Prognostic Meteorological Discussion
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FXUS10 KWNH 051845
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 PM EDT THU MAY 05 2016

VALID MAY 05/1200 UTC THRU MAY 09/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

12Z MODEL EVALUATION INCLUDING PREFERENCES/CONFIDENCE

GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.

...SYSTEM MOVING INTO THE SOUTHWEST AND GREAT BASIN...CONTINUING
INTO THE CENTRAL ROCKIES AND ADJACENT PLAINS THIS WEEKEND...

PREFERENCE: GFS/UKMET/ECMWF CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 06Z-12Z NAM IS SLOW/LOWERS HEIGHTS FURTHER SOUTHWEST WITH THE
500 MB TROUGH THAN THE OTHER MODELS ACROSS AZ/ADJACENT NORTHWEST
MEXICO WITH THIS SYSTEM ON SATURDAY NIGHT/SUNDAY MORNING.  THE
OTHER MODELS SHOW VERY GOOD AGREEMENT, SO PREFER A CONSENSUS OF
THE CANADIAN/UKMET/GFS/12Z ECMWF AND THE 12Z GEFS MEAN.  THE 12Z
ECMWF TRENDED WEAKER WITH THE 700 MB LOW IN WY DAY 3...BRINGING IT
INTO BETTER AGREEMENT WITH THE OTHER MODELS.  THE 00Z ECMWF
ENSEMBLE MEAN CLUSTERED WELL WITH THE SREF MEAN/GEFS MEAN.


...LOW MOVING EAST OF NEW ENGLAND TONIGHT TO NOVA SCOTIA AND
BEYOND FRI....

PREFERENCE: 12Z ECMWF/NAM BLEND
CONFIDENCE: AVERAGE

THE 12Z GUIDANCE IS SHOWING A TREND TOWARDS CONVERGENCE OF
SOLUTIONS, ALTHOUGH THE 12Z GFS/06Z GEFS MEAN ARE STILL EAST OF
THE NAM/ECMWF/UKMET/09Z SREF MEAN/12Z CANADIAN GLOBAL LOW TRACK
FORECASTS.  A CONSENSUS APPROACH WOULD TAKE THE LOW WEST OF THE
GFS/GEFS MEAN.  THE 12Z UKMET MARKS THE SLOW EDGE OF THE GUIDANCE
SUITE.  THIS IS CONSIDERED A LOW PROBABILITY SOLUTION AS THE LOW
IS EJECTING DOWNSTREAM FROM THE CLOSED LOW IN THE MID ATLANTIC AND
NO BLOCK IS IN PLACE TO PREVENT STEADY FORWARD PROGRESSION.


LOW DRIFTING NORTH ACROSS THE MID-ATLANTIC FRIDAY/SATURDAY

PREFERENCE: 09Z SREF MEAN/12Z GEFS MEAN BLEND
CONFIDENCE: AVERAGE

THE MODELS PERSIST IN SHOWING TIMING/INTENSITY DIFFERENCES WITH
THE LOW AS IT MOVES SLOWLY NORTH NEAR THE MID ATLANTIC COAST.  THE
12Z ECMWF/UKMET ARE ON THE FAST SIDE OF THE GUIDANCE SUITE IN
MOVING THE LOW NORTH THROUGH 00Z SAT.  THE 00Z ECMWF ENSEMBLE MEAN
SHOWS A PROGRESSION A FEW HOURS SLOWER THAN THE OPERATIONAL
RUN...AND CLUSTERS WELL WITH THE 12Z GEFS MEAN/09Z SREF MEAN.  DUE
TO GOOD OVERLAP/CLUSTERING OF THESE SOLUTIONS... PREFER A
COMPROMISE OF THOSE SOLUTIONS.  THE 12Z GFS IS AT TIMES DEEPER
WITH THE 700 MB CLOSED LOW AND SLOWER TO WEAKEN THE LOW THAN OTHER
GUIDANCE...WITH THE MEAN CLOSER TO THE INTENSITY OF THE OTHER
MODELS/ENSEMBLE MEANS.  CONSEQUENTLY...LOW WEIGHTING SHOULD ALSO
BE PLACED ON THE OPERATIONAL GFS/GFS PARALLEL AND MORE ON THE GFS
ENSEMBLE MEAN.

...SYSTEM CROSSING THE PACIFIC NORTHWEST AND NORTHERN ROCKIES
SATURDAY NIGHT...DRIFTING EAST ON TO THE NORTHERN HIGH PLAINS
SUN...

PREFERENCE: CONSENSUS OF 12Z GEFS MEAN/12Z GFS/12Z CANADIAN
GLOBAL/UKMET
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS/ENSEMBLE MEANS SHOW AN UPPER LEVEL TROUGH MOVING FROM
THE EASTERN PACIFIC MOVING ONSHORE SAT LATE AFTERNOON/EVENING AND
CONTINUING INTO THE NORTHERN ROCKIES SAT NIGHT/EARLY SUN AND
FURTHER EAST ON TO THE NORTHERN HIGH PLAINS SUNDAY.  TYPICAL
AMPLITUDE DIFFERENCES AND TIMING DIFFERENCES EXIST IN THE GUIDANCE
SUITE.  THE 12Z ECMWF HAS SHARPENED THE WAVE AMPLITUDE AND MOVED
THE 500 MB TROUGH EAST FASTER...
WHICH MAKES IT FASTER TO LOWER HEIGHTS IN THE NORTHERN ROCKIES AND
HIGH PLAINS THAN THE OTHER MODELS. THE BIG DIFFERENCE SIN WITH THE
TRACK OF THE CLOSED LOW IN WESTERN CANADA...WITH DIFFERENCES LOWER
IN MAGNITUDE AND/OR TIMING IN THE US. THE ECMWF ENSEMBLE MEAN WAS
NOT QUITE AS AMPLIFIED AS THE OPERATIONAL RUN AND IN BETTER
AGREEMENT WITH THE GFS.  THE 12Z CANADIAN GLOBAL NOW CLUSTERS
BETTER TIMING WISE WITH THE OTHER MODELS/ENSEMBLE MEANS. THE 09Z
SREF MEAN AND 12Z GEFS MEAN CLUSTER WELL WITH THE OPERATIONAL
NAM/GFS SO A CONSENSUS OF THESE SOLUTIONS IS PREFERRED...ALONG
WITH THE UKMET.

...FRONT CROSSING THE UPPER MS VALLEY FRI/GREAT LAKES TO NEW YORK
AND MID ATLANTIC SATURDAY/NEW ENGLAND SUNDAY...

PREFERENCE: MULTI-MODEL CONSENSUS/12Z GEFS MEAN
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS ARE IN GOOD AGREEMENT ON THE DEPICTION OF A COLD FRONT
EMERGING FROM THE NORTHERN PLAINS THU NIGHT AND CROSSING THE UPPER
MS VALLEY FRI AND THE GREAT LAKES FRI NIGHT-SAT.  A WAVE OF LOW
PRESSURE IS FCST TO DEVELOP ALONG THE FRONT BY THE MODELS OVER
LAKE HURON AND SOUTHEAST ONTARIO FRI NIGHT AND MOVE INTO QUEBEC
SAT/SUN.  THE TRAILING FRONT CROSSES NY/MID ATLANTIC SAT NIGHT AND
NEW ENGLAND SUN.  MINOR TIMING/DIFFERENCES AMONG THE
MODELS/ENSEMBLE MEANS ARE NOTED WITH A CONSENSUS APPROACH USED TO
MITIGATE THESE DIFFERENCES.  NO ONE FORECAST STANDS OUT AS AN
OUTLIER THROUGH 12Z SUN...WITH THE 12Z NAM BECOMING THE SLOWER
MOVING FORECAST WITH LOW PRESSURE IN QUEBEC. THE 12Z UKMET CHANGED
CONTINUITY AND ASSERTIVELY LOWERS HEIGHTS IN NEW ENGLAND MORE THAN
OTHER MODELS SUN SO IS CONSIDERED TO BE A LOW PROBABILITY SOLUTION.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

PETERSEN

$$





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