397
FXUS10 KWNH 021855
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 PM EDT SUN AUG 02 2020
VALID AUG 02/1200 UTC THRU AUG 06/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...MID-LEVEL SHORTWAVE LIFTING FROM THE LOWER GREAT LAKES INTO
SOUTHEASTERN CANADA THROUGH TONIGHT WITH ACCOMPANYING SURFACE
LOW...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM. NO SIGNIFICANT CHANGES
WERE NOTED IN THE 12Z ECMWF/UKMET/CMC COMPARED TO THEIR PREVIOUS
00Z CYCLES.
..TROPICAL STORM ISAIAS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 03Z NHC ADVISORY PACKAGE
BEST MODEL PROXY: THROUGH 12Z/04: NON 12Z NAM BLEND
00Z/05 - 12Z/05: 12Z ECMWF/UKMET/CMC BLEND
00Z/06: NEAR THE 12Z ECMWF
..19Z UPDATE
ONLY MINOR TIMING CHANGES WERE NOTED WITH THE SPEED/TRACK OF
TROPICAL STORM ISAIAS IN THE LATEST 12Z ECMWF/UKMET/CMC COMPARED
TO THEIR PREVIOUS 00Z CYCLES. THE 12Z ECMWF/UKMET REMAIN SLOWER
THAN THE 15Z NHC ADVISORY, WHILE THE 12Z CMC IS GENERALLY FASTER
AND A BIT WEAKER THAN THE DETERMINISTIC CONSENSUS. A BLENDED
APPROACH OF NON-NCEP GUIDANCE IS REASONABLY CLOSE TO THE 15Z NHC
ADVISORY AFTER MONDAY NIGHT, WITH THE 12Z ECMWF CLOSEST AT THE END
OF THE SHORT RANGE PERIOD...OR 00Z/06 (WEDNESDAY EVENING).
..PREVIOUS DISCUSSION FOLLOWS
THE 15Z NHC FORECAST TRACK OF TROPICAL STORM ISAIAS IS OVERALL
CLOSEST NOW TO A MULTI-MODEL BLEND CONSISTING OF THE 12Z GFS, 00Z
ECMWF, 00Z UKMET AND 00Z CMC. THE MODEL'S PROXIMITY TO NHC VARIES
OVER THE COURSE OF THE NEXT 3 DAYS, BUT THE 12Z NAM STANDS OUT THE
GREATEST WITH A TIMING THAT IS 6 TO 12 HOURS SLOWER THAN THE NHC
TRACK THROUGH WEDNESDAY MORNING. INDIVIDUAL MODEL TIMING VARIES
CONSIDERABLY COMPARED TO THE NHC TRACK, WHERE SOME MODELS THAT ARE
INITIALLY SLOWER THAN NHC (00Z UKMET), SPEED UP THEIR TIMING TO BE
FASTER THAN NHC BY WEDNESDAY AFTERNOON. HOWEVER, ALL OF THE MODELS
SUPPORT THE SYSTEM RAPIDLY LIFTING THROUGH NEW ENGLAND BY THE END
OF THE PERIOD. PLEASE CONSULT THE LATEST NHC FORECAST ADVISORY
PACKAGE FOR MORE DETAILS.
...NORTHERN STREAM TROUGH SETTING UP OVER THE GREAT LAKES ON
MONDAY/TUESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE
..19Z UPDATE
ADJUSTMENTS IN THE LATEST 12Z NON-NCEP SUITE OF GUIDANCE MAKE FOR
TWO CAMPS OF SOLUTIONS REGARDING THE EVENTUAL CLOSED LOW THAT SETS
UP NEAR THE GREAT LAKES REGION FOR TUESDAY. THE 12Z NAM/GFS/CMC
REPRESENT A MORE CONSOLIDATED AND SYMMETRIC CLOSED LOW AT 500 MB,
WHILE THE 12Z ECMWF/UKMET SHOW AN ELONGATED MID-LEVEL LOW WITH TWO
MAIN VORTICITY MAXIMA (ONE NORTH AND ONE SOUTH). HOWEVER, THE
RECENT TREND BY THE 12Z ECMWF/UKMET IS GETTING THE MODELS CLOSE
ENOUGH THAT THE IMPACTS DUE TO THESE DIFFERENCES ARE MAINLY INTO
CANADA. EVEN THEN, THE DIFFERENCES ARE SHRINKING SO THAT A GENERAL
MODEL BLEND CAN NOW BE USED HERE.
..PREVIOUS DISCUSSION FOLLOWS
NORTHERN STREAM ENERGY WILL BE DIGGING DOWN ACROSS THE GREAT LAKES
THROUGH SUNDAY WITH LIKELY DEVELOPMENT OF AN ELONGATED CLOSED LOW
A BIT FARTHER NORTH OVER ONTARIO BY MONDAY AND TUESDAY. THE 00Z
ECMWF/UKMET AND 00Z CMC DIFFER WITH THE HANDLING OF TWO MAIN
VORTICITY MAXIMA WITHIN THE LARGER SCALE TROUGH. THE 00Z ECMWF
STANDS OUT THE GREATEST FROM THE DETERMINISTIC/ENSEMBLE GUIDANCE
BUT THERE IS GROWING SUPPORT FOR A SOLUTION EDGING IN THE
DIRECTION OF THE 00Z ECMWF NOTED BY ITS MEAN AND THE 00Z
UKMET/CMC. HOWEVER, A BLENDED APPROACH NEAR THE 12Z NAM, 12Z GFS
AND 00Z UKMET IS NEAREST TO THE PREFERENCE OF THE ENSEMBLE MEANS
AT THIS POINT, WITH THE ENSEMBLE MEANS CONSIDERED BEST.
..UPPER LOW/TROUGH CROSSING THE PACIFIC NORTHWEST TONIGHT
...ENERGY DROPPING DOWN OVER THE NORTHERN PLAINS/MIDWEST FOR
TUESDAY/WEDNESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE
..19Z UPDATE
TRENDS IN THE 12Z ECMWF/UKMET/CMC COMPARED TO THEIR PREVIOUS 00Z
CYCLES SHOWED EITHER SLOWING OR STRENGTHENING WITH THE MID-LEVEL
VORTICITY MAXIMUM TRACKING NEAR THE U.S./CANADIAN BORDER. HOWEVER,
THE UKMET REMAINS A BIT WEAKER WITH ITS 12Z CYCLE WHILE THE 12Z
CMC CONTINUES TO APPEAR AS A NEAR OUTLIER WITH ITS STRENGTH ON
WEDNESDAY. THE 12Z ECMWF TRENDED A LITTLE SLOWER AND SOUTH WITH
THE TRACK OF THE VORT MAX, PUTTING IT CLOSE ENOUGH TO A FAVORED
MIDDLE GROUND...WHEN COMBINED WITH THE 12Z GFS...TO ALLOW
INCLUDING AS PART OF THE PREFERENCE.
..PREVIOUS DISCUSSION FOLLOWS
AN UPPER TROUGH WILL CROSS IN THROUGH BRITISH COLUMBIA AND THE
PACIFIC NORTHWEST TONIGHT AND THEN TRACK WELL INLAND THROUGH
MONDAY AND TUESDAY WITH THE MAIN FOCUS OF THE HEIGHT FALLS
REMAINING ACROSS WESTERN AND CENTRAL CANADA. HOWEVER, THE GUIDANCE
SUPPORTS SOME ENERGY IN THE BASE OF THE TROUGH SEPARATING OUT
ACROSS THE FAR NORTHERN ROCKIES AND THEN ADVANCING SOUTHEAST BY
WEDNESDAY ACROSS THE NORTHERN PLAINS AND MIDWEST. THE 12Z NAM/GFS
REMAIN ON THE STRONGER SIDE OF THE GUIDANCE WITH THIS ENERGY OVER
THE NORTHERN U.S. MONDAY NIGHT THROUGH TUESDAY...AS IS THE 00Z
CMC. THIS IS REFLECTED IN THE LATEST ENSEMBLE SPAGHETTI PLOTS
WHICH INDICATE THE NAM/GFS/CMC ON THE EDGES OF THE LATEST MEMBER
DISTRIBUTION. HOWEVER, THE 00Z ECMWF/UKMET ARE WEAKER AND FASTER
WITH THIS SYSTEM TRACKING NEAR THE U.S./CANADIAN BORDER. THE 00Z
UKMET AND 00Z CMC ARE ON THE EDGES OF THE LATEST DETERMINISTIC
GUIDANCE, AND SO THE PREFERENCE IS TO EQUALLY WEIGHT THE 12Z NAM,
12Z GFS AND 00Z ECMWF. THE THINKING HERE IS THAT A BLENDED
APPROACH OF THESE MODELS WILL BE CLOSEST TO VERIFICATION, LYING IN
THE MIDDLE OF THE MODEL SPREAD AND NEAR THE MIDDLE GROUND
CONSIDERING TRENDS.
..SOUTHERN STREAM TROUGH MOVING INTO CA BY WEDNESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
THE MODELS SHOW SIMILARY WITH THIS SYSTEM. NO SIGNIFICANT CHANGES
WERE NOTED IN THE 12Z ECMWF/UKMET/CMC COMPARED TO THEIR PREVIOUS
00Z CYCLES.
...MID-UPPER LEVEL TROUGH NEARING THE PACIFIC NORTHWEST LATE
WEDNESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE
ONLY MINOR TIMING DIFFERENCES WERE NOTED, BUT AGREEMENT IS FAIRLY
GOOD FOR A DAY 3 FORECAST. NO SIGNIFICANT CHANGES WERE NOTED IN
THE 12Z ECMWF/UKMET/CMC COMPARED TO THEIR PREVIOUS 00Z CYCLES.
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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