Prognostic Meteorological Discussion
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000
FXUS10 KWNH 211854
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 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 MODEL EVALUATION WITH PREFERENCES/CONFIDENCE INTERVALS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


SYSTEM APPROACHING THE PACIFIC NORTHWEST MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: UKMET/NAM/ECMWF COMPROMISE; CONFIDENCE AVERAGE

THE 12Z CANADIAN/12Z GFS WERE THE QUICKEST WITH THIS SYSTEM`S
MOVEMENT WHILE THE 12Z UKMET/12Z ECMWF/12Z NAM WERE 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 12Z
UKMET/12Z ECMWF/12Z NAM IS PREFERRED WITH AVERAGE CONFIDENCE.


UPPER LOW NEAR CALIFORNIA SUNDAY/MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THIS FEATURE.  A COMPROMISE
OF THE 12Z CANADIAN, 12Z UKMET, 12Z 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
12Z CANADIAN, 12Z UKMET, 12Z GFS, AND 12Z 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: NON-UKMET BLEND; CONFIDENCE SLIGHTLY ABOVE AVE

THE 12Z UKMET WAS THE QUICKEST AND MOST ELONGATED WITH THIS
FEATURE BY LATE MONDAY.  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 12Z ECMWF/12Z NAM/12Z UKMET/12Z
CANADIAN 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, 12Z
CANADIAN, AND 12Z ECMWF IS PREFERRED WITH CONFIDENCE SLIGHTLY
ABOVE AVERAGE.  FOR RAINFALL FORECAST PREFERENCES, SEE OUR QPF
DISCUSSION (QPFPFD).


SHORTWAVE MOVING THROUGH THE NORTHERN MID-ATL LATE SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/ECMWF/UKMET COMPROMISE; CONFIDENCE ABOVE AVERAGE

THE 12Z NAM/12Z CANADIAN WERE STRONG OUTLIERS, PARTICULARLY WITH
THEIR 700 HPA REFLECTIONS OF THIS FEATURE, COMPARED TO THE OTHER
GUIDANCE -- THEIR USUAL BIAS.  A COMPROMISE OF THE 12Z GFS, 12Z
UKMET, AND 12Z 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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