943
FXUS10 KWNH 160429
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1228 AM EDT TUE JUN 16 2020
VALID JUN 16/0000 UTC THRU JUN 19/1200 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...CLOSED LOW LINGERING ACROSS THE SOUTHEAST THROUGH WEDNESDAY,
LIFTING BACK INTO CENTRAL APPALACHIANS BY THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/NAM AND 12Z ECWMF BLEND
CONFIDENCE: ABOVE AVERAGE
GUIDANCE CONTINUES TO BE WELL CLUSTERED WITH THE EVOLUTION OF THE
EASTERN US CLOSED LOW. OBVIOUSLY, SMALLER SCALE AFFECTS OF
CONVECTION AND MINOR MASS DIFFERENCES/STRENGTH OF THE RIDGE TO THE
NORTH PLAY A LARGER ROLE IN THE MODEL SPREAD BY DAY 3. FOR
EXAMPLE, THE 12Z UKMET DRIFTS NORTH A BIT FASTER DUE TO FINDING
THE GREATEST WEAKNESS/RIDGING RELATIVE TO THE CLOSED LOW TO THE NW
AND THE RIDGE TO ITS NORTH. IT IS MINOR AND WITHIN THE REALM OF
POSSIBILITIES BUT DRIFTS OUT OF BEST CONSENSUS AND CONTINUITY, TO
PERHAPS WEIGHT A BIT LOWER. EQUALLY, THE CMC IS A BIT WEAKER TOO.
SO FROM A BLENDING/CONFIDENCE PERSPECTIVE, A STRONGER/TIGHTER
BLEND OF THE 00Z GFS/NAM AND 12Z ECWMF WILL PROVIDE HIGHER
PRESCIENCE TO THE FORECAST, BUT A GENERAL MODEL BLEND WOULD BE
ACCEPTABLE TO ACCOUNT FOR THE INHERENT UNCERTAINTY IN ANY CLOSED
LOW. GIVEN THE OVERALL SMALLER SPREAD AND CONTINUED SOLID
VERIFICATION OF THE SYSTEM WITH THE GUIDANCE, WILL SUPPORT THE
HIGHER PRECISION IN A 00Z GFS/NAM AND 12Z ECMWF BLEND. CONFIDENCE
IS ABOVE AVERAGE GIVEN SMALLER OVERALL SPREAD IN THE GUIDANCE
SUITE INCLUDING ENSEMBLE SOLUTIONS.
...CLOSED LOW MOVING INTO THE NORTHWEST TUESDAY INTO THE NORTHERN
HIGH PLAINS BY THURS...
..NORTHERN PLAINS SURFACE LOWS/N-S FRONTAL ZONE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND UP TO 60HRS (18.12Z)
12Z UKMET/CMC/ECMWF BLEND (INCL GEFS/ECENS IF DESIRED)
CONFIDENCE: AVERAGE TO SLIGHTLY ABOVE AVERAGE
BROAD TROF/CLOSED LOW OVER THE PACIFIC NW WILL CONTINUE TO SHIFT
EASTWARD, THE LEADING SHORTWAVE/HEIGHT-FALLS WILL EXPAND EASTWARD
AND ALLOW THE SECONDARY/MAIN INNER CORE TO THE CLOSED LOW TO
SHARPENS THE TROF AS A WHOLE THROUGH THE SNAKE RIVER PLAIN, BEFORE
CONSOLIDATING ACROSS THE SOUTHERN PRAIRIES OF CANADA. THE
EVOLUTION LOOKS QUITE CONSISTENT AND REALISTIC THROUGH 60HRS
(18.12Z) BUT BIASES START TO MANIFEST AND LEAD TO INCREASED
SPREAD. THE 00Z GFS SHOWS A FASTER EVOLUTION, WHICH PULLS IT
OUTSIDE OF THE ENSEMBLE SUITE, WHILE THE 00Z NAM RETAINS A MORE
COMPACT BASE TO THE TROF, LEADING TO A SLOWER AND STRONGER SURFACE
WAVE EMERGING INTO THE PLAINS LATE THURSDAY INTO FRIDAY; BOTH
TYPICAL OF KNOWN NEGATIVE BIASES. THE 12Z ECMWF APPEARS TO HAVE A
NORTHWARD BIAS WITHIN THE ENSEMBLE SUITE AND REMAINING GUIDANCE
BUT COMBINED WITH THE UKMET/CMC THROUGH THE DEPTH OF THE
TROPOSPHERE SEEMS A PRUDENT WITH MILD TO ABOVE AVERAGE CONFIDENCE
IN THE RESULTANT BLEND.
GALLINA
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