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000
FXUS10 KWNH 250434
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1233 AM EDT MON SEP 25 2017

VALID SEP 25/0000 UTC THRU SEP 28/1200 UTC

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

00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...HURRICANE MARIA...
~~~~~~~~~~~~~~~~~~~~~~~~~
PROXY PREFERENCE: 21Z SREF/12Z CMC BLEND (THOUGH TOO WEAK)
CONFIDENCE: REFER NHC FORECAST

MODELS CONTINUE TO STRUGGLE WITH THE STRENGTH OF THE RIDGE TO THE
NORTH AND EAST OF MARIA WHICH ONLY FURTHER COMPOUNDS AS INFLUENCE
FROM TROF LIFTING ACROSS THE GREAT LAKES BEGINS TO DIRECT THE MEAN
FLOW TOWARD AN EASTWARD TRACK AFTER 60HRS.  THE 12Z UKMET/ECMWF
CONTINUE TO BE MOST WESTWARD WITHIN THE GUIDANCE SUITE AND
GENERALLY ARE THE SLOWEST TO BREAK DOWN THE 7H RIDGE ACROSS THE
NORTHERN MID-ATLANTIC ALLOWING FOR A SLIGHTLY SLOWER TRACK AS WELL
THOUGH ARE QUITE CENTRAL TO THE 12Z ECENS GUIDANCE.  THE 00Z NAM
SHOWS A SLOWING TREND AFTER 54HRS WITH RESPECT TO THE 12Z RUN AND
IS A SLIGHT BIT WEST OF THE RUN AS WELL; HOWEVER THE 00Z NAM
REMAIN EAST OF THE FORECAST TRACK.  THE 18Z GEFS AND OPERATIONAL
RUN DEPICT A SLIGHT WEAKNESS NORTHEAST IN THE LOW LEVEL RIDGE EVEN
BY 36HRS AND START ACCELERATING NORTH AND EAST TOWARD IT BREAKING
FROM OTHER GUIDANCE WHILE ALSO WELL EAST OF THE NHC FORECAST
TRACK. THIS FURTHER COMPOUNDS AS THE INFLUENCE OF THE UPSTREAM
TROF HAS MORE INFLUENCE (BEING AS MARIA IS FURTHER NORTH) AND
BEGINS TO ACCELERATE THE REMAIN STORM NORTHEAST AND IS EVEN PAST
THE OFFICIAL 96HR FORECAST POINT AT 84HRS.  THE 00Z GFS HAS SLOWED
A BIT COMPARED TO THE 18Z RUNS BUT REMAINS INITIALLY EAST OF THE
NHC FORECAST BEFORE TRENDING WEST AND NEAR THE OFFICIAL FORECAST
AFTER 72HRS.  INTERESTINGLY...LESS RELIABLE GUIDANCE OF THE 21Z
SREF AND 12Z CMC SEEM TO BE MIDDLE GROUND AND GENERALLY CLOSEST TO
THE FORECAST TRACK...HOWEVER ARE MUCH WEAKER THAN THE OFFICIAL
FORECAST SUGGESTS PARTICULARLY TOWARD THE END OF THE FORECAST
PERIOD.  STILL THIS MAY BE THE BEST PROXY FOR THE 03Z NHC
FORECAST.


...UPPER TROUGH LIFTING FROM THE FOUR CORNERS UP TO THE DAKOTAS BY
LATE MONDAY EXITING THROUGH SOUTHEAST CANADA AND CLIPPING NORTHERN
NEW ENGLAND LATE WED/THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z CMC/ECMWF/UKMET BLEND (WEIGHTED TOWARD CMC)
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

IMPRESSIVE COMPACT CLOSED LOW OVER SW WY PER GOES-WV LOOP WILL
CONTINUE TO LIFT NORTHEAST FOSTERING HEIGHT FALLS AND SURFACE LOW
DEVELOPMENT ACROSS N WI BY TUES MORNING THAT QUICKLY DEEPENS
ACROSS ONTARIO AND OCCLUDING INTO QUEBEC WED DRAPING THE QUICK
MOVING COLD FRONT ACROSS THE NORTHEAST BY THURS MORNING.  THE 12Z
ECMWF TRENDED A BIT DEEPER AND FASTER THAN PRIOR GUIDANCE WITH A
MORE AGGRESSIVE NATURE THAN THE 00Z RUN...WHICH HAS BEEN A NOTED
BIAS FOR THE 12Z RUNS WITH RESPECT TO THE 00Z...AND ITS ECENS
MEAN.  THE 12Z UKMET GENERALLY MATCHES IT IN BOTH DEPTH AND SPEED
WHICH IS A KNOWN BIAS OF THE UKMET...SO THE 12Z CMC WHICH IS MORE
TEMPERED/ROUNDED AND SLIGHTLY SLOWER SEEMS A BETTER MATCH TO
CONTINUITY/ENSEMBLE SUITE OVERALL.  THE 00Z NAM MATCHES THE ECMWF
TROF IN SPEED AND DEPTH BUT THE CENTER OF THE WAVE IS A SHADE
SOUTH...AND IS BEST REFLECTED IN THE SURFACE WAVE WHICH REMAINS A
BIT SOUTHEAST OF THE AGREED UPON LOCATION FROM THE ECMWF/UKMET.
THE 18Z GEFS MEAN IS A THE CLEAR OUTLIER AND REMAIN SLOW AND A BIT
SOUTH OF THE MAIN PACKING (INCLUDING THE REMAINING ENSEMBLE
MEMBERS) ESPECIALLY NOW THAT THE 00Z GFS HAS TRENDED A BIT QUICKER
STARTING TO MATCH THE TIMING OF THE 00Z NAM.  HOWEVER...IT WAS AT
A COST OF RESOLVING A MUCH WEAKER WAVE OVERALL WHICH SEEMS A BIT
UNLIKELY GIVEN ITS PRESENTATION CURRENTLY/OTHER GUIDANCE AND
LIMITED OPPORTUNITY FOR OTHER FACTORS TO DEGRADE THE INTENSITY OF
THE WAVE THIS MUCH.  AS SUCH WILL FAVOR THE FASTER BUT DEEPER
TREND NOTED BY THE UKMET/ECMWF AND CMC; HOWEVER WOULD PREFER
HIGHER WEIGHTING OF THE MASS FIELDS TOWARD THE 12Z CMC.  THE
GUIDANCE IS STRONG ENOUGH TO SUPPORT SLIGHTLY ABOVE AVERAGE
CONFIDENCE IN THIS 12Z CMC AND UKMET/ECMWF BLEND.


...NORTHERN STREAM KICKER SHORTWAVE ENTERING NORTHERN TIER THURS
WITH ATTENDANT COLD FRONT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/GFS AND 12Z ECMWF BLEND
CONFIDENCE: AVERAGE

SHORTWAVE ENERGY EMERGES FROM THE NORTHERN CANADIAN ROCKIES OVER
THE MEAN RIDGE TUES INTO WED AND BEGINS TO DESCEND AND AMPLIFY IN
THE WAKE OF THE EXITING TROF (SECTION ABOVE) THE CENTRAL
PROVIDENCES BY THURSDAY WITH AN ACCOMPANYING COLD AIR
ADVECTION/FRONTAL ZONE INTO THE NORTHERN TIER.  TYPICAL GUIDANCE
TIMING PLACEMENT IS OCCURRING WITH A FASTER UKMET AND THE CMC
PULLING UP THE REAR.  THERE IS MODEST AGREEMENT TO THE
DEPTH/STRENGTH OF THE WAVE AS WELL AS PLACEMENT AND ORIENTATION BY
12Z THURSDAY IN THE 00Z NAM/GFS AND 12Z ECMWF TO HAVE AVERAGE
CONFIDENCE IN A BLEND OF THESE SOLUTIONS.


...CLOSED LOW PINCHING OFF OVER THE DESERT SOUTHWEST ON
WEDNESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

MODELS CONTINUE TO SHOW MUCH STRONGER AGREEMENT IN EVOLUTION AND
TIMING OF THE SHORTWAVE ENTERING THE US LATE MON...DESCENDING
ACROSS THE GREAT BASIN AND PINCHING OFF A CLOSED LOW IN THE LOWER
COLORADO VALLEY BY WED.  THE 12Z CMC APPEARS SLOW IN TYPICAL
FASHION... THE UKMET LOOKS REASONABLE THOUGH THERE IS SOME
NEGATIVE INFLUENCE OF A VERY DEEP WAVE OFF CENTRAL BAJA CA THAT IS
NOT RESOLVED IN OTHER GUIDANCE MAKING IT LESS DESIRABLE AS WELL.
THE 00Z NAM IS WELL TIMED BUT SHOWS SOME OVER DEEPENING BIAS THAT
ALLOWS FOR A FURTHER SOUTH MANIFESTATION OF THE CLOSED LOW.  GIVEN
THE VERY TIGHT AGREEMENT OF THE 00Z GFS AND THE 12Z
ECWMF...CONFIDENCE IS SLIGHTLY ABOVE AVERAGE IN A PREFERENCE OF
THAT BLEND.


...SHEARED ELEMENTS OF PILAR LIFTING THROUGH CENTRAL MX...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/UKMET BLEND
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE

A LINGERING STATIONARY FRONT REMAINS DRAPED OVER WESTERN TX AS
SHORTWAVE EXITS OVER THE NORTHERN PLAINS BUT REMAINING TROUGHING
EXISTS OVER THE SOUTHWEST...THIS SUPPORTS RETURN FLOW FROM THE
GULF UP THE RIO GRANDE VALLEY AS WELL AS MOISTURE TRANSPORT OFF
THE EASTERN PACIFIC.  THIS MOISTURE IS ASSOCIATED WITH TROPICAL
CYCLONE PILAR THAT CONTINUES TO NEAR THE MX COAST.  MID-LEVEL
SHORTWAVE AND MOISTURE WILL LIFT NORTH...THOUGH THERE IS QUITE A
BIT OF MODEL SPREAD IN OVERALL TIMING AS WELL AS HOW MANY
SHORTWAVE FRAGMENTS LIFT NORTH.  THESE FEATURES ARE LIKELY TO BE A
CATALYST FOR DEEP CONVECTION/FLOODING CONCERNS IN WEST TX NEAR THE
INTERFACE OF THE FRONT.  THE 00Z NAM IS MOST AGGRESSIVE BRINGING
THE BULK OF THE ENERGY OF PILAR NORTH BY 00Z TUES FOLLOWED BY THE
ECMWF AND UKMET...BOTH TIMING NEAR MAXIMUM HEATING/INSTABILITY OF
THE DAY LATE TUESDAY.  THE 00Z GFS CONTINUES TO BE A BIT SLOWER
BUT ALSO ANGLES THE SHORTWAVE ENERGY MORE SW TO NE...GENERALLY A
LESS FAVORABLE ANGLE (WITH RESPECT TO THE LINGERING FRONT)
INTERCEPTING MOISTURE FROM THE GULF RESULTING IN LESS OF A
CONVECTIVE RESPONSE.  THE 12Z CMC SEEMS TO WASH THE ENTIRE
SHORTWAVE OUT.  GIVEN CURRENT NHC FORECAST TRACK AND WV LOOP IT
APPEARS THE ECMWF/UKMET SEEM TO HAVE A SLIGHTLY BETTER HANDLING ON
THE FEATURE/TIMING AT THIS POINT.  AS SUCH WILL CONTINUE TO FAVOR
THEM...THOUGH GIVEN THE LARGE VARIATION IN TIMING OF FEATURES AND
MAGNITUDE OF MOISTURE RETURN CONFIDENCE IS ONLY AVERAGE TO
SLIGHTLY BELOW AVERAGE IN THIS BLEND COMING TO FRUITION.

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

RUBIN-OSTER

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