Prognostic Meteorological Discussion
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000
FXUS10 KWNH 180449
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1249 AM EDT WED OCT 18 2017

VALID OCT 18/0000 UTC THRU OCT 21/1200 UTC

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

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


...UPPER TROUGH DIGGING INTO THE PACIFIC NORTHWEST WEDNESDAY NIGHT
   WITH ASSOCIATED ATMOSPHERIC RIVER EVENT...
LEADING SHORTWAVE MOVING FROM THE SOUTHWEST INTO THE PLAINS
BROAD UPPER TROUGH/COLD FRONT REACHING THE PLAINS FRIDAY/SATURDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NAM/GFS/ECMWF BLEND; CONFIDENCE ABOVE AVERAGE

DIFFERENCES IN THE GUIDANCE SHOWS UP AFTER THE UPPER TROUGH AXIS
MOVES OVER THE INTERMOUNTAIN WEST ON FRIDAY.  THE 12Z CANADIAN IS
THE FASTEST WITH THIS SYSTEM WHILE THE 12Z UKMET IS THE SLOWEST.
WHILE THE SYSTEM IS EMBEDDED WITHIN A QUASI-ZONAL FLOW REGIME --
WHICH COULD SUPPORT A FASTER SOLUTION -- THE CANADIAN ISSUES
APPEAR TO STEM FROM AN UPSTREAM DEEP CYCLONE SOUTH OF AK WHICH IS
HANDLES DIFFERENTLY THAN THE OTHER GUIDANCE.  THE 00Z NAM/00Z
GFS/12Z ECMWF FORM AN INTERMEDIATE COMPROMISE WHICH IS MOST
AGREEABLE WITH THE 12Z ECMWF/18Z GEFS MEAN SOLUTIONS.


DEEP CYCLONE MOVING THROUGH SOUTHERN/EASTERN CANADA
TRAILING COLD FRONT MOVING THROUGH THE NORTHERN U.S. WED-THU
TROUGH MOVING OUT OF THE SOUTHEAST WEDNESDAY/THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THIS SYSTEM.  A COMPROMISE
OF THE 12Z UKMET, 12Z ECMWF, 12Z CANADIAN, 00Z NAM, AND 00Z GFS IS
PREFERRED TO IRON OUT ANY LINGERING DETAIL ISSUES WITH ABOVE
AVERAGE CONFIDENCE.


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

ROTH
$$




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