778
FXUS10 KWNH 231720
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
120 PM EDT MON MAR 23 2020
VALID MAR 23/1200 UTC THRU MAR 27/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..NOR'EASTER DEVELOPING OFF NEW ENGLAND TONIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
MINOR PLACEMENT DIFFERENCES EXIST WITH THIS SYSTEM, PERHAPS THE
12Z GFS STANDS OUT THE GREATEST EARLY TONIGHT WITH ITS SURFACE LOW
TRACK BEING DISPLACED A LITTLE FARTHER OFFSHORE. HOWEVER, THE
DIFFERENCES IN THE GFS DISAPPEAR BEYOND 12Z TUESDAY, WITH A
GENERAL MODEL BLEND FROM START TO FINISH LOOKING FINE FOR THIS
SYSTEM AS THE DIFFERENCES NOTED WITH THE GFS ARE WELL WITHIN THE
TIGHT ENSEMBLE SPREAD.
...MID-LEVEL SHORTWAVE TRACKING FROM THE SOUTHWEST TODAY TO THE
EAST COAST WEDNESDAY MORNING...
...SURFACE LOW TRACKING OFFSHORE OF THE NORTHERN MID-ATLANTIC
COAST WEDNESDAY INTO THURSDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM, 12Z GFS BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
THE 00Z THE TIMING OF THE 00Z ECMWF MID-LEVEL SHORTWAVE IS NOTED
TO BE FASTEST AS IT NEARS THE OHIO VALLEY TUESDAY EVENING AND
OFFSHORE OF THE EAST COAST WEDNESDAY EVENING. THE 00Z ECMWF MEAN
IS NOTED TO BE A LITTLE SLOWER THAN THE DETERMINISTIC ECMWF. THE
REMAINING MODEL SHOW MINOR DIFFERENCES WITH THE SHORTWAVE TIMING
BUT MORE NOTABLE DIFFERENCES SHIFT TO THE RELATED SURFACE LOW.
ENSEMBLE SCATTER LOW PLOTS HAD BEEN CONSISTENT OVER THEIR PAST FEW
CYCLES, VALID 12Z/26, WITH A CENTROID JUST EAST OF THE 40N/70W
BENCHMARK. HOWEVER, THE LATEST (00Z/23) ENSEMBLE CYCLE HAS SHIFTED
THE ECMWF/GEFS/CMC SURFACE LOWS SOUTHEAST OF THE BENCHMARK OR MORE
OFFSHORE. IT IS UNCLEAR IF THIS TREND IS A TEMPORARY SHIFT OR A
NEW DIRECTION THAT THE GUIDANCE WILL ALL SHIFT TOWARD. FOR NOW,
PREFER TO PLAY THE MIDDLE OF THE TWO CAMPS, OR BY BLENDING THE 12Z
NAM AND 12Z GFS. THE 12Z GFS IS SUPPORTED BY THE 00Z UKMET, WHILE
THE 00Z CMC WHICH IS STRONGER AND CLOSEST TO THE COAST IS NOT
CONSIDERED LESS LIKELY TO VERIFY GIVEN LACK OF SUPPORT, ESPECIALLY
WEDNESDAY EVENING.
..LONGWAVE TROUGH OVER THE WESTERN U.S
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/CMC BLEND
CONFIDENCE: AVERAGE
THE AMPLIFIED PATTERN OVER THE EASTERN PACIFIC WILL END UP
PRODUCING A POSITIVELY TILTED LONGWAVE TROUGH AXIS WHICH WILL WORK
DOWN THE WEST COAST AND EVENTUALLY MOVE INLAND INTO THE SOUTHWEST
FRIDAY MORNING. THERE HAVEN'T BEEN MANY TRENDS IN THE ENSEMBLES
AND THERE IS A MODERATE AMOUNT OF SPREAD WITH THE TIMING BY
THURSDAY EVENING. THE 12Z GFS AND 12Z NAM ARE JUST A LITTLE FASTER
THAN THE MAJORITY OF ENSEMBLE SPAGHETTI HEIGHT PLOTS WHILE THE 00Z
UKMET IS TOWARD THE SLOWER SIDE. PREFER TO STAY TOWARD THE MIDDLE,
OR NEAR THE 00Z ECMWF/CMC AT THIS TIME, WITH THINKING THAT THE 12Z
NAM/GFS ARE LESS LIKELY TO VERIFY WITH A FASTER PROGRESSION WITHIN
THE AMPLIFIED FLOW REGIME.
...NEGATIVELY TITLED MID-LEVEL SHORTWAVE CROSSING SOUTHERN
ONTARIO/QUEBEC ON THURSDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z GFS BLEND
CONFIDENCE: AVERAGE
THE 12Z GFS APPEARED TO BE A FASTER OUTLIER HERE WHICH IS AN OFTEN
SEEN BIAS IN THE GFS CONCERNING SHORTWAVE TROUGH PROGRESSION.
GIVEN ONLY THE GEFS SUPPORTS THE FASTER TIMING OF THE 12Z GFS BY
LATE THURSDAY, A NON 12Z GFS BLEND WILL BE PREFERRED.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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