903
FXUS10 KWNH 150645
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
144 AM EST SUN DEC 15 2019
VALID DEC 15/0000 UTC THRU DEC 18/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...MID-LEVEL TROUGH TRACKING FROM THE WESTERN U.S. TODAY TO THE
EASTERN U.S. WEDNESDAY MORNING...
...SURFACE LOW ORGANIZING EAST OF THE MISSISSIPPI RIVER MONDAY
INTO TUESDAY MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/ECMWF/UKMET BLEND
CONFIDENCE: AVERAGE
..07Z UPDATE
REGARDING THE TIMING OF THE 500 MB TROUGH MOVING EAST, THE CMC
REMAINS FASTER WITH ITS 00Z CYCLE, WHILE THE 00Z ECMWF SLOWED DOWN
RELATIVE TO ITS PREVIOUS 12Z CYCLE. THE 00Z UKMET REMAINED
RELATIVELY SIMILAR WITH TIMING BUT WAS SLIGHTLY SLOWER AT 500 MB.
THERE WAS A SOUTHWARD SHIFT FROM THE 00Z ECMWF/UKMET/CMC WITH THE
WARM FRONT FROM THE MISSISSIPPI RIVER TO THE EAST COAST, COMPARED
TO THEIR PREVIOUS 12Z CYCLES. THE SHIFT PLACES THE NEW 00Z
NON-NCEP GUIDANCE IN BETTER AGREEMENT WITH THE 00Z GFS. THIS
AGREEMENT SHOULD NOT BE SEEN AS A LOWERING OF UNCERTAINTY THOUGH,
AS RUN TO RUN CHANGES WILL STILL BE POSSIBLE WITH A SUBTLE SHIFT
BACK TO THE NORTH OR EVEN FARTHER SOUTH A POSSIBILITY.
..PREVIOUS DISCUSSION FOLLOWS
TIMING DIFFERENCES APPEAR WITH THE 700-500 MB TROUGH AXIS AS IT
REACHES THE GREAT PLAINS WITH THE 00Z NAM SLOWER AND 12Z CMC
FASTER. ENSEMBLE AGREEMENT WITH THIS TROUGH LOOKS BETTER THAN
YESTERDAY TO SUPPORT A 12Z ECMWF, 00Z GFS AND 12Z UKMET BLEND.
THERE ARE LARGER DIFFERENCES AT THE SURFACE HOWEVER, REGARDING THE
LATITUDE OF A WARM FRONT EXTENDING EAST OF A SURFACE LOW THAT
DEVELOPS OVER THE LOWER MISSISSIPPI VALLEY ON MONDAY. THE 00Z GFS
IS FARTHEST SOUTH, WHILE THE 12Z UKMET/ECMWF ARE NORTH WITH THE
BOUNDARY. ENSEMBLE MEANS SUPPORT A MIDDLE GROUND WHICH WILL BE
PREFERRED, ESSENTIALLY BLENDING THE 00Z GFS, 12Z ECMWF AND 12Z
UKMET.
...MID-LEVEL SHORTWAVE CLIPPING THE GREAT LAKES TUESDAY INTO
WEDNESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
..07Z UPDATE
THE 00Z UKMET TRENDED TOWARD THE PREFERRED NAM/GFS/ECMWF BUT THE
00Z CMC CONTINUED TO STRAY FROM THE BETTER MODEL CLUSTERING WITH A
500 MB LOW TRACK FARTHER SOUTH AND WEST BY WEDNESDAY MORNING.
..PREVIOUS DISCUSSION FOLLOWS
A DEEP CLOSED BUT SOMEWHAT COMPACT LOW IS EXPECTED TO REACH THE
GREAT LAKES REGION TUESDAY NIGHT. THERE IS GOOD AGREEMENT IN THE
LATEST DETERMINISTIC GUIDANCE THROUGH TUESDAY MORNING BUT THEN
SOME DIFFERENCES BEGIN TO DEVELOP. ENSEMBLE MEANS SUPPORT A 00Z
NAM, 00Z GFS AND 12Z ECMWF BLEND, WITH THE 12Z CMC FASTER AND 12Z
UKMET SLOWER WITH THE CLOSED LOW BY WEDNESDAY MORNING.
..TROUGH APPROACHING THE WESTERN U.S. TUESDAY EVENING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z CMC BLEND, LED BY THE 00Z GFS
CONFIDENCE: BELOW AVERAGE
..07Z UPDATE
THE 00Z CMC TRENDED FASTER WITH THE 500 MB TROUGH NEARING THE WEST
COAST TUESDAY NIGHT, AND IT IS NOW FASTER THAN THE REMAINING
DETERMINISTIC GUIDANCE. THE 00Z ECMWF TRENDED TOWARD THE PREVIOUS
PREFERENCE HOWEVER, WHILE THE 00Z UKMET SHOWED ONLY MINOR CHANGES
FROM ITS PRIOR 12Z CYCLE. THE NEW PREFERENCE INCLUDES THE NEW 00Z
ECMWF BUT EXCLUDES THE 00Z CMC WITH FORECAST THINKING UNCHANGED
FROM THE PREVIOUS DISCUSSION BELOW.
..PREVIOUS DISCUSSION FOLLOWS
LARGE DIFFERENCES EXIST IN THE ENSEMBLE AND DETERMINISTIC GUIDANCE
WITH THIS SYSTEM. DIFFERENCES ARE WITH WEATHER MORE OF THE ENERGY
WITHIN THE APPROACHING TROUGH FOCUSES FARTHER SOUTH INTO A CLOSED
LOW OR STRETCHES LATITUDINALLY INTO AN ELONGATED NORTH/SOUTH AXIS
BY TUESDAY EVENING. THE 12Z ECMWF APPEARS TO STAND OUT THE
GREATEST WITH THREE MAIN AND SEPARATE VORTICITY MAXIMA WITHIN THE
TROUGH AXIS WHEREAS THE REMAINING DETERMINISTIC GUIDANCE SHOWS
TWO. THE RESULT IS THAT THE 12Z ECMWF TAKES A COMPACT CLOSED LOW
FARTHER SOUTH/MORE OFFSHORE OF THE CALIFORNIA COAST BY WEDNESDAY
MORNING AND THE REMAINING GUIDANCE TAKES THE FEATURE INLAND ACROSS
CALIFORNIA AND NEVADA. WHILE DIFFERENCES REMAIN AMONG THE NON 12Z
ECMWF GUIDANCE, A NON-12Z ECMWF BLEND IS PREFERRED AT THIS TIME,
LED BY THE 00Z GFS.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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