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FXUS10 KWNH 211842
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
141 PM EST SAT JAN 21 2017

VALID JAN 21/1200 UTC THRU JAN 25/0000 UTC

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

12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

COMPACT CLOSED MID-LEVEL LOW REACHING THE UPPER MS VALLEY TONIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


SURFACE LOW TRACKING NEWD TO THE MID-ATLANTIC COAST THIS EVENING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS HAVE COME INTO BETTER AGREEMENT WITH THIS LOW NOW THAT
IS HAS FORMED...LOCATED ALONG THE AL/GA BORDER AS OF 15Z TODAY.
THE LOW WILL TRACK TOWARD THE MID-ATLANTIC COAST BY EARLY SUN
MORNING...WITH ONLY THE 00Z CMC SHOWING DIFFERENTLY FROM THE
REMAINING MODEL CONSENSUS WITH A STRONGER LOW PRESSURE CENTER
WHILE BEING LOCATED ON THE WRN EDGE OF THE LATEST ENSEMBLE
MEMBERS.

WITH THE 12Z CMC ADJUSTING TOWARD THE DIRECTION OF THE REMAINING
CONSENSUS...A GENERAL MODEL BLEND CAN NOW BE USED.


CLOSED LOW ACROSS THE LOWER MS VALLEY SUN WITH ASSOCIATED STRONG
  SFC LOW LIFTING THROUGH THE MID-ATLANTIC MON...NEW ENGLAND ON TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS...12Z ECMWF BLEND ALOFT
    12Z GFS/ECMWF BLEND FOR SFC LOW TRACK THROUGH
00Z/24
    12Z ECMWF FOR SFC LOW TRACK 00Z/24 - 00Z/25
CONFIDENCE: AVERAGE

A MODERATE AMOUNT OF ENSEMBLE SPREAD REMAINS FROM THE LATEST CYCLE
REGARDING THE EVOLUTION OF THE CLOSED LOW THROUGH THE SOUTHEAST
AND INTO THE MID-ATLANTIC REGION. THE NAM IS THE MOST DIFFERENT
FROM THE REMAINING GUIDANCE IN SHOWING MORE ELONGATION TO THE
UPPER LOW ON THE NORTH SIDE AND LESS RIDGING UPSTREAM ACROSS THE
OHIO VALLEY. LITTLE SUPPORT EXISTS FOR THE 12Z NAM IN THE ENSEMBLE
GUIDANCE.

THE ENSEMBLES SUPPORT A MIXTURE BETWEEN THE 12Z GFS...00Z ECMWF
AND 00Z UKMET WITH NO SINGLE MODEL APPEARING IDEAL FOR THE ENTIRE
FORECAST PERIOD THROUGH 00Z/25. THE 12Z GFS IS QUICKER TO LIFT THE
CLOSED LOW THROUGH MON/MON NIGHT AT WHICH POINT THE 00Z ECMWF
CATCHES UP AND THE 00Z UKMET SHOWS SLOWER AND CLOSER TO THE COAST
WITH THE GFS/ECMWF MORE INLAND. WHILE THE ENSEMBLE MEANS SHOW GOOD
AGREEMENT FOR THE SURFACE LOW TO BE SOUTHEAST OF CNTRL LONG ISLAND
BY 12Z/24...THE TRENDS HAVE BEEN NORTH IN THE DETERMINISTIC
GUIDANCE. THERE APPEARS TO BE MORE SUPPORT FOR FUTURE MODEL CYCLES
TO GO SLOWER/SOUTH THAN QUICKER/NORTH WITH THE LOW TRACK THROUGH
TUE...BUT 12Z GFS TRENDS ARE OFTEN IN THE RIGHT DIRECTION WHICH IS
WHY A BROAD 3-WAY BLEND OF THE 12Z GFS/00Z ECMWF/00Z UKMET IS
PREFERRED.

19Z UPDATE...THE 12Z UKMET TRENDED TOWARD THE 12Z GFS...AND THE
12Z ECMWF ADJUSTED AWAY FROM THE 12Z GFS. A 12Z GFS/ECMWF BLEND
REPRESENTS A SOLID MIDDLE GROUND...ALTHOUGH PERHAPS THE 12Z ECMWF
IS IN A BETTER POSITION WITH THE SURFACE LOW AS IT TRACKS NEAR THE
NEW ENGLAND COAST ON TUE...GIVEN BETTER PLACEMENT TOWARD THE
MIDDLE OF THE LATEST ENSEMBLE SCATTER LOW PLOTS...WITH THE 12Z GFS
DISPLACED FARTHER EAST ON THE FAR EDGE OF THE ENSEMBLE LOW
CLUSTERING AFTER 00Z/24.


COLD FRONT REACHING THE WEST COAST TONIGHT
LONGWAVE TROUGH OVER THE WEST COAST BY MON MORNING
DOWNSTREAM SURFACE LOW INTO THE PLAINS FOR TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

SIGNIFICANT DIFFERENCES BEGIN TO APPEAR WITH THE TIMING OF THE
LONGWAVE TROUGH THROUGH THE WRN U.S. BY EARLY MONDAY WITH ENSEMBLE
SPAGHETTI HEIGHTS SUPPORTING THE MIDDLE GROUND. WHILE THE 12Z CMC
SPED UP FROM ITS PREVIOUS RUN...IT STILLS APPEARS ON THE SLOW SIDE
OF THE ENSEMBLE GUIDANCE  REGARDING THE PROGRESSION OF THE TROUGH
DOWNSTREAM WHILE THE 12Z GFS APPEARS TOWARD THE LEADING EDGE OF
THE ENSEMBLE GUIDANCE. THIS IS REFLECTED IN THE EXPECTED SURFACE
LOW TRACK AS WELL WITH THE 12Z CMC SLOWER...AND 12Z GFS FASTER. A
MIDDLE GROUND IS BEST REPRESENTED BY A 12Z ECMWF/UKMET BLEND. THE
12Z NAM WAS REMOVED FROM THE PREFERENCE GIVEN UNFAVORABLE FLATTER
MID-LEVEL RIDGING ACROSS THE MID-MS VALLEY AND OH VALLEY.

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

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

OTTO

$$





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