THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


MODEL DIAGNOSTIC DISCUSSION


[Abbreviations and acronyms used in this product]
Geographic boundaries:    Map 1- [Color] [B/W Print Version]      Map 2 - [Color] [B/W Print Version]



MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1150 AM EST TUE NOV 21 2017

VALID NOV 21/1200 UTC THRU NOV 25/0000 UTC

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

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


...UPPER TROUGH AXIS CURRENTLY OVER THE GREAT LAKES...MOVING TO
THE NORTHWEST ON WED...
...SURFACE LOWS TRACKING ALONG AND OFFSHORE OF THE NEW ENGLAND
COAST ON WED...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF / 12Z GFS / 00Z UKMET BLEND
CONFIDENCE: ABOVE AVERAGE

ENSEMBLE SCATTER LOW PLOT TRENDS HAVE BEEN TO SHIFT THE GULF OF
MAINE LOW ALONG AT 18Z/22 - 00Z/23 TOWARD THE SOUTH WITH THE
LATEST MODEL CONSENSUS APPEARING IN REASONABLE AGREEMENT WITH THIS
FIRST LOW.

A SECOND LOW SHOWS A BIT MORE SPREAD...FORECAST TO TRACK EAST OF
THE 40N/70W BENCHMARK LATE WED. THE MORE PROGRESSIVE UPPER TROUGH
SHOWN IN THE 12Z NAM AND 00Z CMC DO NOT FIT WELL TO THE LATEST
ENSEMBLE SPAGHETTI HEIGHT CHARTS AND THE 00Z ECMWF/12Z GFS SHOW
TOWARD THE DEEPER SIDE. GIVEN TRENDS AND THE LATEST ENSEMBLE
CLUSTERING...A BLEND OF THE SLIGHTLY MORE PROGRESSIVE 00Z UKMET
WITH THE MORE WOUND UP 12Z GFS AND 00Z ECMWF APPEARS BEST AT THIS
TIME.


...UPPER TROUGH AXIS CROSSING THE PACIFIC NORTHWEST ON THU AND
REACHING THE N-CNTRL U.S. BY LATE FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS...00Z ECMWF...00Z CMC BLEND
CONFIDENCE: AVERAGE

DIFFERENCES WITH THIS SYSTEM ARISE FROM HOW THE MODELS HANDLE
INTERACTIONS WITH SHORTWAVE ENERGY TRACKING NORTH OF THE MAIN
TROUGH AXIS. ENSEMBLES SHOW THE 00Z UKMET AND 12Z NAM AS NEAR
OUTLIERS WITH THE DEPTH/PLACEMENT OF THE TROUGH AXIS BY FRI
AFTERNOON...WITH A BLEND OF THE 12Z GFS...00Z ECMWF...00Z CMC
CLOSEST TO THE ENSEMBLE CONSENSUS.


...BROAD MID-LEVEL TROUGH AXIS CLIPPING THE GREAT LAKES AND
NORTHEAST THU/FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE TWO SYSTEMS EMBEDDED WITHIN THIS TROUGH SHOW GOOD AGREEMENT
OVER THE NEXT FEW DAYS.  A COMPROMISE OF THE 00Z GFS, 00Z NAM, 00Z
ECMWF, 00Z UKMET, AND 00Z CANADIAN IS FAVORED WITH ABOVE AVERAGE
CONFIDENCE.


...SLOW MOVING MID-UPPER LEVEL TROUGH ALONG THE GULF COAST...
...SURFACE LOWS IN THE EASTERN GULF OF MEXICO/NEAR FLORIDA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS...00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

STARTING THURSDAY MORNING...THE NAM STARTS DIVERGING FROM THE
OTHER GUIDANCE IN BECOMING DEEPER/SLOWER ALOFT WITH THIS SYSTEM.
ENSEMBLE SPREAD IS FAIRLY LARGE WHICH LOWERS CONFIDENCE A BIT
LOWER THAN NORMAL...BUT THE LATEST ENSEMBLE SCATTER LOW PLOTS SHOW
THE 00Z UKMET/CMC ON THE WESTERN SIDE OF THE SPREAD WITH THE
SURFACE LOW AS IT NEARS THE SOUTHEAST COAST ON FRI. THE 00Z ECMWF
AND 12Z GFS APPEAR LIKE THE MOST REASONABLE BLEND FOR THIS SYSTEM
AT THIS TIME. FOR QPF CONSIDERATIONS...SEE OUR QUANTITATIVE
PRECIPITATION DISCUSSION (QPFPFD).


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

OTTO





Last Updated: 1150 AM EST TUE NOV 21 2017