159
FXUS10 KWNH 180445
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1144 PM EST MON FEB 17 2020
VALID FEB 18/0000 UTC THRU FEB 21/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z INITIAL MODEL EVALUATION WITH LATEST PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PAIR OF SHORTWAVES CROSSING THE GREAT LAKES/NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC 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 MAIN
DIFFERENCE WITH THE MODELS AT THIS POINT IS A WEAKER AMPLITUDE
WITH THE CMC ON THE FIRST SHORTWAVE TROUGH, ALTHOUGH ALL OF THE
MODELS ARE NOW SIMILAR ON TIMING WITH THE COLD FRONT PASSAGE.
BROAD TROUGH AXIS TRACKING FROM THE ROCKIES TO THE EASTERN U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/18Z 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 CMC REMAINS ON THE STRONGER SIDE OF THE MODEL
GUIDANCE WITH THE TROUGH AXIS ACROSS THE ROCKIES AND NORTHERN
PLAINS. THE 12Z NAM BECOMES STRONGER AS THE SYSTEM APPROACHES THE
EASTERN U.S. AND THE GFS IS A LITTLE MORE PROGRESSIVE. 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.
SHORTWAVE REACHING THE PACIFIC NORTHWEST THURSDAY NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/18Z 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 FROM THE GULF OF AK 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: NON-CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THE MODELS SHOW A STRONG SPLIT IN THE UPPER FLOW PATTERN BY
THURSDAY WITH A SUBSTANTIAL SOUTHERN STREAM TROUGH AND CLOSED LOW
EMERGING WEST OF CALIFORNIA AS STRONG NORTHERN STREAM PACIFIC FLOW
ADVANCES THROUGH WESTERN CANADA, WITH THE UPPER LOW EXPECTED TO
EVOLVE THURSDAY AFTERNOON AND THEN SLOWLY TRACK WESTWARD TOWARDS
THE COAST. THE CMC APPEARS DISPLACED EAST OF THE MODEL CONSENSUS,
AND ALL OF THE MODELS ARE SIMILAR IN THE INTENSITY OF THE UPPER
LOW.
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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