Prognostic Meteorological Discussion
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000
FXUS10 KWNH 301652
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1251 PM EDT SAT AUG 30 2014

VALID AUG 30/1200 UTC THRU SEP 03/0000 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...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...UPPER-LEVEL ENERGY LIFTING FROM THE LOWER MS VALLEY UP TOWARD
THE OH VALLEY...

PRELIMINARY PREFERENCE: 12Z GFS AND 00Z ECMWF/CMC ARE USEFUL
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

AN UPPER LOW WHICH IS ALONG THE WESTERN GULF COAST HAS BEEN
RESPONSIBLE FOR VERY HEAVY RAINFALL THIS MORNING ACROSS LA. AS THE
SYSTEM LIFTS NORTH AND EAST...IT WILL GRADUALLY SHEAR AS IT MOVES
THROUGH THE TN VALLEY AND EVENTUALLY INTO THE CENTRAL
APPALACHIANS. THE 12Z NAM/00Z UKMET SHOW TWO DISTINCT WAVES MOVING
THROUGH THE REGION WHILE THE 12Z GFS AND 00Z ECMWF/CMC FOCUS ON
ONE SHORTWAVE. FEEL MORE COMFORTABLE LEANING ON THIS LATTER
CLUSTERING AS THEY FIT MORE REASONABLY WITH THE ENSEMBLE MEANS.


...SHORTWAVE MIGRATING FROM THE UPPER MS VALLEY TO NORTHERN NEW
ENGLAND...

PRELIMINARY PREFERENCE: A NON-00Z CMC MODEL COMPROMISE
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

NORTHERN STREAM ENERGY MOVING THROUGH THE UPPER GREAT LAKES WILL
QUICKLY MOVE THROUGH THE GREAT LAKES AND EVENTUALLY INTO NORTHERN
NEW ENGLAND. LIKE THE 00Z CMC YESTERDAY...IT BECOMES FASTER THAN
THE MODEL CONSENSUS FAIRLY EARLY IN THE PERIOD. GIVEN THIS
ASSESSMENT WILL RECOMMEND A NON-00Z CMC MODEL COMPROMISE.


...LONGWAVE TROF SETTING UP ACROSS THE WESTERN TO CENTRAL U.S...
...ADVANCING COLD FRONT...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z ECMWF WITH THE 06Z
GEFS/00Z ECMWF ENSEMBLE MEANS
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE PATTERN BECOMES MORE PROGRESSIVE DURING THIS HOLIDAY WEEKEND
AS HEIGHT FALLS TRANSLATE FROM THE NORTHWESTERN U.S. TOWARD THE
MIDDLE OF THE COUNTRY. DURING THE INITIAL 24 HOURS OF THE
PERIOD...THERE IS SYNOPTIC AGREEMENT AMONG THE MODELS WHILE
DIFFERING WITH THE SHORTWAVE DETAILS. BY DAY 2...THE 12Z NAM
BECOMES SLOWER WITH THE PROGRESSION OF THE NORTHERN EXTENT OF THE
LONGWAVE TROF WHILE THE 00Z ECMWF/ECMWF ENSEMBLE MEAN CONTINUE
THEIR THEME OF DIGGING MORE ENERGY ON THE BACK SIDE OF THE TROF
ACROSS THE NORTHERN GREAT BASIN. THE PAST THREE SETS OF 564-DM
SPAGHETTI PLOTS SHOW THIS QUITE WELL WITH ONLY THE ECMWF ENSEMBLE
MEMBERS SUPPORTING THIS SOLUTION. DIFFERENCES BECOME RATHER LARGE
WITH THE POSITION OF THE SURFACE LOW(S) ACROSS ONTARIO. WILL LEAN
A LITTLE MORE HEAVILY ON THE ENSEMBLE MEANS GIVEN THE GROWING
SPREAD BUT INCORPORATE PORTIONS OF THE 00Z ECMWF SOLUTION AS IT
FITS THEM MOST CLOSELY. THE AFOREMENTIONED DIFFERENCE IN THE ECMWF
SOLUTIONS DOES NOT APPEAR TO HAVE DISCERNIBLE IMPACTS ON THE
RESULTANT PATTERN.


...AMPLIFYING SHORTWAVE NEARING THE PACIFIC NORTHWEST BY TUESDAY
AFTERNOON...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z ECMWF WITH THE 06Z
GEFS/00Z ECMWF ENSEMBLE MEANS
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

AS A LONGWAVE TROF EXTENDS FROM THE EASTERN PACIFIC INTO THE GREAT
LAKES REGION...ANOTHER AMPLIFIED SHORTWAVE WILL DIVE TOWARD THE
PACIFIC NORTHWEST BY EARLY/MID NEXT WEEK. THE 12Z NAM/GFS AND 00Z
CMC/UKMET FAVOR A SLOWER SOLUTION WHILE THE 00Z ECMWF IS
DEFINITELY QUICKER. THESE SOLUTIONS DO SEEM WITHIN REASON BASED ON
THE SPREAD IN THE SPAGHETTI PLOTS. FOR NOW WILL MIX BETWEEN THE
TWO CAMPS AND INCORPORATE ENSEMBLE MEANS FOR UNCERTAINTY PURPOSES.
A BLEND OF THE 00Z ECMWF WITH THE 06Z GEFS/00Z ECMWF ENSEMBLE
MEANS WILL FOLLOW SUIT WITH THE PREFERENCE DOWNSTREAM.


...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

$$





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