Prognostic Meteorological Discussion
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000
FXUS10 KWNH 200446
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1245 AM EDT FRI OCT 20 2017

VALID OCT 20/0000 UTC THRU OCT 23/1200 UTC

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

00Z MODEL EVALUATION ALONG WITH LATEST MODEL PREFERENCES/CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...SHORTWAVE CURRENTLY CLIPPING NORTHERN NEW ENGLAND...
...ASSOCIATED COLD FRONT CROSSING THE NORTHEAST BY WEEKS END...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM...SO A GENERAL
MODEL COMPROMISE WILL BE PREFERRED.


...SOUTHERN STREAM UPPER TROUGH REACHING THE SOUTHERN PLAINS FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM EJECTING OUT
ACROSS THE SOUTHERN HIGH PLAINS OUT AHEAD OF THE STRONGER UPSTREAM
LONGWAVE TROUGH MOVING INTO THE WEST...SO A GENERAL MODEL
COMPROMISE WILL BE PREFERRED.


...LONGWAVE TROUGH EVOLUTION INTO THE WESTERN U.S. THROUGH FRI...
...EJECTING OUT INTO THE PLAINS ON SAT ALONG WITH COLD FRONT...
...SURFACE LOW DEEPENING OVER SOUTHERN CANADA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE...THROUGH 48 HOURS
            12Z ECMWF...AFTER 48 HOURS
CONFIDENCE: AVERAGE

THE MODELS ARE IN GOOD AGREEMENT THROUGH SATURDAY WITH THE
EVOLUTION OF THE LONGWAVE TROUGH AND ASSOCIATED COLD FRONT MOVING
THROUGH THE WESTERN U.S. BUT DIFFERENCES BECOME NOTICEABLE BY
SUNDAY AS THE ELONGATED N/S TROUGH AXIS ADVANCES ACROSS THE
PLAINS. THE 00Z GFS BECOMES A BIT OF A STRONGER OUTLIER ON SUNDAY
WITH ITS HEIGHT FALL EVOLUTION ACROSS SOUTHERN CANADA AND THIS
RESULTS IN A STRONGER SURFACE LOW COMPARED THE TO THE REMAINING
GUIDANCE. THE 00Z NAM AND 12Z CMC ALSO TEND TO BE ON THE STRONGER
SIDE OF THE MODEL SUITE...WITH THE 12Z ECMWF AND 12Z UKMET A BIT
WEAKER.

OVERALL...THE ENSEMBLE SPAGHETTI PLOTS GENERALLY SUGGEST THE NAM
AND GFS ARE STILL A TAD TOO STRONG WITH THE NORTHERN PORTION OF
THE TROUGH AXIS...WITH THE EURO AND CANADIAN MEMBERS STRONGLY
SUPPORTIVE OF THE OPERATIONAL ECMWF BY 60 HOURS ONWARD. SO BASED
ON THE LATEST TRENDS AND CLUSTERING...WILL PREFER A GENERAL MODEL
COMPROMISE THROUGH 48 HOURS...AND THEN FAVOR THE ECMWF THEREAFTER
WITH THE MASS FIELD DETAILS AT THE SURFACE AND ALOFT.


...SOUTHERN STREAM LOWER MS VALLEY CLOSED LOW DEVELOPMENT BY MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC CONSENSUS
CONFIDENCE: AVERAGE

THE MODELS BREAKING AWAY THE SOUTHERN PORTION OF THE LONGER WAVE
TROUGH EJECTING OUT OF THE WEST AND INTO THE PLAINS STATES ON
SUNDAY...WITH THIS ENERGY DIGGING SOUTHEAST INTO THE LOWER MS
VALLEY SUNDAY NIGHT AND RESULTING IN A CLOSED LOW FORMATION BY
MON. THIS WILL STILL BE INTERACTING WITH THE SOUTHERN PORTION OF A
N/S ORIENTED FRONTAL ZONE AND THE MODELS SUGGEST A WAVE OF LOW
PRESSURE WILL DEVELOP ALONG THE BOUNDARY ACROSS PARTS OF THE DEEP
SOUTH. THE 12Z CMC SOLUTION IS A BIT OF A FASTER AND WEAKER
OUTLIER WITH THIS SOUTHERN STREAM EVOLUTION...WITH THE 00Z NAM/GFS
AND 12Z UKMET/ECMWF SOLUTIONS ALL A BIT SLOWER. THE ECMWF IS JUST
A TAD FARTHER NORTH THAN THE MODEL CONSENSUS BUT IS WELL WITHIN
THE EURO AND CANADIAN ENSEMBLE SPREAD. THE GFS AND GEFS MEMBERS
ARE SEEN OVERALL BEING A BIT WEAKER THAN THE ECMWF AND THE EURO
ENSEMBLE CLUSTER. BASED ON THE LATEST DETERMINISTIC SPREAD...A
MULTI-MODEL BLEND WILL BE PREFERRED MINUS THE CMC SOLUTION...AND
THUS A NON-CMC CONSENSUS.


...NEXT UPPER TROUGH SWEEPING ACROSS THE NORTHERN PLAINS MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODEL ALLOWING ADDITIONAL UPPER TROUGHING TO SWING ACROSS THE
NORTHERN PLAINS BY SUNDAY NIGHT AND MONDAY ALONG WITH A COLD
FRONT. THE 12Z UKMET IS A LITTLE FASTER THAN THE MODEL
CONSENSUS...WITH THE 00Z GFS JUST A TAD SLOWER. THE 00Z NAM/12Z
CMC AND 12Z ECMWF ARE GENERALLY THE SLOWEST. OVERALL...A CONSENSUS
OF THE GFS AND ECMWF WOULD TEND TO APPROXIMATE THE MODEL
CONSENSUS...SO A BLEND OF THESES TWO SOLUTIONS WILL BE PREFERRED.


...SHORTWAVE REACHING BRITISH COLUMBIA SAT WITH WARM FRONT...
...NEXT ATMOSPHERIC RIVER ARRIVING OVER THE PACIFIC NORTHWEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET CONSENSUS
CONFIDENCE: ABOVE AVERAGE

THE NEXT ATMOSPHERIC RIVER WILL BE IMPACTING THE PACIFIC NORTHWEST
BY LATER FRIDAY NIGHT AND SATURDAY AS A STRONG PACIFIC JET AND
EMBEDDED SHORTWAVE ENERGY ARRIVES ALONG WITH A WARM FRONT. THERE
IS MINIMAL MASS FIELD SPREAD AS THE SYSTEM INITIALLY ARRIVES BY
SATURDAY. STRONG ONSHORE FLOW IS EXPECTED TO CONTINUE FOR WESTERN
WA/OR THROUGH EARLY SUNDAY BEFORE THEN SUBSIDING. THE ONLY REAL
MASS FIELD DIFFERENCE OF NOTE IS WITH THE 12Z UKMET WHICH APPEARS
BY LATER SATURDAY AND SUNDAY TO BE SHIFTING ITS AXIS OF STRONGER
ONSHORE FLOW A BIT FARTHER NORTH COMPARED TO THE REMAINING MODELS
WHICH ARE WELL CLUSTERED. WILL PREFER A NON-UKMET CONSENSUS.

www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

ORRISON

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