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239
FXUS10 KWNH 141656
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1155 AM EST THU DEC 14 2017

VALID DEC 14/1200 UTC THRU DEC 18/0000 UTC

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

12Z MODEL EVALUATION...WITH LATEST PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...EXITING UPPER TROUGH OVER THE NORTHEAST...
...CLIPPER SHORTWAVE/LOW EXITING OFFSHORE NEW ENGLAND TODAY..
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW GOOD AGREEMENT WITH THE DETAILS OF THE EXITING
LARGER SCALE TROUGH OVER THE NORTHEAST AND THE CLIPPER
SHORTWAVE/SURFACE LOW EXITING AROUND THE BASE OF THIS TROUGH AND
OFFSHORE NEW ENGLAND THROUGH TODAY. WILL PREFER A GENERAL MODEL
BLEND WITH ABOVE AVERAGE CONFIDENCE.


...SHORTWAVE DIGGING SOUTH ACROSS THE PLAINS...
...ENERGY CROSSING THE LOWER MS/TN VALLEYS ON FRI...
...POSSIBLE SURFACE LOW DEVELOPMENT OFF THE MID-ATLANTIC ON FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A SHORTWAVE WILL DROP SOUTH DOWN ACROSS THE PLAINS TODAY BEFORE
SWEEPING ACROSS THE LOWER MS AND TN VALLEY REGION ON FRIDAY. THIS
ENERGY IS EXPECTED TO HELP RELOAD A LARGER SCALE LONGWAVE TROUGH
ACROSS THE EASTERN U.S. BY THE END OF THE WEEK AND WILL ENCOURAGE
A SURFACE LOW DEVELOPING OFFSHORE THE MID-ATLANTIC BY FRIDAY
NIGHT. THE GUIDANCE SHOWS GOOD AGREEMENT OVERALL WITH THE
SHORTWAVE DETAILS...WITH SOME MINOR TIMING DIFFERENCES.
HOWEVER...AT THE SURFACE...THE 00Z CMC A BIT FARTHER NORTH AND A
BIT STRONGER THAN THE REMAINING GUIDANCE AS LOW PRESSURE DEVELOPS
OFFSHORE THE MID-ATLANTIC. GIVEN REASONABLY GOOD MODEL CLUSTERING
SEEN OTHERWISE ALONG WITH ENSEMBLE SUPPORT...A NON-CMC CONSENSUS
WILL BE PREFERRED.


...NEW UPPER LOW DROPPING SOUTH TOWARD THE GREAT LAKES BY FRI...
...ENERGY ADVANCING INTO NEW ENGLAND ON SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS TAKE ARCTIC SHORTWAVE ENERGY DROPPING SOUTH FROM
NUNAVUT IN NORTHERN CANADA DOWN TO THE SOUTH OVER THE NEXT COUPLE
OF DAYS WHICH RESULTS IN A NEW UPPER LOW DROPPING SOUTH OVER
HUDSON BAY AND THEN ACROSS ONTARIO BY FRIDAY. THIS WILL RESULT IN
HEIGHT FALLS ENCROACHING ON THE GREAT LAKES REGION AND A WAVE OF
LOW PRESSURE IMPACTING THIS REGION. THEREAFTER GOING INTO THE
WEEKEND...THE ENERGY WILL PIVOT ACROSS NEW ENGLAND. THE 00Z CMC
DROPS ITS HEIGHT FALLS JUST A TAD FARTHER SOUTH WHICH RESULTS IN
ITS SURFACE LOW DROPPING A BIT FARTHER SOUTH AS WELL COMPARED TO
THE REMAINING GUIDANCE. THE 12Z GFS IS ALSO PERHAPS JUST A TAD
MORE PROGRESSIVE TO SHIFT THE ENERGY FARTHER EAST INTO NEW
ENGLAND. AT THIS STAGE...THE CMC IS A BIT MORE OF AN OUTLIER...AND
SO A NON-CMC CONSENSUS WILL BE PREFERRED.


...SHORTWAVE TROUGH ARRIVING ACROSS THE PACIFIC NORTHWEST ON FRI...
...TROUGHING DIGGING ACROSS THE INTERMOUNTAIN WEST/PLAINS...
...COLD FRONT SETTLING OVER THE PLAINS/MIDWEST BY SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/00Z UKMET/00Z ECMWF...AT SURFACE
            BLEND OF THE 12Z UKMET AND 12Z ECMWF...ALOFT W/TROUGH
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE MODELS BREAK DOWN THE WESTERN NORTH AMERICA RIDGE BY THE END
OF THE WEEK AND THIS ALLOWS A SHORTWAVE TROUGH AND ASSOCIATED COLD
FRONT TO ARRIVE ACROSS THE PACIFIC NORTHWEST BY THE END OF THE
WEEK. AS ALL OF THE ENERGY INITIALLY COMES INTO THE PACIFIC
NORTHWEST...THE 12Z GFS IS JUST A TAD MORE PROGRESSIVE WITH THE
ENERGY COMPARED TO THE MODEL CONSENSUS...WITH THE 00Z CMC A TAD
SLOWER. THE REMAINING GUIDANCE IS WELL CLUSTERED AND OVERALL THE
MODEL SPREAD WITH THE INITIAL ARRIVAL OF THE HEIGHT FALLS IS QUITE
SMALL.

ALL OF THIS ENERGY ALONG WITH A COLD FRONT WILL ADVANCE SOUTHEAST
ACROSS THE INTERMOUNTAIN WEST AND THEN OUT ACROSS THE PLAINS AND
MIDWEST FRIDAY NIGHT THROUGH SATURDAY. THE GUIDANCE SUPPORTS THE
NORTHERN PORTION OF SOME OF THE UPPER TROUGHING CROSSING THE UPPER
MIDWEST BY EARLY SATURDAY ALONG WITH A CLIPPER-STYLE SURFACE LOW.
THE 00Z CMC IS MUCH SLOWER AND WEAKER WITH THIS SYSTEM...WITH THE
REMAINING GUIDANCE RATHER WELL CLUSTERED. THIS ENERGY THEN DAMPENS
OUT AS IT DIGS SOUTHEAST...BUT ALL OF THE MODELS SHOW A COLD FRONT
ADVANCING SOUTHEAST DOWN THROUGH THE PLAINS...WITH A NEW AREA OF
LOW PRESSURE BY LATE SATURDAY FORCING OVER THE SOUTH-CENTRAL HIGH
PLAINS REGION. THE 12Z NAM GENERALLY KEEPS ITS ENTIRE FRONTAL ZONE
SOUTHEAST OF THE MODEL CONSENSUS...WITH THE 00Z CMC A BIT FARTHER
NORTH. THE 12Z GFS/00Z UKMET AND 00Z ECMWF ARE CLUSTERED IN
BETWEEN. THE DETAILS OF LOW PRESSURE OVER THE HIGH PLAINS AND THE
FRONTAL PLACEMENT WILL TEND TO BE RELATED TO THE DETAILS OF HEIGHT
FALLS DROPPING SOUTH ACROSS THE INTERMOUNTAIN WEST AND INTO THE
FOUR CORNERS REGION. THE 12Z NAM AND TO SOME EXTENT THE 00Z ECMWF
TAKE THE TROUGHING OVER THE FOUR CORNERS REGION A BIT FARTHER EAST
COMPARED TO THE 12Z GFS AND 00Z UKMET. HOWEVER...THE GFS HAS MUCH
MORE JET ENERGY DIGGING INTO THE BASE OF THE TROUGH COMPARED TO
THE OTHER MODELS. THE 00Z CMC ON THE OTHER HAND MAINTAINS MORE
TROUGHING AND A CLOSED LOW FEATURE MUCH FARTHER WEST COMPARED TO
ANY OTHER MODEL. ACCOUNTING FOR THE OUTLIER SOLUTIONS...WILL
PREFER A BLEND OF THE UKMET/GFS AND ECMWF WITH THE FRONT/SURFACE
LOW PLACEMENT GIVEN GOOD MODEL CLUSTERING....BUT A BLEND OF THE
UKMET AND ECMWF WITH THE TROUGH ALOFT.


...UPPER LEVEL LOW OVER THE BAJA PENINSULA/GULF OF CALIFORNIA...
...PORTION OF ENERGY LIFTING TOWARD THE RIO GRANDE VALLEY...
...ENERGY SHEARING NORTHEAST ACROSS THE LOWER MS VALLEY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A WEAK SHORTWAVE DROPPING SOUTH DOWN TOWARD NORTHWEST MEXICO WILL
MERGE UP WITH THE UPPER LOW CURRENTLY OVER THE BAJA PENINSULA
TODAY...WITH THE RESULTANT PHASED ENERGY THEN RESULTING IN NEW
CLOSED LOW EVOLUTION THAT MOVES EAST ACROSS WESTERN MAINLAND
MEXICO BEFORE THEN LIFTING NORTHEAST TOWARD THE RIO GRANDE VALLEY
ON SATURDAY IN RESPONSE TO UPSTREAM HEIGHT FALLS DROPPING INTO THE
SOUTHWEST U.S. AND ADJACENT FOUR CORNERS REGION. ON SUNDAY...THIS
ENERGY WILL SHEAR NORTHEAST AND DOWNSTREAM ACROSS THE SOUTHERN
PLAINS AND LOWER MS VALLEY. THE 00Z CMC IS A SLOW OUTLIER TO EJECT
THE ENERGY OUT OF MAINLAND MEXICO AND ACROSS THE RIO GRANDE
VALLEY. THE REMAINING GUIDANCE IS WELL CLUSTERED...SO A NON-CMC
CONSENSUS WILL BE PREFERRED.


...UPPER LOW DEVELOPMENT OVER CALIFORNIA ON SAT...
...ENERGY DIGGING TOWARD THE NORTHERN BAJA PENINSULA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM AND 00Z UKMET
CONFIDENCE: BELOW AVERAGE

THE MODELS TAKE A PORTION OF THE UPPER TROUGH CROSSING THE PACIFIC
NORTHWEST ON FRIDAY AND DROP IT SOUTH DOWN ACROSS CALIFORNIA ON
SATURDAY WHERE MOST OF THE MODELS SHOW IT AMPLIFYING AND
SEPARATING OUT INTO A COMPACT CLOSED LOW THAT ARRIVES TOWARD
SOUTHERN CALIFORNIA BY LATE SATURDAY. THE 12Z GFS IS MORE
AGGRESSIVE IN SWINGING THE ENERGY SOUTHEAST TOWARD THE DESERT
SOUTHWEST AND THEN EASTWARD TOWARD PARTS OF THE FOUR CORNERS
REGION WHERE IT ATTEMPTS TO PHASE WITH ENERGY DROPPING SOUTH OVER
THE INTERMOUNTAIN WEST. THE 00Z ECMWF KEEPS A CLOSED LOW FEATURE
TOWARD THE END OF THE PERIOD THAT IS WELL WEST OF THE MODEL
CONSENSUS. THE 12Z NAM AND 00Z UKMET ARE CLUSTERED A BIT FARTHER
EAST IN BETWEEN THE GFS AND ECMWF. THE 06Z GEFS MEAN IS A LITTLE
FARTHER EAST BY COMPARISON WHICH IS SUPPORTED BY THE 00Z CMC. WILL
PREFER A BLEND OF THE NAM AND GFS AS A COMPROMISE WHICH IS
SUPPORTED BY THE 00Z ECENS MEAN AS A COMPROMISE.


MODEL TRENDS AT www.wpc.ncep.noaa.gov/html/model2.shtml
500 MB FORECASTS AT www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

ORRISON


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