MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1243 AM EDT TUE JUN 18 2013

VALID JUN 18/0000 UTC THRU JUN 21/1200 UTC

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

INITIAL 00Z MODEL EVALUATION...INCLUDING THE 00Z NAM/GFS AND
INITIAL PREFERENCES


...BROAD UPPER LEVEL TROUGHING OVER THE GREAT LAKES AND
NORTHEAST...
 
PREFERENCE: NON 00Z NAM COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE 

THE MOST RECENT GUIDANCE SHOWS DECENT AGREEMENT WITH BROAD UPPER
LEVEL TROUGHING AND A CLOSED CENTER TRACKING EASTWARD THROUGH
QUEBEC. THERE ARE A COUPLE OF TRAILING WAVE WHICH PROGRESS ACROSS
THE NORTHEAST.  ONE ON DAY TWO SHOWS THE NAM/21Z SREF MEAN WITH A
HIGHER AMPLITUDE WAVE THAN THE ECMWF/GFS/CANADIAN GLOBAL/UKMET AND
THE GEFS/ECMWF ENSEMBLE MEANS. THE MODEL MAJORITY PERSISTS WITH
THE SLOW MOVING TROUGH AXIS IN THE NORTHEAST ON DAY THREE WHILE
THE NAM EJECTS A WAVE OFF THE COAST AND STARTS RAISING HEIGHTS IN
RESPONSE TO THE FASTER MOVING CYCLONE IN THE NORTHWEST.  THE
BETTER THAN NORMAL CLUSTERING OF THE GFS/ECMWF/CANADIAN/UKMET/GFS
ENSEMBLE MEAN/ECMWF ENSEMBLE MEAN SUGGESTS A NON-NAM CONSENSUS BE
USED.

...LOW-MID LEVEL WAVE ADVANCING EAST ACROSS THE SOUTHERN
APPALACHIANS/MID-ATLANTIC/SOUTHEAST...
...WEAK SFC LOW TRACKING TOWARD THE CNTRL MID-ATLANTIC COAST...
 
PREFERENCE: 12Z ECMWF/UKMET BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE 
 
A 700 MB SHORTWAVE AND ATTENDANT SFC LOW/FRONTAL BNDRY IS FORECAST
TO TRACK EWD FROM THE TN VALLEY ACROSS THE SOUTHERN APPALACHIANS
TO THE MID-ATLANTIC STATES.

THE 12Z ECMWF/UKMET CLUSTER WELL WHILE THE GFS FLIPPED TO A LOWER
AMPLITUDE AND FASTER SOLUTION. THE LATEST ENSEMBLE MEANS ARE
SLOWER THAN THE NAM/GFS IN MOVING THE WAVE OFF THE MID
ATLANTIC/SOUTHEAST COASTS...AND ARE CLOSER TO THE 12Z ECMWF/UKMET.


...DEEP CLOSED LOW MOVING ACROSS THE PACIFIC NORTHWEST AND
NORTHERN ROCKIES...

PREFERENCE: BLEND OF THE 12Z GFS/ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

STARTING EARLY THU...MODELS BEGIN TO DIFFER WITH THE SPEED OF THE
CLOSED LOW MOVING THROUGH THE NORTHWEST. THE 00Z NAM/21Z SREF/12Z
UKMET ARE QUICKEST WITH THE CENTER OF THE CLOSED LOW BY THU
MORNING.  THE 00Z GFS/12Z ECMWF/12Z CANADIAN GLOBAL ARE IN THE
SLOWER CLUSTER AND THE 18Z GEFS MEAN/12Z ECMWF ENSEMBLE MEAN ARE
IN BETWEEN THESE SOLUTIONS.  GIVEN THE HIGH AMPLITUDE WAVE PATTERN
AND CLOSED LOW USUALLY MOVE SLOWLY...PREFER A BLEND OF THE
GFS/ECMWF AND THEIR ENSEMBLE MEANS.  THE ONE AREA THE GFS LOOKS
LIKE A LOW PROBABILITY IS WITH ITS LOWER PRESSURE IN RESPONSE TO
CONVECTION THU NIGHT NEAR THE ND/MN BORDER.

...500 MB WAVE MOVING FROM THE CENTRAL PLAINS-UPPER MS VALLEY ON
DAY TWO AND OHIO VALLEY DAY THREE...

PREFERENCE:  BLEND OF THE 00Z GFS/12Z ECMWF/21Z SREF MEAN
CONFIDENCE:  SLIGHTLY ABOVE AVERAGE

THE MODELS SHOW A LOW AMPLITUDE 500 MB WAVE MOVING EAST IN
CONFLUENT FLOW FROM THE CENTRAL PLAINS TO MS VALLEY ON DAY TWO AND
OHIO VALLEY ON DAY 3.  THERE ARE SLIGHT TIMING AND AMPLITUDE
DIFFERENCES WITH THE WAVE AMONGST THE MODELS/ENSEMBLE MEANS.  THE
12Z UKMET WAS FASTER DUE A SLIGHTLY LOWER AMPLITUDE WHILE THE NAM
WAS THE HIGHEST AMPLITUDE SOLUTION. CLUSTERING IS GOOD AMONG THE
00Z GFS/12Z ECMWF/21Z SREF MEAN/18Z GEFS MEAN TO SUGGEST A BLEND
OF THESE SOLUTIONS BE USED.


...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