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Model Diagnostics Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0641Z Mar 27, 2015)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 AM EDT FRI MAR 27 2015

VALID MAR 27/0000 UTC THRU MAR 30/1200 UTC

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

...AN EVALUATION OF THE 00Z MODEL GUIDANCE ALONG WITH FINAL
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...FULL-LATITUDE TROF REACHING THE WESTERN ATLANTIC BY MIDDAY
SUNDAY...
...WAVY FRONTAL BOUNDARY EXITING THE EAST COAST...

FINAL PREFERENCE: BLEND OF THE 00Z GFS/ECMWF WITH THE 00Z GEFS MEAN
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

A DEEP AMPLIFIED TROF CURRENTLY SWINGING THROUGH THE MS RIVER
VALLEY IS COMPRISED OF A SERIES OF SMALLER-SCALE VORTICITY MAXIMA.
THE STRONG HEIGHT FALLS TRACKING EASTWARD ARE DRIVING A
WELL-DEFINED BAROCLINIC ZONE ACROSS THE EASTERN SEABOARD SPREADING
A BROAD AXIS OF LIGHT TO MODERATE PRECIPITATION. IT WILL TAKE A
WHILE FOR THE ENTIRE SYSTEM TO EXIT THE EAST COAST AS THE
MULTITUDE OF SHORTWAVES WORK THEIR WAY EASTWARD. A MAJORITY OF THE
MODELS SHOW THE UPPER TROF MOVING INTO THE WESTERN ATLANTIC BY
SOMETIME SUNDAY MORNING/AFTERNOON. MUCH OF THE UNCERTAINTY IN THE
FORECAST IS REGARDING THE PLACEMENT OF THE SURFACE WAVES TRACKING
ALONG THE WAVY FRONT. THIS WILL ULTIMATELY DICTATE WHERE THE
INVERTED TROF WILL SET UP STRETCHING BACK TOWARD THE NORTHEASTERN
U.S. WHILE THE ENSEMBLE SURFACE LOW PLOTS SHOW QUITE A BIT OF
SPREAD...IT DOES APPEAR THE 00Z NAM/CMC/UKMET AND 21Z SREF MEAN
SOLUTIONS ARE TOO SLOW. THE STRONGEST MODEL CONSENSUS IS WITH THE
00Z GFS/ECMWF AS SUPPORTED BY THE 00Z GEFS MEAN. GIVEN THE GROWING
SPREAD AT HAND...WILL TOSS THE ENSEMBLE MEAN INTO THE MIX TO
ACCOUNT FOR UNCERTAINTY.


...PROGRESSIVE HEIGHT FALLS CROSSING THE PACIFIC NORTHWEST ON
FRIDAY NIGHT...
...AMPLIFIED FLOW MOVING INTO THE GREAT LAKES...

FINAL PREFERENCE: BLEND OF THE 00Z ECMWF/UKMET
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE BROAD UPPER RIDGE INITIALLY ANCHORING THE WESTERN THIRD OF THE
CONUS WILL QUICKLY GIVE WAY TO A STRONG SHORTWAVE RACING TOWARD
THE PACIFIC NORTHWEST. MODELS ARE IN AGREEMENT THAT THE INITIAL
HEIGHT FALLS SHOULD REACH THE WA/OR COAST BY 28/0600Z. WHAT
HAPPENS AFTERWARD STILL REMAINS UP FOR DEBATE AS THE SPREAD GROWS
MARKEDLY BEYOND THE DAY 1 FORECAST PERIOD. BY 28/1200Z...THE 21Z
SREF MEAN STANDS OUT AS A FAST OUTLIER WHILE BEING QUICKER THAN
ANY DETERMINISTIC SOLUTION. THE 00Z NAM/GFS SHOW SOME SUPPORT FOR
THESE SOLUTIONS BUT ARE STILL SLOWER OVERALL. MEANWHILE...THE
00Z/12Z ECMWF/UKMET INDICATE MORE OF A SOUTHEASTERN MOTION
DRAGGING THE SHORTWAVE TOWARD THE CENTRAL PLAINS BY SUNDAY
MORNING. THE 564-DM SPAGHETTI PLOT SHOWS QUITE A FEW ENSEMBLE
SUPPORTING A BIT MORE DIGGING THAN THE NCEP MODELS ARE SHOWING.
THUS...THE 00Z/12Z ECMWF/UKMET DO HAVE SOME ENSEMBLE SUPPORT.
TOWARD THE END OF THE WEEKEND AND INTO EARLY NEXT WEEK...THERE IS
A STRONG CONSENSUS THAT A NORTHERN STREAM TROF WILL DIG DOWN INTO
THE GREAT LAKES. GIVEN THE MORE NORTHWARD DISPLACEMENT OF THE 00Z
NAM/GFS...THESE MODELS END UP SHOWING THE INITIAL SHORTWAVE
BECOMING ABSORBED INTO THE LARGE-SCALE SYSTEM WHILE THE 00Z/12Z
ECMWF/UKMET KEEP THEM MORE SEPARATED. WHILE NOT IN COMPLETE
AGREEMENT...WPC WILL CONTINUE TO SUPPORT THE 00Z ECMWF/UKMET
SOLUTION MORE THAN THE 00Z NAM/GFS.


...MID-LEVEL WEAKNESS NEAR BAJA CA ON SUNDAY/MONDAY...

FINAL PREFERENCE: BLEND OF THE 00Z ECMWF/GEFS MEAN
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

THIS SECTOR OF THE COUNTRY DEFINITELY CONTAINS THE MOST SPREAD AS
A COMPLEX SYNOPTIC PATTERN UNFOLDS. A PAIR OF SYSTEMS APPEAR TO
AFFECT THE REGION WITH VARYING DIFFERENCES NOTED. FIRST...THE
SHORTWAVE CROSSING THE PACIFIC NORTHWEST LATE FRIDAY ENDS UP
DRAGGING SOME SHEARED MID-LEVEL ENERGY INTO THE DESERT SOUTHWEST.
THE AMOUNT AND STRENGTH OF THIS VORTICITY SEEMS UNCERTAIN AT THIS
TIME. MEANWHILE...ANOTHER SYSTEM WELL TO THE WEST ALONG 30N WILL
POTENTIALLY CARRY ADDITIONAL SHORTWAVE ENERGY TOWARD BAJA CA LATE
IN THE PERIOD. THE OUTLIER IS NOW ONLY THE 12Z ECMWF ENSEMBLE MEAN
AS THE 00Z ECMWF LITERALLY PARALLELS THE OUTPUT OF THE 00Z GEFS
MEAN. ADDITIONALLY...THE 00Z CMC DEPICTS A SIMILAR SOLUTION WHILE
BEING A BIT STRONGER ALOFT. PLAN ON INCLUDING THE 00Z ECMWF INTO
THE MIX ALONG WITH THE PREVIOUS PREFERENCE OF THE 00Z GEFS MEAN.
WILL RAISE THE CONFIDENCE ACCORDINGLY GIVEN THE DIMINISHING SPREAD.


...SOUTHWESTERLY FLOW INTO VANCOUVER ISLAND BY LATE IN THE
PERIOD...

FINAL PREFERENCE: A NON-00Z CMC MODEL COMPROMISE
FORECAST CONFIDENCE: AVERAGE

BY DAY 3...THE IDEA OF A BROAD LONGWAVE TROF CROSSING THE
NORTHEASTERN PACIFIC IS WELL SUPPORTED IN THE GUIDANCE. THE MODELS
VARY WITH THE EXACT PLACEMENT OF THIS FEATURE WITH THE 00Z/12Z CMC
CONTINUING TO BE THE MOST OUTLYING SOLUTION WITH THE UPPER TROF
DISPLACED NORTHWARD. THIS LEADS TO A DIFFERENT SURFACE LOW TRACK
THAN THE ENSEMBLE LOW PLOTS SUPPORT. THE 00Z/12Z CMC DEPICT
PARALLEL FLOW ALONG THE LOCAL TERRAIN ACROSS COASTAL WA AND
VANCOUVER ISLAND WHICH LIMITS THE QPF ACROSS THE REGION. THE
PREVIOUS WPC PREFERENCE WILL STAND HERE.



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