Prognostic Meteorological Discussion
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000
FXUS10 KWNH 031624
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1223 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 NAM 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.  THIS LOOKS BETTER WITH THE TRACK AND INTENSITY NOT
FAR FROM THE 00Z ECMWF.  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 00Z GEFS/ECMWF ENSEMBLE MEAN/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.
THE 06Z GEFS MEAN SFC FRONT AND LOW PRESSURE AGREE BETTER WITH THE
OTHER MODELS FURTHER SOUTH THAN THE OPERATIONAL GFS.


DEEP TROUGH MOVING ACROSS THE NORTHWEST TO THE NORTHERN ROCKIES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: ECMWF/GFS/NAM 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/12Z NAM/12Z GFS WITH ABOVE AVERAGE
CONFIDENCE.  THE 00Z CANADIAN GLOBAL MODEL WAS A SLOW OUTLIER.

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


LOW PRESSURE MOVING FROM FL NORTHEAST TO THE CAROLINA COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM/GFS/09Z SREF MEAN
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 UKMET SHOWS THE MOST DEVELOPMENT WITH THIS SYSTEM
NORTHEAST OF CAPE HATTERAS.  THE 06Z-12Z GFS AND 09Z SREF MEAN/12Z
NAM 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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