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000
FXUS10 KWNH 211635
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1235 PM EDT FRI JUL 21 2017

VALID JUL 21/1200 UTC THRU JUL 25/0000 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 MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: UKMET/ECMWF COMPROMISE; CONFIDENCE AVERAGE

THE 00Z CANADIAN WAS THE QUICKEST WITH THIS SYSTEM`S MOVEMENT
WHILE THE 00Z UKMET WAS THE SLOWEST.  THIS SYSTEM IS IN A COMPLEX
FLOW REGIME WITH RIDGING BUILDING OVER ITS TOP IN THE GULF OF AK
WHILE ANOTHER CLOSED LOW LURKS TO ITS SOUTHWEST -- BOTH ARGUE FOR
SLOWER PROGRESSION.  SINCE THE SYSTEM APPEARS REMOVED FROM THE
INFLUENCE OF ANY KICKER SHORTWAVES, BELIEVE A SLOWER SOLUTION IS
BEST HERE.  A COMPROMISE OF THE 00Z UKMET/00Z ECMWF IS PREFERRED
WITH AVERAGE CONFIDENCE.


UPPER LOW NEAR CALIFORNIA SUNDAY/MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THIS FEATURE.  A COMPROMISE
OF THE 00Z CANADIAN, 00Z UKMET, 00Z ECMWF, 12Z NAM, AND 12Z GFS IS
ADVISED WITH ABOVE AVERAGE CONFIDENCE.


SYSTEM MOVING THROUGH SOUTH-CENTRAL CANADA LATE MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM COMPROMISE; CONFIDENCE ABOVE AVERAGE

THE 12Z NAM IS A BIT FASTER WITH THIS SYSTEM, WHICH IMPACTS ITS
FRONTAL PROGRESSION IN THE DAKOTAS MONDAY.  A COMPROMISE OF THE
00Z CANADIAN, 00Z UKMET, 12Z GFS, AND 00Z ECMWF IS PREFERRED HERE
WITH ABOVE AVERAGE CONFIDENCE.


SYSTEM MOVING FROM THE PRAIRIE PROVINCES OF CANADA THROUGH
THE GREAT LAKES AND INTO THE NORTHEAST MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NAM/ECMWF/GFS COMPROMISE; CONFIDENCE AVERAGE

THE 00Z CANADIAN WAS A SLOW OUTLIER -- ITS USUAL BIAS.  THE 00Z
UKMET WAS THE QUICKEST.  OTHERWISE, THERE ARE LATITUDE ISSUES WITH
THE BULK OF THE 500/700 HPA ENERGY MOVING INTO THE NORTHEAST, WITH
THE 12Z GFS THE FARTHEST NORTH AND THE 00Z ECMWF/12Z NAM MORE
SOUTHERLY.  AS A RIDGE UPSTREAM IS STRENGTHENING, A MORE
AMPLIFIED/ SLOWER AND SOUTHERN SOLUTION MAKES SENSE HERE.  TO
ACCOUNT FOR UNCERTAINTY, A COMPROMISE OF THE 12Z GFS, 12Z NAM, AND
00Z ECMWF IS PREFERRED WITH CONFIDENCE NO BETTER THAN AVERAGE.
FOR RAINFALL FORECAST PREFERENCES, SEE OUR QPF DISCUSSION (QPFPFD).


SHORTWAVE MOVING THROUGH THE NORTHERN MID-ATL LATE SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM COMPROMISE; CONFIDENCE ABOVE AVERAGE

THE 12Z NAM WAS A STRONG OUTLIER, PARTICULARLY WITH ITS 700 HPA
REFLECTION OF THIS FEATURE, COMPARED TO THE OTHER GUIDANCE -- ITS
USUAL BIAS.  A COMPROMISE OF THE 12Z GFS, 00Z CANADIAN, 00Z UKMET,
AND 00Z ECMWF IS PREFERRED WITH ABOVE AVERAGE CONFIDENCE FOR MASS
FIELDS.  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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