Prognostic Meteorological Discussion
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000
FXUS10 KWNH 211657
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1155 AM 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 NAM/GFS MODEL EVALUATION...INCLUDING PRELIMINARY PREFERENCES

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

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

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

MID/LATE MORNING WV/IR IMAGERY SHOWING DEVELOPING CLOSED LOW OVER
THE WEST CENTRAL GULF COAST. GOOD MODEL AGREEMENT WITH DEVELOPING
AN ANOMALOUSLY STRONG 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 OF THE GUIDANCE ENVELOPE.
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.

...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: 00Z 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...BUT THE GFS REMAINS A BIT FASTER THAN THE
00Z ECMWF/UKMET. THE 12Z NAM IS NOW A STRONG/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. THE 00Z UKMET AND 00Z ECMWF BOTH IN BETWEEN
THE SLOW NAM AND THE FASTER GFS/CMC CAMP. 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.

...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: 00Z ECMWF/06Z 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.

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

PREFERENCE: 06Z 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.



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

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

MONTEFUSCO

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