Prognostic Meteorological Discussion
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FXUS10 KWNH 201847
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 PM EDT SUN AUG 20 2017

VALID AUG 20/1200 UTC THRU AUG 24/0000 UTC

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

...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL
PREFERENCES/FORECAST CONFIDENCE...


...MID-LEVEL PERTURBATION TRACKING TOWARD THE UPPER GREAT LAKES
DURING THE NEXT 6 TO 12 HOURS...

FINAL PREFERENCE: A NON-00Z ECMWF ENSEMBLE MEAN MODEL CONSENSUS
FORECAST CONFIDENCE: ABOVE AVERAGE

WATER VAPOR IMAGERY AND MID-LEVEL MODEL FIELDS SHOW A PRONOUNCED
SHORTWAVE PUSHING INTO FAR EASTERN IA WITH RESIDUAL CONVECTION
IMPACTING AREAS IN THE WAKE ALONG AN OLD MCS OUTFLOW BOUNDARY.
RECENT SOLUTIONS AGREE ON CARRYING THIS VORTICITY CENTER TOWARD
THE UPPER OH VALLEY BY 21/0600Z WITH THE FEATURE BEING STRETCHED
OUT AND WEAKENED. THE LATEST 12Z MODEL GUIDANCE HAVE SHIFTED THEIR
FORECAST SOUTH MORE TOWARD THE CURRENT POSITION OF THE SHORTWAVE.
THE EXCEPTION AT THIS POINT IS THE 00Z ECMWF ENSEMBLE MEAN AS IT
IS AN OLDER PIECE OF GUIDANCE. A NON-00Z ECMWF ENSEMBLE MEAN
CONSENSUS SOLUTION IS RECOMMENDED.


...TUTT CELL SLIDING WESTWARD ACROSS THE GULF OF MX...

FINAL PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: AVERAGE

VISIBLE SATELLITE IMAGERY SHOWS A BROAD CYCLONIC CIRCULATION
ASSOCIATED WITH A TUTT CELL MOVING WESTWARD FROM THE EASTERN GULF
OF MX. THE MOST VERTICALLY DEVELOPED CLOUD FEATURES REMAIN ON THE
EASTERN FLANK WITH SOME FLAREUPS JUST WEST OF THE LOWER FL KEYS.
THE WESTWARD TRACK OF THIS FEATURE SHOULD CONTINUE AS A MID-LEVEL
594-DM RIDGE EXPANDS TOWARD THE OZARKS/LOWER MS VALLEY  IN TIME.
GENERAL AGREEMENT EXISTS IN TAKING THIS SYSTEM TOWARD THE TX GULF
COAST BY 23/0000Z WITH VORTICITY CENTERS STRETCHING SSW-NNE OVER
THE COASTAL WATERS. FURTHER SHEARING OCCURS THEREAFTER WITH
BUILDING MODEL SPREAD ON DAY 3/WEDNESDAY. THE END OF THE FORECAST
CONTINUES TO BE PLAGUED BY UNCERTAINTIES WITH THE REMAINS OF THIS
SYSTEM SO WILL MAINTAIN A GENERAL MODEL COMPROMISE.


...POTENT IMPULSE LIFTING OUT OF THE SOUTHERN ROCKIES TOWARD THE
CENTRAL HIGH PLAINS...

FINAL PREFERENCE: BLEND OF THE 12Z NAM/GFS/ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

A SUFFICIENTLY DEVELOPED IMPULSE IS CURRENTLY LIFTING NORTHWARD
INTO WEST-CENTRAL NM AND WILL CONTINUE TO MOVE NORTHEASTWARD
DURING THE NEXT DAY OR SO. THE 09Z SREF MEAN SEEMS TO BE THE
SLOWEST IN CARRYING THIS SYSTEM INTO EASTERN CO/WESTERN KS WHERE
THE SPEED WILL GRADUALLY INCREASE AS IT IS PICKED UP BY AMPLIFIED
NORTHERN STREAM FLOW. ACTIVE CONVECTION WILL LIKELY ACCOMPANY THIS
SHORTWAVE AND WILL ERR ON THE QUICKER SIDE WHICH INCLUDES THE 12Z
NAM/GFS/ECMWF. FOR NOW WILL KEEP FORECAST CONFIDENCE SLIGHTLY
BELOW AVERAGE GIVEN BUILDING UNCERTAINTIES WITH THE EVOLUTION OF
THIS SYSTEM.


...DEEP UPPER TROUGH AMPLIFYING ACROSS THE GREAT
LAKES/NORTHEASTERN U.S. BY TUESDAY/WEDNESDAY...
...ATTENDANT SURFACE CYCLONE AND PROGRESSIVE COLD FRONT...

FINAL PREFERENCE: BLEND OF THE 12Z GFS/ECMWF
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

AMPLIFIED FLOW INITIALLY CONFINED TO CENTRAL CANADA SHOULD
GRADUALLY DIG FURTHER SOUTH BRINGING SUFFICIENT HEIGHT FALLS FROM
THE NORTH-CENTRAL U.S. TOWARD NEW ENGLAND DURING THE PERIOD. THIS
IS EXPECTED TO BE IN RESPONSE TO AN UPSTREAM SHORTWAVE APPROACHING
SOUTHERN SASKATCHEWAN/MANITOBA BY MIDDAY MONDAY. THIS WILL SLIDE A
FAIRLY IMPRESSIVE MID/LATE AUGUST UPPER TROUGH THROUGH THE UPPER
MIDWEST INTO THE NORTHEASTERN U.S. THE 12Z GFS 500-MB FORECAST
HEIGHT ANOMALIES ARE AROUND 2 STANDARD DEVIATIONS BELOW AVERAGE.
ENSEMBLE SPAGHETTI PLOTS SHOW FAIRLY GOOD CLUSTERING AMONG THE
INDIVIDUAL MEMBERS. SUCH PLOTS ALSO SHOW THE 00Z CMC/UKMET TO BE A
BIT LESS AMPLIFIED WITH THE RIDGE/TROUGH COUPLET ACROSS
CENTRAL/EASTERN NORTH AMERICA...RESPECTIVELY. THERE ARE ALSO A FEW
DIFFERENCES IN THE SURFACE LOW TRACK WITH MANY OF THE ECMWF
ENSEMBLES WEST OF THE GEFS ACROSS ONTARIO. WILL CONTINUE TO SPLIT
THE DIFFERENCE BETWEEN THE 12Z GFS/ECMWF.


...NEARLY QUASI-STATIONARY UPPER LOW LINGERING ACROSS
SOUTHERN/CENTRAL CA...

FINAL PREFERENCE: A NON-12Z CMC MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

A BROAD CIRCULATION GENERALLY REMAINS A FIXTURE IN THE FORECAST
ACROSS SOUTHERN/CENTRAL CA THROUGHOUT THE PERIOD. WHILE SOLUTIONS
ARE CLOSE TO ONE ANOTHER...THE 12Z CMC TRENDED EAST WHICH BRINGS
TO THE FAR EASTERN SIDE OF THE SPREAD. OF NOTE...THE 12Z ECMWF DID
MOVE AWAY FROM ITS PREVIOUS SLOWER SOLUTION AS EXPECTED. THE
FAVORED SOLUTION WILL BE A NON-12Z CMC MODEL COMPROMISE.


...AMPLIFIED FLOW REACHING THE PACIFIC NORTHWEST/BRITISH COLUMBIA
COAST BY MID-WEEK...

FINAL PREFERENCE: BLEND OF THE 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: AVERAGE

TOWARD THE END OF THE FORECAST PERIOD...AMPLIFIED FLOW RETURNS TO
THE PACIFIC NORTHWEST NORTHWARD INTO BRITISH COLUMBIA. COMPARING
THE SPAGHETTI PLOTS FROM THE PAST FOUR ENSEMBLE SPAGHETTI PLOTS
HAS SHOWN THE GEFS SOLUTIONS TO BE WEST OF THE STRONGER
CLUSTERING. PLAN ON FAVORING THE MORE CONSISTENT 12Z ECMWF/00Z
ECMWF ENSEMBLE MEAN.



www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

RUBIN-OSTER

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