Prognostic Meteorological Discussion
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FXUS10 KWNH 301916
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
315 PM EDT TUE AUG 30 2016

VALID AUG 30/1200 UTC THRU SEP 03/0000 UTC

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

12Z FINAL PRELIMINARY MODEL EVALUATION AND PREFERENCES


...UPPER TROUGH TRACKING ACROSS SOUTHERN CANADA THROUGH MID-WEEK...
...TROUGH AMPLIFICATION INTO THE EASTERN U.S....
...ATTENDANT COLD FRONT PROGRESSION...

PREFERENCE: CONSENSUS OF THE 12Z GFS/ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

GENERALLY HAVE GOOD AGREEMENT IN THE GUIDANCE WITH THE LARGE SCALE
EVOLUTION AND FRONTAL PROGRESSION. HOWEVER DO SEE DIFFERENCES IN
HOW THE MODELS PROGRESS AND INTERACT TWO WAVES EMBEDDED WITHIN THE
TROUGH...THE MAIN SHORTWAVE THAT COMES FROM THE CURRENTLY CLOSED
UPEPR LOW OVER CANADA...AND A SECOND SHORTWAVE AT THE BASE OF THE
TROUGH MOVING THROUGH THE GREAT LAKES WEDNESDAY NIGHT. THESE
DIFFERENCES END UP RESULTING IN SLIGHT FRONTAL TIMING
DIFFERENCES...AS WELL AS DIFFERENCES IN A POTENTIAL COASTAL LOW
DEVELOPMENT EAST OF MAINE ON THURSDAY.

MODELS HAVE BEEN PRETTY INCONSISTENT RUN TO RUN WITH THIS
EVOLUTION. HOWEVER AM BEGINNING TO SEE SOME SIGNS OF A TREND
TOWARDS A COMMON SOLUTION...WITH THE GOOD MIDDLE GROUND CONSENSUS
CURRENTLY RESIDING SOMEWHERE BETWEEN THE 12Z GFS AND 0Z ECMWF. THE
12Z NAM AND 0Z GEM/UKMET OVERALL APPEAR TO BE LAGGING TRENDS A BIT.

19Z UPDATE: THE FULL 12Z SUITE OF GUIDANCE DID NOT ADD ANY CLARITY
TO THE EVOLUTION OF THE DEVELOPING TROUGH AND HOW THE TWO PIECES
OF SHORTWAVE ENERGY MENTIONED ABOVE INTERACT. THE ECMWF DID SPEED
UP A BIT WITH ITS FRONTAL PROGRESSION ON THURSDAY...AND IS NOW
CLOSE TO THE GFS/NAM. HOWEVER BY THURSDAY NIGHT INTO FRIDAY
CONFIDENCE REMAINS LOW WITH EVOLUTION OF THE TROUGH AND POTENTIAL
SURFACE LOW DEVELOPMENT NEAR MAINE. GIVEN THE LOW RUN TO RUN
CONTINUITY SEE NO REASON TO STRAY FROM OUR GFS/ECMWF BLEND FOR NOW.


...UPPER LOW/TROUGH DIGGING SOUTH OFFSHORE BRITISH COLUMBIA...
...ENERGY PIVOTING INTO THE WEST COAST BY LATE TUES/WED...
...LEAD SHORTWAVE CROSSING NORTHERN CA ON TUES...

PREFERENCE: NON NAM BLEND
CONFIDENCE: BELOW AVERAGE

THE GUIDANCE IS IN GOOD AGREEMENT ON THE DEPTH AND TIMING OF A
LEAD SHORTWAVE IMPULSE THAT ARRIVES ACROSS NORTHERN CA TODAY OUT
AHEAD OF A LARGER SCALE DEEP TROUGH AND CLOSED LOW THAT ADVANCES
SOUTH FROM OFFSHORE BRITISH COLUMBIA AND THEN BEGINS DIGGING INTO
THE NORTHWEST U.S. THURS AND FRI. THE 0Z GEM EVENTUALLY BECOMES
THE SLOWEST SOLUTION...AND APPEARS LESS LIKELY AT THIS TIME.
MEANWHILE THE 12Z NAM GENERALLY APPEARS TOO WEAK WITH THE EMBEDDED
SHORTWAVES WITHIN THE TROUGH. THE 12Z GFS/00Z UKMET AND 00Z ECMWF
CLUSTER TOGETHER REASONABLY WELL WITH THE PROGRESSION OF THE
LOW/TROUGH. HOWEVER...THE 12Z GFS REMAINS THE DEEPEST SOLUTION.
SINCE THE GEFS MEAN TENDS TO SUPPORT THE SLIGHTLY STRONGER
DETERMINISTIC GFS...AND IN GENERAL MODEL RUN TO RUN CONSISTENCY
HAS BEEN LOW SUGGESTING COMPLEX EVOLUTION WITH LOW
PREDICTABILITY...WILL SUGGEST A MULTI-MODEL CONSENSUS HERE...AS
CAN NOT RULE OUT THE GFS SOLUTION.

19Z UPDATE: MODEL SPREAD REMAINS ABOVE AVERAGE WITH THIS
FEATURE...WITH THE 12Z ECMWF/UKMET REMAINING FURTHER NORTH AND NOW
A BIT MORE PROGRESSIVE THAN THE GFS SOLUTION. THE 12Z GEM DID
SPEED UP TO A SIMILAR PACE AS THE GFS...BUT IS ALSO FURTHER NORTH.
WOULD APPEAR THE GFS REPRESENTS A LESS LIKELY SOLUTION...BUT GIVEN
IT HAS SUPPORT FROM ITS 12Z GEFS MEAN CAN NOT COMPLETELY RULE IT
OUT. THUS WILL PREFER A NON NAM BLEND FOR NOW...WHICH INCORPORATES
THE FURTHER SOUTH GFS...ALTHOUGH MORE WEIGHT GIVEN TO THE NORTHERN
SOLUTIONS.


...SHEAR AXIS/FRONT PUSHING SOUTH/WEAKENING ACROSS THE SOUTHWEST
AND PLAINS...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS ARE IN REASONABLY GOOD AGREEMENT WITH THIS
FEATURE...ALTHOUGH SOME MINOR TIMING DIFFERENCES ARE SEEN WITH THE
SOUTHEAST PROGRESSION OF THE FRONT AND MOISTURE AXIS. IN GENERAL A
MODEL BLEND SHOULD SUFFICE.


...WEAK MID LEVEL LOW OVER THE WESTERN GULF COAST...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THIS SYSTEM IS EXPECTED TO GRADUALLY WEAKEN AS IT DRIFTS
SOUTHWEST...WITH THE GUIDANCE SHOWING RELATIVELY MINOR DIFFERENCES.


...WAVE DEVELOPING ALONG THE SOUTHEAST COAST WED-THU...

PREFERENCE: 12Z GFS/ECMWF/UKMET CONSENSUS
CONFIDENCE: SLIGHTLY BELOW AVERAGE

WHILE MOST MODELS ARE INDICATING SOME LOW LEVEL/SURFACE WAVE
DEVELOPMENT OVER NORTHERN FL AND THEN NORTHEAST ALONG A COASTAL
TROUGH POSITIONED ALONG THE GA/SC COAST...THERE IS LARGE SPREAD
WITH RESPECT TO THE TIMING AND AMPLITUDE OF THIS FEATURE. ALL OF
THE GUIDANCE SHOWS THIS LOW CENTER LIFTING NORTHEAST ON THE HEELS
OF T.D. NINE WHICH WILL EXITING AWAY FROM THE EAST COAST. THE 0Z
GEM/UKMET BOTH SEEM TOO AGGRESSIVE IN DEVELOPING THIS
FEATURE...WITH THE 12Z NAM APPEARING TOO CLOSE TO THE COAST. FOR
NOW WILL LEAN TOWARDS THE WEAKER STRENGTH SUGGESTED BY THE 12Z GFS
AND 0Z ECMWF. THE GFS REMAINS MORE PROGRESSIVE THAN THE
ECMWF...AND WILL PREFER A MIDDLE GROUND SOLUTION FOR NOW.

19Z UPDATE: THE 12Z ECMWF REMAINS PRETTY SIMILAR TO ITS 0Z
RUN...WITH THE 12Z UKMET VERY CLOSE TO IT AS WELL. THESE TWO
SOLUTIONS REMAIN SLOWER THAN THE 12Z GFS RUN. WILL CONTINUE TO
PREFER THE WEAKER EVOLUTION SUGGESTED BY THE
GFS/ECMWF/UKMET...WITH A TIMING IN BETWEEN THE QUICKER GFS AND
SLOWER ECMWF/UKMET.


...T.D. EIGHT MOVING OFF THE MID-ATLANTIC COAST...

PREFERENCE: PLEASE CONSULT THE LATEST NHC FORECAST ADVISORY

GOOD AGREEMENT SEEN WITH THE 12Z GFS/NAM AND 0Z ECMWF WITH THIS
SYSTEM...WITH THE 15Z NHC TRACK FOLLOWING CLOSE TO THIS AS WELL.
PLEASE CONSULT THE LATEST NHC FORECAST ADVISORY FOR MORE
INFORMATION.


...T.D. NINE MOVING INTO THE GULF OF MEXICO...

PREFERENCE: PLEASE CONSULT THE LATEST NHC FORECAST ADVISORY

OVERALL SEE A PRETTY GOOD CLUSTERING IN THE GUIDANCE WITH REGARDS
TO THE EVENTUAL TRACK OF T.D. 9...WHICH SHOULD TURN NORTH AND
EVENTUALLY NORTHEASTWARD TOWARD THE NORTHWEST FLORIDA COAST ON
THURSDAY. SOME MINOR DIFFERENCES EXIST WITH THE EXACT TRACK...WITH
SLIGHTLY BIGGER DIFFERENCES ON THE TIMING. THE 12Z GFS AND 0Z GEM
ARE SLIGHTLY FURTHER NORTH WITH TRACK...WITH THE 12Z NAM AND 0Z
ECMWF/UKMET FURTHER SOUTH. THE 15Z NHC TRACK MATCHES CLOSER TO THE
TRACK SHOWN BY THE LATTER (NAM/ECMWF/UKMET). WITH REGARDS TO
TIMING...THE 0Z ECMWF REMAINS QUITE A BIT QUICKER THAN THE OTHER
GLOBAL GUIDANCE. THE 15Z NHC FORECAST REMAINS CLOSER TO THIS
QUICKER ECMWF SOLUTION THROUGH 12Z THURSDAY...BEFORE TRENDING A
BIT SLOWER...MORE TOWARDS A GFS/ECMWF/UKMET CONSENSUS TIMING BY
THE END OF DAY 3 OFF THE SC COAST.

WILL HAVE TO CONTINUE TO MONITOR TRENDS...AS IMPACTS ALONG THE GA
AND CAROLINA COAST WILL BE SENSITIVE TO THE EXACT TRACK OF THE
SYSTEM...WITH THE ONSET OF BIGGER IMPACTS ALONG THE WESTERN FL
PANHANDLE SENSITIVE TO THE TIMING. PLEASE CONSULT THE LATEST NHC
FORECAST ADVISORY FOR MORE INFORMATION.

19Z UPDATE: THE 12Z ECMWF TRENDED SLOWER FROM ITS 0Z RUN. BOTH THE
12Z ECMWF AND UKMET TRENDED NORTHWEST WITH THEIR TRACK AS WELL.
WILL HAVE TO CONTINUE TO MONITOR TRENDS...AS THESE SHIFTS WOULD
HAVE A SIGNIFICANT SENSIBLE WEATHER IMPACT ON PORTIONS OF FL AND
THE SOUTHEAST. GIVEN THAT THE STORM STILL APPEARS RATHER
DISORGANIZED...FUTURE SHIFTS IN THE MODELS ARE PROBABLY LIKELY.
SEE THE LATEST NHC FORECAST ADVISORY FOR MORE INFORMATION ON THE
OFFICIAL TRACK FORECAST.


CHENARD

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

$$





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