Prognostic Meteorological Discussion
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277
FXUS10 KWNH 161632
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1131 AM EST SAT DEC 16 2017

VALID DEC 16/1200 UTC THRU DEC 20/0000 UTC

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

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

...SHORTWAVE TROUGH EXITING THROUGH THE NORTHEAST TODAY/TONIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE LATEST MODELS ARE IN GOOD AGREEMENT WITH THE DETAILS OF THE
SHORTWAVE TROUGH CROSSING THROUGH THE NORTHEAST TODAY AND EXITING
THROUGH THE CANADIAN MARITIMES TONIGHT. A GENERAL MODEL BLEND WILL
BE PREFERRED.


...UPPER LEVEL LOW CURRENTLY OVER NORTHERN MEXICO...
...EJECTING NORTHEAST ACROSS THE SOUTHERN PLAINS BY TONIGHT...
...DEAMPLIFYING ON SUNDAY AS IT SHEARS DOWNSTREAM...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PREFERENCE: NON-CMC BLEND
CONFIDENCE: ABOVE AVERAGE

THE 00Z CMC GRADUALLY BECOMES A LITTLE SLOWER THAN THE MODEL
CONSENSUS WITH THE UPPER LOW EJECTING NORTHEAST OUT OF NORTHERN
MEXICO AND THEN WEAKENING INTO AN OPEN WAVE BEFORE SHEARING OUT
OVER THE NEXT 24 TO 36 HOURS. THE REMAINING GUIDANCE IS GENERALLY
WELL CLUSTERED WITH THEIR TIMING AND DEPTH...SO WILL FAVOR A
NON-CMC BLEND AT THIS TIME.


...SHORTWAVE DIGGING SHARPLY THROUGH SOUTHERN CA...
...CLOSED LOW DEVELOPMENT OVER THE DESERT SOUTHWEST/NW MEXICO...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z UKMET
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS ARE IN VERY GOOD AGREEMENT DIGGING A SHORTWAVE TROUGH
DOWN THROUGH SOUTHERN CA TODAY AND THEN ACROSS THE NORTHERN BAJA
PENINSULA TONIGHT WHERE THE ENERGY SHOULD DEEPEN AND CLOSE OFF. A
CLOSED LOW CENTER IS THEN EXPECTED TO GRADUALLY PIVOT EAST ACROSS
FAR NORTHWEST MEXICO THROUGH MONDAY BEFORE THEN ADVANCING
DOWNSTREAM OUT ACROSS THE SOUTHERN PLAINS THROUGH TUESDAY. THE
HEIGHT FALLS WILL LIKELY INDUCE AT LEAST A WEAK AREA OF LOW
PRESSURE ACROSS THE SOUTHEAST TX COASTAL PLAIN BY LATE TUESDAY
WHICH SHOULD BE FOCUSED ALONG A FRONTAL ZONE. THE GUIDANCE IS IN
RATHER GOOD AGREEMENT UNTIL TUESDAY WHEN THE 00Z CMC AND 00Z ECMWF
BECOME A LITTLE SLOWER THAN THE 12Z NAM AND 12Z GFS. THE 00Z UKMET
IS ESSENTIALLY THE MODEL CONSENSUS AND SPLITS THE DIFFERENCE
BETWEEN THE CAMPS AT THE END OF THE PERIOD. THE LATEST GEFS MEAN
AND ECENS MEAN SUPPORT THEIR RESPECTIVE DETERMINISTIC SOLUTIONS.
SO WILL FAVOR A SOLUTION IN BETWEEN WHICH IS THE UKMET AT THIS
TIME.


...SHORTWAVE TRAVERSING THE NORTHERN ROCKIES/PLAINS TODAY/SUNDAY...
...ENERGY DAMPENING OUT OVER THE GREAT LAKES/NORTHEAST BY MONDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE

THE NORTHERN PORTION OF THE SHORTWAVE TROUGH THAT CAME INTO THE
PACIFIC NORTHWEST LAST NIGHT WILL MOVE ACROSS THE NORTHERN ROCKIES
TODAY AND ACROSS THE NORTHERN PLAINS ON SUNDAY. ON MONDAY THE
ENERGY WILL BEGIN TO DAMPEN OUT AS IT CROSSES THE GREAT LAKES
REGION AND THE NORTHEAST. A WEAK AREA OF LOW PRESSURE ALONG A
FRONTAL ZONE OVER THE CENTRAL PLAINS/MIDWEST WILL BREAK AWAY AND
CROSS PARTS OF THE GREAT LAKES AND NORTHEAST AS THIS ENERGY
CROSSING THE NORTHERN TIER OF THE COUNTRY. DIFFERENCES WITH THIS
SYSTEM ARE SMALL SCALE AND MAINLY NOTED WITH THE 00Z UKMET AND 00Z
ECMWF FAVORING A SLIGHTLY STRONGER REMNANT SHORTWAVE FEATURE THAT
CROSSES THE NORTHEAST...VERSUS THE WEAKER 12Z NAM/12Z GFS AND 00Z
UKMET. THE FLOW DOES BECOME QUITE ZONAL ACROSS THE REGION BY
MONDAY WHICH WOULD TEND TO SUPPORT A WEAKER/SHEARED SOLUTION...BUT
FOR NOW WILL RECOMMEND A GENERAL MODEL BLEND TO RESOLVE THE
SMALLER SCALE DIFFERENCES.


...AMPLIFYING NORTHERN STREAM TROUGH OVER SOUTHERN CANADA MONDAY...
...ENERGY DIGGING ACROSS THE MIDWEST/GREAT LAKES BY TUESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS TAKE SHORTWAVE ENERGY THAT ARRIVES ACROSS NORTHERN
BRITISH COLUMBIA FROM THE GULF OF AK AND DIGS IT AGGRESSIVELY
SOUTHEAST OVER THE NEXT FEW DAYS WHICH ALLOWS A RATHER STRONG
NORTHERN STREAM TROUGH TO CROSS SOUTHERN CANADA AND THE NORTHERN
U.S. WITH IMPACTS ACROSS THE NORTHERN PLAINS/MIDWEST AND GREAT
LAKES THROUGH MONDAY AND TUESDAY. A STRONG COLD FRONT WILL
ACCOMPANY THESE HEIGHT FALLS. THE MODELS ARE IN RATHER GOOD
AGREEMENT WITH THE LARGE SCALE DETAILS OF THE TROUGH AND THE COLD
FRONT...BUT THERE IS A LITTLE BIT OF SPREAD WITH THE SURFACE
LOW...MAINLY RESULTING FROM THE 00Z UKMET TRACKING ITS SURFACE LOW
FARTHER SOUTH ACROSS CANADA. THE REMAINING GUIDANCE IS CLUSTERED
TOWARD A DOMINANT SURFACE LOW THAT TRACKS ACROSS CENTRAL CANADA
TOWARD HUDSON BAY. THE LATEST GEFS MEAN AND ECENS MEAN SUPPORT THE
NON-UKMET CLUSTER...SO A NON-UKMET BLEND WILL BE PREFERRED AS A
RESULT.


...DEEP UPPER TROUGH/CLOSED LOW CROSSING THE GULF OF AK MONDAY...
...ENERGY DIGGING SHARPLY INTO THE PACIFIC NORTHWEST ON TUESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS TAKE A NORTHERN STREAM SHORTWAVE TROUGH OVER THE GULF
OF AK AND AMPLIFY IT SOUTHEAST TOWARD THE PACIFIC NORTHWEST ON
TUESDAY WHICH ALLOWS FOR SOME STRONG HEIGHT FALLS TO ARRIVE IN
CONJUNCTION WITH A DEEPENING AREA OF LOW PRESSURE. THIS LOW
PRESSURE WAVE MOVES ACROSS NORTHWEST WA BY LATE TUESDAY. THE
MODELS ARE WELL CLUSTERED WITH TIMING AND DEPTH...WITH EXCEPTION
OF THE 00Z ECMWF WHICH IS SLOWER THAN ANY OTHER MODEL. THE SLOWER
ECMWF DOES HAVE SOME SUPPORT FROM THE ECENS MEAN...BUT THE LATEST
GEFS MEAN SUPPORTS THE SLIGHTLY MORE PROGRESSIVE CONSENSUS. THUS A
NON-ECMWF BLEND WILL BE PREFERRED.


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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