Prognostic Meteorological Discussion
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801
FXUS10 KWNH 121628
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1127 AM 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: NON-CMC CONSENSUS
CONFIDENCE: SLIGHTLY 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 00Z CMC WAS A LITTLE SLOWER THAN THE
MODEL CONSENSUS...AND WITH THE REMAINING GUIDANCE RATHER WELL
CLUSTERED...A NON-CMC CONSENSUS WILL BE PREFERRED.


...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: NON-NAM CONSENSUS
CONFIDENCE: 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 NAM IS
OVERALL THE SLOWEST AND STRONGEST MODEL WITH THIS FEATURE...WITH
THE REMAINING GUIDANCE RATHER WELL CLUSTERED TOWARD A SOMEWHAT
MORE PROGRESSIVE AND FLATTER SOLUTION. 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. WILL PREFER A NON-NAM
CONSENSUS AT THIS TIME.


...NEW UPPER LOW DROPPING SOUTH TOWARD THE GREAT LAKES BY FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/00Z CMC AND 00Z 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 00Z
UKMET GENERALLY THE FARTHEST EAST AND MORE OVER TOWARD EASTERN
ONTARIO. THE 12Z GFS/00Z CMC AND 00Z ECMWF ARE ALL CLUSTERED OVER
CENTRAL ONTARIO BY THE END OF THE PERIOD. THE 06Z GEFS MEAN AND
00Z ECENS MEAN SUPPORT THE GFS/CMC/ECMWF CLUSTER AND SO A BLEND OF
THESE SOLUTIONS WILL BE PREFERRED.


...SHORTWAVE TROUGH ARRIVING ACROSS THE PACIFIC NORTHWEST ON FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z 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 00Z CMC IS A SLOW OUTLIER AND EVEN THE 00Z ECMWF ALSO
APPEARS TO BE A LITTLE SLOWER THAN THE MODEL CONSENSUS. THE 12Z
NAM/12Z GFS AND 00Z UKMET ARE ALL MORE PROGRESSIVE WHICH IS
SUPPORTED BY THE 00Z ECENS MEAN AND 06Z 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/00Z UKMET AND 00Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE 12Z NAM AND 00Z CMC GRADUALLY CLUSTER THE UPPER LOW OVER THE
BAJA PENINSULA DOWN TO THE SOUTH THROUGH THE PERIOD...AND WELL
WEST OF THE 12Z GFS/00Z UKMET AND 00Z ECMWF BY FRIDAY. THE
GFS/UKMET AND ECMWF SOLUTIONS TAKE THE UPPER LOW MORE SOUTHEAST
AND DOWN OVER NORTHWEST MAINLAND MEXICO. THE 00Z ECENS MEAN
SUPPORTS THE FARTHER EAST CONSENSUS...HOWEVER THE 06Z GEFS MEAN
FAVORS THE FARTHER WEST NAM/CMC CAMP. WILL FOR NOW LEAN TOWARD THE
FARTHER EAST CONSENSUS VIA A BLEND OF THE GFS/UKMET AND ECMWF.
CONFIDENCE IS SOMEWHAT LIMITED.


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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