Prognostic Meteorological Discussion
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000
FXUS10 KWNH 230700
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST THU NOV 23 2017

VALID NOV 23/0000 UTC THRU NOV 26/1200 UTC

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

00Z MODEL EVALUATION...WITH PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...UPPER TROUGH EXITING THE NORTHEAST THROUGH EARLY THANKSGIVING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN VERY GOOD AGREEMENT WITH THE DEPARTURE OF THE
UPPER TROUGH OVER THE NORTHEAST...SO A GENERAL MODEL BLEND WILL BE
PREFERRED.


...SLOW-MOVING UPPER LEVEL TROUGH OVER THE GULF OF MEXICO LIFTING
ACROSS THE FL PENINSULA...
...SURFACE LOWS OVER THE EASTERN GULF OF MEXICO/NEAR
FLORIDA...TRACKING NORTH OVER THE WESTERN ATLANTIC THIS WEEKEND...
...REINFORCING UPPER TROUGH OVER THE GULF OF MEXICO BY SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z ECMWF...12Z ECENS MEAN...00Z GEFS MEAN
CONFIDENCE: BELOW AVERAGE

THE MODELS GRADUALLY LIFT THE SOUTHERN STREAM UPPER TROUGH OVER
THE EASTERN GULF OF MEXICO OFF TO THE NORTHEAST OVER THE NEXT
COUPLE OF DAYS WITH THE ENERGY CROSSING THE FL PENINSULA AND THEN
LIFTING OFFSHORE THE SOUTHEAST COAST OUT OVER THE WESTERN
ATLANTIC. THE GUIDANCE IS IN RATHER GOOD AGREEMENT IN DEVELOPING A
PAIR OF SURFACE LOWS ALONG A FRONTAL ZONE DRAPED OVER THE
REGION...WITH ONE LOW INITIALLY OVER THE EASTERN GULF OF MEXICO
AND THEN GRADUALLY A SECONDARY LOW OFFSHORE THE SOUTHEAST COAST AS
THE HEIGHT FALLS BEGIN TO LIFT OFF TO THE NORTHEAST. THIS
SECONDARY LOW WILL BECOME THE DOMINANT LOW BY SATURDAY AND THEN
COME UNDER THE INFLUENCE OF NORTHERN STREAM TROUGHING MOVING
TOWARD THE EAST COAST BY SATURDAY NIGHT AND SUNDAY.

THE MODELS ARE GENERALLY IN RATHER GOOD AGREEMENT WITH THEIR MASS
FIELDS THROUGH FRIDAY...ALTHOUGH THE 00Z CMC IS SEEN AS GENERALLY
HAVING ONE MAIN LOW CENTER THAT EJECTS OUT OF THE GULF OF MEXICO
AND ACROSS THE FL PENINSULA VERSUS HAVING TWO SEPARATE LOWS LIKE
THE REMAINDER OF THE GUIDANCE INDICATES. ALSO...THE CMC ON
SATURDAY AND SUNDAY SHOWS MUCH MORE IN THE WAY OF INTERACTION WITH
THE NORTHERN STREAM ENERGY WHICH RESULTS IN A MUCH STRONGER
SURFACE LOW LIFTING UP OFF THE EAST COAST AND TOWARD NOVA SCOTIA.
THE REMAINING GUIDANCE SHOWS BETTER CLUSTERING TOWARD A SOMEWHAT
WEAKER AND MORE PROGRESSIVE LOW THAT TRACKS WELL OFF THE EAST
COAST AND SOUTHEAST OF NOVA SCOTIA BY SUNDAY. THE 00Z GFS/00Z
UKMET AND 00Z ECMWF ARE ALL IN AGREEMENT NOW ON A FARTHER EAST
SOLUTION...WITH THE GFS AND UKMET THE WEAKEST SOLUTIONS. THE 00Z
NAM IS A BIT LEFT OF THE ECMWF...BUT WELL EAST OF THE CMC
SOLUTION. OVERALL AT THIS POINT THE ECMWF IS CLOSEST TO THE MODEL
CONSENSUS. HOWEVER...THE 00Z GEFS MEAN AND 12Z ECENS MEAN BOTH
SUGGEST THAT THE ECMWF MAY BE A TAD TOO FAR EAST WITH ITS LOW OFF
THE EAST COAST BY THE END OF THE PERIOD. THEY SUGGEST EVEN MORE SO
THAT THE OPERATIONAL GFS AND UKMET ARE EASTERLY OUTLIERS. BY THE
END OF THE PERIOD...THE MODELS ALSO SUGGEST A REINFORCING SURGE OF
SHORTWAVE ENERGY DIGGING TOWARD THE GULF COAST WHICH WILL RENEW A
TROUGH OUT OVER THE GULF OF MEXICO. SPREAD WITH THIS LATTER
FEATURE IS FAIRLY MINIMAL ALTHOUGH THE CMC IS BIT MORE OUT OF
TOLERANCE RELATIVE TO THE OTHER MODELS. BASED ON THE MODEL SPREAD
IN PARTICULAR WITH THE SYSTEM IMPACTING THE FL PENINSULA AND
OFFSHORE THE EAST COAST...CONFIDENCE BECOMES LIMITED...BUT WILL
AGAIN PREFER TO BLEND THE ECMWF WITH THE LATEST ENSEMBLE MEANS
SINCE THIS BEST APPROXIMATES THE MODEL CONSENSUS.


...UPPER TROUGH AXIS CROSSING THE PACIFIC NORTHWEST AND REACHING
THE GREAT LAKES BY FRIDAY NIGHT...
...ASSOCIATED SURFACE LOW CROSSING SOUTHERN CANADA...
...POSSIBLE SHORTWAVE AMPLIFICATION OVER THE NORTHEAST SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND...WITH THE SURFACE LOW
            00Z UKMET/00Z ECMWF BLEND WITH THE HEIGHT FALLS
CONFIDENCE: AVERAGE

A POSITIVELY-TILTED UPPER TROUGH CROSSING THE PACIFIC NORTHWEST ON
THANKSGIVING DAY WILL QUICKLY ADVANCE EAST ACROSS SOUTHERN CANADA
AND THEN SOUTHEAST ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST
THROUGH FRIDAY. THIS WILL DRIVE A STRONG AREA OF LOW PRESSURE
ACROSS SOUTHERN CANADA WITH A TRAILING COLD FRONT THAT WILL CROSS
THE NORTHWEST AND THEN ADVANCE RAPIDLY THROUGH THE EASTERN U.S.
THIS WEEKEND AS THE ENERGY LIFTS TOWARD SOUTHEAST CANADA THIS
WEEKEND. THERE WILL BE A FAST-MOVING SHORTWAVE TROUGH/JET MAX THAT
WILL BE FOLLOWING VERY CLOSE ON THE HEELS OF THE INITIAL SYSTEM
THAT TRAVERSES SOUTHERN CANADA...AND THE GUIDANCE SUGGESTS SOME
POSSIBLE SHORTWAVE AMPLIFICATION OVER THE NORTHEAST BY SUNDAY. THE
00Z CMC AGAIN TENDS TO TRACK ITS LOW CENTER FARTHER SOUTH ACROSS
SOUTHERN CANADA COMPARED TO THE OTHER GUIDANCE. THE 00Z GFS THOUGH
IS NOW A STRONGER OUTLIER COMPARED TO THE OTHER GUIDANCE BY THE
END OF THE PERIOD WITH THE ENERGY ATTEMPTING TO AMPLIFY OVER THE
GREAT LAKES AND NORTHEAST SATURDAY AND SUNDAY. WILL PREFER A
NON-CMC BLEND WITH THE DETAILS OF THE SURFACE LOW OVER SOUTHERN
CANADA AND THE TIMING OF THE COLD FRONT EVOLUTION...BUT WILL
SUGGEST A BLEND OF THE 00Z UKMET AND 00Z ECMWF WITH ALL OF THE
HEIGHT FALLS GIVEN THEIR MORE FAVORABLE CLUSTERING AND
APPROXIMATION OF THE MODEL CONSENSUS THROUGHOUT THE PERIOD.


...LOW PRESSURE LIFTING UP OFF THE WEST COAST ON SATURDAY...
...DEEP UPPER TROUGH OFFSHORE THE WEST COAST THROUGH SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z GEFS MEAN AND 12Z ECENS MEAN
CONFIDENCE: BELOW AVERAGE

ENERGY THAT IS NEAR THE BASE OF THE POSITIVELY-TILTED UPPER TROUGH
THAT IS NEAR AND OFFSHORE THE PACIFIC NORTHWEST WILL BREAK AWAY
AND DRIFT SLOWLY SOUTH OVER THE NEXT COUPLE OF DAYS BEFORE THEN
GETTING PICKED UP BY A STRONGER INTRUSION OF NORTHERN STREAM
HEIGHT FALLS FROM THE GULF OF AK. THE SOUTHERN STREAM ENERGY WILL
GET SLINGSHOT NORTHEAST TOWARD THE WA/OR COASTAL RANGES AND
VANCOUVER ISLAND BY SATURDAY NIGHT AS AN AREA OF LOW PRESSURE
DEVELOPS AND STRENGTHENS OFFSHORE THE PACIFIC NORTHWEST. THE 00Z
UKMET IS A DEEP OUTLIER WITH THIS LOW CENTER...WITH THE 00Z CMC BY
FAR THE WEAKEST. THE 00Z NAM/00Z GFS AND 00Z ECMWF SPLIT THE
DIFFERENCE BETWEEN STRONG AND WEAK SOLUTIONS...BUT THE ECMWF IS A
TAD STRONGER OUT OF THESE THREE SOLUTIONS. THE ECMWF HAS TRENDED
WEAKER FROM ITS PREVIOUS RUN AND IS A LITTLE SLOWER AND STRONGER
THAN THE GFS AT THIS POINT. THE ENSEMBLE GUIDANCE IS STILL
GENERALLY MORE SUPPORTIVE OF THE OPERATIONAL GFS...ALTHOUGH THE
GFS MAY BE A TAD TOO FAR EAST AT THE END OF THE PERIOD. WILL STAY
AWAY FROM THE DEEPER UKMET AND WEAKER CMC SOLUTIONS AND COMPROMISE
AGAIN TOWARD THE ENSEMBLE MEANS AS PER THE 00Z GEFS MEAN AND 12Z
ECENS MEAN FOR NOW. CONFIDENCE REMAINS LIMITED GIVEN THE SPREAD IN
THE AMOUNT OF DEEPENING OF THIS LOW CENTER.


www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

ORRISON

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