836
FXUS10 KWNH 071919
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
319 PM EDT TUE APR 07 2020
VALID APR 07/1200 UTC THRU APR 11/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...SURFACE WAVE MOVING THROUGH THE GREAT LAKES TONIGHT, THEN
SLIDING OFFSHORE ALONG 40N WED/THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-12Z NAM BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
..19Z UPDATE
ADJUSTMENTS FROM THE 12Z ECMWF/UKMET/CMC WERE SMALL BUT IN THE
DIRECTION OF THE PREVIOUS PREFERENCE NOTED BELOW. THIS LEAVES THE
12Z NAM AS A FASTER/STRONGER OUTLIER WITH THIS SYSTEM. THE FINAL
PREFERENCE IS FOR A NON-12Z NAM BLEND
..PREVIOUS DISCUSSION FOLLOWS
LARGE EAST/WEST SPREAD IN THE ENSEMBLE SCATTER LOW PLOTS, BUT A
SUBTLE TREND TOWARD THE FASTER CAMP RULES OUT THE SLOWER 00Z CMC.
THE 12Z NAM IS FASTEST AND STRONGEST WITH THE LOW LEVEL WAVE, BUT
THE PREFERENCE IS TO BE CLOSER TO THE MIDDLE TO FASTER SIDE OF THE
LATEST GUIDANCE. THERE IS SOME LATITUDINAL SPREAD AS WELL, BUT A
BLEND OF THE 12Z GFS, 00Z ECMWF AND 00Z UKMET APPEARS REASONABLE
AT THIS TIME GIVEN THEIR PLACEMENT AWAY FROM THE EXTREMES.
...UPPER TROUGH DIGGING ACROSS GREAT LAKES; SURFACE LOW DEVELOPING
OFF NEW ENGLAND COAST THURSDAY NIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE
..19Z UPDATE
ADJUSTMENTS FROM THE 12Z UKMET/CMC WERE IN THE DIRECTION OF THE
12Z GFS AND 00Z ECMWF, SHIFTING THE SURFACE LOW A LITTLE FARTHER
NORTH. THE 12Z ECMWF IS SIMILAR WITH POSITION, BUT JUST A LITTLE
WEAKER WITH THE SURFACE LOW. THIS LEAVES THE 12Z NAM AS FARTHER
SOUTH THAN THE LATEST 12Z CONSENSUS BUT THE DIFFERENCES ARE SMALL
ENOUGH, EVEN CONSIDERING THE NAM, TO ALLOW FOR A GENERAL MODEL
BLEND. CONFIDENCE REMAINS ONLY AVERAGE GIVEN THE TIME FRAME OF THE
FORECAST AND POTENTIAL FOR FUTURE SHIFTS.
..PREVIOUS DISCUSSION FOLLOWS
MODEL SPREAD IS RELATIVELY SMALL, BUT THERE IS STRONG AGREEMENT
FOR A RAPIDLY DEEPENING SURFACE LOW IN THE GULF OF MAINE LATE
THURSDAY INTO FRIDAY.
PRIOR TO THURSDAY, ONLY MINOR TIMING DIFFERENCES EXIST WITH THE
SHORTWAVE TROUGH AS IT SWINGS EAST THROUGH THE UPPER OHIO VALLEY
INTO THE NORTHEAST WITH THE 12Z GFS/00Z ECMWF A LITTLE AHEAD OF
THE REMAINING 12Z NAM/00Z UKMET/00Z CMC. VALID 00Z/10, THE
ENSEMBLE SCATTER LOW PLOTS WOULD SUGGEST THE 00Z CMC IS TOO
SLOW/SOUTH WITH LOW DEVELOPMENT SO IT WILL NOT BE PREFERRED. THE
12Z NAM/00Z UKMET ARE LOCATED A BIT FARTHER SOUTH AS WELL WHILE
THE 12Z GFS AND 00Z ECMWF ARE FARTHER NORTH. THERE HAS BEEN A
SUBTLE TREND IN THE GUIDANCE SINCE YESTERDAY TO BE SLIGHTLY
QUICKER/MORE NEGATIVELY TILTED WITH THE MID-LEVEL TROUGH AXIS
WHICH WOULD PLACE THE SURFACE LOW A LITTLE FARTHER NORTH AND
PERHAPS INLAND. THE LATEST ENSEMBLE MEANS ALSO SUPPORT A SOLUTION
CLOSER TO THE NORTHERN 12Z GFS/00Z ECMWF BUT CANNOT RULE OUT THE
12Z NAM/00Z UKMET.
ENSEMBLE SPREAD IS RELATIVELY TIGHT FOR A DAY 3 SYSTEM AND ALL OF
THE MODELS AGREE WITH BOMB-CYCLOGENESIS, BUT THE PREFERENCE WILL
FAVOR THE MIDDLE TO NORTHERN SIDE OF THE NON-00Z CMC DETERMINISTIC
GUIDANCE.
...SLOW MOVING SOUTHERN STREAM (S CA/DESERT SOUTHWEST) CLOSED
LOW...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF MEAN OR (12Z ECMWF/UKMET/CMC BLEND)
CONFIDENCE: AVERAGE
..19Z UPDATE
THE 12Z ECMWF/UKMET REMAIN SIMILAR TO THEIR PREVIOUS CYCLES AND
THE 12Z CMC SHIFTED WESTWARD A BIT. THE 00Z ECMWF MEAN IS STILL
PREFERRED WITH THE 12Z ECMWF/UKMET WEST OF THE ECMWF MEAN, AND 12Z
CMC EAST OF THE 12Z ECMWF MEAN (NEAR THE 12Z GEFS MEAN).
..PREVIOUS DISCUSSION FOLLOWS
TRENDS SINCE YESTERDAY SUPPORT A WESTWARD SHIFT WITH THE 500 MB
CLOSED LOW OVER THE SOUTHWEST VALID FRIDAY. THE 12Z NAM AND 12Z
GFS ARE FARTHEST EAST WITH THE CLOSED LOW BUT THEIR TREND HAS BEEN
TOWARD THE WEST. BY THURSDAY AND FRIDAY, THE ECMWF AND GEFS MEAN
SPLIT THE DIFFERENCE BETWEEN THE FARTHER EAST 12Z NAM/GFS AND
FARTHER WEST 00Z ECMWF/UKMET. THE 00Z CMC IS ALSO A BIT EAST, BUT
NOT TO THE DEGREE OF THE 12Z NAM/GFS.
GIVEN WESTWARD TRENDS, PREFER TO LEAN TOWARD THE SLOWER/WESTWARD
SIDE OF THE MIDDLE OF THE ENSEMBLE SPREAD, OR NEAR THE 00Z ECMWF
MEAN. NO SINGLE DETERMINISTIC MODEL IS IN GREAT AGREEMENT WITH THE
00Z ECMWF MEAN, BUT PERHAPS THE 00Z ECMWF IS CLOSEST.
...UPPER TROUGH AND RELATED SURFACE COLD FRONT REACHING MT/ND ON
FRIDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z CMC BLEND
CONFIDENCE: AVERAGE
..19Z UPDATE
NO SIGNIFICANT CHANGES WERE NOTED WITH THE 12Z ECMWF/UKMET/CMC
COMPARED TO THEIR PREVIOUS 00Z CYCLES.
..PREVIOUS DISCUSSION FOLLOWS
MODEL AGREEMENT IS FAIR WITH THIS SYSTEM, BUT THE 00Z CMC BECOMES
A DETERMINISTIC OUTLIER FOR LATE FRIDAY WITH A MORE AGGRESSIVE
LOW, DISPLACED SOUTH OF THE MAJORITY OF GUIDANCE. OUTSIDE OF THE
00Z CMC, A BLEND OF GUIDANCE LOOKS JUST FINE. THE 12Z NAM TIMING
LOOKS REASONABLE AS COLD AIR FILTERS SOUTH INTO MT/ND, BUT IT IS
STRONGER WITH THE LOW LEVEL FLOW AND THEREFORE COLDER BY 00Z/11
WITH THE SURFACE TO 700 MB LAYER INTO MT AND ND.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
OTTO
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