Prognostic Meteorological Discussion
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FXUS10 KWNH 200423
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1122 PM EST SUN FEB 19 2017

VALID FEB 20/0000 UTC THRU FEB 23/1200 UTC

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

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

...CLOSED LOW DEVELOPMENT NEAR NORTHERN NEW ENGLAND/NOVA SCOTIA
THROUGH MON...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM THROUGH MON...SO
WILL PREFER A GENERAL MODEL COMPROMISE.


...SHORTWAVE CROSSING OUT INTO THE NORTHERN PLAINS...
...UPPER TROUGH EJECTING OUT OF THE SOUTHWEST INTO THE PLAINS...
...ENERGY REACHING THE UPPER MIDWEST MON NIGHT...
...SURFACE LOW PRESSURE/COLD FRONT CROSSING THE PLAINS/MIDWEST
THROUGH TUES...

PREFERENCE: NON-NAM CONSENSUS
CONFIDENCE: AVERAGE

A NORTHERN STREAM TROUGH EJECTING OUT ACROSS THE NORTHERN PLAINS
ON MON COUPLED WITH THE NORTHERN PORTION OF THE SOUTHERN STREAM
TROUGH EJECTING OUT OF THE SOUTHWEST WILL WORK IN TANDEM TO DRIVE
LOW PRESSURE ACROSS THE DAKOTAS EARLY MON AND THEN UP TOWARD
HUDSON BAY ON TUES AS A TRAILING COLD FRONT CROSSES THE
PLAINS/MIDWEST AND GREAT LAKES. THE 00Z NAM BECOMES A BIT SLOWER
THAN THE MODEL CONSENSUS WITH THE ENERGY IN THE SOUTHERN STREAM
THAT GETS PULLED NORTHEAST IN TANDEM WITH THE NORTHERN STREAM
TROUGH AND ENDS UP WITH A SLOWER FRONTAL PROGRESSION. THE
REMAINING MODELS ARE REASONABLY WELL CLUSTERED... WITH THEIR MASS
FIELDS...AND SO WILL PREFER A NON-NAM CONSENSUS.


...SHORTWAVE/SURFACE LOW APPROACHING CROSSING THE WEST COAST ON
MON...

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

THE 00Z NAM IS A TAD SLOWER WITH THE SHORTWAVE/SURFACE LOW
ARRIVING EARLY MON ACROSS WESTERN OREGON COMPARED TO THE
WELL-CLUSTERED 00Z GFS/12Z UKMET AND 12Z ECMWF. THE 12Z CMC IS A
WEAK OUTLIER SOLUTION. THEREFORE...WILL PREFER THE MODEL CONSENSUS
WHICH CLOSEST TO A 00Z GFS/12Z UKMET AND 12Z ECMWF BLEND.


...SHORTWAVE/SURFACE LOW CROSSING THE WEST COAST MON NIGHT/EARLY
TUES...
...SURFACE LOW REACHING THE NORTHERN PLAINS/UPPER MIDWEST BY WED...
...SURFACE LOW/COLD FRONT CROSSING THE GREAT LAKES BY THURS...

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

THE 12Z CMC IS THE MOST PROGRESSIVE WITH THE NEXT IN A SERIES OF
SHORTWAVE/SURFACE LOWS THAT IMPACT THE WEST COAST BY MON NIGHT AND
EARLY TUES. THE 00Z NAM ON THE OTHER HAND IS THE SLOWEST
SOLUTION...WITH THE 00Z GFS/12Z UKMET AND 12Z ECMWF CLUSTERED IN
BETWEEN. THE MODELS TAKE THIS ENERGY QUICKLY INLAND AND OUT INTO
THE NORTHERN PLAINS BY WED WITH A PROGRESSIVE SURFACE LOW THAT
THEN TRAVELS ACROSS THE UPPER MIDWEST THROUGH WED. BY THURS...THIS
SURFACE LOW WILL BE DEEPENING WHILE CROSSING THE GREAT LAKES
REGION AS TRAILING COLD FRONT APPROACHES THE OH VALLEY. THROUGH
THE LATER STAGES OF THE PERIOD...THE 12Z CMC REMAINS A PROGRESSIVE
OUTLIER...WITH THE 00Z NAM SLOWER AND TOO DEEP OVER THE GREAT
LAKES. THE 00Z GFS/12Z UKMET AND 12Z ECMWF CLUSTER IN BETWEEN.
WILL PREFER A BLEND OF THESE SOLUTIONS AT THIS TIME.


...LONGWAVE TROUGH FINALLY REACHING THE WEST COAST BY WED...
...LOW PRESSURE DEVELOPING OVER THE CENTRAL/SOUTHERN HIGH PLAINS...

PREFERENCE: BLEND OF THE 12Z UKMET AND 12Z ECMWF
CONFIDENCE: ABOVE AVERAGE...BECOMING AVERAGE BY WED/THURS

A LONGWAVE TROUGH WILL MOVING ACROSS THE WEST COAST ON WED AND
BEGIN TRAVERSING THE INTERMOUNTAIN REGION. THIS WILL LEAD TO AN
ELONGATED AREA OF LOW PRESSURE DEVELOPING OVER THE CENTRAL AND
SOUTHERN HIGH PLAINS ALONG A FRONTAL ZONE EAST OF THE ROCKIES. THE
00Z NAM AND 12Z CMC TEND TO BE PERHAPS A LITTLE DEEPER/SHARPER
WITH THE TROUGH AS IT ARRIVES OVER THE WEST WITH THE 00Z GFS/12Z
UKMET AND 12Z ECMWF A LITTLE FLATTER. TOWARD THE END OF THE
PERIOD...THE 00Z GFS IS THE FLATTEST SOLUTION WITH ITS HEIGHT
FALLS OVER THE INTERMOUNTAIN REGION...AND BY THEN THE 12Z CMC IS
THE SHARPEST. CONSEQUENTLY...THE 00Z GFS IS A BIT WEAKER BY EARLY
THURS WITH ITS LEE-SIDE CYCLOGENESIS. THERE IS A BIT BETTER MODEL
CLUSTERING BETWEEN THE 12Z UKMET AND 12Z ECMWF BY THE END OF THE
PERIOD..AND SO WILL LEAN TOWARD THIS CONSENSUS.


...SOUTHERN STREAM TROUGH/CLOSED LOW EVOLUTION NEAR THE GULF
COAST...

PREFERENCE: BLEND OF THE 12Z ECMWF/18Z GEFS MEAN AND 12Z ECENS MEAN
CONFIDENCE: AVERAGE

THERE REMAINS SOME SPREAD WITH THE CLOSED LOW EVOLUTION THAT
IMPACTS THE WESTERN AND CENTRAL GULF COAST AREA TUES THROUGH
THURS. THE 12Z CMC AND 12Z UKMET BOTH BECOME A LITTLE SLOWER THAN
THE MODEL CONSENSUS AS THE ENERGY PUSHES OUT INTO THE GULF OF
MEXICO...WITH THE 12Z CMC ALSO A BIT FARTHER SOUTH. THE 00Z GFS
PLACES MORE ENERGY A BIT FARTHER NORTH...WITH THE 12Z ECMWF IN
BETWEEN THE CMC/UKMET CAMP AND THE GFS. THE 00Z NAM IS A BIT
WEAKER AND MORE PROGRESSIVE WITH THE ENERGY. THE 12Z ECMWF FOR NOW
HAS BETTER ENSEMBLE SUPPORT...AND SO WILL BLEND THE ECMWF WITH THE
LATEST GEFS MEAN AND ECENS MEAN.

www.wpc.ncep.noaa.gov/html/model2.shtml...

www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

ORRISON

$$





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