Prognostic Meteorological Discussion
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000
FXUS10 KWNH 201720
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
120 PM EDT WED AUG 20 2014

VALID AUG 20/1200 UTC THRU AUG 24/0000 UTC

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

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


WEAK SHORTWAVE LIFTING NEWD FROM THE NRN HIGH PLAINS TODAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  12Z GFS
CONFIDENCE:  SLIGHTLY BELOW AVERAGE

THE 00Z ECMWF/UKMET BECOME SUSPICIOUSLY STRONG EARLY ON WITH
MID-LEVEL VORTICITY MOVING THROUGH THE DAKOTAS LATER THIS EVENING
AND END UP ON THE NRN EDGE OF THE LATEST GUIDANCE WITH A
CORRESPONDING SURFACE LOW AND WARM FRONT TO TRACK ACROSS THE UPPER
MISSISSIPPI VALLEY. TRENDS IN THE ECMWF/UKMET THROUGH THEIR 00Z/20
CYCLE ARE NORTH WITH THIS LOW BUT ENSEMBLE LOW PLOTS OF THE
ECMWF/CMC/GEFS SUPPORT SOMETHING CLOSER TO THE 12Z GFS. CONFIDENCE
IS REDUCED GIVEN THE CONVECTIVE INGREDIENT IN THIS SETUP ACROSS
THE DAKOTAS AND ITS POTENTIAL INFLUENCE ON THE DEVELOPMENT OF A
SURFACE LOW.


UPPER TROUGHING MOVING FROM THE GREAT LAKES ACROSS THE NORTHEAST
COLD FRONT SINKING SWD THROUGH THE EAST COAST STATES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  12Z GFS...00Z ECMWF COMPROMISE
CONFIDENCE:  AVERAGE

THE 12Z NAM ENDS UP ON THE DEEPER END OF THE GUIDANCE CONCERNING
THE 500 MB TROUGH EVOLVING IN THE WRN ATLANTIC BY THIS WEEKEND
WHICH CAUSES THE NAM TO BE ON THE SOUTH SIDE WITH A COLD FRONT
SINKING THROUGH THE SERN STATES. WHILE THE OTHER MODELS SUPPORT A
NON-NAM CONSENSUS...THE 12Z GFS AND 00Z ECMWF MAKE UP A DECENT
COMPROMISE WITH GOOD SUPPORT FROM THE ENSEMBLE MEANS.


WEAKENING MID-LEVEL DISTURBANCE LIFTING NEWD FROM THE SOUTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  00Z ECMWF
CONFIDENCE:  AVERAGE

THE 12Z NAM...12Z GFS AND 00Z UKMET HAVE TRENDED SLOWER WITH THIS
FEATURE AS IT CROSSES THE ROCKIES...WITH THE MOST RECENT SUITE OF
GUIDANCE SHOWING A TIMING SPREAD BY FRI EVENING. THE 00Z UKMET AND
00Z CMC ARE FASTEST...WITH THE 00Z ECMWF SHOWING THE LEAST RUN TO
RUN SPREAD...WITH THE 00Z/20 ECMWF FALLING IN THE MIDDLE OF THE
LATEST SPREAD.


UPPER TROUGHING ACROSS THE PACIFIC NORTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  12Z NAM...12Z GFS...00Z ECMWF COMPROMISE
CONFIDENCE:  AVERAGE

THE 00Z UKMET/CMC END UP MUCH FASTER WITH THIS UPPER TROUGH...OR
AT LEAST MORE BROAD IN SCALE...BY SAT MORNING. THE NAM/GFS/ECMWF
SHOW GOOD AGREEMENT WITH EACH OTHER AND HAVE SUPPORT FROM THE
ENSEMBLE MEANS.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

OTTO

$$




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