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Model Diagnostics Discussion
 
(Latest Discussion - Issued 1852Z Apr 24, 2017)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 PM EDT MON APR 24 2017

VALID APR 24/1200 UTC THRU APR 28/0000 UTC

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

12Z MODEL EVALUATION WITH PREFERENCES/CONFIDENCE INTERVALS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

DEEP SYSTEM MOVING UP THE EAST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z NAM IS FAST WITH THE TROPICAL ORIGIN LOW AS IT SWINGS BACK
TOWARD THE CAROLINA COAST MERGING WITH THE COASTAL SURFACE WAVE
THAT IS DIRECTLY UNDER THE UPPER LOW.  THIS FAST NATURE KEEPS THE
SOLUTION ON THE NORTHERN/FASTER SIDE OF THE GUIDANCE...AND
THEREFORE IS LESS PREFERABLE. 

AS THE SYSTEM CONSOLIDATES AND VERTICALLY STACKS ON LATE TUESDAY
THERE IS SOME DISAGREEMENT ON THE DEVOLUTION AS THE SYSTEM LIFTS
TOWARD LONG ISLAND/SE NEW ENGLAND...POSSIBLY INFLUENCED BY THE
UPSTREAM EVOLUTION OVER THE GREAT LAKES.  THE ENSEMBLE TREND THERE
HAS BEEN FOR SLOWER INCREASING RIDGING...WHICH IS BEST REPRESENTED
BY THE 00Z ECMWF/ECENS MEAN AND CMC...THE FASTER WEAKENING
SOLUTIONS BEST REPRESENTED BY THE GFS TAKE A DRAMATIC RIGHT TURN
SE OF NEW ENGLAND THURSDAY WHICH SEEMS A BIT DRAMATIC GIVEN THE
ENSEMBLE TRENDS AND WHILE THE 00Z ECMWF/ECENS MEAN SHOW THE
NEGATIVE BIAS OF RETAINING A VERY STRONG/WOUND UP UPPER LOW...THIS
COMBINED WITH THE WEAKER AND SLIGHTLY EASTWARD 00Z CMC MAY BE A
NICE COMPROMISE TO ACCOUNT FOR THE TRENDS WHILE KEEPING SOME
CONTINUITY AND INCLUSION OF THE EASTWARD TURNING POSSIBILITY.  A
NON-NAM BLEND IS SUPPORTED THROUGH 26/12Z TRANSITIONING TO A 00Z
ECMWF/CMC BLEND AFTERWARD.  CONFIDENCE IS SLIGHTLY ABOVE AVERAGE
PRIOR TO 26/12Z BUT FALLING TO AVERAGE GIVEN THE CHANGE/SPREAD FOR
DAY 3.

19Z UPDATE: SLIGHT EASTWARD ADJUSTMENTS BY THE ECMWF/CMC INDICATES
BETTER OVERALL ALIGNMENT WITH THE GFS/UKMET SINCE BOTH SHIFTED
SLIGHTLY WEST WITH THERE 12Z RUNS.  STILL FAVOR THE DEEPER
SOLUTIONS OF THE ECMWF/CMC BUT OVERALL A NON-NAM BLEND COULD BE
SUPPORTED THROUGH THE DURATION OF THE EVENT AFTER 26/12Z.


BROAD TROF IN THE WEST AMPLIFYING TO BROAD POSITIVE TILT TROF
ACROSS PLAINS WED WITH SURFACE LOW/ELONGATED SURFACE TROF TRACKING
OUT OF TX/OK PANHANDLES INTO UPPER MIDWEST/GREAT LAKES THURS 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF (12Z GEFS/00Z ECENS IF DESIRED)
CONFIDENCE: SLIGHTLY BELOW AVERAGE

WV LOOP SHOWS THE DUAL SHORTWAVE FEATURES OVER THE NORTHWEST
STATES CURRENTLY WITH THE UNDERCUTTING JET STREAK INFLUENCED WAVE
ENTERING NV WITH THE OLDER MORE CONSOLIDATED CENTER JUST OFF THE
WA COAST.  IN THE SHORT TERM THE SPACING BETWEEN THE TWO WILL
EXPAND BROADENING THE LARGER SCALE TROF AND SPURRING THE INITIAL
SURFACE LOW ACROSS THE TX/OK PANHANDLE WITH INVERTED SURFACE TROF
EXTENDING TO THE REFLECTION OF THE PRIOR EXITING WAVE ENTERING THE
UPPER MIDWEST LATER TODAY(WHICH IS NOW WELL AGREED UPON WITHIN THE
GUIDANCE).    EVENTUALLY THE LEAD WAVE ELONGATES AND ACTS AS THE
PIVOT DRAWING THE OLDER CONSOLIDATED WAVE THROUGH THE ROCKIES
DEEPENING THE UPPER TROF ACROSS THE SOUTHERN PLAINS WED.  THE
TREND HAS BEEN FAVORING THE A SLOWER/DEEPENING UPSTREAM WAVE
THOUGH THE SPACING BETWEEN THE WAVES CONTINUES TO BE THE GREATEST
UNCERTAINTY.   THE GFS HAS BEEN FAST TO PRESS/SHEAR THE LEAD WAVE
FURTHER EAST AND NORTH WHICH IS GENERALLY AWAY FROM THE ENSEMBLE
TRENDS INCLUDING A MAJORITY OF THE 06Z GEFS MEMBERS. 
HOWEVER...THE 12Z GFS SEEMS TO HAVE RESPONDED IN TURN SLOWING AS
WELL; WHILE STILL A BIT FURTHER EAST THAN THE ECMWF/ECENS MEAN OR
FASTER (NORTH) OF THE GEFS MEAN IT IS MORE IN LINE WITH THE
OVERALL TREND/WPC PREFERENCE AND COULD BE INCLUDED PERHAPS A
SLIGHTLY LOWER WEIGHTING IN THE PREFERENCE.

THE 12Z NAM ON THE OTHER HAND IS LIKE THE 00Z UKMET SUGGESTING A
STRONG WOUND UP AND MUCH FURTHER SOUTHERLY SOLUTION BEFORE
SWINGING THE SHORTWAVE NORTH THROUGH THE MID-MS VALLEY. THIS MAY
BE TOO AGGRESSIVE OF A CHANGE TO JUMP TOO PARTICULARLY AS THE 00Z
UKMET HAS BEEN MUCH SLOWER BEING AN OUTLIER AND HAS SHIFTED FASTER
TO COMPROMISE TOWARD A COMMON SOLUTION PRESENTED IN THE ENSEMBLE
SUITE... CLOSEST TO THE 00Z ECMWF.  THE 00Z CMC HAS SOME
COMPROMISE OVERALL WITH THE ECMWF/ECENS PARTICULARLY IN TIMING
THOUGH IT...LIKE THE UKMET/NAM IS A BIT MORE WOUND UP LIFTING
NORTH AND IN DOING SO BENDS WESTWARD BECOMING A WESTERN MEMBER OF
THE ENSEMBLE CLUSTER OVERALL.  AS SUCH WPC PREFERENCE IS THE 00Z
ECMWF HEAVY WEIGHTING WITH THE 12Z GFS INCLUDING SOME 06Z GEFS/00Z
ECENS MEAN TO ACCOUNT FOR THE LARGE REMAINING SPREAD IN
POSSIBILITIES.  CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE IN THIS
BLEND/PREDICTABILITY OF PATTERN. 

19Z UPDATE: BOTH UKMET/CMC SHIFTED TOWARD THE ECMWF SOLUTION
THOUGH BOTH REMAIN A BIT MORE WOUND UP AND THEREFORE TRACK A BIT
WEST OF THE ECMWF/00Z ECENS MEAN.  THE 12Z ECMWF SHOWS LITTLE
CHANGE REMAINING THE MOST MIDDLE GROUND AND A BIT FLATTER THAN THE
UKMET/CMC/NAM THOUGH IS A BIT FASTER AND FURTHER NORTH THAN THE
ECENS MEAN.  THE 12Z GEFS MEAN LIKE THE FAVORABLE 06Z ENSEMBLE
SUPPORTS THE ECENS MEAN/ECMWF MORE THAN THE 12Z GFS ITSELF.  WITH
LARGE SPREAD BUT GOOD AGREEMENT IN THE ENSEMBLES...WILL FAVOR THE
12Z ECMWF AS WPC PREFERENCE BUT AT SLIGHTLY BELOW AVERAGE
CONFIDENCE.


SYSTEM MOVING INTO THE WEST WEDNESDAY RELOADING LARGE SCALE TROF
IN INTERMOUNTAIN WEST THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

STRONG BUT DRIFTING EASTWARD BLOCKING PATTERN OVER WESTERN CANADA
FORCES SHORTWAVE ENERGY TO EITHER REINFORCE CYCLONE TO THE WEST
OVER THE EASTERN GULF OF AK OR UNDERCUT THE RIDGE INTO THE PACIFIC
NORTHWEST BY WED.  EVENTUALLY THE STRONG JET AND NUMEROUS EMBEDDED
SHORTWAVES WILL FURTHER EXPAND THE LARGE SCALE TROF THAT DOMINATES
THE CENTRAL AND WESTERN PORTION OF THE CONUS BY 00Z FRIDAY. 
OVERALL THE GUIDANCE IS QUITE AGREEABLE THOUGH OBVIOUSLY SMALLER
SCALE EMBEDDED WAVE TIMING DIFFERENCES LEAD TO SMALLER SCALE
VARIABILITY TO WX ACROSS THE INTERMOUNTAIN WEST.  AS SUCH A
GENERAL MODEL BLEND IS SUPPORTED AT ABOVE AVERAGE CONFIDENCE
THROUGH THIS FORECAST PERIOD.


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