Prognostic Meteorological Discussion
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FXUS10 KWNH 280429
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1229 AM EDT THU APR 28 2016

VALID APR 28/0000 UTC THRU MAY 01/1200 UTC

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

00Z MODEL EVALUATION...INCLUDING THE NAM/GFS AND PRELIMINARY MODEL
PREFERENCES


...LOW PRESSURE SYSTEM OVER THE CENTRAL PLAINS/MIDWEST MOVING TO
THE MID-ATLANTIC BY FRIDAY...

PRELIMINARY PREFERENCE: 12Z ECMWF
CONFIDENCE: AVERAGE

THE UPPER-LEVEL LOW OVER THE CENTRAL PLAINS/MIDWEST TONIGHT IS
FORECAST BY ALL MODELS TO OPEN INTO A WEAKER SHORTWAVE AS IT MOVES
EAST ACROSS THE GREAT LAKES TO THE MID-ATLANTIC STATES BY FRIDAY.
THE OCCLUDED SURFACE LOW WILL WEAKEN OVER THE OHIO VALLEY WHILE A
NEW SURFACE LOW DEVELOPS OVER THE CAROLINAS AND MOVES INTO THE
ATLANTIC OCEAN. THE GFS KEEPS THE SHORTWAVE STRONGER (AND SLIGHTLY
SLOWER) AS IT CROSSES THE GREAT LAKES RELATIVE TO THE NAM AS WELL
AS THE 12Z ECMWF. AT THE SURFACE...THE GFS SEEMS TO BE MORE
SIMILAR TO OTHER GUIDANCE...AND IS WELL WITHIN CONSENSUS AS THE
NEW SURFACE LOW DEVELOPS OVER THE NORTH CAROLINA THURSDAY AND
MOVES NORTHEAST INTO THE ATLANTIC. HOWEVER...GIVEN THE ISSUES WITH
THE GFS WITH THE AMPLITUDE OF THE UPPER TROUGH...PREFER THE 12Z
ECMWF WHICH HAS THE SUPPORT OF THE 12Z ECMWF ENSEMBLE MEAN AS WELL
AS THE 18Z GEFS MEAN.


...LOW PRESSURE SYSTEM CROSSING THE SOUTHWESTERN U.S. ON THURSDAY
AND EMERGING INTO THE SOUTHERN PLAINS ON FRIDAY...

PRELIMINARY PREFERENCE: GFS/12Z ECMWF COMPROMISE THROUGH 00Z SUNDAY
                        12Z ECMWF AFTER 00Z SUNDAY
CONFIDENCE: AVERAGE

THE NAM AND GFS ARE COMPARABLE TO THE MODEL CONSENSUS WITH RESPECT
TO THIS FEATURE THROUGH THURSDAY NIGHT. AS THE SURFACE LOW EMERGES
INTO THE SOUTHERN PLAINS ON FRIDAY...THE NAM BECOMES A LITTLE
FASTER THAN CONSENSUS WITH THE UPPER-LEVEL TROUGH AND WITH THE
SURFACE LOW. THE GFS LOOKS SIMILAR TO CONSENSUS AT THE
UPPER-LEVELS...BUT ITS SURFACE LOW LAGS A LITTLE SLOWER THAN
CONSENSUS (IT DOES HAVE THE SUPPORT OF ITS ENSEMBLE MEAN HOWEVER).
THROUGH SUNDAY...WILL PRELIMINARILY RECOMMEND A COMPROMISE BETWEEN
THE 12Z ECMWF (WHICH IS A LITTLE FASTER THAN ITS ENSEMBLE MEAN)
AND THE SLOWER 00Z GFS. STARTING SUNDAY AFTERNOON...THE GFS BEGINS
TO WEAKEN THE UPPER-LEVEL WAVE A LITTLE MORE QUICKLY THAN
CONSENSUS... AND THUS SHUNTS THE SURFACE LOW EAST INTO THE OHIO
VALLEY A LITTLE MORE QUICKLY. AS A RESULT...WILL RECOMMEND THE 12Z
ECMWF AFTER 00Z SUNDAY...AS ITS SLOWER SOLUTION ALIGNS MORE WITH
THE DETERMINISTIC AND ENSEMBLE GUIDANCE CONSENSUS.


...UPPER-LEVEL TROUGH/PACIFIC COLD FRONT REACHING THE NORTHWEST
THURSDAY NIGHT...
...CLOSED UPPER-LEVEL LOW OVER THE SOUTHWEST ON SATURDAY...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE GFS IS INITIALLY A LITTLE FASTER THAN CONSENSUS WITH BRINGING
THE UPPER TROUGH INTO THE PACIFIC NORTHWEST ON FRIDAY...WHILE THE
NAM IS WELL WITHIN THE MIDDLE OF CONSENSUS. BY THE TIME THE TROUGH
BEGINS TO CLOSE OFF INTO AN UPPER LOW OVER THE SOUTHWESTERN U.S.
ON SATURDAY THE NAM AND GFS ARE BOTH WELL WITHIN A REASONABLE
RANGE OF CONSENSUS THAT INCLUDES THE 12Z ECMWF/UKMET AS WELL AS
THE 12Z ECMWF ENSEMBLE MEAN/18Z GEFS MEAN. THEREFORE...A GENERAL
MODEL COMPROMISE IS RECOMMENDED.


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

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

RYAN

$$





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