Prognostic Meteorological Discussion
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000
FXUS10 KWNH 031839
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT MON AUG 03 2015

VALID AUG 03/1200 UTC THRU AUG 07/0000 UTC

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

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


MID LEVEL WAVES CROSSING THE ROCKIES/PLAINS/MS VALLEY/OH VALLEY
SURFACE LOW CROSSING THE CENTRAL PLAINS TO MID MS RIVER VALLEY WED
AND OH VALLEY THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/06Z GEFS MEAN COMPROMISE
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE 00Z UKMET WAS ALONE IN DEVELOPING A CLOSED 850-700 MB LOW NEAR
THE SD/NE BORDER AND FOLLOWING SLOW FORWARD PROGRESSION.  THE 12Z
NAM/GFS HAVE AMPLIFIED THE WAVE CROSSING THE NORTHERN PLAINS AND
CONFIDENCE IS LOW IN THEIR RUN TO RUN CHANGE, SO THE 12Z NAM/GFS
APPEAR TO BE A LOW PROBABILITY SOLUTION IN THE DAKOTAS AND MN/IA.
THE 12Z ECMWF HAS A SIMILAR PROBLEM WITH AMPLIFYING A WAVE NEAR
THE ND/MN BORDER WED NIGHT AND MN/MANITOBA BORDER THU.

THE 12Z NAM/ECMWF BACKED OFF THE INTENSITY OF THE 06Z RUN WITH THE
850-700 MB LOW CROSSING KS/MO TO THE OH VALLEY, AND TRENDED A FEW
HOURS FASTER.  THE 12Z NAM APPEARS TO SUFFER FROM GRID SCALE
FEEDBACK WITH A SECOND CIRCULATION IN NORTHERN IN/OH ON DAY 3, SO
THE NAM APPEARS TO BE A LOW PROBABILITY SOLUTION IN NORTHERN
IN/OH.  HOWEVER NEAR THE OH RIVER THE 12Z NAM IS CLOSE TO THE 00Z
ECMWF LOW POSITION ON THU.  THE 12Z ECMWF BIG CHANGE TO ELIMINATE
THE 700 MB CLOSED LOW IN THE OH VALLEY LEADS TO LOW CONFIDENCE IN
CHOOSING A PREFERRED SOLUTION.

THE 06Z GEFS/OPERATIONAL 00Z ECMWF SOLUTIONS ARE PREFERRED WITH
SLIGHTLY BELOW AVERAGE CONFIDENCE.  THE 12Z GFS LOW IN THE OH
VALLEY IS NORTH OF THE NAM/ECMWF IN RESPONSE TO AN ANOMALOUSLY
STRONGER/HIGHER AMPLITUDE 700 MB WAVE IN THE UPPER MS
VALLEY...WITH LOW CONFIDENCE IN THE GFS SOLUTION IN IL/IN THU.


DEEP TROUGH MOVING ACROSS THE NORTHWEST TO THE NORTHERN
ROCKIES/NORTHERN PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/12Z GFS/09Z SREF MEAN COMPROMISE
CONFIDENCE: AVERAGE

THE MODELS FORECAST A SLOW EAST PROGRESSION OF A DEEP LAYER TROUGH
ACROSS BRITISH COLUMBIA/PACIFIC NORTHWEST AND THEN
ALBERTA/NORTHERN ROCKIES AND HIGH PLAINS THU.
THE 00Z UKMET FORECAST THE HIGHEST AMPLITUDE/SHORTEST WAVELENGTH
500 MB TROUGH.  WITH THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS CLOSE
TO THEIR RESPECTIVE 12Z GFS AND 00Z ECMWF OPERATIONAL RUNS, FAVOR
A COMPROMISE OF THE 00Z ECMWF/09Z SREF MEAN/12Z GFS WITH ABOVE
AVERAGE CONFIDENCE.  THE 00Z-12Z CANADIAN GLOBAL MODEL RUNS WERE A
SLOW OUTLIER.

ONCE THE LEAD 700 MB WAVE REACHES THE NORTHERN PLAINS THU...THE
12Z NAM/12Z UKMET BECOME AMPLIFIED OUTLIERS.  THE 09Z SREF MEAN
WAS LESS AMPLIFIED AND AGREES BETTER WITH THE LOWER AMPLITUDE 12Z
GFS/UKMET/ECMWF FORECASTS.


LOW PRESSURE MOVING FROM FL NORTHEAST TO THE CAROLINA COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM/GFS/09Z SREF MEAN/12Z ECMWF
CONFIDENCE: AVERAGE

THE MODELS SHOW A WEAK CIRCULATION OVER NORTHERN FL MOVING
NORTHEAST NEAR THE GA/SC COAST AND POSSIBLY EITHER SHEARING OUT OR
REFORMING AS A LOW MOVING NORTHEAST FROM JUST OFF CAPE HATTERAS
NC.
THE 00Z-12Z UKMET SHOWS THE MOST DEVELOPMENT WITH THIS SYSTEM
NORTHEAST OF CAPE HATTERAS.  THE 06Z-12Z GFS AND 09Z SREF MEAN/12Z
NAM/12Z ECMWF CLUSTER WELL IN MAINTAINING SPATIAL AND TEMPORAL
CONTINUITY WITH THE 700 MB WAVE SO A BLEND OF THESE SOLUTIONS IS
PREFERRED.

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

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

PETERSEN

$$





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