908
FXUS10 KWNH 180645
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
144 AM EST TUE FEB 18 2020
VALID FEB 18/0000 UTC THRU FEB 21/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z FINAL MODEL EVALUATION WITH LATEST PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PAIR OF SHORTWAVES CROSSING THE GREAT LAKES AND THEN THE NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
A SHORTWAVE AND ASSOCIATED SURFACE LOW WILL CROSS THE GREAT LAKES
REGION ON TUESDAY AND THEN ADVANCE EAST-NORTHEAST AND CLIP
PORTIONS OF NORTHERN NEW ENGLAND THROUGH EARLY WEDNESDAY. IN THE
WAKE OF THIS INITIAL SHORTWAVE, THERE WILL BE ANOTHER NORTHERN
STREAM SHORTWAVE THAT WILL FOLLOW WITH ABOUT 12 HOURS WORTH OF
SEPARATION. ALL OF THIS ENERGY BY LATE WEDNESDAY WILL BE EXITING
NORTHERN NEW ENGLAND AND LIFTING THROUGH EASTERN CANADA. THE 00Z
RUN OF THE CMC HAS TRENDED IN LINE WITH THE MODEL CONSENSUS
COMPARED TO ITS EARLIER RUN, AND SO A GENERAL DETERMINISTIC MODEL
BLEND IS NOW ADVISABLE.
BROAD TROUGH AXIS TRACKING FROM THE ROCKIES TO THE EASTERN U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z UKMET/00Z GEFS MEAN
CONFIDENCE: AVERAGE
AS A TRANSIENT DEEP LAYER RIDGE MOVES INTO SOUTHWEST CANADA AND
ACROSS THE PACIFIC NORTHWEST BY WEDNESDAY, THERE WILL BE A
POSITIVELY TILTED AND BROAD LONGWAVE TROUGH DOWNSTREAM THAT WILL
CROSS FROM THE NORTHERN ROCKIES AND NORTHERN PLAINS TO THE MIDWEST
STATES. BY THURSDAY, THIS TROUGHING WILL CROSS THE GREAT LAKES AND
NORTHEAST. THE 12Z NAM BECOMES STRONGER BY WEDNESDAY EVENING AS
THE SYSTEM APPROACHES THE MIDWEST AND GREAT LAKES, AND BECOMES
EVEN MORE SO BY FRIDAY MORNING NEAR THE EAST COAST. THE GFS
REMAINS A LITTLE MORE PROGRESSIVE ACROSS THE NORTHEAST, AND THE
00Z ECMWF SLIGHTLY SLOWER. SURFACE CYCLOGENESIS FROM THIS
SHORTWAVE IS EXPECTED TO OCCUR WELL OFFSHORE FROM THE SOUTHEAST
U.S., WITH THE NAM INDICATING THE LOW POSITION CLOSER TO THE COAST
COMPARED TO THE MODEL CONSENSUS, AND THE 00Z CMC MORE PROGRESSIVE.
THE UKMET AND THE GEFS MEAN APPEAR TO BE A REASONABLE MIDDLE
GROUND FOR MODEL CHOICES.
SHORTWAVE REACHING THE PACIFIC NORTHWEST THURSDAY NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/00Z GEFS MEAN
CONFIDENCE: AVERAGE
A NORTHERN STREAM SHORTWAVE IS FORECAST TO REACH THE PACIFIC
NORTHWEST BY THURSDAY NIGHT AS THE PATTERN TRANSITIONS TO VERY
STRONG PACIFIC FLOW CROSSING THE NORTHEAST PACIFIC TO WESTERN AND
CENTRAL CANADA. THIS SHORTWAVE WILL BEGIN BREAKING DOWN THE
WESTERN U.S. RIDGE THAT IS EXPECTED TO BE IN PLACE MIDWEEK. THE
NAM AND GFS ARE INDICATING A GREATER DEGREE OF AMPLITUDE, IN
CONTRAST TO THE FLATTER SOLUTIONS OF THE NON-NCEP GUIDANCE. THE
UKMET AND CMC ALSO APPEAR TO BE MORE PROGRESSIVE WITH THIS FEATURE
CROSSING THE PACIFIC NORTHWEST.
UPPER TROUGH/CLOSED LOW OFFSHORE CALIFORNIA BY THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THE MODELS SHOW A STRONG SPLIT IN THE UPPER FLOW PATTERN BY
THURSDAY WITH A PRONOUNCED SOUTHERN STREAM TROUGH AND CLOSED LOW
EMERGING WEST OF CALIFORNIA AS STRONG NORTHERN STREAM PACIFIC FLOW
ADVANCES ACROSS WESTERN CANADA, WITH THE UPPER LOW EXPECTED TO
EVOLVE THURSDAY AFTERNOON AND THEN SLOWLY TRACK WESTWARD TOWARDS
THE COAST. THE CMC HAS TRENDED CLOSER TO THE MODEL CONSENSUS
COMPARED TO ITS EARLIER RUN, AND A GENERAL MODEL BLEND CAN BE
INCORPORATED FOR NOW.
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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