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000
FXUS10 KWNH 240433
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1233 AM EDT SUN SEP 24 2017

VALID SEP 24/0000 UTC THRU SEP 27/1200 UTC

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

...00Z MODEL EVALUATION INCLUDING PREFERENCE AND FORECAST
CONFIDENCE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...HURRICANE MARIA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF
CONFIDENCE: REFER NHC 03Z FORECAST

A FEW FACTORS WILL BE CRUCIAL TO THE TRACK FORECAST OF
MARIA...PARTICULARLY THE STRENGTH OF THE RIDGE ALONG THE NORTHERN
AND EASTERN HEMISPHERES WHICH IS ALSO RELATED TO THE RATE OF
JOSE`S WEAKENING (PLEASE SEE SECTION BELOW).  GIVEN SMALL
VARIATION IN STRENGTH/PLACEMENT OF THIS RIDGE (AFFECTED BY THE
TROF OVER THE CENTRAL US TOWARD WED TOO) ARE LIKELY TO LEAD TO
LARGE VARIATION IN THE TRACK OF MARIA AS DEPICTED WITHIN THE LARGE
WEST TO EAST SPREAD BY WED OFF THE NC COAST.  THE 12Z UKMET
CONTINUES TO BE AGGRESSIVE/STRONG BUT ALSO HAS A STRONGER RIDGE
THROUGH THE MID-LEVELS TO THE NORTH/EAST OF THE SYSTEM AND DRIVES
MARIA VERY CLOSE TO THE OUTER BANKS WELL WEST OF THE NHC FORECAST.
 THE 12Z CMC LIKE THE UKMET HAS A STRONG RIDGE BUT HAS ALSO
SIGNIFICANTLY BACKED OFF THE WESTWARD TREND AS WELL A SLOWING EVER
SO SLIGHTLY AND IS NOW JUST EAST OF THE OFFICIAL FORECAST.  THE
00Z NAM CONTINUES TO BE A CLEAR OUTLIER WELL SLOW AND SOUTH OF THE
MAIN GUIDANCE.  THE 18Z GEFS MEAN LOOKS QUITE SIMILAR TO THE UKMET
 WHILE THE 18Z OPERATIONAL GFS REMAINED SLOWER AND EAST OF THE
GEFS...THE 00Z RUN HAS TRENDED IN STEP WITH 18Z GEFS MEAN AND THE
UKMET LIKELY IN RESPONSE TO THE SLIGHTLY MORE
AMPLIFIED/SOUTHEASTWARD EXTENDING TROF WITH RESPECT TO THE PRIOR
RUN.  WHILE THE 12Z ECENS IS ALSO WEST OF THE OFFICIAL
TRACK....THE 03Z OFFICIAL FORECAST FROM NHC APPEARS TO BE VERY
CLOSE TO THE 12Z ECMWF SOLUTION WHICH IS SLOWER AND FURTHER EAST
NEARER TO 73W.  AS SUCH THE 12Z ECMWF IS CONSIDERED THE
PREFERENCE/OR BEST PROXY TO THE OFFICIAL 03Z FORECAST.  PLEASE
REFER TO NHC FORECAST DISCUSSION: WTNT45 KNHC FOR MORE DETAILS.


...REMNANT CIRCULATION FROM JOSE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z ECMWF BLEND
CONFIDENCE: AVERAGE

GLOBAL GUIDANCE CONTINUES TO PRESENT A NEAR STATIONARY RAPIDLY
FILLING VERTICALLY STACKED LOW TO THE SOUTHEAST OF CAPE COD AND
THE 40N70W BENCHMARK BETWEEN TWO STRENGTHENING LOW LEVEL/SFC
RIDGES OVER THE NORTHEAST AND NE OF BERMUDA.  THE RATE OF JOSE`S
WEAKENING WITHIN THE STRENGTHENING RIDGING WILL HELP DETERMINE THE
WEST/EASTWARD FATE OF MARIA AS WELL.   THE SYSTEM BECOMES AN OPEN
INVERTED TROF TO MARIA`S CIRCULATION AROUND SUNDAY NIGHT/MONDAY
MORNING WITH FASTER WEAKENING SYSTEMS SUCH AS THE 12Z UKMET
SHIFTING EASTWARD WHILE THE 12Z ECMWF/00Z GFS CONTINUE TO BE THE
SLOWEST WEAKENING THOUGH ALSO SLIP SOUTH AND EAST TOWARD MARIA
WITH TIME.  THE MID-LEVEL RIDGING IS STRONGEST WITH THE UKMET/CMC
AND MUCH WEAKER WITH THE 00Z NAM.  ALL IN ALL A BLENDED SOLUTION
NEAR THE 00Z GFS AND 12Z ECMWF BEST REPRESENTS THE MIDDLE GROUND
OF THE GLOBAL GUIDANCE AS WELL AS THE ENSEMBLES AND PROMOTES A
BETTER MASS FIELD IN DEFERENCE TO THE OFFICIAL NHC FORECAST TO
MARIA.  SMALL VARIATIONS IN RATE OF WEAKENING OF SFC LOW OR
STRENGTH OF RIDGE ARE LIKELY TO LEAD TO APPRECIABLE DIFFERENCES TO
MARIA/SENSIBLE WEATHER NEAR SOUTHEAST NEW ENGLAND AS SUCH
CONFIDENCE IS ONLY AVERAGE IN THIS PREFERENCE.


...INITIAL SURFACE WAVE EJECTING FROM SOUTHWESTERN ONTARIO PASSING
NORTHERN ME SUN...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

A SURFACE WAVE CURRENTLY ACCELERATING THROUGH SOUTHWESTERN ONTARIO
SHOULD GRADUALLY WEAKEN ON ITS PATH TOWARD SOUTHERN QUEBEC AND
REACH NORTHERN ME BY LATE SUNDAY.  THE ATTENDANT COLD FRONT SHOULD
SEE ITS FORWARD PROGRESSION HALTED WHILE ENCOUNTERING A DOWNSTREAM
RIDGE. EVENTUALLY A NORTHWARD RETURN AS A WARM FRONT IS EXPECTED
IN ADVANCE OF THE NEXT SHORTWAVE AND SURFACE LOW CROSSING ONTARIO
LATE SUN/MON.  OVERALL  THE GUIDANCE IS IN GOOD AGREEMENT WITH
THIS WAVE AS WELL AS SETTING UP THE NEXT...AND AS SUCH A GENERAL
MODEL BLEND CAN BE PREFERRED WITH ABOVE AVERAGE CONFIDENCE.


...DEEP/ANOMALOUS UPPER TROUGH INITIALLY POSITIONED OVER THE
WESTERN U.S...
...GRADUAL EASTWARD PROGRESSION OF THE SYSTEM...REACHING THE
DAKOTAS BY 26/1800Z...
...ATTENDANT SURFACE FRONT/WAVES OF LOW PRESSURE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/GFS AND 12Z ECMWF BLEND (WEIGHTED TO GFS)
CONFIDENCE: AVERAGE

GOES-WV MOSAIC DEPICTS A WELL DEFINED NEARLY SYMMETRIC BASE
CROSSING THROUGH UT ATTM WITH MODEST RIDGE ACROSS THE NORTHERN
HIGH PLAINS IN ADVANCE OF ELONGATED NORTHERN STREAM SHORTWAVE.  A
SHORTWAVE IN THE WARM CONVEYOR EAST OF THE DEEP LOW OVER WY ATTM
IN CONCERT WITH THE NORTHERN STREAM WAVE SPUR A SURFACE WAVE TO
AMPLIFY ON THE NORTHERN EDGE OF THE GREAT PLAINS SURFACE TROF OVER
MN BY SUNDAY NIGHT...THE FEATURES WILL RAPIDLY ACCELERATE ACROSS
ONTARIO/QUEBEC MON/EARLY TUESDAY WITH STRONG MODEL
AGREEMENT...WITH THE 00Z GFS SIGNIFICANTLY SHIFTING FASTER WITH
THE WAVE/FRONTAL ZONE CROSSING N ME...THIS LEAVES THE 18Z GEFS
MEAN THE MAIN LAGGING SOLUTION FOR THIS WAVE.

THE MAIN CORE TO THE TROF CURRENTLY OVER UT WILL LIFT NORTHEAST
ACROSS THE CENTRAL ROCKIES INTO THE NORTHERN GREAT PLAINS MON INTO
TUES EVENTUALLY RECONSOLIDATING NEAR THE MN/ND/CANADIAN BORDER
LATE TUES INTO WED...SPURRING THE LAST SIGNIFICANT SURFACE WAVE
OVER THE WESTERN GREAT LAKES/CENTRAL ONTARIO INTO WED MORNING.
WHILE THE OVERALL PATTERN EVOLUTION CONTINUES TO BE FAIRLY WELL
AGREED UPON THE INTERNAL DETAILS WITH RESPECT TO S/W FEATURES
CONTINUE TO LEAD TO MILD MODEL SPREAD/DIFFERENCES IN
TIMING/PLACEMENT.  THE 00Z GFS/NAM BOTH HAVE TRENDED TOWARD MORE
AMPLIFIED SOLUTION THAT WAS INITIALLY PRESENTED BY THE 12Z
UKMET/ECMWF THOUGH BOTH HAVE SPLIT THE DIFFERENCE IN TIMING AS THE
ECMWF REMAINS A BIT SLOWER. THE 12Z ECMWF DOES HAVE ITS
PECULIARITIES ATYPICAL OF NORMAL BIAS WITH A RAPID ACCELERATION OF
THE BASE OF THE TROF POSSIBLE NEGATIVE TILT BY THE END OF THE
FORECAST PERIOD AND MAY BE A ONE OFF FOR THIS PARTICULAR RUN
HAVING DEPARTED A BIT FROM THE EC MEAN.  THE 12Z CMC IS A BIT SLOW
TO THE OVERALL SOLUTIONS.  ALL CONSIDERED WOULD SUPPORT A 00Z
NAM/GFS AND 12Z ECMWF SOLUTION WEIGHTING HEAVIER TO THE GFS
SOLUTION (NEARER THE ENSEMBLE SOLUTIONS).  CONFIDENCE IS ONLY
AVERAGE IN THIS BLEND AS THE SUBTLE BUT IMPORTANT SENSIBLE WX
DRIVING INTERNAL WAVES SUGGEST MODEST VARIATION LEFT TO RESOLVE.


...SHORTWAVE AND ASSOCIATED SURFACE WAVE ENTERING CENTRAL BC
MONDAY...DESCENDS TOWARD THE WEST COAST/GREAT BASIN AND LEAD TO
EVENTUAL CLOSED LOW PINCHING OFF OVER THE DESERT SOUTHWEST TOWARD
WED...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z CMC BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

MODELS ARE QUITE AGREEABLE WITH TIMING/STRENGTH OF THE SHORTWAVE
AND ASSOCIATED SURFACE WAVE ENTERING BC LATE MONDAY...DIFFERENCE
THEREAFTER BECOME QUITE LARGE IN HOW EACH MODEL HANDLES THE
SHORTWAVE ENERGY THROUGH THE MEAN GLOBAL TROF OVER THE WEST
LEADING TO EVENTUAL CLOSED LOW OVER THE SOUTHWEST US BY WED.  THE
12Z ECMWF AND 12Z ECENS MEAN SUGGEST A SLIGHTLY INCREASED SW-NE
RIDGE ACROSS THE PACIFIC NORTHWEST LATE MONDAY...WHICH DEFLECTS
THE TIMING/TRACK OF THE SHORTWAVE ENTERING THE BACKSIDE OF THE
TROF INTO TUES.  THIS IN COMBINATION WITH LESS SPACING BETWEEN THE
EXITING WAVE OVER THE ROCKIES ALLOWS FOR SOME LOSS TO THE EAST AND
DELAY OF THE SHORTWAVE DESCENDING INTO THE GREAT BASIN LATE TUES.
AS SUCH THE WAVE PINCHES OFF WELL NORTH AND LATER THAN ANY OTHER
PIECE OF GUIDANCE.

THE 12Z UKMET IS NEXT IN SIMILARITY TO THE ECMWF WITH STRONGER
RIDGING OVER THE PACIFIC NORTHWEST; HOWEVER UNLIKE THE
ECMWF...THERE IS PRECURSORY ENERGY NEAR THE COAST OF CA THAT WILL
DESCEND INTO A DEEPER MORE MERIDIONAL TROF DIGGING AS FAR SOUTH AS
BAJA CA BY WED...EVEN THOUGH THE INNER CORE OF THE EVENTUAL CLOSED
LOW IS FURTHER NORTH NEAR THE ECMWF SOLUTION...AND NARROWER THOUGH
THE LENGTH OF THE TROF (GENERALLY UNFAVORABLE RESULT).  THE 00Z
NAM LIKE THE UKMET HAS A PRECURSORY WAVE BUT UNLIKE THE UKMET HAS
A MUCH WEAKER RIDGE...THIS ALLOWS FOR A FURTHER SOUTH BUT
INCREASED INTERACTION/MORE SYMMETRIC EVOLUTION TO THE BASE OF THE
TROF.  MORE IN LINE WITH THE OVERALL ENSEMBLE SUITE.

THE 00Z GFS TRENDED FASTER WITH THE EXITING WAVE...THIS ALLOWED
FOR INCREASED SHORTWAVE RIDGE BETWEEN THE THIS FEATURE COMPARED TO
THE 18Z RUN CREATING A MORE ELONGATED SOLUTION DELAYING THE
EVENTUAL CLOSED LOW IN THE SW AND REDUCING THE SOUTHWARD PUSH
OVERALL.  THIS IS QUITE SIMILAR TO THE 12Z CMC WHICH SEEM A NICE
COMPROMISE BETWEEN THE ECMWF AND NAM/UKMET SOLUTIONS AND NEARER
THE OVERALL ENSEMBLE MEANS.  AS SUCH A 00Z GFS/12Z CMC BLEND IS
SUPPORTED BUT AGAIN LARGE END RESULT VARIATION ON SMALL
AMPLITUDE/SPACING DIFFERENCES PROVIDE AMPLE FUEL FOR REDUCED
CONFIDENCE AND FUTURE RUN TO RUN VARIATION.  AS SUCH CONFIDENCE
REMAINS SLIGHTLY BELOW AVERAGE FOR THIS PREFERENCE.

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

GALLINA

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