553
FXUS10 KWNH 300651
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
251 AM EDT SAT MAY 30 2020
VALID MAY 30/0000 UTC THRU JUN 2/1200 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
UPPER LEVEL TROUGH AND COLD FRONT ACROSS THE EASTERN U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/ECMWF/UKMET
CONFIDENCE: HIGH
AN AMPLIFYING UPPER LEVEL TROUGH OVER THE EASTERN U.S. WILL HERALD
A CHANGE IN THE RECENT WEATHER PATTERN, WITH A STRONG COLD FRONT
USHERING IN A PRISTINE AIRMASS FROM THE GREAT LAKES TO THE
MID-ATLANTIC, AND ALSO FOR THE NORTHEAST. BY THE END OF THE
FORECAST PERIOD, THE TROUGH AXIS WILL LIKELY BE ACROSS THE EASTERN
CANADIAN PROVINCES. WITH THE EXCEPTION OF A SLIGHTLY WEAKER 12Z
CMC SOLUTIONS, THE GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH
ABOUT 12Z MONDAY. BEYOND THAT, THERE ARE SOME DIFFERENCES
REGARDING WHETHER AN UPPER LOW PINCHES OFF BY TUESDAY MORNING,
WITH THE GFS, ECMWF, AND UKMET ON BOARD WITH THIS IDEA. THE CMC
AND NAM CONTINUE TO SUPPORT THE IDEA OF AN ELONGATED TROUGH WITH
NO CLOSED LOW DEVELOPING YET, AND THE NAM IS ALSO SLIGHTLY WEAKER
BY THIS TIME. SINCE THERE IS DECENT ENSEMBLE PLOT SUPPORT FOR THE
GFS/ECMWF/UKMET SOLUTION, THIS WILL BE THE PREFERENCE.
UPPER LEVEL LOW THAT REACHES NORTHERN MEXICO ON FRIDAY NIGHT AND
BECOMES SLOW MOVING THROUGH THE WEEKEND
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: MODERATE-HIGH
A BROAD UPPER LEVEL LOW OVER NORTHERN MEXICO, MOST EVIDENT ABOVE
250 MB, IS EXPECTED TO REMAIN NEARLY STATIONARY UNDERNEATH THE
BUILDING RIDGE ACROSS THE PLAINS, AND SLOWLY MOVE NORTHWARD BY
EARLY TUESDAY. THERE IS ENOUGH MODEL AGREEMENT HERE TO MERIT A
MULTI-DETERMINISTIC MODEL BLEND.
TROUGH EVOLUTION ALONG THE WEST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/UKMET/CMC FOR FIRST SHORTWAVE
GENERAL MODEL BLEND (OFFSHORE WESTERN TROUGH)
CONFIDENCE: MODERATE
AN UPPER LEVEL LOW WITH SUBTROPICAL ORIGINS WILL REACH NORTHERN
CALIFORNIA BY MIDDAY SATURDAY, AND THEN EVOLVE INTO AN OPEN
SHORTWAVE AS IT LIFTS NORTH ACROSS THE PACIFIC NORTHWEST AND
EVENTUALLY CROSSES THE NORTHERN PERIPHERY OF THE GREAT PLAINS
UPPER RIDGE OVER SOUTH-CENTRAL CANADA. WHEN THAT SYSTEM EXITS,
THE TROUGH REBUILDS ACROSS THE WEST COAST REGION AS THE OVERALL
SYNOPTIC PATTERN BECOMES MORE AMPLIFIED, AND SHOULD EVENTUALLY
BECOME A CUT-OFF LOW SITUATED OFF THE COAST OF SOUTHERN CALIFORNIA
BY TUESDAY MORNING. THE GEFS ENSEMBLE MEMBERS ARE SLIGHTLY
STRONGER THAN THE ECENS MEMBERS WITH THE LARGE SCALE TROUGH
DEVELOPING BY THE END OF THE FORECAST PERIOD, AND RIGHT NOW A
GENERAL MODEL BLEND SHOULD SUFFICE. THE ECMWF IS SLIGHTLY
STRONGER THAN THE MODEL CONSENSUS AND A LITTLE SLOWER, BUT STILL
DEPICTS A REASONABLE EVOLUTION FOR THE OFFSHORE SYSTEM. THERE IS
INCREASING MODEL SPREAD WITH THE SHORTWAVE CROSSING SOUTHERN
CANADA AND CONFIDENCE DECREASES BEYOND 12Z MONDAY, WITH THE ECMWF
SLIGHTLY AHEAD OF THE OTHER GUIDANCE. THE NAM IS A LITTLE
DISPLACED TO THE NORTH WITH THE TRACK OF THE SURFACE LOW ACROSS
SOUTHERN CANADA BY SUNDAY AFTERNOON AND BEYOND. TAKING THESE
FACTORS INTO ACCOUNT, BLENDING THE GFS/UKMET/CMC SHOULD WORK AS A
STARTING POINT ACROSS THE NORTHERN ROCKIES AND NORTHERN PLAINS.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
HAMRICK
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