Prognostic Meteorological Discussion
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000
FXUS10 KWNH 250431
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1230 AM EDT SAT APR 25 2015

VALID APR 25/0000 UTC THRU APR 28/1200 UTC

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

00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS

...DEEP TROUGH/CLOSED LOW DIGGING INTO SOUTHWEST U.S. THIS
WEEKEND...
...LOW PRESSURE DEVELOPING OVER THE SOUTHERN PLAINS BY MON...

PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THERE IS FAIRLY GOOD MASS FIELD AGREEMENT ALOFT WITH THE DETAILS
OF THE UPPER TROUGH AND CLOSED LOW EVOLUTION OVER THE FOUR CORNERS
REGION AND OUT INTO THE SOUTHERN PLAINS THROUGH MON. MORE NOTABLE
DIFFERENCES THOUGH BEGIN TO SHOW AT THE END OF THE PERIOD AT THE
SURFACE WHEN THE 12Z UKMET AND 00Z NAM BEGIN TO FOCUS A
BETTER-DEFINED AREA OVER SOUTHERN LA OR JUST OFFSHORE. THE
MULTI-MODEL CONSENSUS TENDS TO SUGGEST A BROADER AREA OF LOW
PRESSURE OVER THE NORTHWEST GULF OF MEXICO BY THE END OF THE
PERIOD. THE LATEST GEFS MEAN AND ECENS MEAN GENERALLY FAVOR THE
BROAD LOW PRESSURE SCENARIO. STRONGER MODEL CLUSTERING OVERALL
FAVORS A BLEND OF THE GFS AND ECMWF.


...SOUTHERN STREAM TROUGH TRAVELING FROM THE PLAINS TO THE
MID-ATLANTIC THROUGH SUN...
...ASSOCIATED SURFACE LOW CROSSING THE REGION...

PREFERENCE: NON-GEM CONSENSUS
CONFIDENCE: AVERAGE

THERE IS BETTER MASS FIELD AGREEMENT AMONG THE GLOBAL MODELS WITH
THE DETAILS OF THE SOUTHERN STREAM TROUGH CROSSING THE CENTRAL
PLAINS CURRENTLY AND ITS EXPECTED TRACK TO THE EAST INTO THE
MID-ATLANTIC BY SUN. THE ENERGY IS FORECAST TO DAMPEN OUT RATHER
QUICKLY DOWNSTREAM OVER THE OH VALLEY AND MID-ATLANTIC REGION AS
IT ENTERS CONFLUENT LARGER SCALE FLOW SOUTH OF THE DEEP CLOSED LOW
OVER THE NORTHEAST. NEVERTHELESS...A WAVE OF LOW PRESSURE WILL
TRACK EAST FROM THE CENTRAL PLAINS TO JUST WEST OF THE CENTRAL
APPALACHIANS BY SAT NIGHT...WITH A LEAD AREA OF LOW PRESSURE
DEVELOPING ALONG THE MID-ATLANTIC COAST AND THEN BECOMING THE
DOMINANT LOW OFFSHORE ON SUN. THE 12Z GEM IS STILL A LITTLE SLOWER
THAN THE MULTI-MODEL CONSENSUS WITH THE TRAILING LOW CENTER. THE
REST OF THE GUIDANCE IS REASONABLY WELL CLUSTERED...THUS A NON-GEM
CONSENSUS WILL BE PREFERRED.


...DEEP CLOSED LOW REMAINING ACROSS NEW ENGLAND...

PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF
CONFIDENCE: AVERAGE

THERE ARE SEVERAL SMALL SCALE VORTICITY MAXIMA DEPICTED IN THE
GUIDANCE THAT WILL MOVE THROUGH THE WESTERN PORTION OF THIS LARGE
CLOSED LOW CURRENTLY OVER NEW ENGLAND. THE RESULT WILL BE AN
ELONGATION OF THE CLOSED LOW AS THE MEAN CENTER OF IT GRADUALLY
SHIFTS OFFSHORE SOUTHEAST CANADA THROUGH THE PERIOD. THE 12Z GEM
AND 12Z UKMET HANG MORE ENERGY BACK OVER NEW ENGLAND COMPARED TO
THE 00Z NAM/00Z GFS AND 12Z ECMWF. THE STRONGER MODEL CLUSTERING
FAVORS A BLEND OF THE GFS AND ECMWF AND THIS IS SUPPORTED BY THE
18Z GEFS MEAN AND 12Z ECENS MEAN.


...TROUGH/FRONT CROSSING THE NORTHERN PLAINS/UPPER MS VALLEY SUN
THRU TUES...

PREFERENCE: 12Z ECMWF
CONFIDENCE: AVERAGE

A NORTHERN STREAM TROUGH WILL GRADUALLY CROSS THE NORTHERN PLAINS
AND UPPER MIDWEST SUN THROUGH TUES ALONG WITH AN ATTENDANT FRONTAL
ZONE. THE 00Z NAM AND 00Z GFS GRADUALLY BECOME SLOWER THAN THE 12Z
ECMWF/12Z UKMET AND TO A LESSER EXTENT THE 12Z GEM. THE 12Z UKMET
BECOMES THE DEEPEST SOLUTION BY THE END OF THE PERIOD. THE
NON-NCEP SOLUTIONS MINUS THE UKMET HAVE STRONGER SUPPORT FROM THE
18Z GEFS MEAN AND 12Z ECENS MEAN...AND SO A PREFERENCE TOWARD THE
12Z ECMWF IS CURRENTLY SUGGESTED.


...TROUGH/FRONT APPROACHING THE PACIFIC NORTHWEST BY TUES...

PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF
CONFIDENCE: ABOVE AVERAGE

THE 00Z GFS HAS TRENDED TOWARD THE MULTI-MODEL CONSENSUS WITH WITH
RESPECT TO THE MID LEVEL TROUGH AND ASSOCIATED COLD FRONT
APPROACHING THE PACIFIC NORTHWEST BY TUES. THE OUTLIER SOLUTIONS
ARE GENERALLY THE 12Z UKMET WHICH HAS THE SHARPEST TROUGH...AND
THE 00Z NAM WHICH IS THE FLATTEST. THE STRONGER MODEL CLUSTERING
FAVORS A BLEND OF THE 00Z GFS AND 12Z ECMWF AND THIS WILL BE THE
PREFERENCE.

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

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

ORRISON

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