647
FXUS10 KWNH 121701
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
100 PM EDT FRI JUN 12 2020
VALID JUN 12/1200 UTC THRU JUN 16/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z PRELIMINARY MODEL EVALUATION INCLUDING PREFERENCES AND
FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..TROUGH AMPLIFYING ACROSS THE EAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS, 00Z UKMET/ECENS, LIGHT WEIGHT 12Z NAM
CONFIDENCE: AVERAGE
MULTIPLE SHORTWAVES DIGGING ACROSS THE EAST WILL AMPLIFY A
LONGWAVE TROUGH WHICH WILL LIKELY CLOSE OFF NEAR THE TN VLY BY
MONDAY. THE LEAD SHORTWAVE WHICH WILL ROTATE ACROSS UPSTATE NY AND
THEN NORTHEAST INTO CANADA SATURDAY NIGHT HAS GENERALLY GOOD MODEL
AGREEMENT WITH ITS AMPLITUDE AND EVOLUTION. THE ONLY EXCEPTION IS
THE 00Z/CMC WHICH CLOSES OFF THIS FEATURE AND MAKES IT THE
DOMINANT SHORTWAVE, CLOSING IT OFF NEAR NEW ENGLAND. THIS IS
UNLIKELY AND HAS NO ENSEMBLE SUPPORT, SO IS REMOVED FROM THE
BLEND. THEREAFTER, ONLY THE 00Z/ECMWF IS VASTLY DIFFERENT AS IT
ROTATES TWO DISTINCT PERTURBATIONS THROUGH THE LONGWAVE TROUGH,
WHILE THE REMAINING GUIDANCE DEPICTS ONE MORE CONSOLIDATED
IMPULSE. THE CONSOLIDATED IDEA HAS HAD THE MOST CONTINUITY THE
PAST FEW DAYS, SO THAT COMBINED WITH THE BETTER AGREEMENT SUGGESTS
THIS IS MORE LIKELY. DUE TO THE SEPARATE IMPULSES, THE ECMWF
BECOMES OUT OF PHASE WITH ITS SHORTWAVE RIDGE/TROUGH PATTERN, AND
EVENTUALLY CLOSES OFF A LOW OVER THE OH VLY, WEST AND MORE SLOWLY
THAN THE REMAINING CONSENSUS. ON D3, THE NAM TROUGH AXIS IS A BIT
WEST OF THE OTHERS, AND CLOSES OFF THE LOW SLIGHTLY FURTHER SOUTH
WHICH COULD IMPACT QPF LIFTING INTO THE CAROLINAS/MID-ATLANTIC.
DESPITE THE SPREAD BEING WITHIN THE TYPICAL D3 ENVELOPE, THE
ENHANCED QPF AS A RESULT CAUSES IT TO HAVE A LIGHTER WEIGHT IN THE
PREFERENCES.
...LONGWAVE TROUGH OFF THE WEST COAST AND SHORTWAVE LIFTING
ONSHORE CALIFORNIA BY THE WEEKEND...
..CLOSED LOW DEVELOPING ACROSS THE NORTHERN ROCKIES SUNDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NON-NCEP AND 12Z NAM
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THROUGH 48 HOURS, SUNDAY MORNING, THE GLOBAL SUITE IS VERY WELL
ALIGNED WITH THE OVERALL EVOLUTION OF THE SHORTWAVE LIFTING
ONSHORE CA AND EJECTING NORTHEAST AS A LONGWAVE TROUGH SHIFTS
TOWARDS THE COAST. AFTER 48 HOURS, THE GFS ONCE AGAIN BECOMES
STRONG AND FAST WITH THIS FEATURE, LIKELY IN RESPONSE TO BETTER
VENTILATION ALOFT THROUGH THE LFQ OF A MORE ROBUST JUST STREAK
LIFTING AROUND A CLOSED LOW MOVING ONSHORE WA STATE. THIS LEADS TO
A STRONGER SURFACE LOW, HIGHER QPF, AND A MORE NORTHERLY CLOSED
LOW NEAR THE CANADIAN ROCKIES ON MONDAY, WHICH IS WELL REMOVED THE
DETERMINISTIC CONSENSUS, AND EVEN WELL NORTH OF THE GEFS MEAN
PLACEMENT. WHILE THERE REMAINS SOME UNCERTAINTY INTO HOW
INTERACTION WITH THE SHORTWAVE LIFTING UP FROM CA, AND THE
WEAKENING CLOSED LOW ADVECTING ONSHORE WA WILL OCCUR, THE NON-NCEP
SUITE INDICATES THE LATTER WILL REMAIN DOMINANT AND LEAD TO A
WEAKER NEGATIVELY TILTED TROUGH ACROSS THE NW/NORTHERN ROCKIES
WITH ZONAL FLOW UNDERCUTTING THE FEATURE TO THE EAST. WHILE THE
NAM IS A BIT FURTHER NORTH AND MORE AMPLIFIED WITH THE END RESULT,
ITS EVOLUTION TO GET TO THAT POINT LOOKS OTHERWISE WITHIN A
REASONABLE SPREAD AND CLOSE TO THE GEFS MEAN, AND CAN BE INCLUDED
IN THE BLEND. THIS WILL ALSO ALLOW FOR SOME POTENTIAL FOR A SUBTLY
MORE NORTHERN TROUGH MONDAY SHOULD THE LEADING SHORTWAVE OUT OF CA
BE STRONGER THAN CURRENT PROGS SUGGEST.
WEISS
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500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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