Prognostic Meteorological Discussion
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000
FXUS10 KWNH 200659
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT THU JUL 20 2017

VALID JUL 20/0000 UTC THRU JUL 23/1200 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

...THE PARALLEL GFS WAS UPGRADED TO THE OPERATIONAL GFS WITH THE
12Z MODEL CYCLE WEDNESDAY 7/19...

00Z MODEL EVALUATION WITH FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


...CLOSED LOW ENTERING PAC NW/SW CANADA TODAY...MOVING INTO THE
GREAT LAKES SATURDAY...
...SURFACE LOW TRACKING FROM THE PLAINS ON FRI TO THE GREAT
LAKES/OHIO VALLEY BY SUN MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS / 00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

500 MB VORTICITY MAX DIFFERENCES ARE RELATIVELY MINOR BUT THE 00Z
UKMET/CMC ARE FASTER WITH THE MID-LEVEL SHORTWAVE BY SAT NIGHT
NEAR THE GREAT LAKES. LARGER DIFFERENCES ARE NOTED WITH THE 700 MB
SHORTWAVE AND SURFACE LOW. SPREAD IN THE LATEST ENSEMBLE SPAGHETTI
LOW PLOTS IS MODERATE TO LARGE...BUT PERCEIVED CLUSTERING IS
CLOSEST TO A BLEND OF THE 00Z GFS AND 00Z ECMWF. THE 00Z NAM GOES
ASTRAY FROM THE BETTER CLUSTERING STARTING LATE SAT NIGHT BUT
APPEARS USABLE UNTIL THEN. THE 00Z UKMET/CMC SURFACE REFLECTIONS
SHOW LARGER DEPARTURES FROM THE ENSEMBLES. DESPITE ADJUSTMENTS
TOWARD THE 00Z GFS/ECMWF...THE 00Z UKMET/CMC CONTINUE TO APPEAR A
BIT FARTHER NORTH AND FASTER WITH THE LOW TRACK SUN MORNING.


...LINGERING SHORTWAVE IN THE CAROLINAS DROPPING DOWN AND
RETROGRADING ALONG THE GULF COAST THROUGH SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT WITH THIS
SHORTWAVE...ONLY DISPLAYING MINOR PLACEMENT/STRENGTH DIFFERENCES
THROUGH SUN MORNING. A GENERAL MODEL COMPROMISE IS ADVISED WITH
SLIGHTLY ABOVE AVERAGE CONFIDENCE.


...FRONTAL WAVE/COLD FRONT MOVING THROUGH THE GREAT LAKES TODAY
AND REACHING THE NORTHEAST ON FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM...00Z GFS...00Z UKMET BLEND
CONFIDENCE: AVERAGE

WHILE DIFFERENCES APPEAR TO BE MORE TIED TO CONVECTIVE DIFFERENCES
ON THE MESOSCALE...THE 00Z ECMWF/CMC BECOME FASTER WITH THE
FRONTAL PASSAGE ACROSS NEW ENGLAND EARLY ON FRI. A MAJORITY OF THE
GUIDANCE SUPPORTS A BLEND OF THE 00Z NAM...00Z GFS AND 00Z UKMET.


...WEAK MID-UPPER LEVEL SHORTWAVE NEARING THE NRN CA COAST BY SUN
MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE

WHILE THE 00Z ECMWF REMAINS A BIT FASTER THAN THE REMAINING
CONSENSUS...IT SLOWED ENOUGH COMPARED TO ITS 12Z RUN TO INCLUDE IT
AS PART OF A GENERAL MODEL BLEND FOR THE MID-UPPER LEVEL SHORTWAVE
NEARING THE WEST COAST THIS WEEKEND.


www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

OTTO

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