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
146 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

---18Z UPDATE---
NO CHANGE TO THE PRELIMINARY PREFERENCE. THE 12Z ECMWF DID TREND
SLIGHTLY FASTER WITH THE PROGRESSION OF THE TROUGH AND LOW
ALOFT...WHICH PLACES IT INTO SLIGHTLY BETTER AGREEMENT WITH THE
GFS. A GENERAL MODEL BLEND IS STILL PREFERRED TO ACCOUNT FOR MODEL
VARIABILITY.

---PREV. DISCUSSION---
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: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

---18Z UPDATE---
THE 12Z CMC HAS MOVED INTO MUCH BETTER AGREEMENT WITH OTHER
MODELS...SO A GENERAL MODEL BLEND IS NOW PREFERRED.

---PREV. DISCUSSION---
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 / 12Z ECMWF / 12Z CMC
CONFIDENCE: SLIGHTLY BELOW AVERAGE

---18Z UPDATE---
NO CHANGE TO THE PRELIMINARY PREFERENCE. THE GFS...ECMWF...AND CMC
CONTINUE TO BE IN THE BEST AGREEMENT OVERALL...AND ARE ALSO CLOSER
TO THE 00Z ECMWF ENSEMBLE MEAN. THEREFORE...CONTINUITY OF THE
PRELIMINARY PREFERENCE IS RECOMMENDED.

---PREV. DISCUSSION---
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







Last Updated: 146 PM EST SAT JAN 20 2018