766
FXUS10 KWNH 131932
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
332 PM EDT SAT JUN 13 2020
VALID JUN 13/1200 UTC THRU JUN 17/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z FINAL MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..CLOSED LOW DEVELOPING IN SOUTHERN APPALACHIANS MON/TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE ECMWF HAS CONTINUED TO TREND SOUTH AND IS A BIT
SOUTH OF THE CONSENSUS BY THE END OF D3. OTHERWISE, THE SPREAD IS
MINIMAL ENOUGH OUTSIDE OF THE MORE AMPLIFIED NAM THAT THE GFS HAS
BEEN ADDED BACK IN AND THE GEFS MEAN IS ALSO REASONABLE. THE CMC
REMAINS ON THE NE EDGE OF THE SPREAD, BUT HAS BEEN CONSISTENT AND
IS WITHIN THE ENVELOPE EXPECTED BY D3.
PREVIOUS DISCUSSION:
A SHORTWAVE DROPPING THROUGH THE GREAT LAKES TONIGHT WILL
EVENTUALLY GET CUT OFF FROM THE FLOW AND BEGIN TO DROP NEARLY DUE
SOUTH INTO EARLY NEXT WEEK AS A CLOSED LOW. THE TREND IN THE
GUIDANCE OVER THE PAST SEVERAL RUNS HAS BEEN FOR A MORE SOUTHERLY
POSITION OF THIS CLOSED FEATURE BY TUESDAY, WITH THE CONSENSUS NOW
FAVORING A SUPPRESSION TO GEORGIA. WHILE THE GUIDANCE IS IN VERY
GOOD AGREEMENT IN THE INITIAL DEVELOPMENT OF THE POTENT SHORTWAVE
DROPPING INTO THE OHIO VALLEY THROUGH 36 HOURS, THERE IS SOME
SPREAD THAT DEVELOPS THEREAFTER AS THE LOW OPENS INTO A MORE
DIFFUSE BUT STILL CLOSED FEATURE ALOFT. THE NAM REMAINS A STRONG
S/W OUTLIER, WHICH HAS CONSIDERABLE IMPACTS ON QPF PLACEMENT AND
INTENSITY, WHICH AS NOTED BY THE PREVIOUS FORECASTER IS A KNOWN
BIAS OF THIS MODEL, DESPITE ITS POTENTIAL TO RESOLVE MESOSCALE
INTENSITY FEATURES BETTER THAN THE GLOBAL GUIDANCE, WHILE THE GFS
FEATURES LESS RUN-TO-RUN CONSISTENCY THAN THE NON-NCEP SUITE.
OTHERWISE, DESPITE A SUBTLY MORE NE POSITION AND EVOLUTION OF THIS
CLOSED FEATURE BY THE CMC, THE SPREAD AMONGST THE NON-NCEP MODELS
IS MINIMAL, AND HAS SUPPORT FROM THE ECENS.
...INTERACTION OF SHORTWAVE LIFTING THROUGH THE ROCKIES WITH A
CLOSED LOW ADVECTING ONSHORE WASHINGTON SUNDAY...
..SECONDARY CLOSED LOW MOVING INTO THE NORTHWEST TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NCEP BLEND THROUGH D2
ECMWF/CMC D3
CONFIDENCE: SLIGHTLY BELOW AVERAGE
19Z UPDATE: BIGGEST CHANGE WITH THE 12Z NON-NCEP SUITE WAS WITH
THE UKMET BECOMING MUCH MORE AMPLIFIED WITH THE CLOSED LOW/GYRE
ACROSS THE WEST BY THE END OF D3. THERE IS QUITE A BIT OF SPREAD
IN THE AMPLITUDE OF THAT TROUGH AFTER 60 HOURS, LIKELY DUE TO
COMPLEX INTERACTIONS NOTED BELOW. THE ECMWF/CMC APPEAR TO BE VERY
CLOSELY MATCHED AND HAVE SHOWN LESS RUN-TO-RUN DISCONTINUITY
SUGGESTING HIGHER CONFIDENCE IN THEIR EVOLUTION.
PREVIOUS DISCUSSION:
A COMPLEX SERIES OF SHORTWAVES AND CLOSED LOWS WILL INTERACT
ACROSS THE NORTHWEST THROUGH EARLY NEXT WEEK. THE LEADING
SHORTWAVE WILL MOVE THROUGH THE GREAT BASIN TODAY AND INTO THE
CANADIAN ROCKIES TONIGHT, SLINGING AROUND A CLOSED LOW DROPPING
INTO WASHINGTON. THE GUIDANCE HAS TRENDED A BIT FASTER WITH THIS
FEATURE AS THE GEOSTROPHIC FLOW BECOMES PINCHED TO THE EAST, BUT
THE GFS REMAINS A STRONG AND FAST OUTLIER WITH THE LEADING
SHORTWAVE. THIS CREATES A SITUATION IN WHICH THE STRONGER/FURTHER
NORTH ENERGY PULLS THE WEAKENING CLOSED LOW NORTHWARD DURING ITS
INTERACTION, AND PRODUCES A CLOSED LOW ACROSS PARTS OF SW CANADA.
THE NAM IS A BIT WEAKER BUT SHOWS A SIMILAR EVOLUTION, WITH THE
GEFS MEAN JUST A BIT WEAKER STILL. THE NON-NCEP CAMP SHEARS OUT
THE GREAT BASIN SHORTWAVE MORE QUICKLY, LEAVING LESS ENERGY DURING
THE INTERACTION AND ALLOWS THE WEAKENING CLOSED LOW TO REMAIN
DOMINANT PRODUCING A SHEARED AND ELONGATED NW TO SE TROUGH BY LATE
SUNDAY. THE WEAKER SOLUTION OF THE PRIMARY SHORTWAVE IS MORE
REASONABLE DUE TO STRENGTHENING MID-LEVEL SHEAR, SO THE NON-NCEP
CAMP IS PREFERRED INTO D2.
THEREAFTER, YET ANOTHER CLOSED LOW DIVES OUT OF THE GULF OF
ALASKA, AND THE BINARY INTERACTION OF THIS FEATURE WITH THE TROUGH
AHEAD OF IT WILL LEAVE A LARGE GYRE SPREAD FROM WESTERN CANADA
INTO THE PACIFIC. THE GFS IS ACTUALLY NOW ON THE SLOW EDGE OF THE
GUIDANCE IN DROPPING THIS NEXT CLOSED FEATURE SOUTHWARD, AGAINST
ITS TYPICAL BIAS, AND MUCH DIFFERENT FROM PREVIOUS RUNS. THE NAM
REMAINS ON THE FAST SIDE AS THE LOW GETS PULLED EASTWARD, LIKELY
DUE TO A STRONGER LEAD FEATURE DURING THE INTERACTION. FOR
CONTINUITY, AND DUE TO THE BETTER AGREEMENT/CONSISTENCY OF THE
NON-NCEP MODELS, WILL MAINTAIN A PREFERENCE OF THE NON-NCEP SUITE
BUT BY D3 A LITTLE LESS WEIGHT ON THE UKMET WHICH IS ALSO SHOWING
ITS FAST BIAS, BUT NOTE THAT DESPITE DIFFERENCES IN THE MASS
FIELDS, ONLY THE UKMET REALLY SUGGESTS SIGNIFICANT DIFFERENCES IN
QPF.
WEISS
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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