286
FXUS10 KWNH 311709
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1208 PM EST TUE DEC 31 2019
VALID DEC 31/1200 UTC THRU JAN 04/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES/CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..LOW DEPARTING FROM NEW ENGLAND TODAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.
..CLOSED LOW ENTERING MEXICO AND WEAKENING WEDNESDAY NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS, 00Z ECMWF, 00Z UKMET BLEND
CONFIDENCE: AVERAGE
TIMING DIFFERENCES ARE STILL APPARENT AS A CLOSED LOW ENTERS
MEXICO ON WEDNESDAY, WITH THE 12Z NAM AND 00Z CMC SLOWEST WHILE
THE 12Z GFS AND 00Z ECMWF ARE SLIGHTLY FASTER. TRENDS IN THE
ENSEMBLE SPAGHETTI PLOTS OF 500 MB HEIGHTS SHOW A SUDDEN SLOWING
VALID 00Z/04 AFTER WHAT HAD BEEN FAIRLY CONSISTENT TIMING FROM
CYCLE TO CYCLE. WHILE THERE COULD BE A FLIP BACK TOWARD THE FASTER
SIDE, PREFER FOR NOW TO STAY TOWARD THE MIDDLE TO FASTER SIDE OF
THE LATEST AVAILABLE GUIDANCE, OR NEAR THE 12Z GFS, 00Z ECMWF AND
00Z UKMET.
...ATMOSPHERIC RIVER INTO PAC NW TODAY AND AMPLIFYING LONGWAVE
TROUGH ACROSS THE CENTRAL U.S. THURSDAY EVENING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS, 00Z ECMWF, 00Z UKMET BLEND
CONFIDENCE: AVERAGE
A LONGWAVE TROUGH DEVELOPS OVER THE GREAT PLAINS THURSDAY INTO
FRIDAY WITH MODEL DIFFERENCES WITH THE EVOLUTION OF SHORTWAVES
WITHIN. THE 12Z NAM STANDS OUT THE GREATEST WITH A MORE POSITIVE
TILT TO THE SOUTHERN PORTION OF THE MID-LEVEL TROUGH AXIS BY
FRIDAY EVENING. THE 12Z GFS, 00Z ECMWF AND 00Z UKMET ARE IN THE
MIDDLE BUT THE 00Z ECMWF IS WEAKEST WITH AN 850 MB LOW WHICH IS
EXPECTED TO TRACK FROM THE SOUTHERN PLAINS INTO THE MIDWEST, BUT
THE 12Z GFS/00Z UKMET MAY BE TOO STRONG HERE. A BLENDED APPROACH
IS CONSIDERED BEST WITH BETTER AGREEMENT ON POSITION COMPARED TO
INTENSITY.
...SHORTWAVE TROUGH AND SURFACE LOW APPROACHING PACIFIC NORTHWEST
FRIDAY/SATURDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NEAR THE 12Z NAM
CONFIDENCE: SLIGHTLY BELOW AVERAGE
THE ENSEMBLES SHOW A FAIR DEGREE OF SPREAD WITH THE TIMING OF THE
NEXT SHORTWAVE TO NEAR THE PACIFIC NORTHWEST BY THE WEEKEND.
UPSTREAM FLOW BECOMES ZONAL OVER THE CENTRAL PACIFIC WHICH WOULD
IMPLY A FASTER PROGRESSION DOWNSTREAM INTO THE PACIFIC NORTHWEST.
INDEED, TRENDS HAVE BEEN FASTER IN THE ENSEMBLE SPAGHETTI HEIGHT
PLOTS OVER THEIR PAST 4 00Z/12Z CYCLES. HOWEVER, CAUTION IS
ADVISED WITH THE FASTEST AND OFTEN BIASED GFS WHICH IS OUT AHEAD
OF THE GEFS/ECMWF/CMC ENSEMBLE MEMBERS. THE 12Z NAM APPEARS TO BE
A BETTER FIT WHICH IS TOWARD THE FASTER SIDE OF THE DETERMINISTIC
GUIDANCE BUT NOT AS SLOW AS THE 00Z ECMWF/UKMET/CMC.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
OTTO
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