Prognostic Meteorological Discussion
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000
FXUS10 KWNH 280424
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1223 AM EDT WED SEP 28 2016

VALID SEP 28/0000 UTC THRU OCT 01/1200 UTC

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

00Z GFS/NAM EVALUATION WITH PRELIMINARY MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


BINARY INTERACTION NEAR THE WEST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: BELOW AVERAGE

THERE ARE MODEST DIFFERENCES ALOFT NEAR AND OFFSHORE THE WEST
COAST WHICH HAVE SOME BEARING ON THE MOVEMENT OF THE SYSTEM IN THE
MIDWEST/OHIO VALLEY.  THE 12Z CANADIAN/00Z GFS ARE THE
SLOWEST/MOST AMPLIFIED WITH THE TROUGH NEAR CA FRIDAY NIGHT, WHILE
THE 00Z GFS/12Z UKMET ARE THE MOST NORTHERLY WITH THE DEEP CYCLONE
OFFSHORE SOUTHWEST CANADA.  THE GFS MAKES INTERNAL SENSE AS ITS
CLOSED LOW OFFSHORE HAIDA GWAII AND VANCOUVER ISLANDS IS FARTHER
NORTH, IMPLYING LESS INTERACTION BETWEEN THE TWO.  HOWEVER,
BINARY/FUJIWHARA INTERACTIONS SUCH AS THESE ARE TRICKY, AND LEAD
TO BELOW AVERAGE FORECAST CONFIDENCE.  FOR THE TIME BEING, PREFER
A COMPROMISE OF THE AVAILABLE GUIDANCE.


DEEP CYCLONE ACROSS MIDWEST DOUBLING BACK TOWARDS MI
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-GFS COMPROMISE
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE 00Z GFS ENDS UP BEING THE FARTHEST SOUTH WITH THIS SYSTEM BY
FRIDAY NIGHT.  THIS APPEARS TO BE DUE TO ITS SLOWER UPPER TROUGH
OFFSHORE THE WEST COAST AND DOWNSTREAM RIDGING ACROSS THE PLAINS
WHICH IS MORE ENHANCED THAN MUCH OF THE GUIDANCE.  WE HAVE TWO
COMPETING INFLUENCES WITH THIS SYSTEM`S MOVEMENT -- THE
STRONG/NORTHERLY DISPLACED SUBTROPICAL RIDGE NORTH OF THE SARGASSO
SEA AND THE UPSTREAM TROUGH/RIDGE COUPLET.  NO MATTER WHICH
SOLUTION YOU PICK, THE ATLANTIC RIDGE IS STRONG AND SHOULD LEAD TO
SOME NORTHERLY RETURN AFTER THURSDAY NIGHT AS THE RIDGE IN THE
PLAINS IS WEAKENED BY A SHORTWAVE MOVING THROUGH MT.  FOR NOW,
WILL CONSIDER THE 00Z GFS A LOWER PROBABILITY ALTERNATIVE SCENARIO
AND GO WITH A COMPROMISE OF THE CONSENSUS -- THE 12Z UKMET/12Z
ECMWF/00Z NAM/12Z CANADIAN -- WITH SLIGHTLY BELOW AVERAGE
CONFIDENCE.


CLOSED LOW LIFTING OUT OF THE SOUTHWEST
SHORTWAVE LIFTING MOVING THROUGH MT EARLY FRI MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THESE SYSTEMS.  A
COMPROMISE OF THE AVAILABLE GUIDANCE IS PREFERRED TO DEAL WITH ANY
LINGERING DETAIL ISSUES WITH ABOVE AVERAGE CONFIDENCE.



...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

ROTH
$$





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