Prognostic Meteorological Discussion
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FXUS10 KWNH 231658
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EST THU NOV 23 2017

VALID NOV 23/1200 UTC THRU NOV 27/0000 UTC

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

12Z NAM/GFS EVALUATION...WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...SLOW-MOVING MID-LEVEL TROUGH OVER THE GULF OF MEXICO LIFTING
ACROSS THE FL PENINSULA ON FRI...
...SURFACE LOWS OVER THE EASTERN GULF OF MEXICO/NEAR
FLORIDA...TRACKING NORTH OVER THE WESTERN ATLANTIC THIS WEEKEND...
...REINFORCING UPPER TROUGH OVER THE GULF OF MEXICO BY SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM/12Z GFS/00Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE CURRENT 15Z SURFACE ANALYSIS ALIGN BEST WITH THE 12Z NAM/GFS
AND 00Z ECMWF WHEREAS THE 00Z UKMET/CMC ARE DISPLACED WITH THE
SURFACE LOW POSITION CURRENTLY LOCATED WEST OF THE FL PENINSULA.
ENSEMBLE TRENDS WERE REASONABLY WELL CLUSTERED YESTERDAY AND ARE
SO TODAY BUT THEY THE BEST LOW CLUSTERING HAS SIGNIFICANTLY
ADJUSTED TOWARD THE MINORITY OF SURFACE LOW PLOTS FROM
YESTERDAY...CURRENTLY ALIGNED WITH THE 12Z NAM/12Z GFS/00Z ECMWF.
GIVEN THE AGREEMENT FROM THE 12Z NAM/GFS TO CURRENT CONDITIONS AND
THE LARGE ADJUSTMENTS SEEN IN THE ENSEMBLES...WILL GO WITH THE
MORE RECENTLY INITIALIZED MODELS AND THE 00Z ECMWF WHICH AGREES
WITH THE 12Z NAM/12Z GFS.

AS THE SURFACE LOW TRACKS UP THE WESTERN ATLANTIC...THE 12Z NAM IS
CLOSER TO THE EAST COAST THAN THE 12Z GFS AND 00Z ECMWF.
HOWEVER...A 3-WAY BLEND OF THESE THREE MODELS IS CONSIDERED BEST
AND IS SUPPORTED AMONG THE SPREAD IN ENSEMBLE SCATTER LOW PLOTS
THROUGH SUNDAY MORNING.


...UPPER TROUGH AXIS CROSSING THE PACIFIC NORTHWEST AND REACHING
THE GREAT LAKES BY FRIDAY NIGHT...
...ASSOCIATED SURFACE LOW CROSSING SOUTHERN CANADA...
...POSSIBLE SHORTWAVE AMPLIFICATION OVER THE NORTHEAST SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-12Z NAM BLEND...WITH THE SURFACE LOW
            12Z GFS/00Z ECMWF BLEND WITH THE HEIGHT FALLS
CONFIDENCE: AVERAGE

THE 12Z NAM IS SLOWEST WITH THE TRACK OF THE INITIAL UPPER TROUGH
ACROSS THE N-CNTRL U.S.FRI INTO SAT AND IS CONSIDERED UNLIKELY TO
VERIFY GIVEN A LACK OF SUPPORT FROM THE OTHER MODEL SOLUTIONS. A
NON-12Z NAM BLEND IS BELIEVED TO BE BEST FOR THIS PORTION OF THIS
SYSTEM.

A REINFORCING UPPER TROUGH BUILDS OVER THE NORTHEAST SAT
NIGHT...WITH A BLEND BETWEEN THE DEEPER 12Z GFS AND LESS AMPLIFIED
00Z ECMWF APPEARING MOST REASONABLE GIVEN THE LATEST DISTRIBUTION
OF ENSEMBLE MEMBERS FROM THE GEFS/ECMWF/CMC.


...LOW PRESSURE LIFTING UP OFF THE WEST COAST ON SATURDAY...
...DEEP UPPER TROUGH OFFSHORE THE WEST COAST THROUGH SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z ECMWF AND 12Z NAM
CONFIDENCE: BELOW AVERAGE

LOW CONFIDENCE FORECAST GIVEN ABOVE AVERAGE SPREAD AND CHANGES
FROM RUN TO RUN BUT THERE SEEMS TO BE A SLIGHT TREND TOWARD BETTER
AGREEMENT WITH THE 00Z ENSEMBLE SUITE. THESE ENSEMBLES SHOW THE
12Z GFS AND 00Z UKMET AS NEAR OUTLIERS WITH THE DEPTH OF THE
SURFACE LOW TO TRACK OFF OF THE NORTHWEST COAST GIVEN ONLY A
MINORITY OF ENSEMBLES SHOW A CORRESPONDINGLY DEEP 500 MB HEIGHT
CONTOUR. WHILE THE 00Z ECMWF AND 12Z NAM MAY BE TOO WEAK WITH THE
SYSTEM...THEY ARE THE CLOSEST DETERMINISTIC GUIDANCE TO WHAT IS
BELIEVED TO BE THE SOLUTION MOST LIKELY TO VERIFY. THE 00Z CMC IS
LESS AGGRESSIVE WITH SHORTWAVE ENERGY AND WEAKEST WITH THE
CORRESPONDING SURFACE LOW OFF OF THE NORTHWEST COAST...AND FALLS
INTO A STRONG MINORITY OF SOLUTIONS.


www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

OTTO

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