288
FXUS10 KWNH 111830
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
129 PM EST WED DEC 11 2019
VALID DEC 11/1200 UTC THRU DEC 15/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...SOUTHERN STREAM/SOUTHEAST TO MID ATLANTIC AND NORTHEAST SURFACE
LOW FRI/SAT...
PREFERENCE: 12Z GFS/NAM AND 00Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE
ALL THE MODELS HAVE THE SAME GENERAL IDEA OF AN AREA OF LOW
PRESSURE DEVELOPING OVER THE SOUTHEAST AND MOVING UP THE COAST
FRIDAY NIGHT INTO SATURDAY...HOWEVER DIFFERENCES WITH THE DETAILS
OF THE EVOLUTION REMAIN. QUITE A FEW PIECES OF SHORTWAVE ENERGY
INTERACTING WITHIN A QUICK ZONAL FLOW, THUS MAKES SENSE THAT
MODELS WOULD STRUGGLE A BIT WITH THE DETAILS OF HOW EVERYTHING
COMES TOGETHER. THE INITIAL WAVE THAT TRIGGERS THE LOW DEVELOPMENT
SEEMS PRETTY WELL FORECAST, HOWEVER IT IS THE TRAILING, STRONGER,
ENERGY THAT EVENTUALLY CATCHES THIS LOW THAT IS A BIT LESS
CERTAIN. THE 12Z GFS/NAM AND 00Z ECMWF SEEM PRETTY WELL CLUSTERED
WITH THE SYSTEM, AND WHILE DIFFERENCES STILL EXIST WITHIN THESE
SOLUTIONS, A COMPROMISE OF THE THREE SEEMS LIKE A PRETTY GOOD
STARTING POINT. THE 06Z GFS WAS AN OUTLIER IN HOW IT HANDLED THE
EVOLUTION, BUT THE 12Z RUN APPEARS MUCH MORE ALIGNED WITH THE
BETTER CONSENSUS. THE 00Z CMC APPEARS TOO STRONG WITH THE LEAD
WAVE, WHICH ALLOWS FOR A STRONGER LOW INITIALLY MOVING UP THE
COAST. WHILE THIS IS NOT IMPOSSIBLE, IT APPEARS LIKE A LOWER
PROBABILITY EVENT. THE 00Z UKMET IS MUCH STRONGER WITH THE
TRAILING SHORTWAVE ENERGY CAUSING AN EARLIER FORMATION OF A
NEGATIVELY TILTED TROUGH AND A FURTHER WEST LOW TRACK...AND THIS
TOO SEEMS LESS LIKELY AT THIS POINT. THUS BOTH THE 00Z CMC AND
UKMET ARE NOT IN OUR PREFERRED BLEND AT THIS TIME.
...NORTHERN STREAM SHORTWAVES ACROSS THE NORTHERN PLAINS TO THE
UPPER MS VALLEY AND UPPER GREAT LAKES...
PREFERENCE: 12Z GFS/NAM AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THE NORTHERN STREAM 500 MB SHORTWAVE DEPARTS THE NORTHERN ROCKIES
ACROSS THE NORTHERN PLAINS TONIGHT AND INTO THE UPPER MS VALLEY
THU. THE WAVE DEAMPLIFIES AND TURNS NORTHEAST ACROSS THE UPPER
GREAT LAKES THU NIGHT AND ACROSS THE CANADIAN BORDER. MINOR
DIFFERENCES IN WAVE AMPLITUDE AND PHASING AND GENERAL GOOD
CLUSTERING OF SOLUTIONS LEAD TO A RECOMMENDATION TO USE A
MULTI-MODEL BLEND.
THE NEXT SHORTWAVE DROPS OUT OF SOUTHWEST CANADA INTO THE NORTHERN
PLAINS THU AFTERNOON AND NIGHT.
THIS WAVE GRADUALLY AMPLIFIES AS IT CROSSES THE NORTHERN PLAINS
INTO THE UPPER MS VALLEY FRI WITH THE SOUTHERN STREAM PORTION
NOTED ABOVE DEVELOPING IN THE MID TO LOWER MS VALLEY. THE 12Z
ECMWF HAS SLIGHTLY AMPLIFIED THIS WAVE TO REDUCE THE DIFFERENCES.
THE NORTHERN STREAM PORTION OF THE TROUGH IS SLOW TO MOVE OUT OF
THE UPPER MS VALLEY WITH A SLOW DRIFT TOWARDS THE UPPER GREAT
LAKES ON SAT. THERE IS GOOD AGREEMENT ON THE LOCATION AND TIMING
AMONG THE NAM, GFS, AND ECMWF AS A RESULT OF THE SLOW MOVEMENT,
SUPPORTED BY THE 12Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN.
...PACIFIC NORTHWEST TO THE NORTHERN GREAT BASIN, NORTHERN TO
CENTRAL ROCKIES/CENTRAL PLAINS...
PREFERENCE: 06Z GEFS MEAN IN THE PACIFIC NORTHWEST, IN BETWEEN THE
12Z NAM/GFS OVER THE GREAT BASIN TO THE ROCKIES AND CENTRAL PLAINS
CONFIDENCE: AVERAGE
FOR DAYS 1-2 ACROSS THE PACIFIC NORTHWEST, CA, AND THE GREAT
BASIN, A PARADE OF SMALL AMPLITUDE SHORTWAVES IN THE STRONG ZONAL
UPPER JET GRAPHIC IS BEST HANDLED BY A GENERAL MODEL BLEND .
STILL, TOWARD THE END OF THE TRAIN, A STRONGER/GREATER AMPLITUDE
SHORTWAVE TRACKS THROUGH WITH SOME MODERATE NEUTRAL TO NEGATIVE
TILT ORIENTATION LATE FRIDAY INTO EARLY MORNING SAT WITH AN
ASSOCIATED SURFACE CYCLONE. REMARKABLY, THE GLOBAL GUIDANCE IS
FAIRLY AGREEABLE WITH THE TIMING AND MASS FIELDS AS A WHOLE,
PROVIDING SOME CONFIDENCE. THE LARGE DIFFERENCES ARE THE WIDTH OF
THE UPPER LEVEL SYSTEM, WITH THE GFS A BIT MORE SLOWER AND BROADER
SUPPORTED MORE BY THE CMC WHILE THE NAM/ECMWF ARE WELL
PLACED/SHAPED BUT NARROWER AND THE UKMET IS MOST NARROW AND
NEGATIVELY TILTED. WILL HEDGE MORE OF A COMPROMISE BETWEEN THE
00Z NAM/GFS AND 12Z ECWMF.
THE LATTER HALF OF DAY 2 THROUGH DAY 3, DIFFERENCES DEVELOP IN THE
700 MB WAVE STRUCTURE FROM THE CENTRAL GREAT BASIN ACROSS THE
CENTRAL ROCKIES AND HIGH CENTRAL PLAINS. THE 00Z-12Z ECMWF IS
FASTER THAN THE NAM/GFS/UKMET, WITH THE SLOWER NAM AND UKMET ALSO
MORE AMPLIFIED. CONFIDENCE IS LOWER HERE AS THE GFS TRENDED FASTER
ON THE 12Z RUN. I RECOMMEND INTERMEDIATE TIMING AND AMPLITUDE
BETWEEN THE FASTER/LESS AMPLIFIED ECMWF/GFS AND THE SLOWER/MORE
AMPLIFIED NAM/UKMET. THE 12Z ECMWF HAS INCREASED THE AMPLITUDE OF
THE CENTRAL PLAINS 700 MB TROUGH SAT TO NARROW THE GAP IN WAVE
AMPLITUDE, SO THE 12Z RUN LOOKS GOOD.
BY DAY 3 IN THE PACIFIC NORTHWEST, THE UPSTREAM CLOSED LOW OVER
THE NORTHEAST PACIFIC DRIFTS SLOWLY EAST, WITH MOST SOLUTIONS
OPENING THE CLOSED LOW AT 500 MB INTO AN OPEN WAVE DURING THE DAY
SATURDAY, WITH THE 500 MB WAVE POSSIBLY APPROACHING THE CA COAST
LATE SAT. THE GFS IS SLOWER OPENING UP THE CLOSED LOW INTO A WAVE,
RESULTING IN STRONGER HEIGHT FALLS FROM WESTERN OR INTO NORTHWEST
CA SAT AFTERNOON. THE 12Z GEFS MEAN CLUSTERS WELL WITH THE 12Z NAM
500 MB WAVE TIMING AND A BIT LESS AMPLIFIED THAN THE OPERATIONAL
GFS. A BLEND OF THE 12Z ECMWF AND UKMET MESHES WELL WITH THE 12Z
GEFS MEAN.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
PETERSEN/CHENARD
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