Prognostic Meteorological Discussion
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816
FXUS10 KWNH 210652
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
151 AM EST TUE FEB 21 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/GFS/UKMET/CMC AND ECMWF

...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: GENERAL MODEL COMPROMISE
CONFIDENCE: SLIGHTLY 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. BY THURS AND FRI...THE
00Z GFS IS A TAD SLOWER THAN THE MODEL CONSENSUS...WITH THE 00Z
NAM A TAD FASTER...BUT THERE IS OVERALL SUFFICIENTLY GOOD ENOUGH
MASS FIELD AGREEMENT THAT A GENERAL MODEL COMPROMISE CAN BE
PREFERRED FOR NOW TO RESOLVE SOME OF THESE MODEST TIMING
DIFFERENCES.


...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 00Z UKMET AND 00Z ECMWF
CONFIDENCE: AVERAGE

THE MODELS ARE WELL CLUSTERED 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 GUIDANCE
INDICATES 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 00Z GFS
IS NOW THE STRONGEST AND MOST PROGRESSIVE SOLUTION. THE 00Z CMC
HAS 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 NAM BECOMES THE SLOWEST SOLUTION...WITH THE 00Z
UKMET AND 00Z ECMWF BOTH IN BETWEEN THE SLOW NAM AND THE FASTER
GFS/CMC CAMP. 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 BY WED...
...ADDITIONAL NORTHERN STREAM SHORTWAVE CROSSING THE PACIFIC
NORTHWEST...
...LOW PRESSURE DEVELOPING OVER THE CENTRAL/SOUTHERN HIGH PLAINS...

PREFERENCE: BLEND OF THE 00Z ECMWF AND 00Z 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 KEY LATITUDINAL
DIFFERENCES. THE 00Z GFS REMAINS THE STRONGEST SOLUTION WITH THE
LOW PRESSURE LIFTING TOWARD THE MIDWEST BY EARLY FRI...HOWEVER THE
00Z ECMWF DID TREND A BIT STRONGER TOO AND IS ONLY A LITTLE WEAKER
THAN THE GFS. THE GFS THOUGH IS A BIT FARTHER NORTH WITH ITS LOW
TRACK. THE 00Z NAM IS THE WEAKEST AND FASTEST. THE 00Z UKMET AGAIN
BECOMES THE SLOWEST WITH THE 00Z CMC IN BETWEEN THE ECMWF AND
UKMET TRACKS. BASED ON THE 00Z GEFS MEAN...THE 00Z GFS APPEARS AS
THOUGH IT MAY BE STILL A BIT TOO DEEP AND POSSIBLY TOO FAR NORTH
WITH ITS LOW TRACK. THE 00Z ECMWF HAS BETTER AGREEMENT GENERALLY
FROM THE 00Z GEFS MEAN AND IS NOW A BIT NORTH OF THE 12Z ECENS
MEAN. WILL LEAN TOWARD A BLEND OF THE ECMWF AND 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...

PREFERENCE: BLEND OF THE 00Z GFS AND 00Z 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 TIMING DETAIL DIFFERENCES...BUT
GENERALLY THERE IS BETTER CLUSTERING BETWEEN THE 00Z GFS AND 00Z
ECMWF ALONG WITH THEIR ENSEMBLE MEANS. SO WILL PREFER 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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