWAVE TROUGH INFLUENCING THE GREAT BASIN/N. ROCKIES THIS
WEEKEND...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  BLEND GFS/ECMWF
CONFIDENCE:  AVERAGE

MODELS SHOW STRONG AGREEMENT IN MAINTAINING THE HIGH OVER TEXAS
THROUGH THE WEEKEND WITH ITS ASSOCIATED SHORTWAVE RIDGE EXTENDING
INTO OREGON...BUT BEGINNING TO ERODE ALONG ITS WESTERN EDGES BY
LATE SATURDAY.

BY LATE SATURDAY INTO EARLY SUNDAY...MODELS REMAIN CONSISTENT
MOVING SHORTWAVE ENERGY ACROSS THE GREAT BASIN AND EVENTUALLY INTO
THE NORTHERN ROCKIES.  WHILE THESE SOLUTIONS INVOLVE THE
INTERACTIONS OF NUMEROUS SHORT WAVELENGTH ELEMENTS INCLUDING THE
INFLUENCE OF CONVECTION THAT MAY RESULT IN DIFFERENT OUTCOMES IN
FUTURE CYCLES...THE GENERAL MODEL EVOLUTION APPEARS REASONABLE.

REGARDING MODEL CHOICES...THE 12Z GFS AND 0Z ECMWF REMAIN THE MOST
CONSISTENT AND CLOSEST TO THE ENSEMBLE MEANS. THE 0Z UKMET AND 0Z
CMC ARE TRENDING CLOSER TO THE ECMWF/GFS AS WELL. THE 12Z NAM
BREAKS DOWN THE UPPER RIDGE QUICKER AND APPEARS TO BE AN OUTLIER
WITH THIS SOLUTION. THUS AT THIS TIME A BLEND OF THE 12Z GFS AND
0Z ECMWF REMAINS THE PREFERRED SOLUTION.

FINAL PREFERENCE UPDATE:
THE 12Z ECMWF/CMC/UKMET ALL CAME IN WITH SIMILAR SOLUTIONS TO THE
PREVIOUS PREFERENCE. THUS WILL CONTINUE TO SUGGEST AN ECMWF/GFS
BLEND WITH GROWING CONFIDENCE.


UPPER TROUGH EXTENDING FROM THE GREAT LAKES SOUTHWARD...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/ECMWF BLEND
CONFIDENCE: AVERAGE

MODELS IN GOOD AGREEMENT WITH THE GENERAL IDEA OF A TROUGH
BUILDING INTO THE EAST. HOWEVER THEY DIFFER WITH THE EXACT TIMING
OF INDIVIDUAL SHORTWAVES MOVING ACROSS THE GREAT LAKES. IN GENERAL
THE TREND AMONG THE GUIDANCE HAS BEEN TO INJECT SLIGHTLY MORE
ENERGY INTO THE TROUGH...RESULTING IN A SLIGHTLY QUICKER AND
DEEPER SOLUTION. THE LATEST 12Z NAM/GFS CONTINUE TO TREND IN THIS
DIRECTION...WITH THE 0Z ECMWF ON THE SLOWER SIDE AND MORE IN LINE
WITH THE 0Z CMC. THE 0Z UKMET APPEARS TO OFFER A LESS PROBABLE
SOLUTION...BEING MUCH WEAKER THAN THE REMAINDER OF THE GUIDANCE.
GIVEN RECENT TRENDS WOULD HEDGE A BIT TOWARDS THE QUICKER 12Z
NAM/GFS SOLUTIONS...ALTHOUGH LIKELY NOT AS DEEP AS THE NAM.
ENSEMBLE MEANS ARE SLOWER THAN THE DETERMINISTIC RUNS...BUT THE
MEANS CAN BE LATE TO CATCH ON TO TRENDS AT TIMES.  GIVEN
THIS...WOULD NOT COMPLETELY RULE OUT A SLOWER SOLUTION CLOSER TO
THE ECMWF...AND THUS THE WPC PREFERENCE WILL REMAIN A BLEND OF THE
ECMWF/GFS THOUGH HEDGED TOWARDS THE GFS.

FINAL PREFERENCE UPDATE:
THE 12Z ECMWF/UKMET/CMC DID IN GENERAL TREND TOWARDS THE NAM/GFS
WITH REGARDS TO TIMING. HOWEVER THEY REMAIN ON THE WEAKER SIDE.
THUS AT THIS TIME THE 12Z NAM SEEMS TO OFFER A LESS PROBABLE
SOLUTION GIVEN ITS SHORTWAVE STRENGTH AND DEEPER TROUGH. THUS AN
EVEN BLEND OF THE 12Z GFS/ECMWF STILL SEEMS LIKE A GOOD PREFERENCE
REPRESENTING A MIDDLE GROUND SOLUTION.

CLOSED LOW NEARING THE PACIFIC NORTHWEST SUNDAY NIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/ECMWF BLEND
CONFIDENCE: AVERAGE

THE 0Z UKMET AND 12Z GFS ARE NOW ON THE QUICKER SIDE OF THE
GUIDANCE WITH THIS FEATURE...THE 12Z NAM AND 0Z ECMWF IN
BETWEEN...AND THE 0Z CMC ON THE SLOWER SIDE. THE TREND AMONG THE
DETERMINISTIC GUIDANCE HAS DEFINITELY BEEN FOR A QUICKER SOLUTION.
THIS WOULD SEEM TO SUGGEST THE CMC IS AN UNLIKELY SOLUTION. THE
12Z GFS AND 0Z UKMET ARE QUICKER THAN THEIR ENSEMBLE MEANS...BUT
STILL REPRESENT A POSSIBLE SOLUTION. THUS FOR NOW THE WPC
PREFERENCE IS BETWEEN THE 12Z GFS AND 0Z ECMWF...AGAIN HEDGED
TOWARDS THE 12Z GFS GIVEN TRENDS.

FINAL PREFERENCE UPDATE:
THE 12Z ECMWF/CMC DID BOTH TREND QUICKER WITH THIS UPPER LOW AND
THE 12Z UKMET A BIT SLOWER. THIS IN GENERAL DECREASED THE SPREAD
AMONG THE GUIDANCE...WITH THE 12Z GFS NOW BEING A FAST OUTLIER.
HOWEVER GIVEN RECENT TRENDS FOR A QUICKER SOLUTION...IT CAN NOT BE
COMPLETELY RULED OUT. THUS A BLEND OF THE 12Z GFS/ECMWF STILL
SEEMS TO OFFER THE BEST CONSENSUS POSITION AT THIS TIME.

...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


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