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Model Diagnostics Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1705Z Jan 20, 2018)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1205 PM EST SAT JAN 20 2018

VALID JAN 20/1200 UTC THRU JAN 24/0000 UTC

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

12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...TROUGH OVER THE INTERMOUNTAIN WEST KICKING INTO THE PLAINS ON
SUNDAY WITH DEVELOPING CYCLONE TRACKING INTO THE GREAT LAKES BY
MONDAY-TUESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
            WEIGHTED MORE TOWARD THE GEFS/ECMWF ENS MEANS
CONFIDENCE: AVERAGE

OVERALL MODELS ARE REASONABLY CLOSELY CLUSTERED IN THEIR MASS
FIELDS THROUGH THE COURSE OF THE CYCLOGENESIS PROCESS WITH THIS
SYSTEM...WITH NORMAL MODEL VARIABILITY LEADING TO SLIGHTLY
DIFFERENT TIMING AND POSITIONING OF KEY FEATURES. ONE IMPORTANT
DIFFERENCE IS WITH TIMING OF THE WAVE AND ASSOCIATED SURFACE
CYCLONE AS THEY SHIFT TO THE EAST/NORTHEAST OVER THE NEXT SEVERAL
DAYS. THE 00Z ECMWF AND 12Z UKMET CONTINUE TO BE ON THE SLOW END
OF MODEL SPREAD...WHILE THE 12Z NAM AND 12Z GFS ARE FASTER...WITH
THE 00Z ECMWF ENS MEAN AND 06Z GEFS MEAN IN BETWEEN THESE
EXTREMES. THESE DIFFERENCES HAVE ACTUALLY BECOME MORE PRONOUNCED
OVER THE LATEST MODEL CYCLE. THE 12Z GFS IS SLIGHTLY FASTER WITH
THE PROGRESSION OF THE MID-UPPER LEVEL TROUGH THAN ITS 06Z
RUN...WHILE THE 00Z ECMWF WAS SLIGHTLY SLOWER THAN ITS 12Z RUN
YESTERDAY. ENSEMBLE SENSITIVITY ANALYSIS ON THE 00Z MODEL CYCLE
FOR THE NCEP/CMC ENSEMBLE MEMBERS SHOWED THE GREATEST AMOUNT OF
VARIANCE WAS RELATED TO TIMING DIFFERENCES (APPROXIMATELY 70
PERCENT OF THE VARIANCE BY MONDAY EVENING)...WITH MOST OF THE
REMAINING UNCERTAINTY RELATED TO THE LOW POSITION AND HOW FAR
NORTHWEST IT WILL TRACK.

GIVEN THE LARGEST AMOUNT OF REMAINING UNCERTAINTY IS RELATED TO
TIMING...THE PREFERENCE IS TO ACCOUNT FOR THIS WITH A GENERAL
MODEL BLEND...BUT WEIGHTED MORE TOWARD THE ENSEMBLE MEANS (ECMWF
AND GEFS) WHICH STRIKE A BALANCE BETWEEN THE VARIABILITY OF THE
OPERATIONAL MODELS. THIS PREFERENCE IS STRENGTHENED BY THE
TENDENCY OF THE ECMWF TO BE SLOWER WITH THE PROGRESSION OF
CYCLONES AND THE GFS TO BE FASTER. A BALANCE OF THESE MODEL
TIMINGS MAY BE CLOSER TO THE MOST LIKELY SOLUTION.


...BROAD GULF COAST TROUGH PUSHING QUICKLY EAST TO OVER THE
ATLANTIC BY SUNDAY AFTERNOON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 00Z CMC SHIFTS THE TROUGH MORE QUICKLY TO THE EAST THAN ALL
THE OTHER OPERATIONAL MODELS AND THE ECMWF AND GEFS ENSEMBLE
MEANS...AND IT ALSO BUILDS THE RIDGE INTO THE SOUTHEAST MORE
RAPIDLY THAN OTHER MODELS. GIVEN THE LACK OF SUPPORT FROM OTHER
AVAILABLE MODELS...THE CMC IS EXCLUDED FROM THE PREFERENCE.
OTHERWISE...THE MODELS ARE IN FAIRLY GOOD AGREEMENT AND A GENERAL
BLEND IS PREFERRED TO ACCOUNT FOR SMALL DETAIL DIFFERENCES.


...GULF OF ALASKA TROUGH WITH BROAD SURFACE CYCLONE...
...STRONG EMBEDDED SHORTWAVE ROTATING AROUND TO THE SOUTHERN
PERIPHERY OF THE TROUGH BY TUESDAY...
...RESULTING SURFACE LOW DEVELOPMENT OFFSHORE PAC NW MON-TUE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS / 00Z ECMWF / 00Z CMC
CONFIDENCE: SLIGHTLY BELOW AVERAGE

MODELS ARE IN FAIRLY GOOD AGREEMENT OVERALL THROUGH AROUND 23/00Z
(MONDAY AFTERNOON)...BEFORE DIFFERENCES EMERGE WITH THE DEVELOPING
CYCLONE IN THE VICINITY OF 140W. THE 12Z UKMET KICKS THE SHORTWAVE
OUT TO THE EAST FASTER THAN ALL OTHER OPERATIONAL MODELS AND MANY
OF THE ENSEMBLE MEMBERS...WHICH ALLOWS FOR EARLIER
CYCLOGENESIS...ONE OF THE DEEPER SURFACE CYCLONES...AND A POSITION
OF THE OCCLUDED LOW FURTHER NORTHWEST OF OTHER MODELS BY 24/00Z.
MEANWHILE...THE 12Z NAM SHOWS FAR LESS DEEPENING OF THE SURFACE
CYCLONE THAN OTHER MODELS...WHICH MAY BE RELATED TO THE STRENGTH
OF THE SHORTWAVE ROUNDING THE BASE OF THE TROUGH...AND THE
ASSOCIATED POSITIONING OF SYNOPTIC FEATURES LIKE JET STREAKS. THE
PREFERENCE IS TO LEAN TOWARD THE 12Z GFS...00Z ECMWF...AND 00Z CMC
WHICH ARE ALL VERY CLOSE IN THE POSITION AND INTENSITY OF THE
EVOLVING SURFACE CYCLONE AND REASONABLY CLOSE WITH THE STRUCTURE
OF THE TROUGH ALOFT.


MODEL TRENDS AT www.wpc.ncep.noaa.gov/html/model2.shtml
500 MB FORECASTS AT www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

LAMERS