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000
FXUS10 KWNH 211704
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1203 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 NAM/GFS EVALUATION INCLUDING PRELIMINARY 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: NON 00Z CMC 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.


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...00Z ECMWF...00Z UKMET BLEND
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.


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 NAM/00Z ECMWF 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. CURRENTLY...THE
00Z CMC APPEARS TOO SLOW TO PROGRESS 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 00Z CMC SLOWER...AND 12Z GFS FASTER. A MIDDLE GROUND
IS BEST REPRESENTED BY A 12Z NAM/00Z ECMWF BLEND.

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

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

OTTO

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