984
FXUS10 KWNH 181855
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
154 PM EST WED DEC 18 2019
VALID DEC 18/1200 UTC THRU DEC 22/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCE AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..CLOSED MID-LEVEL LOW CROSSING NEW ENGLAND ON THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
THE MODELS ARE IN VERY GOOD AGREEMENT WITH THIS SYSTEM, SO A
GENERAL MODEL BLEND WILL BE PREFERRED.
..SOUTHERN STREAM TROUGH CROSSING THE SOUTHWEST THROUGH THURS
..CROSSING THE SOUTHERN PLAINS/GULF COAST STATES FRI/SAT
..CYCLOGENESIS OVER THE GULF OF MEXICO
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND...THROUGH 36 HOURS
BLEND OF THE 12Z ECMWF/12Z GEFS MEAN AND 00Z ECENS
MEAN...AFTER 36 HOURS
CONFIDENCE: AVERAGE
A SOUTHERN STREAM TROUGH ADVANCING INTO CENTRAL CA TODAY WILL
ADVANCE EAST-SOUTHEAST AND CROSS THE SOUTHWEST THROUGH THURSDAY.
THE ENERGY IS THEN EXPECTED TO CROSS THE SOUTHERN PLAINS AND GULF
COAST STATES THROUGH SATURDAY WHILE DRIVING CYCLOGENESIS OVER THE
CENTRAL GULF OF MEXICO. THE GUIDANCE IS IN RATHER GOOD AGREEMENT
AT LEAST MASS FIELD WISE WITH THE SYSTEM THROUGH 36 HOURS,
HOWEVER, THEREAFTER THE 12Z NAM BEGINS TO DROP THE ENERGY FARTHER
SOUTH AND TO THE SOUTH OF THE GLOBAL MODEL CONSENSUS. BY THE END
THE PERIOD, THE NAM SUGGESTS A CLOSED MID-LEVEL LOW OVER THE
NORTHWEST GULF OF MEXICO WHICH IS WELL SOUTH OF THE GLOBAL MODEL
ENSEMBLE SUITES. THE NAM REFLECTS MORE BACKING OF THE
MID/UPPER-LEVEL FLOW DOWNSTREAM OVER THE GULF COAST WHICH DRIVES
ITS GULF OF MEXICO SURFACE CYCLOGENESIS FARTHER NORTH THAN THE
GLOBAL MODELS AND THUS A WETTER SOLUTION WITH STRONGER MOISTURE
TRANSPORT AS A RESULT. OVERALL, THE 12Z GFS APPEARS TO BE A TAD
TOO PROGRESSIVE AS THE ENERGY BEGINS TO CROSS THE GULF COAST
STATES. THE 12Z ECMWF, 12Z GEFS MEAN AND 00Z ECENS MEAN ARE ALL
SLOWER THAN THE GFS. THE 12Z CMC IS OVERALL RATHER CLOSE TO THE
ECMWF SOLUTION, WITH THE 12Z UKMET FARTHER NORTH WITH ITS CLOSED
LOW AND ALSO NOW THE SLOWEST SOLUTION. A GENERAL MODEL BLEND
SHOULD SUFFICE THROUGH 36 HOURS, BUT THEREAFTER, A BLEND OF THE
ECMWF/ECENS MEAN AND GEFS MEAN WILL BE PREFERRED.
..NORTHERN STREAM TROUGH CROSSING THE NORTHERN PLAINS/MIDWEST
..ENERGY ARRIVING ACROSS THE GREAT LAKES/NORTHEAST BY SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
A NORTHERN STREAM SHORTWAVE EJECTING ACROSS THE PACIFIC NORTHWEST
AND THE NORTHERN ROCKIES THROUGH THURSDAY WILL ADVANCE DOWNSTREAM
ACROSS THE NORTHERN PLAINS AND MIDWEST THROUGH FRIDAY. THEREAFTER
THE ENERGY WILL PROGRESSIVELY CROSS THE GREAT LAKES AND NORTHEAST.
MODEL SPREAD IS MINIMAL WITH THIS SYSTEM, BUT AS THE ENERGY
CROSSES THE GREAT LAKES AND NORTHEAST, THE 12Z NAM APPEARS TO BE A
TAD TOO DEEP. WILL PREFER THE NON-NAM GLOBAL MODEL CONSENSUS.
..DEEP UPPER TROUGH OFFSHORE THE WEST COAST
..ATMOSPHERIC RIVER IMPACTING THE PACIFIC NORTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS
BLEND OF THE 12Z ECMWF/12Z GEFS MEAN AND 00Z ECENS
MEAN...AFTER 60 HOURS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
ONSHORE FLOW INTO THE PACIFIC NORTHWEST ON THURSDAY BEGINS TO
ALTER AS A LARGE MID-UPPER LEVEL TROUGH UPSTREAM OVER THE EASTERN
PACIFIC BEGINS TO AMPLIFY AND ENCROACH ON THE WEST COAST.
PERSISTENT LOW-LEVEL SOUTHWEST FLOW WILL BE IMPACTING THE COASTAL
RANGES OF WASHINGTON/OREGON WITH A TENDENCY FOR THE FLOW TO
GRADUALLY BACK IN NATURE WITH TIME AS THE TROUGH AMPLIFIES, BUT
ALSO AS MULTIPLE WAVES OF LOW PRESSURE RIDE NORTHEAST UP ALONG AN
ATTENDANT FRONT. ONE FRONTAL WAVE WILL APPROACH VANCOUVER ISLAND
BY THURSDAY EVENING, WITH A SECOND WAVE APPROACHING BY FRIDAY
MORNING A BIT FARTHER SOUTH DOWN TOWARD COASTAL AREAS OF NORTHWEST
OREGON AND SOUTHWEST WASHINGTON. THERE IS VERY MODEST SPREAD WITH
THE TIMING DETAILS OF THESE WAVES, BUT THERE IS EXCELLENT
AGREEMENT OUT OF THE GUIDANCE IN BRINGING SOME VERY STRONG ONSHORE
FLOW INTO THE COASTAL RANGES AS A SOUTHWEST LOW-LEVEL JET OF AS
MUCH AS 70 TO 80 KTS IS EXPECTED TO BE ARRIVING JUST AHEAD OF THE
FRONT AND THESE SURFACE WAVES THURSDAY NIGHT AND FRIDAY MORNING.
ADDITIONAL WAVE ACTIVITY IS FORECAST TO LIFT UP ALONG THE FRONT
FRIDAY NIGHT AND SATURDAY AS THE FRONT SETTLES SLOWLY
SOUTHEASTWARD AND BEGINS TO EDGE INLAND FARTHER SOUTH DOWN ACROSS
NORTHWEST CALIFORNIA. THE 12Z UKMET SATURDAY APPEARS TO BE A
LITTLE TOO SLOW WITH THE WAVE ACTIVITY AND IT ASSOCIATED FRONTAL
TIMING, WHEREAS THE 12Z GFS MAY BE A TAD TOO FAST. A GENERAL MODEL
BLEND SHOULD SUFFICE WITH THE DETAILS OF ALL OF THIS ENERGY GOING
THROUGH ABOUT 60 HOURS, BUT THEREAFTER, A BLEND OF THE 12Z ECMWF,
AND THE ENSEMBLE MEANS (00Z ECENS MEAN AND 12Z GEFS MEAN) WILL BE
PREFERRED GIVEN BETTER OVERALL CLUSTERING.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
ORRISON
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