Prognostic Meteorological Discussion
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FXUS10 KWNH 181722
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1222 PM EST SAT FEB 18 2017

VALID FEB 18/1200 UTC THRU FEB 22/0000 UTC

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

12Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SHORTWAVE/COLD FRONT CROSSING THE NORTHERN TIER STATES THROUGH SUN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


DEEPENING TROUGH/CLOSED LOW DEVELOPMENT NEAR NRN NEW ENGLAND BY MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE ENSEMBLES SHOW THE BEST SUPPORT FOR THE 12Z GFS/00Z ECMWF WITH
THE 12Z NAM ADJUSTING SOUTH WITH THE TRACK OF THE CLOSED LOW AS IT
EXITS NOVA SCOTIA. THE 00Z CMC IS NEXT CLOSEST TO THE PREFERENCE
BUT WAS A BIT WEAKER WITH THE STRENGTH OF THE CLOSED LOW.


UPPER TROUGH CROSSING THE SOUTHWEST THROUGH SUN
ENERGY EJECTING OUT ACROSS THE PLAINS/UPPER MIDWEST MON/TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF BLEND THROUGH 00Z/21
            06Z GEFS/00Z ECMWF MEAN BLEND 00Z/21-00Z/22
CONFIDENCE: BELOW AVERAGE

THE QUICKENING TREND IN THE ENSEMBLES APPEARS TO HAVE ENDED WITH
THE 12Z/17 CYCLE GIVEN THE 00Z/18 CYCLE FROM LAST NIGHT WAS NO
FASTER OR SLOWER...JUST PERHAPS A BIT SHALLOWER WITH THE MID-LEVEL
TROUGH VALID 00Z/20 OVER THE CNTRL/SRN ROCKIES. AS THE UPPER
TROUGH EJECTS ACROSS THE PLAINS...THERE IS SOME INTERACTION WITH
THE TROUGH COMING INTO THE NORTHWEST U.S. DESCRIBED 3 SYSTEMS DOWN
FROM THIS SECTION AND HAS IMPACTS ON THE LAST SYSTEM DESCRIBED IN
THIS DISCUSSION.

THE 00Z UKMET/CMC ARE ON THE FASTER/FLATTER EDGES OF THE ENSEMBLE
ENVELOPE BY MON MORNING...AND BY TUE...THE 12Z GFS BEGINS TO PULL
AWAY WHILE THE 00Z ECMWF IS SLOWER...SHOWING MORE INTERACTION WITH
A CLOSED LOW CROSSING THE SOUTHERN U.S. NO DETERMINISTIC MODEL OR
BLEND LOOKS FAVORABLE BEYOND 00Z/21 WHICH IS WHY A BLEND OF THE
REASONABLY SIMILAR 06Z GEFS MEAN AND 00Z ECMWF MEAN IS PREFERRED.
THIS PREFERRED POSITION IS BETWEEN THE FASTER 12Z GFS AND SLOWER
00Z ECMWF.

FOR WHAT IT IS WORTH...THERE APPEARS TO BE MORE SUPPORT FOR A
GFS-LIKE PROGRESSION COMPARED TO THE 00Z ECMWF...BUT CONFIDENCE IS
NOT HIGH ENOUGH TO GO IN THAT DIRECTION AT THIS TIME.


WEAK NORTHERN STREAM TROUGH CROSSING THE PACIFIC NORTHWEST TODAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


UPPER TROUGH TRACKING ACROSS THE TN VALLEY/SOUTHEAST THROUGH SUN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

ONLY MINOR DIFFERENCES REMAIN...WITH THE STRENGTH OF THE CORE OF
THE MID-LEVEL TROUGH/LOW AS IT CROSSES THE EAST COAST STATES.
GIVEN ANY SIGNIFICANT DIFFERENCES WITH THIS SYSTEM DO NOT SHOW UP
UNTIL AFTER THE TROUGH AXIS HAS MOVED WELL OFFSHORE OF THE
SOUTHEAST COAST...A GENERAL MODEL COMPROMISE CAN BE USED HERE.


SHORTWAVE/SURFACE LOW APPROACHING THE PACIFIC NORTHWEST EARLY SUN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z CMC BLEND
CONFIDENCE: BELOW AVERAGE

DESPITE TRENDING DEEPER THE 00Z CMC REMAINED FLATTER WITH THE
TROUGH AXIS THROUGH 00Z/20 ACROSS THE NORTHWEST. A NON 00Z CMC
BLEND IS RECOMMENDED HERE GIVEN SIMILAR OUTPUT OUTSIDE OF THE CMC.


AMPLIFYING UPPER TROUGH/SURFACE LOW APPROACHING THE WEST COAST MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE 00Z ECMWF HAS REMAINED RELATIVELY CONSISTENT FROM RUN TO RUN
AND IS SUPPORTED BY THE 12Z GFS. THE ENSEMBLE MEANS ARE IN
FAVORABLE AGREEMENT SUPPORTING A GFS/ECMWF BLEND. WHILE THE 12Z
GFS REMAINS STRONGEST WITH THE SURFACE LOW APPROACHING THE PACIFIC
NORTHWEST...IT HAS TRENDED WEAKER FROM PREVIOUS CYCLES AND IS OKAY
TO USE WHEN BLENDED WITH THE 00Z ECMWF. THE 00Z UKMET IS A CLOSE
SECOND OPTION BUT ITS UPPER TROUGH AND LOW POSITION ARE A BIT
FASTER/SOUTH THAN SUPPORTED BY THE LATEST ENSEMBLE SPAGHETTI
HEIGHTS AND SCATTER LOW PLOTS. THE 00Z CMC LOOKS THE LEAST
FAVORABLE WITH RESPECT TO THE ENSEMBLE GUIDANCE.


SOUTHERN STREAM TROUGH/CLOSED LOW DEVELOPMENT OVER THE GULF COAST/
  GULF OF MEXICO BY TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF BLEND THROUGH 00Z/21
           06Z GEFS/00Z ECMWF MEAN BLEND OR 00Z UKMET 00Z/21-00Z/22
CONFIDENCE: BELOW AVERAGE

ENERGY IN THE BASE OF THE UPPER TROUGH/CLOSED LOW IMPACTING THE
SOUTHWEST THAT EJECTS OUT ACROSS THE PLAINS THROUGH SUN AND MON
WILL SEPARATE OUT AND LEAD TO A NEW SOUTHERN STREAM TROUGH AND
POSSIBLE CLOSED LOW OVER EASTERN TX AND THE ADJACENT LOWER MS
VALLEY BY TUES. DIFFERENCES IN THE EVOLUTION OF THIS TROUGH ARE
DEPENDENT ON HOW THE NRN PORTION EVOLVES...DESCRIBED ABOVE WITH
LOWER THAN AVERAGE CONFIDENCE. THE ENSEMBLES SHOW THE 00Z ECMWF AS
RATHER STRONG AND PROGRESSIVE. THE 06Z GEFS MEAN AND 00Z ECMWF
MEAN ARE AN IDEAL MIDDLE GROUND BEYOND 00Z/21 WITH THE 12Z GFS
MORE HELD BACK ALONG THE WRN GULF OF MEXICO WHILE THE 00Z ECMWF IS
LOCATED OVER THE LOWER MS VALLEY. THE 00Z UKMET POSITION SPLITS
THE DIFFERENCE SEEN HERE AND MAY BE INCLUDED IN THE PREFERENCE IF
MORE SUPPORT IS GAINED FOR THE 00Z UKMET WHEN THE REMAINING 12Z
MODEL GUIDANCE COMES IN.


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

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

OTTO

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