Prognostic Meteorological Discussion
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000
FXUS10 KWNH 221640
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1240 PM EDT SAT JUL 22 2017

VALID JUL 22/1200 UTC THRU JUL 26/0000 UTC

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

12Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


SYSTEM APPROACHING THE PACIFIC NORTHWEST LATE TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CANADIAN; CONFIDENCE SLIGHTLY ABOVE AVE

THE 00Z CANADIAN IS OFF TO THE RACES WITH THIS SYSTEM, BRINGING
THE TROUGH INTO WESTERN CANADA/NORTHWEST WA TUESDAY AFTERNOON.
THE REMAINDER OF THE GUIDANCE IS QUITE A BIT SLOWER, MORE
SUPPORTIVE OF THE 00Z ECMWF/06Z GEFS MEAN SOLUTIONS.  BOTH RIDGING
BUILDING OVER THE TOP OF THIS SYSTEM IN SOUTHERN AK AND A TRAILING
SYSTEM A BIT TO ITS SOUTHWEST SUPPORT A SLOWER FORWARD
PROGRESSION.  A COMPROMISE OF THE 12Z NAM, 12Z GFS, 00Z UKMET, AND
00Z ECMWF WITH DEAL WITH THIS MAIN ISSUE ALONG WITH HOW MUCH
LEADING SHORTWAVE ENERGY MOVES AHEAD OF IT INTO SOUTHWEST CANADA
EFFECTIVELY.


UPPER LOW NEAR CALIFORNIA SUNDAY-TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND; CONFIDENCE ABOVE AVERAGE

THE 00Z UKMET IS QUICKER TO LIFT THIS SYSTEM OUT THAN THE OTHER
GUIDANCE, EVEN THOUGH IT HANDLES THE POTENTIAL UPSTREAM KICKER
SHORTWAVE OFFSHORE THE AK PENINSULA REASONABLY.  A COMPROMISE OF
THE 00Z CANADIAN, 00Z ECMWF, 12Z GFS, AND 12Z NAM IS PREFERRED
WITH ABOVE AVERAGE CONFIDENCE.


SYSTEM MOVING THROUGH SOUTH-CENTRAL CANADA MONDAY/TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: ECMWF/NAM BLEND; CONFIDENCE SLIGHTLY ABOVE AVE

THE 00Z UKMET IS THE QUICKEST WITH THIS SYSTEM WHILE THE 12Z GFS
IS THE SLOWEST.  THE 06Z GEFS/00Z ECMWF ENSEMBLE MEAN SOLUTIONS
FAVOR THE INTERMEDIATE COMPROMISE OF THE 00Z ECMWF/12Z NAM, WHICH
IS FAVORED WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE.


SHORTWAVE MOVING ACROSS THE GREAT LAKES SUN/NORTHEAST MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: ECMWF/GFS BLEND; CONFIDENCE AVERAGE

THE 12Z NAM/00Z CANADIAN ARE SLOW/DEEP OUTLIERS -- THEIR USUAL
BIAS -- WHILE THE 00Z UKMET IS THE QUICKEST.  A COMPROMISE OF THE
00Z ECMWF AND 12Z GFS SPLITS THE DIFFERENCE SEEN IN THE GUIDANCE
WHILE DEALING WITH THEIR SLIGHT DEPTH ISSUES AT 500 HPA --
CONFIDENCE IS AVERAGE IN THIS CHOICE.  FOR RAINFALL FORECAST
PREFERENCES, SEE OUR QPF DISCUSSION (QPFPFD).


SHORTWAVE MOVING THROUGH THE NORTHERN MID-ATL TODAY/SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET COMPROMISE; CONFIDENCE ABOVE AVE

THE 00Z UKMET APPEARS SLOW/DELAYED WITH THE EASTWARD PROGRESSION
OF THIS SYSTEM COMPARED TO THE OTHER GUIDANCE, WITH SHOWS UP BOTH
WITHIN THE 700 HPA HEIGHT PATTERN AND THE SURFACE PATTERNS.  A
COMPROMISE OF THE 12Z GFS, 12Z NAM, 00Z ECMWF, AND 00Z CANADIAN
WILL EFFECTIVELY DEAL WITH OTHER LINGERING ISSUES SUCH AS THE
NAM`S STRONGER SOLUTION ALOFT -- CONFIDENCE IS ABOVE AVERAGE. FOR
RAINFALL FORECAST PREFERENCES...SEE OUR QPF DISCUSSION (QPFPFD).


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

ROTH

$$





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