Prognostic Meteorological Discussion
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000
FXUS10 KWNH 301719
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
117 PM EDT THU JUL 30 2015

VALID JUL 30/1200 UTC THRU AUG 03/0000 UTC

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

12Z NAM/GFS MODEL EVALUATION WITH ANALYSIS AND  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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/NAM AND 0Z 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.


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

MODELS START OFF IN GOOD AGREEMENT WITH THE TROUGH AXIS AND
GENERAL CORRIDOR OF VORTICITY MAXIMA THURSDAY INTO THE DAY ON
FRIDAY. SPREAD AMONG THE GUIDANCE BEGINS TO INCREASE SOME BY LATER
FRIDAY INTO THE WEEKEND.

MODELS STILL SEEM TO DIVERGE SOME ON WHICH AREAS OF VORTICITY
BECOMES 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. ALTHOUGH
MODEL DIFFERENCES APPEAR TO BE MORE MINOR COMPARED TO YESTERDAY.

IN THE BROADEST SENSE...THE 12Z GFS/NAM AND 0Z ECMWF STAYED WITH
THE IDEA THAT MORE OF THE SHORTWAVE ENERGY WOULD BE OFF THE EAST
COAST OF FL AND PULLING TOWARDS THE EAST WHILE LEAVING LESSER
AMOUNTS OF ENERGY OVER THE GULF OF MEXICO. ONLY THE 0Z UKMET
APPEARS TO BE A STRONG OUTLIER WITH HOW IT HANDLES THE VORT ENERGY
IN THE SHEAR AXIS. HOWEVER EVEN THE GFS/NAM/ECMWF/CMC DIFFER ON
HOW THEY HANDLE THE ENERGY THAT IS LEFT BEHIND...WITH THE ECMWF
MOVING IT MORE OVER FLORIDA...AND THE NAM/GFS FURTHER EAST CLOSER
TO THE BAHAMAS AND THE CMC JUST WEAKER IN GENERAL. UNFORTUNATELY
WITH A LACK OF A CONSISTENT TREND NO ONE SOLUTION CAN BE PREFERRED
OVER ANOTHER AT THIS TIME...WITH A GENERAL CONSENSUS APPROACH
SEEMING TO BE BEST...WITH BELOW AVERAGE CONFIDENCE CONTINUING.



ADDITIONAL SHORTWAVE ENERGY OVER BRITISH COLUMBIA ADVANCING INTO
THE GREAT LAKES DEEPENING THE LARGE SCALE TROF THU INTO SAT.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~
PREFERENCE: 12Z GFS AND 0Z 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 THE WEEKEND ACTING TO DEEPEN THE LARGE SCALE TROUGH OVER THE
EASTERN PORTION OF THE COUNTRY.

WITH THE FIRST SHORTWAVE...THE 12Z GFS/NAM AND THE 00Z ECMWF/CMC
SEEM TO HAVE THE BEST HANDLE ON TIMING AND STRENGTH...WHILE THE 0Z
UKMET REMAINED ON THE FAST SIDE.

AS ADDITIONAL SHORTWAVE ENERGY MOVES INTO THE GREAT LAKES REGION
FRIDAY INTO THE WEEKEND...SPREAD INCREASES WITH REGARDS TO
STRENGTH/TIMING WHICH ALSO IMPACTS HOW DEEP THE EAST COAST TROUGH
BECOMES. THE 0Z UKMET REMAINS A SHARP OUTLIER...INITIALLY QUICKER
AND DEEPER THAN THE OTHER GUIDANCE AND EVENTUALLY LESS AMPLIFIED
WITH THE TROUGH BY DAY 3. THE 12Z NAM REMAINS ON THE DEEPER MORE
AMPLIFIED SIDE OF THINGS. IT HAS SUPPORT FROM THE SREF MEAN...BUT
RECENT TRENDS WITH THE NAM ARE FOR A WEAKER SOLUTION...CLOSER TO
THE GFS/ECMWF. THUS AT THIS POINT STILL BELIEVE A CONSENSUS OF THE
0Z ECMWF AND 12Z GFS IS PREFERRED AT THIS TIME FOR THE
STRENGTH/LOCATION OF THE EAST COAST TROUGH...WHICH BOTH HAVE
SUPPORT FROM THEIR ENSEMBLE MEANS. THE 0Z CMC IS ALSO PRETTY CLOSE
TO THIS IDEA.


SHORTWAVES EMBEDDED AND AROUND THE SUBTROPICAL RIDGE ACROSS THE
SOUTH CENTRAL
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
PREFERENCE: 12Z GFS AND 0Z ECMWF
CONFIDENCE: BELOW AVERAGE

SUBTLE SHORTWAVES EMBEDDED IN THE SUBTROPICAL RIDGE AND MOVING
AROUND ITS PERIPHERY WILL BE COMMON THROUGH THE WEEKEND. GIVEN THE
SUBTLE AND CONVECTIVE NATURE OF SOME OF THESE VORT
MAXES...PREDICTABILITY IS RATHER LOW IN GENERAL. ONE MORE WELL
DEFINED SHORTWAVE SHOULD TRACK ACROSS COLORADO INTO KS/OK LATER
TONIGHT INTO FRIDAY. IN GENERAL THERE IS GOOD AGREEMENT BETWEEN
THE 12Z GFS AND 0Z ECMWF AND THEIR ENSEMBLES ON THE TIMING AND
STRENGTH OF THIS FEATURE. THE 12Z NAM APPEARS A BIT SLOW...WITH
THE 0Z UKMET AN OUTLIER WITH REGARDS TO STRENGTH/POSITION AND THE
0Z CMC SIMILAR TO THE ECMWF/GFS...JUST A BIT STRONGER. THUS FOR
THIS FEATURE WPC PREFERS A CONSENSUS OF THE 12Z GFS AND 0Z ECMWF.

BEYOND FRIDAY...THERE IS GENERAL AGREEMENT WITH THE POSITION OF
THE BUILDING RIDGE...WITH DIFFERENCES ORIGINATING IN THE
PLACEMENT/STRENGTH OF INDIVIDUAL SHORTWAVES. IT APPEAR A MORE WELL
DEFINED SHORTWAVE SHOULD MOVE OUT OF AZ/CA INTO TO NV/UT THIS
WEEKEND. HOWEVER DUE IN PART TO DIFFERENCES IN THE STRENGTH OF THE
BUILDING RIDGE...LOCATION ND TIMING OF THIS WAVE DIFFER. IN
GENERAL THE 12Z NAM/GFS ARE ON THE WEAKER SIDE WITH THE RIDGE AND
THE 0Z ECMWF/CMC ON THE STRONGER SIDE RESULTING IN A MORE WESTERN
SHORTWAVE TRACK. THE 0Z UKMET APPEARS TO BE TOO MUCH OF A
STRONG/WEST OUTLIER AT THIS TIME. IN GENERAL THE TREND HAS BEEN
FOR A STRONGER SHORTWAVE RESULTING IN A WEAKER RIDGE...THUS THE
NAM/GFS SOLUTIONS CAN INTO BE RULED OUT. THUS FOR NOW PREFER A
BLEND OF THE 12Z GFS AND 0Z ECMWF WHICH APPEARS TO OFFER A GOOD
MIDDLE GROUND SOLUTION AND HAS SUPPORT FROM THEIR ENSEMBLE MEANS.

...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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