712
FXUS10 KWNH 160418
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1117 PM EST WED JAN 15 2020
VALID JAN 16/0000 UTC THRU JAN 19/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..CENTRAL TO EASTERN US SYSTEM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/18Z GEFS/12Z ECMWF/UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
AS THE CLOSE LOW FILLS ALONG VANCOUVER ISLAND, THE UPSTREAM JET
DIGS THE TAIL END OF THE SHORTWAVE AND SHARPENS THE TROF ENTERING
CENTRAL CA LATER TODAY (THURSDAY). THE LATITUDE OF THE DEPTH OF
THE TROF APPEARS TO BE HANDLED AT THIS POINT. AS IT PROGRESSES
ACROSS THE ROCKIES, TIMING WITH RESPECT TO SUBTLE SHORTWAVE IN
ADVANCE OF THE TROF IN THE SUBTROPICAL STREAM HAS TIGHTENED IN
SPREAD BUT SMALL TIMING/AMPLIFICATION DIFFERENCES REMAIN. THE 12Z
CMC IS SLOWER IN THE SUBTROPICAL STREAM SUPPORTING A STRONGER,
SOUTHERN TRACK (FASTER COLD FRONT ACROSS THE SOUTHERN PLAINS INTO
LOWER MS VALLEY. THE 00Z GFS/NAM BOTH ARE A BIT FASTER AND SWING
THE BASE OF THE TROF THOUGH THE CENTRAL PLAINS INTO THE MIDWEST A
BIT SHARPER WITH MORE NEGATIVE TILTING COMPARED TO THE
ECMWF/UKMET. THIS ALLOWS THE NAM TO BECOME MUCH STRONGER BY DAY3
AS WELL LEADING TO A DIFFERENT LOCATION TO DEVELOPMENT OF A
SECONDARY COASTAL LOW OFF THE NEW YORK BIGHT BY 19.00Z SUN. THE
18Z GEFS MEAN SUGGESTS THE GFS IS TOO SHARP/FAST RELATIVE TO THE
ECMWF/ECENS BUT OVERALL THIS TIMING/SPREAD IS NOT TOO BAD,
ESPECIALLY AS THE UKMET IS A BIT SLOWER TOO. AS SUCH A 00Z
GFS/18Z GEFS AND 12Z ECMWF/UKMET BLEND IS PREFERRED AT SLIGHTLY
ABOVE AVERAGE CONFIDENCE.
..PACIFIC NORTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE (BY DAY 3...ABOVE PRIOR).
AS THE CLOSED LOW CURRENTLY NEAR THE PACIFIC NW FILLS, IT BECOMES
HIGHLY SHEARED UNDER THE INFLUENCE/APPROACH OF THE NEXT VERY
STRONG/COMPACT WAVE THAT IS ALSO QUITE BROAD. GUIDANCE HAS
TIGHTENS OVERALL WITH THE TIMING/PLACEMENT OF THE WAVE WITH ONLY
SMALL VARIANCE IN VERTICAL TILT OF THE CYCLONE AS A WHOLE. HERE
THE 12Z ECMWF/ECENS MEAN CONTINUES TO LAG (GREATER VERTICAL TILT)
AND A TYPICAL RETENTION/SLOW WEAKENING OF THE OCCLUDED LOW AS THE
SYSTEM SWINGS ALONG THE PACIFIC NW COAST SAT, THIS IS OPPOSED BY
THE FASTER GFS, THAT DUE TO FASTER TRAILING SHORTWAVE RIDGING IS A
BIT SLOWER TO DROP THE FRONTAL ZONE DOWN THE OR/CA COAST BY THE
END OF THE FORECAST PERIOD. THIS IS FAIRLY SMALL, BUT MODERATELY
UNCERTAIN AS BOTH TYPICAL NEGATIVE BIASES ARE IN PLAY. AS SUCH
WILL SPLIT THE DIFFERENCE AND FOCUS ON THE ENSEMBLE MEANS THAT ARE
MORE MIDDLE GROUND. SO A GENERAL MODEL BLEND WILL BE PREFERRED AT
SLIGHTLY ABOVE AVERAGE CONFIDENCE.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
GALLINA
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