Prognostic Meteorological Discussion
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FXUS10 KWNH 041852
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 PM EDT TUE AUG 04 2015

VALID AUG 04/1200 UTC THRU AUG 08/0000 UTC

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

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


CLOSED LOW APPROACHING CA THU NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE GUIDANCE REMAINS IN GOOD AGREEMENT WITH THIS SYSTEM.


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

THE GUIDANCE SHOWS CONSIDERABLE SPREAD WITH THIS SYSTEM.  THE
SYSTEM IS MOVING OVER THE TOP OF A SOUTHERN STREAM RIDGE WOULD
TEND TO ARGUE FOR A FASTER SOLUTION...WHILE THE IDEA THAT IT IS
MOVING WITHIN THE SOUTHWEST PORTION OF AN OMEGA-TYPE BLOCK ACROSS
CANADA ARGUES FOR A SLOWER SOLN.  THE INTERMEDIATE GUIDANCE HERE
OF THE 12Z ECMWF/NAM SPLIT THE DIFFERENCE AND A COMPROMISE OF THE
TWO IS PREFERRED WITH AVERAGE CONFIDENCE.


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

THE 12Z UKMET BECAME EVEN MORE OUT OF SYNC WITH OTHER MODELS...NOW
SHOWING A RIDGE WHERE MOST OF THE OTHER MODELS SHOW A TROF BY
06/18Z.  THE NAM APPEARED TO BE OVERLY DEEP.  REMOVING THOSE TWO
LOOKS LIKE IT SHOULD YIELD A REASONABLE COMPROMISE WITH AVERAGE
CONFIDENCE.


SHORTWAVE CROSSING THE MID-SOUTH/SOUTHEAST WED/THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/ECMWF COMPROMISE
CONFIDENCE: AVERAGE

EVEN THOUGH THE GUIDANCE HAS TRENDED NOTICEABLY WEAKER WITH THIS
SYSTEM SINCE MONDAY...THE MASS FIELDS STILL HAVE A FAIRLY LARGE
SPREAD.  THE 12Z CANADIAN REMAINED A STRONG OUTLIER WHICH IS
TYPICAL BIAS.  A COMPROMISE OF THE 12Z GFS/ECMWF LOOKS REASONABLE
HERE AND LEAVES THE STRONGER NAM ON THE EDGE OF MODEL SOLNS.


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

THE SYSTEM LOOKED BETTER IN TERMS OF CONVECTION AND THE FACT THAT
THE CIRCULATION HAD BECOME BETTER DEFINED AT ABOUT THE TIME OF A
CONVECTIVE BURST EARLIER THIS MORNING.  SINCE THEN THE SYSTEM HAS
AN ELONGATED/SHEARED APPEARANCE.  SO WILL ONCE AGAIN GIVE LEAST
CONSIDERATION TO THE STRONGER CANADIAN AS THE SYSTEM PULLS EAST
AND MERGES WITH A FRONTAL SYSTEM.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

BANN

$$





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