Prognostic Meteorological Discussion
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FXUS10 KWNH 211902
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 PM EST TUE FEB 21 2017

VALID FEB 21/1200 UTC THRU FEB 25/0000 UTC

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

12Z MODEL EVALUATION...INCLUDING FINAL PREFERENCES

...SHORTWAVE CROSSING THE GREAT LAKES/OHIO VALLEY...
...SURFACE LOW PRESSURE/COLD FRONT CROSSING THE REGION THROUGH
TONIGHT...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

19Z UPDATE: THE MODELS ARE IN GOOD AGREEMENT WITH THE EVOLUTION OF
THIS SYSTEM. A GENERAL MODEL COMPROMISE IS PREFERRED AT ABOVE
AVERAGE CONFIDENCE.

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

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

LATE MORNING WV/IR IMAGERY SHOWING DEVELOPING CLOSED LOW OVER THE
WEST CENTRAL GULF COAST. GOOD MODEL AGREEMENT WITH DEVELOPING AN
ANOMALOUSLY STRONG A CLOSED LOW ACROSS THE LOWER MS VALLEY/CENTRAL
GULF COAST THROUGH TONIGHT...WITH THE FEATURE CUTTING OFF FROM
WESTERLIES AND DIVING SE ACROSS THE EASTERN GULF OF MEXICO
WED...TOWARD SOUTH FLORIDA/FLORIDA KEYS BY EARLY THURSDAY. THE
GUIDANCE HANDLES THE EVOLUTION OF THE SYSTEM SIMILARLY FOR LATER
THU AND FRI...WITH GENERAL AGREEMENT IN PROGRESSING THE SYSTEM
NORTH OF THE STRAIT OF FLORIDA TOWARD THE BAHAMAS BY EARLY FRIDAY
BEFORE THE LOW FILLS/WEAKENS OFF THE SOUTHEAST COAST FRIDAY NIGHT.
THE NEW 12Z NAM REMAINS A BIT FASTER THAN THE REMAINDER OF
AVAILABLE GUIDANCE...WITH THE 12Z GFS AND THE ECMWF ON THE SLOW
SIDE. HOWEVER...THERE IS OVERALL VERY LITTLE SPREAD WITH THIS
FEATURE WITH DECENT TO GOOD MASS FIELD AGREEMENT THROUGH THE
PERIOD SUCH THAT A GENERAL MODEL COMPROMISE WILL SUFFICE THROUGH
THE FORECAST PERIOD. GIVEN RELATIVELY LOW SPREAD AND GOOD RUN TO
RUN CONTINUITY...FORECAST CONFIDENCE IS ABOVE AVERAGE WITH THIS
SYSTEM.

19Z UPDATE...OVERALL TREND OF THE 12Z SUITE IS A SLIGHTLY QUICKER
FILLING OF THE UPPER SYSTEM BY THE END OF THE PERIOD FRIDAY NIGHT.


...SHORTWAVE/SURFACE LOW OVER THE PAC NW/INTERMOUNTAIN WEST
TODAY...
...SURFACE LOW REACHING THE NORTHERN PLAINS/UPPER MIDWEST
TONIGHT/WED
...SURFACE LOW/COLD FRONT CROSSING FROM THE NORTHERN/CENTRAL
PLAINS TO THE GREAT LAKES WED/THU...

PREFERENCE: GFS/UKMET/ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS ARE ALSO WELL CLUSTERED WITH THIS LATEST PAC NW
SHORTWAVE AND ASSOCIATED SURFACE LOW...WHICH WILL IMPACT THE WEST
COAST THROUGH TONIGHT. GOOD MODEL AGREEMENT IN EJECTING THE
SHORTWAVE NORTHEAST WED/EARLY THURSDAY. THE ASSOCIATED SURFACE
WAVE AND ATTENDANT SURFACE COLD FRONT WILL QUICKLY TRAVERSE THE
NORTHERN GREAT BASIN/NORTHERN ROCKIES TODAY...BEFORE PUSHING
ACROSS THE DAKOTAS TONIGHT. THE SYSTEM IS EXPECTED TO INTENSIFY A
BIT ON WED AS IT APPROACHES THE UPPER MIDWEST. THE 12Z GFS HAS
TRENDED TOWARD THE ECMWF IN DEPICTING A SLIGHTLY MORE
SHEARED/WEAKER WAVE...ALSO ORIENTED A BIT FARTHER NORTH.
HOWEVER...THE GFS REMAINS SLIGHTLY FASTER THAN THE 00Z
ECMWF/UKMET. THE 12Z NAM IS NOW SLIGHTLY STRONGER THAN THE REST OF
GUIDANCE AND A SLOW OUTLIER WITH THE SYSTEM. 00Z CMC TRENDED
SLOWER BUT OVERALL REMAINS THE WEAKEST AND IS A LITTLE SLOWER THAN
THE GFS AS THE LOW CROSSES THE NORTHERN PLAINS/UPPER MIDWEST.
GIVEN THE TREND OF THE 12Z GFS TOWARD THE ECMWF CAMP WITH MASS
FIELDS...WILL LEAN TOWARD A COMPROMISE BETWEEN THE UKMET AND ECMWF
AT THIS TIME TO APPROXIMATE THE MODEL CONSENSUS.

19Z UPDATE: NO MAJOR CHANGE WITH THE 12Z ECMWF...AND OVERALL
CONVERGENCE WITH GFS SOLUTION BOLSTERS CONFIDENCE A BIT MORE. 12Z
CMC TRENDED TOWARD THE REST OF THE GUIDANCE ENVELOPE WITH A
STRONGER WAVE WED/THU...BUT REMAINS SLOWER THAN GFS/ECMWF/UKMET
CAMP WITH THE SHORTWAVE. WILL FAVOR A GFS/ECMWF/UKMET SOLUTION TO
REFLECT EMERGING CONSENSUS SOLUTION.

...BROAD LONGWAVE TROUGH FINALLY REACHING THE WEST COAST WED...
...ADDITIONAL NORTHERN STREAM SHORTWAVE CROSSING THE PACIFIC
NORTHWEST...
...DEVELOPING SURFACE LOW OVER THE CENTRAL/SOUTHERN HIGH PLAINS
MOVING TOWARD UPPER MIDWEST LATE THU/FRI...

PREFERENCE: 12Z ECMWF/12Z GEFS MEAN
CONFIDENCE: SLIGHTLY BELOW AVERAGE

A LONGWAVE TROUGH WILL FINALLY BEGIN TO DROP SOUTHEAST ACROSS THE
WEST COAST ON WED/EARLY THU...MOVING INLAND AND TRAVERSING THE
INTERMOUNTAIN WEST BY THU/THU NIGHT. 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 ARE WELL RESOLVED BY MODELS AND GOOD
FORECAST CONFIDENCE THAT THIS WILL LEAD TO SURFACE CYCLOGENESIS
ACROSS  THE CENTRAL/SOUTHERN HIGH PLAINS ALONG A FRONTAL ZONE EAST
OF THE ROCKIES LATE THURSDAY.

HOWEVER...THE MODELS STILL DIVERGE TO SOME DEGREE WITH RESPECT TO
THE EVOLUTION OF THE LONGWAVE TROUGH ACROSS THE PLAINS...WITH
RESULTANT IMPACTS REGARDING SURFACE LOW PRESSURE TRAVERSING THE
CENTRAL PLAINS TOWARD THE MID MISSISSIPPI RIVER VALLEY LATER THU
AND FRI. THE 12Z GFS TRENDED A BIT SLOWER WITH THE EVOLUTION OF
THE SYSTEM...BUT REMAINS THE STRONGEST SOLUTION WITH THE LOW
PRESSURE LIFTING FROM EASTERN IA TOWARD THE UPPER MIDWEST BY FRI
MORNING. THE 00Z ECMWF DID TREND A BIT STRONGER TOO AND IS ONLY A
LITTLE WEAKER THAN THE GFS. THE GFS REMAINS IS A BIT FARTHER NORTH
WITH ITS LOW TRACK...WITH THE 06Z GEFS ESSENTIALLY A COMPROMISE
SOLUTION OF THE TWO AT THIS TIME. THE 12Z NAM REMAINS SLIGHTLY
WEAKER AND IS A FAST OUTLIER WITH THIS SYSTEM. THE 00Z UKMET AGAIN
BECOMES THE SLOWEST WITH THE 00Z CMC IN BETWEEN THE ECMWF AND
UKMET TRACKS. BASED ON THE 06Z GEFS MEAN...THE 12Z GFS STILL
APPEARS SLIGHTLY TOO FAR NORTH WITH ITS LOW TRACK...BUT SPATIAL
DIFFERENCES ARE DIMINISHING WITH TIME. THE 00Z ECMWF HAS SHOWN
BETTER CONTINUITY...AND ALIGNS WELL WITH THE 06Z GEFS MEAN AND IS
NOW A BIT NORTH-NORTHWEST OF THE 12Z ECENS MEAN. GIVEN THE TRENDS
STARTED/CONTINUED WITH THE 12Z GFS...WILL STICK WITH A BLEND OF
THE ECMWF AND LATEST GEFS MEAN AS A COMPROMISE AT THIS
POINT...WITH CONFIDENCE LIMITED GIVEN THE OVERALL DETERMINISTIC
MODEL SPREAD.

19Z UPDATE: LIKE THE LATEST 12Z GFS...THE 12Z ECMWF NUDGED A
LITTLE FARTHER NORTH WITH THE SURFACE LOW AND THE ATTENDANT
FRONTAL ZONE. ALSO LIKE THE 12Z GFS...NEW 12Z GEFS HAS AGAIN
SLOWED FROM ITS PAST FEW RUNS AND IS A BIT WEAKER WITH THE SURFACE
LOW. 12Z CMC IS A BIT STRONGER AND TO THE WEST WITH THE SURFACE
LOW...AND IS ON THE SLOW SIDE OF THE GUIDANCE ENVELOPE WITH THE
12Z UKMET. 12Z GFS REMAINS A BIT STRONG AND SLOW WITH ITS SURFACE
LOW BY THE END OF THE PERIOD 00Z-12Z SATURDAY. WILL UPDATE THE
PREFERENCE TO REFLECT THE LATEST ECMWF AND GEFS MEAN TO REFLECT
12Z (NORTH) TREND AND ASSOCIATED FRONTAL ZONE LOCATION.

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

PREFERENCE: 12Z GEFS/00Z ECENS
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 ALONG AND OFFSHORE OF THE PACIFIC NORTHWEST. THERE
ARE SOME TIMING DETAIL DIFFERENCES...THE ECMWF BEING A BIT
STRONGER/SLOWER THAN THE 12Z GFS. HOWEVER...THERE IS DECENT
CLUSTERING AT THIS TIME RANGE BETWEEN THE TWO...AND THEY APPEAR TO
BE CONVERGING WITH THEIR HANDLING OF THIS FEATURE. IN THE
INTERIM...WILL BLEND GEFS AND ECENS AT AVERAGE CONFIDENCE.

19Z UPDATE: 12Z ECMWF TRENDED A BIT SHARPER WITH FEATURE BY EARLY
SATURDAY...WITH TIMING AND SPATIAL DIFFERENCES PERSISTING FOR NOW.
WILL CONTINUE TO USE UPDATED BLEND OF RESPECTIVE ENSEMBLE MEANS TO
SMOOTH OUT THESE DIFFERENCES.

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

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

MONTEFUSCO

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