147
FXUS10 KWNH 291852
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 PM EDT FRI MAY 29 2020
VALID MAY 29/1200 UTC THRU JUN 02/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..UPPER LEVEL TROUGH AND COLD FRONT ACROSS THE EASTERN U.S
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
..19Z UPDATE
THE 12Z CMC SPED UP WITH A LEAD SHORTWAVE TROUGH PASSING THROUGH
SOUTHERN QUEBEC SATURDAY MORNING WHICH PUTS IT IN BETTER AGREEMENT
WITH THE REMAINING MODELS. OTHERWISE, A SMALL TREND TO BE FASTER
SUNDAY INTO MONDAY WITH THE LONGWAVE TROUGH AXIS TOWARD THE EAST
WAS NOTED IN THE 12Z ECMWF/UKMET/CMC COMPARED TO THEIR PREVIOUS
00Z CYCLES.
..PREVIOUS DISCUSSION FOLLOWS
THE MEAN AXIS OF A LONGWAVE TROUGH WILL SLOWLY EDGE EAST FROM THE
GREAT LAKES REGION TODAY, TO THE NORTHEAST ON MONDAY. THE
ORIENTATION OF THE TROUGH AXIS WILL LIKELY BECOME NEGATIVELY
TILTED BY MONDAY MORNING WITH TROUGHING EXTENDING FROM THE
NORTHEAST TO THE EASTERN MID-ATLANTIC REGION. WHILE THE 00Z CMC IS
A BIT SLOWER THAN PREFERRED WITH A LEAD SHORTWAVE EMBEDDED WITHIN
THE FLOW OVER SOUTHERN QUEBEC SATURDAY MORNING, THE MODELS PAINT
AN OVERALL SIMILAR PICTURE FOR THIS AREA OF THE COUNTRY OVER THE
NEXT 3 DAYS. THEREFORE, A GENERAL MODEL BLEND IS RECOMMENDED.
...CLOSED UPPER LEVEL LOW THAT REACHES NORTHERN MEXICO ON FRIDAY
NIGHT AND BECOMES SLOW MOVING THROUGH THE WEEKEND...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z CMC BLEND (LEAST WEIGHT ON 12Z GFS)
CONFIDENCE: AVERAGE
..19Z UPDATE
THE 12Z ECMWF/UKMET/CMC JOINED THE 12Z NAM/GFS WITH THE STRENGTH
OF THE 500-300 MB LOW OVER NORTHERN MEXICO/SOUTHERN TX FOR THE
WEEKEND. THERE IS NOW GOOD AGREEMENT WITH STRENGTH AND POSITION OF
THIS FEATURE BUT THE 12Z GFS REMAINS STRONGEST AND THE 12Z CMC IS
A BIT EAST OF THE CONSENSUS BY LATE MONDAY.
..PREVIOUS DISCUSSION FOLLOWS
A MID-UPPER LEVEL CLOSED LOW WILL DEVELOP OVER NORTHERN MEXICO
LATE TODAY, FOLLOWED BY SOUTHWARD TRANSLATION THROUGH THE DAY ON
SATURDAY AND A NORTHWARD/NORTHWESTWARD DRIFT FOR SUNDAY AND
MONDAY. THE 00Z UKMET/CMC ARE WEAKEST WITH THIS FEATURE, AND THE
12Z GFS IS STRONGEST. ENSEMBLE MEANS SUPPORT 700-500 MB RIDGE
STRENGTH OVER THE CENTRAL PLAINS TO MID-MS VALLEY AND 500-300 MB
LOW STRENGTH OVER NORTHERN MEXICO/SOUTHERN TX...SIMILAR TO A BLEND
OF THE 12Z NAM, 12Z GFS AND 00Z ECMWF. THE 00Z ECMWF IS WEAKEST OF
THE THREE REGARDING THE UPPER LOW WHILE THE 12Z GFS IS STRONGEST.
SUBTLE TRENDS TOWARD A STRONGER SYSTEM WERE NOTED OVER THE PAST
24-36 HOURS OF MODEL CYCLES, BUT PREFER TO HAVE THE LEAST WEIGHT
ON THE MORE AGGRESSIVE GFS AT THIS TIME.
..TROUGH EVOLUTION ALONG THE WEST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z NAM BLEND (FIRST SHORTWAVE)
GENERAL MODEL BLEND (OFFSHORE WESTERN TROUGH)
CONFIDENCE: AVERAGE
..19Z UPDATE
THE 12Z UKMET/CMC ADJUSTED TOWARD THE 12Z GFS/00Z ECMWF WITH THE
LEAD SHORTWAVE TRACKING ACROSS THE NORTHWEST INTO SOUTHERN CANADA.
THE 12Z ECMWF REMAINED SIMILAR TO ITS 00Z CYCLE. NOW, ONLY THE 12Z
NAM SHOWS SIGNIFICANT DIFFERENCES WITH ITS EVOLUTION INTO CANADA.
REGARDING THE OFFSHORE TROUGH AXIS JUST OFF OF THE WEST COAST FOR
SUNDAY AND MONDAY, THE UKMET AND CMC NUDGED SLOWER COMPARED TO
THEIR PREVIOUS 00Z CYCLES, ENOUGH SUCH THAT A GENERAL MODEL BLEND
CAN BE USED.
..PREVIOUS DISCUSSION FOLLOWS
A CLOSED LOW THAT IS CURRENTLY OFFSHORE OF CA WILL REACH THE
MAINLAND TONIGHT AND WEAKEN INTO AN OPEN WAVE AS IT TRACKS THROUGH
INTERIOR PORTIONS OF THE NORTHWEST SATURDAY NIGHT. THE SHORTWAVE
WILL THEN TRACK SOUTH-CENTRAL CANADA, OVER A STRONG RIDGE AXIS
EXTENDING THROUGH THE CENTRAL AND NORTHERN ROCKIES. ON THE HEELS
OF THE EXITING SHORTWAVE FROM THE WEST COAST, AN ELONGATED
MID-UPPER LEVEL TROUGH WILL SETUP JUST OFFSHORE OF WA/OR/CA BY
MONDAY MORNING, WITH NORTHERN AND SOUTHERN STREAM COMPONENTS. AT
LEAST THROUGH MONDAY EVENING, THE ENSEMBLE MEANS FAVOR THE SLOWER
12Z NAM, 12Z GFS AND 00Z ECMWF. GIVEN THE 00Z UKMET/CMC ARE FASTER
TO BRING THIS FEATURE INLAND, THEY WILL NOT BE INCLUDED IN THE
PREFERENCE.
ENSEMBLE SPAGHETTI HEIGHT TRENDS OVER THE PAST FOUR 12/00Z CYCLES
DO NOT SHOW ANY CHANGE WITH RESPECT TO FASTER OR SLOWER TIMING,
AND IF ANYTHING INDICATE A TIGHTENING OF THE MODELS FROM THE WEST
AND THE EAST. HOWEVER, DESPITE THE GOOD AGREEMENT OF THE
SREF/GEFS/EC ENSEMBLE MEANS, THERE IS STILL A FAIR AMOUNT OF
SPREAD IN THE INDIVIDUAL ENSEMBLE MEMBERS SO CONFIDENCE IS ONLY
AVERAGE.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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