944
FXUS10 KWNH 311732
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 PM EDT FRI JUL 31 2020
VALID JUL 31/1200 UTC THRU AUG 04/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z NAM/GFS EVALUATION INCLUDING PRELIMINARY PREFERENCES AND
FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..MID-LEVEL TROUGH DIGGING ACROSS THE MID-MS/TN/OH VALLEYS
...SURFACE LOW TRACKING THROUGH THE OH VALLEY ON SATURDAY AND INTO
SOUTHEASTERN CANADA SUNDAY NIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS, 00Z ECMWF AND 00Z UKMET
CONFIDENCE: AVERAGE
MID-LEVEL ENERGY DIGGING SOUTHEAST ACROSS THE MID-MS VALLEY WILL
DRIVE A TROUGH IN ACROSS MUCH OF THE TN/OH VALLEY GOING THROUGH
THE WEEKEND. THIS WILL BE REINFORCED BY SUNDAY BY AN INTRUSION OF
NORTHERN STREAM TROUGHING DROPPING DOWN ACROSS THE GREAT LAKES
REGION BUT A LEAD SHORTWAVE WITHIN THE INITIAL TROUGHING WILL
COINCIDE WITH A SURFACE LOW TRACKING ACROSS THE MS RIVER VALLEY
INTO THE MIDWEST AND EVENTUALLY SOUTHEASTERN CANADA FOR SUNDAY
NIGHT.
THE 12Z NAM IS STRONGER WITH UPPER LEVEL JET ENERGY IN THE BASE OF
THE TROUGH AXIS NEAR THE GULF COAST SUNDAY MORNING WHICH LEADS TO
A STRONGER AND SOUTHEASTWARD DISPLACED TROUGH AXIS ON ITS
SOUTHEASTERN SIDE BY SUNDAY EVENING. MEANWHILE WITH THE NORTHWARD
TRACKING SURFACE LOW INTO CANADA, THERE ARE ONLY MINOR
DIFFERENCES, BUT THE 00Z ECMWF WAS A LITTLE FASTER THAN THE
CONSENSUS LATE SUNDAY. OVERALL, A 12Z NAM, 12Z GFS, 00Z ECMWF AND
00Z UKMET BLEND IS REASONABLE HERE, BUT NOTE THAT THE FASTER 00Z
ECMWF SHOULD BE ACCOUNTED FOR.
..HURRICANE ISAIAS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: SEE NHC SPECIAL 04Z ADVISORY
BEST MODEL PROXY: 12Z NAM, 12Z GFS, 00Z ECMWF BLEND...THROUGH
12Z/02
00Z GFS/GEFS BLEND...12Z/02 THROUGH 00Z/04
FROM EARLY ON, THE 00Z UKMET DIFFERS SIGNIFICANTLY EAST FROM THE
15Z NHC TRACK FOR ISAIAS, ALSO RESULTING IN A STRONGER SYSTEM. THE
00Z CMC ALSO DIFFERS IN THE OTHER DIRECTION WITH A MORE
SOUTHERN/WESTERN TRACK OVER THE FL PENINSULA RESULTING IN A WEAKER
STORM.
WHILE NOT AN EXACT MATCH TO NHC, A BLEND OF THE 12Z NAM, 12Z GFS
AND 00Z ECMWF APPEARS REASONABLY CLOSE TO NHC THROUGH 12Z/02 BUT
THIS BLEND IS MORE INLAND THAN THE NHC TRACK BY ABOUT 30 MILES.
BEYOND 12Z/02, THE 00Z ECMWF SLOWS THE SPEED OF ISAIAS MORE THAN
THE NAM AND GFS WITH A 12Z NAM/12Z GFS BLEND CLOSER TO THE 15Z NHC
ADVISORY AFTER 12Z/02 UNTIL 00Z/04. THERE IS A NEED FOR INCREASING
WEIGHT ON THE 12Z GFS'S FASTER SPEED FOR 12Z/03 AND 00Z/04, NOTING
BOTH THE NAM AND GFS ARE FARTHER WEST OF THE NHC TRACK BY ABOUT
30-50 MILES.
...NORTHERN STREAM TROUGH SETTING UP OVER THE WESTERN GREAT LAKES
REGION BY MONDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF/00Z UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
DIFFERENCES WITH THE PHASING OF, OR LACK THEREOF, MID-LEVEL ENERGY
TRACKING THROUGH MANITOBA AND ONTARIO AFFECT THE PATTERN EVOLUTION
OVER THE WESTERN GREAT LAKES REGION AND MIDWEST FOR EARLY NEXT
WEEK. ENSEMBLE MEANS SUPPORT A 12Z GFS/00Z ECMWF BLEND WITH THE
12Z NAM AND 00Z CMC INDICATING LESS PHASING TO THE NORTH AND
GREATER AMPLIFICATION OF TROUGHING NEAR LAKE SUPERIOR AND DOWN
INTO THE MS VALLEY ON MONDAY. THE 00Z UKMET IS PLAUSIBLE AS
ANOTHER OPTION SIMILAR TO THE 12Z GFS AND 00Z ECMWF.
..UPPER LOW/TROUGH APPROACHING THE PACIFIC NORTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF/00Z CMC BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
TIMING DIFFERENCES SHOW UP WITH THE TROUGH AXIS AS IT NEARS
BRITISH COLUMBIA AND THE PACIFIC NORTHWEST LATE ON SUNDAY. THE 12Z
NAM AND 00Z UKMET ARE MORE NOTED TO BE MORE PROGRESSIVE WITH A
SHORTWAVE IN THE BASE OF THE TROUGH ON MONDAY. THE PATTERN FROM
THE NORTHEASTERN PACIFIC INTO THE SOUTHERN HALF OF CANADA IS
RATHER AMPLIFIED AND MAY FAVOR SLOWER PROGRESSION. THIS IS
REPRESENTED IN THE AGREEABLE ENSEMBLE MEANS WITH A SLOWER TROUGH
AXIS THAN EVEN THE 12Z GFS, 00Z ECMWF AND 00Z CMC THROUGH MONDAY
NIGHT. THE PREFERENCE IS TO GO WITH THE SLOWER SIDE OF THE
DETERMINISTIC SPREAD AT THIS POINT, NOTING THAT ENSEMBLE SPAGHETTI
PLOTS SHOW A GREAT DEAL OF SPREAD WITH NO DEFINED TRENDS.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
THIS PRODUCT WILL TERMINATE AUGUST 15, 2020:
WWW.WEATHER.GOV/MEDIA/NOTIFICATION/PDF2/SCN20-58PMDHMD_TERMINATION.
OTTO
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