Prognostic Meteorological Discussion
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000
FXUS10 KWNH 201722
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
121 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 NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...


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

PRELIMINARY PREFERENCE: MODEL COMPROMISE BETWEEN THE 12Z NAM/GFS
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

WATER VAPOR IMAGERY AND MID-LEVEL MODEL FIELDS SHOW A PRONOUNCED
SHORTWAVE PUSHING INTO 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. RELATIVE TO THE CURRENT PLACEMENT OF THIS
SYSTEM...THE 00Z ECMWF/UKMET ARE DISPLACED TO THE NORTH SO WILL
RECOMMEND THE CLUSTER OF THE 12Z NAM/GFS HERE.


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

PRELIMINARY 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. DIFFICULT TO SAY WHICH
SOLUTION WILL VERIFY SO WILL LEAN ON A GENERAL MODEL COMPROMISE.


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

PRELIMINARY PREFERENCE: BLEND OF THE 12Z NAM/GFS
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 00Z CMC/09Z SREF MEAN SEEM 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. EVENTUALLY THE 00Z ECMWF SLOWS
DOWN CONSIDERABLY RELATIVE TO THE QUICKER CONSENSUS. ACTIVE
CONVECTION WILL LIKELY ACCOMPANY THIS SHORTWAVE AND WILL ERR ON
THE QUICKER SIDE WHICH IS MORE LIKE THE 12Z NAM/GFS. WILL SEE IF
ANY ADDITIONAL 12Z GUIDANCE JOINS THESE SOLUTIONS. 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...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

AMPLIFIED FLOW INITIALLY CONFINED TO CENTRAL CANADA SHOULD
GRADUALLY DIG FURTHER 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. THE 00Z CMC/UKMET ARE 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. AT THIS POINT...WILL JUST SPLIT THE
DIFFERENCE BETWEEN THE 12Z GFS/00Z ECMWF AND NOT CONSIDER THE 00Z
CMC/UKMET GIVEN THEIR DIVERGENCE FROM THE PACK.


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

PRELIMINARY PREFERENCE: A NON-00Z ECMWF 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 00Z ECMWF TROUGH POSITION IS WEST
OF ITS ENSEMBLE MEAN AND THE REST OF THE GROUP. WILL LIKELY SEE IT
MOVE EASTWARD IN THE 12Z RUN. FOR RIGHT NOW...WILL FAVOR A NON-00Z
ECMWF MODEL COMPROMISE.


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

PRELIMINARY PREFERENCE: BLEND OF THE 00Z ECMWF/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 00Z ECMWF/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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