Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6
000
FXUS10 KWNH 040428
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1227 AM EDT TUE AUG 04 2015

VALID AUG 04/0000 UTC THRU AUG 07/1200 UTC

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

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


CLOSED LOW APPROACHING CA THU NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE 12Z UKMET WAS A SLOW OUTLIER, WITH THE MODEL CONSENSUS IN GOOD
AGREEMENT WITH THE 18Z GEFS AND 12Z ECMWF ENSEMBLE MEANS.  A
NON-UKMET COMPROMISE IS PREFERRED HERE WITH ABOVE AVERAGE
CONFIDENCE.


POSSIBLE CLOSED LOW MOVING ALONG WESTERN US/CAN BORDER
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NAM/ECMWF COMPROMISE
CONFIDENCE: AVERAGE

THE GUIDANCE SHOWS CONSIDERABLE SPREAD WITH THIS SYSTEM, WITH THE
00Z GFS THE QUICKEST AND THE 12Z CANADIAN THE SLOWEST -- BOTH
FITTING KNOWN BIASES.  WITH THE SYSTEM IS MOVING OVER THE TOP OF A
SOUTHERN STREAM RIDGE (ARGUING FOR A FASTER SOLUTION), IT IS
MOVING WITHIN THE SOUTHWEST PORTION OF AN OMEGA-TYPE BLOCK ACROSS
CANADA (WHICH ARGUES FOR SLOWER).  THE INTERMEDIATE GUIDANCE HERE
OF THE 12Z ECMWF/00Z NAM SPLIT THE DIFFERENCE SEEN IN THE 12Z
ECMWF AND 18Z GEFS ENSEMBLE MEANS, AND A COMPROMISE OF THE TWO IS
PREFERRED WITH AVERAGE CONFIDENCE.


NORTHERN STREAM SHORTWAVES CROSSING THE DAKOTAS/MN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/NAM COMPROMISE
CONFIDENCE: AVERAGE

THE 12Z ECMWF WAS ANOMALOUSLY STRONG ALOFT AND AT THE SURFACE WITH
THE FIRST WAVE, WHICH WAS NOT SUPPORTED BY THE 12Z GLOBAL ENSEMBLE
GUIDANCE.  BECAUSE OF THIS, THE ECMWF BECAME FLATTER WITH THE
SECOND WAVE THE REST OF THE GUIDANCE SHOWS A STRONGER SOLUTION FOR
ALOFT.  THE 12Z UKMET IS UP TO ITS OLD TRICKS AND ATTEMPTS TO
DEVELOP A TROPICAL CYCLONE-LIKE LOW WHICH MOVES OUT OF SD INTO
MN...THIS IS NOT PREFERRED.  OVERALL, A COMPROMISE OF THE 00Z
GFS/00Z NAM FITS IN BEST WITH THE 12Z ECMWF/18Z GEFS MEAN
SOLUTIONS.  THIS IS PREFERRED WITH AVERAGE CONFIDENCE.


SHORTWAVE CROSSING THE MID-SOUTH/SOUTHEAST WED/THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/ECMWF COMPROMISE
CONFIDENCE: AVERAGE

THE GUIDANCE HAS TRENDED NOTICEABLY WEAKER WITH THIS SYSTEM SINCE
YESTERDAY.  THE 12Z CANADIAN IS A STRONG OUTLIER -- ITS USUAL
BIAS.  THE 00Z NAM SURFACE LOW LIES COMPLETELY OUTSIDE THE
NORTHEAST FRINGE OF THE 12Z GLOBAL ENSEMBLE SPREAD BY FRIDAY
MORNING.  A COMPROMISE OF THE 00Z GFS/12Z ECMWF LOOKS REASONABLE
HERE, AND IS PREFERRED WITH AVERAGE CONFIDENCE.


LOW PRESSURE MOVING FROM GA COAST TO THE CAROLINA COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/NAM/ECMWF COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THROUGH TUESDAY NIGHT, THE GUIDANCE HANDLES THIS WEAK SYSTEM
SIMILARLY.  BY WEDNESDAY MORNING, BOTH THE 12Z CANADIAN AND 12Z
UKMET DEVELOP THE SYSTEM AS A TROPICAL CYCLONE-LIKE ENTITY AS IT
PULLS AWAY FROM NC, LYING ON THE EASTERN AND SOUTHERN FRINGE OF
THE 12Z GLOBAL ENSEMBLE ENVELOPE OF SOLUTIONS.  A COMPROMISE OF
THE 00Z GFS/00Z NAM/12Z ECMWF LOOKS REASONABLE HERE 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
$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.