Prognostic Meteorological Discussion
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FXUS10 KWNH 170446
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1245 AM EDT THU APR 17 2014

VALID APR 17/0000 UTC THRU APR 20/1200 UTC

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


00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


UPPER TROUGH / SURFACE LOW WEAKENING ACROSS THE GREAT LAKES TODAY
AND REACHING THE NORTHEAST ON SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  NON 12Z UKMET/CMC COMPROMISE
CONFIDENCE:  ABOVE AVERAGE

THERE IS SOME SPREAD VERY EARLY IN THE FORECAST THU MORNING ACROSS
THE UPPER MIDWEST WITH THE SURFACE AND 850 MB LOW. THE 12Z
UKMET/CMC ARE ALREADY SLOW WITH THIS FEATURE COMPARED TO THE 00Z
OBSERVATIONS. THE 00Z NAM/GFS AND 12Z ECMWF HAVE BETTER AGREEMENT
AND CORRESPOND BETTER WITH THE ENSEMBLE MEANS AND LATEST
OBSERVATIONS.

THE SURFACE LOW WEAKENS AS IT MOVES INTO ONTARIO EARLY FRI
MORNING...BUT THE UPPER TROUGH BECOMES REVITALIZED FROM THE NORTH
AS THE SYSTEM APPROACHES THE NORTHEAST FOR SATURDAY. HERE...THE
12Z UKMET/CMC ARE MUCH QUICKER ALOFT THAN THE REMAINING MODEL
CONSENSUS. A NON 12Z UKMET/CMC COMPROMISE IS PREFERRED.


CLOSED MID-LEVEL LOW FORMING OVER THE SOUTHEAST U.S. AT END OF WEEK
CORRESPONDING SURFACE LOW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  12Z ECMWF/UKMET COMPROMISE
CONFIDENCE:  BELOW AVERAGE

DETERMINISTIC AND ENSEMBLE SPREAD REMAINS WELL ABOVE AVERAGE FOR
THE RELATIVELY SHORT FORECAST TIME FRAME. AS WE HEAD INTO EARLY
SATURDAY...THERE IS A SLOWING TREND SEEN IN THE UKMET/CMC BUT NOT
MUCH OF A TREND SEEN IN THE ECMWF. THE GFS IS EARLY TO CLOSE OFF A
MID-LEVEL CENTER COMPARED TO THE REMAINING GUIDANCE AND APPEARS TO
BE SUFFERING FROM SOME GRID-SCALE FEEDBACK WHICH IS A POSSIBLE
REASON FOR WHY THE GFS IS AHEAD MOST WITH THE TIMING OF THE UPPER
TROUGH ACROSS THE SOUTHEAST. THE GEFS IS SIMILAR TO THE GFS.

GIVEN SOME OF THE OBSERVED SLOWING TRENDS...AND THE PLACEMENT OF
THE ECMWF BEING IN THE MIDDLE OF THE CURRENT SPREAD...THE
PREFERENCE IS TO BE JUST A BIT SLOWER THAN THE MIDDLE OF THE
SPREAD...BEST REPRESENTED BY THE 12Z ECMWF AND 12Z UKMET.


UPPER TROUGH REACHING THE PACIFIC NORTHWEST TODAY AND FRI
AND REACHING SOUTH CENTRAL CANADA BY SAT NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  GENERAL MODEL COMPROMISE
CONFIDENCE:  AVERAGE

THE 00Z NAM AND 12Z ECMWF HAVE BETTER AGREEMENT WITH THE ENSEMBLE
MEANS IN BEING A BIT NORTH WITH THE TRACK OF THE VORTICITY CENTER
AS IT REACHES INTO S-CNTRL CANADA COMPARED TO THE 00Z GFS...12Z
UKMET/CMC. HOWEVER...THE MODELS TO THE SOUTH HAVE ALL TRENDED FROM
A POSITION FURTHER NORTH COMPARED TO YESTERDAY. THEREFORE...A
BLEND OF THE NORTH/SOUTH SOLUTIONS IS PREFERRED...GIVEN THE
RELATIVELY SMALL SPREAD...BEST REPRESENTED BY A GENERAL MODEL
COMPROMISE.


UPPER TROUGH REACHING THE SOUTHWEST U.S. FRI AND SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  NON 00Z NAM COMPROMISE
CONFIDENCE:  ABOVE AVERAGE

DIFFERENCES ARE SMALL...BUT THE 00Z NAM APPEARS TO BE A BIT AHEAD
OF THE PACK WITH RESPECT TO THE UPPER TROUGH ACROSS THE SOUTHWEST.
THEREFORE...A NON-00Z NAM COMPROMISE IS PREFERRED.


UPPER TROUGH REACHING THE PACIFIC NORTHWEST ON SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  GENERAL MODEL COMPROMISE
CONFIDENCE:  ABOVE AVERAGE

THE LATEST GUIDANCE SHOWS ONLY SMALL DIFFERENCES WITH THIS
SYSTEM...SO THEREFORE A GENERAL MODEL COMPROMISE 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...

OTTO

$$





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