Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8
000
FXUS10 KWNH 220452
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1251 AM EDT WED OCT 22 2014

VALID OCT 22/0000 UTC THRU OCT 25/1200 UTC

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

...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...UPPER LOW MOVING FROM THE MID-ATLANTIC TO COASTAL NEW ENGLAND
WEDNESDAY THROUGH FRIDAY...
...COASTAL SYSTEM AFFECTING THE NORTHEASTERN U.S...

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

A SLOW-MOVING CLOSED LOW WILL AFFECT A REGION STRETCHING FROM THE
MID-ATLANTIC UP TO NEW ENGLAND THROUGHOUT MUCH OF THE SHORT RANGE
PERIOD. WATER VAPOR IMAGERY SHOWS A MYRIAD OF EMBEDDED SHORTWAVES
SWIRLING AROUND THE UPPER LOW OVER THE MID-ATLANTIC. THE MODELS
DEPICT THIS FEATURE TRACKING OFFSHORE OF THE DELMARVA PENINSULA BY
MIDDAY WEDNESDAY BEFORE GRADUALLY LIFTING NORTHWARD. LIKE
YESTERDAY...THE ENSEMBLE MEANS...18Z GEFS/21Z SREF/12Z ECMWF
ENSEMBLE MEANS ARE FAIRLY CONSISTENT WITH ONE ANOTHER REGARDING
THE SURFACE LOW TRACK THROUGH THURSDAY. THE 00Z NAM IS WELL TO THE
NORTH OF THIS CLUSTER WHILE THE 12Z UKMET TAKES A MORE COASTAL
POSITION. BY 24/0000Z...THE ENSEMBLE LOW SCATTER PLOT SHOWS THE
12Z ECMWF ENSEMBLE MEMBERS ARE SLIGHTLY WEST OF THE 12Z GEFS MEAN.
THERE IS MUCH MORE SCATTER NOTED IN THE 12Z CMC ENSEMBLE MEMBERS.
EVENTUALLY THE SPREAD GROWS FURTHER BUT DOES REMAIN LOW ENOUGH TO
KEEP DETERMINISTIC MODELS IN THE SOLUTION. FEEL THE 00Z GFS/12Z
ECMWF HAVE THE BEST HANDLE ON THE LOW TRACK AND STAY WITHIN THE
CENTER OF THE SPREAD THROUGHOUT THE PERIOD. WPC WILL FAVOR A BLEND
OF THE 00Z GFS/12Z ECMWF WITH CONFIDENCE DEEMED A BIT BELOW
AVERAGE.


....SPLIT FLOW ACROSS THE CENTER OF THE COUNTRY...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z ECMWF WITH THE 12Z ECMWF
ENSEMBLE/18Z GEFS MEANS
FORECAST CONFIDENCE: BELOW AVERAGE

AN AXIS OF HEIGHT FALLS MOVING THROUGH THE NORTHERN ROCKIES SHOULD
REACH THE NORTHERN PLAINS AND UP INTO SOUTHERN
SASKATCHEWAN/MANITOBA BY 23/0000Z. THIS IS WHERE THE FORECAST
BECOMES MORE NEBULOUS AS THE FLOW BECOMES MORE SPLIT IN NATURE.
THE 12Z ECMWF/UKMET ARE FARTHER TO THE SOUTH WITH THE SOUTHERN
SPLIT ACROSS THE MIDDLE MS VALLEY ON THURSDAY MORNING. THE BIG
QUESTION IS HOW DEVELOPED WILL THE SYSTEM BE WHICH MOVES EASTWARD
TOWARD THE UPPER GREAT LAKES/OH VALLEY ON FRIDAY/SATURDAY. THE 00Z
NAM APPEARS TO BE THE OUTLIER HERE SHOWING A MORE SHEARED SYSTEM
IN THE FORECAST. BESIDES THE UNCERTAINTY IN STRENGTH...THE DEPTH
AND TIMING OF THIS SYSTEM ARE ALSO VARIABLE. THE 576-DM SPAGHETTI
PLOT SHOWS A MAJORITY OF THE 12Z ECMWF ENSEMBLE MEMBERS SUPPORTING
A SLOWER SOLUTION THAT DIGS WELL INTO THE TN VALLEY.
MEANWHILE...THE 12Z GEFS MEMBERS ARE MORE PROGRESSIVE AND FLATTER
WHICH APPEARS TO BE WHAT THE 00Z GFS IS ALIASING...ALBEIT IN A
FASTER MANNER. THIS SEPARATION IN CAMPS IS NOTED IN THE PAST TWO
SPAGHETTI PLOTS DATING BACK TO THE 00Z GUIDANCE ON OCTOBER 21. BY
25/1200Z...THE 12Z UKMET DROPS A CLOSED LOW DOWN TOWARD THE FL
PANHANDLE WHICH APPEARS MORE EXTREME AT THIS TIME. THE 12Z ECMWF
SEEMS TO STAY AT THE CENTER OF THE SPREAD RELATIVE TO THE FLATTER
00Z NAM/GFS AND DEEPER 12Z UKMET. WILL INCORPORATE ENSEMBLE MEANS
INTO THE SOLUTION AS WELL GIVEN THE HIGH AMOUNT OF SPREAD.


...INITIAL ENERGY CROSSING THE NORTHWESTERN CONUS...EVENTUAL TROF
OVER THE NORTHERN GREAT LAKES...
...POTENT SYSTEM APPROACHING THE PACIFIC NORTHWEST BY EARLY
SATURDAY...

PRELIMINARY PREFERENCE: INITIAL SYSTEM: MODEL COMPROMISE BETWEEN
THE 00Z GFS AND 12Z ECMWF/UKMET...SECOND SYSTEM: BLEND OF THE 00Z
GFS/12Z ECMWF
FORECAST CONFIDENCE: AVERAGE FOR BOTH

THE FIRST BATCH OF ENERGY WITH THIS SYSTEM WILL ADVANCE THROUGH
THE PACIFIC NORTHWEST DURING THE NEXT 24 TO 36 HOURS. EVENTUALLY
THIS UPPER TROF WILL TRANSLATE EASTWARD ACROSS SOUTH-CENTRAL
CANADA WHILE DRAGGING HEIGHT FALLS INTO THE UPPER MIDWEST/GREAT
LAKES LATE IN THE PERIOD. THE 00Z NAM IS BY FAR THE MOST AMPLIFIED
SOLUTION WITH LITTLE SUPPORT FROM THE ENSEMBLE MEANS.
MEANWHILE...THE 12Z CMC BECOMES RATHER SLOW BY FRIDAY/SATURDAY
WITH BETTER AGREEMENT SEEN IN THE 00Z GFS AND 12Z ECMWF/UKMET.
WILL FAVOR SOME SORT OF COMPROMISE BETWEEN THIS TRIO OF MODELS.

IN THE WAKE OF THIS INITIAL SYSTEM WILL BE A MUCH MORE AMPLIFIED
TROF NEARING THE PACIFIC NORTHWEST BY EARLY SATURDAY. THE 00Z NAM
IS A SLOW OUTLIER AND WILL BE REMOVED FROM CONSIDERATION HERE.
ALSO WILL NOT GO AS FAST AS THE 12Z UKMET WITH THE TROF MOVING
INLAND BY 25/1200Z. THE 564-DM SPAGHETTI PLOT SHOWS ONLY MODEST
SPREAD WITH THIS FEATURE AS GENERAL AGREEMENT IS NOTED BETWEEN THE
GEFS/ECMWF ENSEMBLE MEMBERS. THE PREFERENCE HERE IS A BLEND OF THE
00Z GFS/12Z ECMWF.


...FRONTAL ZONE STALLED ALONG THE FL KEYS THROUGHOUT THE PERIOD...

PRELIMINARY PREFERENCE: A NON-00Z NAM MODEL COMPROMISE
FORECAST CONFIDENCE: AVERAGE

MODELS SHOW A STATIONARY BOUNDARY LINGERING ACROSS SOUTH FL AND
DOWN ACROSS THE FL KEYS THROUGHOUT MUCH OF THE PERIOD. THE
GUIDANCE SHOW SOME VARIABILITY IN THE PLACEMENT AND TIMING OF
WAVES TRACKING ALONG THIS BOUNDARY. IN PARTICULAR...THE 00Z NAM IS
A FARTHER TO THE NORTH WHICH CARRIES HEAVY RAINFALL UP INTO A
MAJORITY OF SOUTH FL. WILL FAVOR A NON-00Z NAM MODEL COMPROMISE
FOR THIS AREA.



...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

RUBIN-OSTER

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.