Prognostic Meteorological Discussion
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000
FXUS10 KWNH 241849
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 PM EST FRI NOV 24 2017

VALID NOV 24/1200 UTC THRU NOV 28/0000 UTC

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

12Z MODEL EVALUATION...WITH FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...DEPARTING MID-LEVEL TROUGH FROM THE SOUTHEAST U.S. TODAY...
...SURFACE LOW TRACKING NORTH THROUGH THE WESTERN ATLANTIC THIS
WEEKEND...
...REINFORCING UPPER TROUGH OVER THE GULF OF MEXICO BY SUN...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE

THE 00Z/24 ENSEMBLE GUIDANCE SHOWS GOOD AGREEMENT WITH LITTLE
CHANGE FROM THE PREVIOUS CYCLE CONCERNING THE SURFACE LOW TRACK.
CURRENTLY...THE 12Z NAM/GFS ARE A BIT WEST OF THE 00Z
ECMWF/UKMET/CMC AND THE ENSEMBLE MEANS ARE IN THE MIDDLE. THE 12Z
ECMWF/UKMET/CMC TRACKED WESTWARD A BIT FROM THEIR PREVIOUS CYCLES
AND ARE NOW NEAR THE LATEST ENSEMBLE MEANS. WHILE THE 12Z GFS HAS
THE FARTHEST WEST SURFACE LOW TRACK LATE SAT INTO SUN...ALL
GUIDANCE IS WELL AWAY FROM THE NEW ENGLAND COAST. A GENERAL MODEL
COMPROMISE CAN BE USED FOR THIS SYSTEM.

REGARDING SECONDARY TROUGHING SETTING UP OVER THE SOUTHEAST...THE
DETERMINISTIC MODEL FORECASTS ARE FOR A BROAD FEATURE WITH
EMBEDDED SMALLER SCALE VORTICITY MAXIMA. OUTSIDE OF SMALLER DETAIL
DIFFERENCES...THERE IS ENOUGH AGREEMENT ACROSS THE SOUTHEAST TO
PREFER A GENERAL MODEL BLEND.


...UPPER TROUGH AXIS REACHING THE GREAT LAKES TONIGHT...
...ASSOCIATED SURFACE LOW CROSSING SOUTHERN CANADA...
...REINFORCING UPPER TROUGH AXES OVER THE NORTHEAST SUN AND MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND UNTIL 12Z/27
            12Z NAM/ECMWF FROM 12Z/27 TO 00Z/28
CONFIDENCE: AVERAGE

DIFFERENCES BEGIN TO APPEAR ACROSS THE NORTHEAST BY SUN MORNING.
CONCERNING THE REINFORCING TROUGHS ACROSS THE NORTHEAST...THERE
ARE TWO TO SPEAK OF. THE FIRST TROUGH AXIS IS FORECAST TO BE
CENTERED OVER WESTERN NEW ENGLAND SUN MORNING. THE 12Z
ECMWF/UKMET/CMC ALL TRENDED SLIGHTLY DEEPER TOWARD THE 12Z
NAM/GFS. ENSEMBLE SPREAD SHOWS THE NAM/GFS TOWARD THE SLIGHTLY
DEEPER SIDE AND ECMWF/UKMET/CMC NEAR THE BETTER CLUSTERING OF THE
AVAILABLE MEMBERS. THE MODEL AGREEMENT IS CLOSE ENOUGH NOW TO
PREFER A GENERAL MODEL BLEND FOR THIS TROUGH.

ANOTHER REINFORCING TROUGH AXIS IS FORECAST TO REACH THE NORTHEAST
ON SUNDAY...THIS ONE A BIT BROADER THAN THE FIRST. THROUGH
00Z/28...THERE ARE ALSO SOME MINOR TIMING/AMPLITUDE DIFFERENCES TO
SPEAK OF WITH THE 12Z GFS AND 12Z UKMET A BIT FASTER TO MOVE THE
TROUGH AWAY FROM THE NORTHEAST...WHEREAS THE 12Z ECMWF/NAM WERE
SLOWER AND 12Z CMC SLOWEST/DEEPEST. THE PREVIOUSLY DEEPER 00Z
ECMWF TRENDED MORE SIMILARLY TO THE 12Z NAM SO THOSE TWO MODELS
ARE RECOMMENDED FOR THIS NEXT REINFORCING TROUGH AXIS.


...LOW PRESSURE LIFTING UP OFF THE WEST COAST ON SAT/SAT NIGHT...
...DEEP UPPER TROUGH OFFSHORE THE WEST COAST THROUGH SUN...
...NORTHERN STREAM TROUGH AXIS AND ASSOCIATED SURFACE LOW ACROSS
SOUTHERN CANADA ON MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z NAM
CONFIDENCE: AVERAGE

ENSEMBLE SCATTER LOW PLOT CLUSTERING SUPPORTS THE TRACK OF THE
SIMILAR 12Z NAM/12Z GFS THE BEST WHILE THE 12Z ECMWF IS DISPLACED
OFF TOWARD THE EAST...12Z UKMET/CMC WEST. STRENGTHS OF THE LOW
HAVE COME INTO BETTER AGREEMENT BUT THE 12Z GFS REMAINS STRONGER
THAN THE 12Z NAM WITH A BLEND OF THE 2 MODELS A FEW MB BELOW THE
ENSEMBLE MEANS.

AS THE UPPER TROUGH PROGRESSES EASTWARD...IT SPLITS WITH THE
NORTHERN PORTION TRACKING ACROSS SOUTHERN ALBERTA/SASKATCHEWAN
INTO MONDAY. THE 12Z NAM IS SLIGHTLY FASTER HERE...BUT NOT BY MUCH
AND GIVEN THE CHANGES WITH THE CORE OF THE UPPER LOW SEEN IN THE
12Z ECMWF COMPARED TO ITS PREVIOUS RUN...A 12Z NAM/GFS BLEND
APPEARS REASONABLE HERE GIVEN PLACEMENT IN THE MIDDLE OF THE
LATEST MODEL SPREAD.


...SOUTHERN STREAM TROUGH AXIS/CLOSED LOW INTO THE SOUTHWEST MON
INTO TUE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z GFS BLEND
CONFIDENCE: AVERAGE

ENSEMBLE TRENDS HAVE BEEN SLOWER OVER THE PAST 4 CYCLES WITH THIS
SYSTEM. THE 12Z GFS IS ON THE FASTER END AND ONLY MINOR
DIFFERENCES OUTSIDE OF THE 12Z GFS. A NON 12Z GFS BLEND IS
PREFERRED HERE...AND THE REMAINING 12Z ECMWF/UKMET/CMC CONTINUE TO
SUPPORT A NON 12Z GFS BLEND FOR THIS SYSTEM.


MODEL TRENDS 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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