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000
FXUS10 KWNH 241719
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1218 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 NAM/GFS EVALUATION...WITH PRELIMINARY 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. 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 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...AND THE 12Z
NAM/GFS ARE DEEPER THAN THE 00Z ECMWF/UKMET/CMC. ENSEMBLE SPREAD
SHOWS THE NAM/GFS TOWARD THE DEEPER SIDE AND ECMWF/UKMET/CMC
TOWARD THE FLATTER SIDE OF THE AVAILABLE MEMBERS SO A SOLUTION IN
THE MIDDLE APPEARS BEST GIVEN RELATIVELY SMALL RUN TO RUN CHANGES
IN THE ENSEMBLE GUIDANCE.

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 00Z UKMET A BIT FASTER TO MOVE THE
TROUGH AWAY FROM THE NORTHEAST...WHEREAS THE 00Z ECMWF/CMC AND 12Z
NAM WERE SLOWER/MORE AMPLIFIED ACROSS THE NORTHEAST. THE 12Z NAM
SEEMED TO SPLIT THESE RELATIVELY MINOR DIFFERENCES AND WILL BE
PREFERRED HERE.


...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 00Z ECMWF
CONFIDENCE: AVERAGE

ENSEMBLE SCATTER LOW PLOT CLUSTERING SUPPORTS THE TRACK OF THE
SIMILAR 12Z NAM/12Z GFS/00Z ECMWF WITH THE 00Z UKMET/CMC DISPLACED
FROM THE ENSEMBLE MEANS REGARDING THE SURFACE LOW FORECAST TO
TRACK WEST OF VANCOUVER ISLAND SAT NIGHT. STRENGTHS OF THE LOW
HAVE COME INTO BETTER AGREEMENT BUT THE 12Z GFS REMAINS STRONGEST
OF THE 3...WITH A BLEND RECOMMENDED TO EVEN OUT THE MINIMUM
CENTRAL PRESSURE.

AS THE UPPER TROUGH PROGRESSES EASTWARD...IT SPLITS WITH THE
NORTHERN PORTION TRACKING ACROSS SOUTHERN ALBERTA/SASKATCHEWAN
INTO MONDAY. THE 12Z NAM IS A LITTLE FASTER HERE...BUT NOT BY
MUCH. A 00Z ECMWF/12Z GFS BLEND APPEARS BEST 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.


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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