688
FXUS10 KWNH 011903
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
303 PM EDT SAT AUG 01 2020
VALID AUG 01/1200 UTC THRU AUG 05/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..MID-LEVEL TROUGH DIGGING ACROSS THE MID-MS/TN/OH VALLEYS
..SURFACE LOW CROSSING THE OH VALLEY/LOWER GREAT LAKES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM/12Z GFS/12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
..19Z UPDATE
THE 12Z UKMET/CMC ADJUSTED CLOSER IN LINE WITH THE CONSISTENT
NAM/GFS/ECMWF, WITH ENOUGH ADJUSTMENT TO ALLOW FOR A GENERAL MODEL
BLEND.
..PREVIOUS DISCUSSION FOLLOWS
MID-LEVEL ENERGY IN PLACE OVER THE LOWER OHIO VALLEY SATURDAY
AFTERNOON WILL DRIVE A SURFACE LOW NORTH-NORTHEASTWARD FROM
SOUTHERN IL/IN INTO SOUTHERN ONTARIO/QUEBEC LATE SUNDAY. THE
SHORTWAVE EMBEDDED WITHIN A LONGWAVE TROUGH AXIS WILL LIFT
NORTHEASTWARD INTO CANADA AS WELL BEFORE SHEARING OUT ACROSS
EASTERN CANADA IN SOUTHWESTERLY MID-LEVEL FLOW.
THE 12Z NAM/GFS CONTINUE TO SHOW GOOD AGREEMENT WITH EACH OTHER
AND THE 00Z ECMWF. THE 00Z ECMWF REMAINS A TAD QUICKER WHILE THE
00Z UKMET IS SLOWER. OVERALL, THESE DIFFERENCES ARE RELATIVELY
MINOR BUT QUICKER TRENDS AND THE EVEN SLOWER/WEAKER 00Z CMC STAND
OUT ENOUGH FROM THE GROUP TO DISCOUNT THE 00Z UKMET/CMC. A BLEND
OF THE 12Z NAM/12Z GFS AND 00Z ECMWF LOOK BEST AT THIS TIME
..HURRICANE ISAIAS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 03Z NHC ADVISORY PACKAGE
BEST MODEL PROXY: NEAR THE 12Z GFS
..19Z UPDATE
NO MAJOR ADJUSTMENTS WERE SEEN IN THE 12Z NON-NCEP GUIDANCE, BUT
GIVEN THE 12Z CMC INCREASED ITS FORWARD SPEED ON TUESDAY ALONG THE
EAST COAST, THE CMC WAS REMOVED FROM THE PREFERENCE. THE 12Z
ECMWF/UKMET REMAIN AS SLOW/SLOWER (RESPECTIVELY) COMPARED TO THEIR
PREVIOUSLY 00Z CYCLES.
..PREVIOUS DISCUSSION FOLLOWS
THE 15Z NHC FORECAST TRACK OF HURRICANE ISAIAS DOES NOT MATCH ANY
SINGLE MODEL OR MODEL BLEND CONSISTENTLY THROUGHOUT THE 84 HOUR
SHORT RANGE PERIOD. HOWEVER, THE 12Z GFS IS FAIRLY CLOSE TO THE
NHC TRACK, BUT THE GFS IS CLOSER TO THE COAST COMPARED TO NHC
THROUGH TUESDAY. BY MONDAY EVENING, THE 00Z CMC (WHICH WAS WEST OR
SOUTH OF THE NHC TRACK EARLY ON) CATCHES UP AND ACTUALLY OUTPACES
THE NHC TRACK BY A LITTLE WHILE THE 12Z GFS FALLS BEHIND SLIGHTLY
IN TIMING COMPARED TO NHC.
THEREFORE, THE CLOSEST MODEL GUIDANCE TO NHC IS THE 12Z GFS
THROUGH 00Z/04, BUT A BLEND OF THE 12Z GFS AND 00Z CMC FROM 00Z/04
TO 00Z/05. AGAIN, NO SINGLE MODEL OR MODEL BLEND MATCHES EXACTLY
WITH THE NHC TRACK SO CONSULT THE LATEST NHC FORECAST
ADVISORY/DISCUSSION FOR MORE DETAILS.
..NORTHERN STREAM TROUGH SETTING UP OVER THE GREAT LAKES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
..19Z UPDATE
THE 12Z UKMET AND 12Z CMC CONTINUED TO TREND TOWARD THE AGREEABLE
NAM/GFS/ECMWF, SUCH THAT THEY CAN NOW BE INCLUDED AS PART OF A
GENERAL MODEL BLEND.
..PREVIOUS DISCUSSION FOLLOWS
NORTHERN STREAM ENERGY WILL BE DIGGING DOWN ACROSS THE GREAT LAKES
REGION THIS WEEKEND WITH SUGGESTION OF AN ELONGATED CLOSED LOW
DEVELOPING A BIT FARTHER NORTH OVER ONTARIO BY MONDAY AND TUESDAY.
THE LATEST GUIDANCE IS IN FAIR AGREEMENT BUT THE 00Z UKMET/CMC
BECOME A LITTLE WEST OR DEEPER THAN THE REMAINING MODEL CONSENSUS
BY TUESDAY MORNING.
..UPPER LOW/TROUGH APPROACHING THE PACIFIC NORTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM, 12Z GFS, 12Z UKMET BLEND
CONFIDENCE: AVERAGE
..19Z UPDATE
THE 12Z ECMWF MADE A SIGNIFICANT ADJUSTMENT IN THAT IT SHOWS
GREATER AMPLIFICATION OF A NORTHERN SHORTWAVE AND GREATER
INTERACTION/PHASING WITH THE SOUTHERN SHORTWAVE ENTERING INTO
BRITISH COLUMBIA SUNDAY NIGHT. THE INTERACTION OF THE TWO PIECES
OF ENERGY SEEN IN THE ECMWF RESULTS IN A WEAKER SURFACE REFLECTION
ACROSS SOUTHERN SASKATCHEWAN COMPARED TO THE REMAINING MODEL
CONSENSUS. THE 12Z CMC REMAINS EXCLUDED FROM THE PREFERENCE DUE TO
ITS FASTER TIMING OF THE SOUTHERN SHORTWAVE ALONG THE
U.S./CANADIAN BORDER.
..PREVIOUS DISCUSSION FOLLOWS
TIMING DIFFERENCES SHOW UP WITH THE TROUGH AXIS AS IT NEARS
BRITISH COLUMBIA AND THE PACIFIC NORTHWEST LATE ON SUNDAY AND THEN
ADVANCES INLAND ACROSS THE FAR NORTHERN ROCKIES AND ADJACENT AREAS
OF SOUTHWEST CANADA ON MONDAY. THE 00Z CMC ENDS UP BEING ON THE
WEAKER AND MORE PROGRESSIVE SIDE OF THE GUIDANCE AS THE ENERGY
ADVANCES INLAND. WHILE MINOR TIMING DIFFERENCES REMAIN AMONG THE
NON 00Z CMC GUIDANCE, AGREEMENT IS GOOD ENOUGH TO SUPPORT A
GENERAL MODEL BLEND (EXCLUDING THE 00Z CMC) AT THIS TIME.
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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