Prognostic Meteorological Discussion
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000
FXUS10 KWNH 121859
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST TUE DEC 12 2017

VALID DEC 12/1200 UTC THRU DEC 16/0000 UTC

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

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

...DEEPENING/NEGATIVELY TILTED CYCLONE IMPACTING THE NORTHEAST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS OVER THE NEXT 36 HOURS SHOW GOOD MASS FIELD AGREEMENT
WITH THE DETAILS OF THE STRENGTHENING AND NEGATIVELY TILTING
TROUGH OVER THE NORTHEAST. LOW PRESSURE INITIALLY OVER WESTERN NY
WILL RECONSOLIDATE OVER SOUTHERN NEW ENGLAND LATER THIS AFTERNOON
AND THEN LIFT NORTH UP ACROSS CENTRAL AND DOWNEAST MAINE BY EARLY
WEDNESDAY. THE SYSTEM WILL EXIT UP ACROSS QUEBEC ON THURSDAY. WILL
PREFER A GENERAL MODEL BLEND AT THIS TIME.


...STRONG SHORTWAVE ENTERING BRITISH COLUMBIA TODAY...
...ENERGY AND ASSOCIATED CLIPPER LOW DIGGING SOUTHEAST...
...CROSSING THE UPPER MIDWEST/OH VALLEY/MID-ATLANTIC WED/THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE GUIDANCE SHOWS A STRONG PACIFIC SHORTWAVE CURRENTLY CROSSING
BRITISH COLUMBIA THAT WILL DIGGING SOUTHEASTWARD OVER THE NEXT 48
HOURS AND AMPLIFY ACROSS THE UPPER MIDWEST/OH VALLEY AND
MID-ATLANTIC REGION. AN ASSOCIATED CLIPPER-TYPE SURFACE LOW WILL
CROSS THE REGION AND THEN QUICKLY EJECT OFFSHORE SOUTHERN NEW
ENGLAND ON THURSDAY. THE 12Z CMC TRENDED A BIT FASTER AND IS CLOSE
TO THE MODEL CONSENSUS WITH THIS SYSTEM. THEREFORE...A GENERAL
MODEL BLEND WILL BE PREFERRED CONSIDERING THE GUIDANCE IS RATHER
WELL CLUSTERED.


...SHORTWAVE DIGGING SOUTH ACROSS THE PLAINS THURS...
...ENERGY CROSSING THE LOWER MS/TN VALLEYS ON FRI...
...POSSIBLE SURFACE LOW DEVELOPMENT OFF THE MID-ATLANTIC ON FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/12Z UKMET AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A SHORTWAVE CRESTING THE TOP OF THE WESTERN NORTH AMERICA RIDGE
AXIS WILL DROP SOUTH DOWN FROM THE NORTHWEST TERRITORIES IN CANADA
AND THEN DOWN ACROSS THE PLAINS THURSDAY 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 AS WELL. THE 12Z CMC IS
NOW THE SLOWEST AND STRONGEST MODEL WITH THIS FEATURE...WITH THE
REMAINING GUIDANCE RATHER WELL CLUSTERED TOWARD A SOMEWHAT MORE
PROGRESSIVE AND FLATTER SOLUTION. HOWEVER...THE 12Z NAM IS ALSO ON
THE SLOW AND SOMEWHAT DEEPER SIDE WITH THE SHORTWAVE. ALL OF THE
MODELS SUPPORT AT LEAST A WEAK SURFACE WAVE OFFSHORE THE
MID-ATLANTIC BY THE END OF THE PERIOD...BUT WITH THE SHORTWAVE
ENERGY GENERALLY SHEARING OUT...THE SURFACE WAVE SHOULD TEND TO BE
ELONGATED AND MAY ACTUALLY TAKE THE FORM OF MULTIPLE WAVES. THE
12Z CMC IS AN OUTLIER WITH ITS STRONGER SOLUTION NEAR THE VA CAPES
AT THE END OF THE PERIOD. WILL PREFER A CONSENSUS OF THE FLATTER
12Z GFS/12Z UKMET AND 12Z ECMWF AT THIS TIME.


...NEW UPPER LOW DROPPING SOUTH TOWARD THE GREAT LAKES BY FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/12Z UKMET AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS TAKE ARCTIC SHORTWAVE ENERGY CURRENTLY UP OVER 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 THE END OF THE WEEK. THIS WILL RESULT
IN HEIGHT FALLS ENCROACHING ON THE GREAT LAKES REGION AND A WAVE
OF LOW PRESSURE IMPACTING THIS REGION. THE 12Z NAM DIGS THE ENERGY
FARTHEST SOUTH AND CROSSING THE UPPER GREAT LAKES...WITH THE 12Z
CMC NOW A BIT SLOWER AND KEEPING MORE ENERGY BACK OVER WESTERN
ONTARIO. THE 12Z GFS/12Z UKMET AND 12Z ECMWF ALL TEND TO CLUSTER
TOGETHER WELL OVER CENTRAL ONTARIO BY THE END OF THE PERIOD AND
HAVE GOOD SUPPORT FROM THE 12Z GEFS MEAN AND 00Z ECENS MEAN. THUS
WILL PREFER A BLEND OF THE GFS/UKMET AND ECMWF.


...SHORTWAVE TROUGH ARRIVING ACROSS THE PACIFIC NORTHWEST ON FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z UKMET
CONFIDENCE: 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. THE 12Z CMC AND 12Z ECMWF ARE BOTH GENERALLY THE SLOWEST
SOLUTIONS WITH THIS SYSTEM. THE 12Z NAM/12Z GFS AND 12Z UKMET ARE
ALL MORE PROGRESSIVE WHICH IS SUPPORTED BY THE 00Z ECENS MEAN AND
12Z GEFS MEAN. HOWEVER...THE NAM MAY BE SLOWING DOWN THE NORTHERN
PORTION OF THE TROUGH AXIS A BIT TOO MUCH BY THE END OF THE PERIOD
OVER WESTERN CANADA. WILL LEAN TOWARD THE MORE PROGRESSIVE
CONSENSUS WITH A BLEND OF THE GFS AND UKMET.


...UPPER LEVEL LOW OVER THE BAJA PENINSULA/GULF OF CALIFORNIA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/12Z UKMET AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z NAM IS A WESTERLY OUTLIER WITH THE EVOLUTION OF THE UPPER
LOW OVER THE BAJA PENINSULA AS IT TAKES THE UPPER LOW SOUTH
THROUGH THE PERIOD...AND WELL WEST OF THE GLOBAL MODELS. THE WELL
CLUSTERED GFS/UKMET AND ECMWF SOLUTIONS TAKE THE UPPER LOW MORE
SOUTHEAST AND DOWN OVER NORTHWEST MAINLAND MEXICO. THE 12Z GEFS
MEAN AND 00Z ECENS MEAN NOW SUPPORT THIS CONSENSUS...AND THUS WILL
PREFER A BLEND OF THE GFS/UKMET AND ECMWF SOLUTIONS.


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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