Prognostic Meteorological Discussion
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000
FXUS10 KWNH 210439
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1138 PM EST MON FEB 20 2017

VALID FEB 21/0000 UTC THRU FEB 24/1200 UTC

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

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

...SHORTWAVE CROSSING THE NORTHERN PLAINS/UPPER MIDWEST/GREAT
LAKES...
...SURFACE LOW PRESSURE/COLD FRONT CROSSING THE REGION...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN GOOD AGREEMENT WITH THE EVOLUTION OF THIS SYSTEM
AND SO A GENERAL MODEL COMPROMISE CAN BE PREFERRED.


...SOUTHERN STREAM CLOSED LOW EVOLUTION FROM THE GULF COAST TO THE
FL KEYS...

PREFERENCE: NON-NAM BLEND
CONFIDENCE: AVERAGE

THE MODELS CONTINUE TO DEVELOP A CLOSED LOW ACROSS THE LOWER MS
VALLEY AND THEN OUT ACROSS THE GULF OF MEXICO TUES AND WED AS
SOUTHERN STREAM TROUGHING BREAKS AWAY AND DIGS EAST-SOUTHEAST
THROUGH THE PERIOD. THE GUIDANCE TAKES THE CLOSED LOW DOWN TOWARD
SOUTH FL AND THE FL KEYS BY EARLY THURS BEFORE IT THEN LIFTS
ADVANCES EAST THROUGH THE BAHAMAS ON FRI. THERE IS REASONABLY GOOD
MASS FIELD AGREEMENT WITH THE SYSTEM UNTIL EARLY WED WHEN THE 00Z
NAM BEGINS TO TRACK THE CLOSED LOW EAST-SOUTHEAST IN A FASHION
THAT IS A LITTLE NORTH OR LEFT OF THE MODEL CONSENSUS. BY
THURS...THE NAM BECOMES WEAKER AND MORE PROGRESSIVE THAN THE MODEL
CONSENSUS. WILL CONTINUE TO PREFER A NON-NAM BLEND AT THIS POINT
GIVEN THE DEGREE OF CLUSTERING SEEN OUT OF THE GLOBAL MODELS.


...SHORTWAVE/SURFACE LOW APPROACHING SOUTHWEST OREGON EARLY TUES...
...SURFACE LOW REACHING THE NORTHERN PLAINS/UPPER MIDWEST TUES
NIGHT/WED
...SURFACE LOW/COLD FRONT CROSSING THE GREAT LAKES BY THURS...

PREFERENCE: BLEND OF THE 12Z UKMET AND 12Z ECMWF
CONFIDENCE: AVERAGE

THE 12Z CMC REMAINS THE WEAKEST AND MOST PROGRESSIVE WITH YET
ANOTHER SHORTWAVE AND ASSOCIATED SURFACE LOW THAT WILL IMPACT THE
WEST COAST THROUGH EARLY TUES AS LOW PRESSURE WILL BE SPECIFICALLY
AIMING TOWARD SOUTHWEST OREGON AND THEN MOVING QUICKLY INLAND. THE
REMAINING MODELS ARE WELL CLUSTERED WITH THE SHORTWAVE EJECTING
ACROSS THE NORTHERN GREAT BASIN BY LATE TUES AND LOW PRESSURE
REDEVELOPING OUT ACROSS THE NORTHERN HIGH PLAINS BY TUES EVE. A
TRAILING PACIFIC COLD FRONT WILL BE CROSSING THE INTERMOUNTAIN
REGION. ON WED...THE SYSTEM IS EXPECTED TO INTENSIFY A BIT AS IT
APPROACHES THE UPPER MIDWEST. THE 12Z CMC REMAINS THE WEAKEST  AND
MOST PROGRESSIVE...WITH THE 00Z NAM BECOMING THE SLOWEST. THE 00Z
NAM ALSO IS FARTHEST SOUTH WITH THE LOW TRACK. THE 00Z GFS/12Z
UKMET AND 12Z ECMWF SPLIT THE DIFFERENCE...BUT THE GFS ACTUALLY IS
THE FARTHEST NORTH OF THOSE SOLUTIONS. THERE IS A BIT BETTER MODEL
CLUSTERING BETWEEN THE UKMET AND ECMWF AND THESE SOLUTIONS HAVE
RATHER STRONG AGREEMENT FROM THE GEFS MEAN AND ECENS MEAN. WILL
LEAN TOWARD A UKMET/ECMWF BLEND.


...BROAD LONGWAVE TROUGH FINALLY REACHING THE WEST COAST BY WED...
...ADDITIONAL NORTHERN STREAM SHORTWAVE CROSSING THE PACIFIC
NORTHWEST...
...LOW PRESSURE DEVELOPING OVER THE CENTRAL/SOUTHERN HIGH PLAINS...

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

A LONGWAVE TROUGH WILL FINALLY BEGIN TO DROP SOUTHEAST ACROSS THE
WEST COAST ON WED...MOVING INLAND AND TRAVERSING THE INTERMOUNTAIN
WEST BY THURS AS A LEAD SHORTWAVE CROSSES NORTHERN CA AND THEN
EJECTS EAST ACROSS THE GREAT BASIN AND THE CENTRAL ROCKIES.
MEANWHILE...AN ADDITIONAL NORTHERN STREAM SHORTWAVE WILL BE
DIGGING SOUTHEAST ACROSS THE PACIFIC NORTHWEST ON THE HEELS OF THE
INITIAL SURGE OF HEIGHT FALLS AND WILL HELP TO BROADEN THE OVERALL
LONGWAVE TROUGH THROUGH THE PERIOD. THE INITIAL SURGE OF HEIGHT
FALLS 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. HOWEVER...THE MODELS THEN BEGIN TO DIVERGE ON
HOW LOW PRESSURE WILL EVOLVE ACROSS THE CENTRAL PLAINS AND TOWARD
THE MIDWEST BY LATER THURS AND FRI WITH SOME KEYS LATITUDINAL
DIFFERENCES. THE 00Z GFS BECOMES A DEEPER OUTLIER WITH LOW
PRESSURE LIFTING TOWARD THE MIDWEST BY EARLY FRI. THE 00Z NAM IS
THE WEAKEST AND FASTEST. THE 12Z UKMET BECOMES THE SLOWEST WITH
THE 12Z CMC ALSO A BIT SLOWER BUT FARTHER NORTH WITH ITS
EVOLUTION. THIS LEAVES THE 12Z ECMWF WHICH HAS SOMEWHAT COMPARABLE
TIMING TO THE 00Z GFS...BUT IS MORE SUPPRESSED AND NOT AS DEEP.
THE 12Z ECENS MEAN AND 12Z/18Z GEFS MEANS ARE VERY SUPPORTIVE OF
THE DETERMINISTIC ECMWF...AND SO AT THIS POINT...WITH CONFIDENCE
LIMITED GIVEN THE OVERALL DETERMINISTIC MODEL SPREAD...A
ECMWF/ECENS MEAN/GEFS MEAN BLEND WILL BE PREFERRED.


...ADDITIONAL HEIGHT FALLS OVER THE PACIFIC NORTHWEST ON FRI...

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

THE MODELS SHOW SOME ADDITIONAL SHORTWAVE ENERGY SETTLING SOUTH
OVER TOP THE STRONG UPPER LEVEL RIDGE/HIGH OVER THE GULF OF AK AND
DROPPING DOWN OVER THE PACIFIC NORTHWEST AND ALSO OFFSHORE THE
WEST COAST. THERE ARE SOME DETAIL DIFFERENCES...BUT GENERALLY
THERE IS BETTER CLUSTERING BETWEEN THE 00Z GFS AND 12Z ECMWF ALONG
WITH THEIR ENSEMBLE MEANS. THE 12Z UKMET AND 12Z ECMWF OVERALL
WERE A LITTLE MORE OUT OF PHASE COMPARATIVELY...AND SO WILL FAVOR
A BLEND OF THE GFS AND ECMWF FOR NOW.


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

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

ORRISON

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