Prognostic Meteorological Discussion
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000
FXUS10 KWNH 251605
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1205 PM EDT SUN SEP 25 2016

VALID SEP 25/1200 UTC THRU SEP 29/0000 UTC

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

12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

DEEP CYCLONE MOVING NEAR THE US/CANADIAN BORDER BEFORE MOVING
SOUTH THROUGH CENTRAL GREAT LAKES TUES/WED...FRONT THROUGH EAST
COAST BY WED MIDDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/NAM AND 00Z UKMET BLEND
CONFIDENCE: ABOVE AVERAGE

MODEL AGREEMENT IS VERY STRONG THROUGH MUCH OF THE DEPTH OF
CYCLONE THROUGH 27/12Z WITH ONLY THE 00Z CMC LAGGING EVER SO
SLIGHTLY.  SLIGHT DIFFERENCES MANIFEST IN THE TIMING/SHAPE OF THE
FRONTAL ZONE THROUGH NEW ENGLAND ON TUESDAY EVENING WITH THE 00Z
UKMET/ECMWF BOTH SUGGESTING A STRONGER TRIPLE POINT AND
PROGRESSING FRONT THROUGH NEW ENGLAND MUCH FASTER THAN THE GFS.
THIS SEEMS PLAUSIBLE GIVEN THE STRENGTH OF DARKENING SEEN IN
WV/STRATOSPHERIC INTRUSION CURRENTLY SEEN OVER ND...SO TO HEDGE
WILL BLEND THE SUITE WITH THIS TIMING.

AFTERWARD...SPREAD INCREASES ALOFT MAINLY WITH THE OCCLUSION/UPPER
LOW ACROSS THE GREAT LAKES.  THE 00Z CMC BEING FURTHER WEST KEEPS
RIDGING BETWEEN THIS ENERGY AND DESCENDING SHORTWAVE ENERGY FROM
THE DAVIS STRAIT/LABRADOR SEA.  THE REST OF THE GUIDANCE BREAKS
THE RIDGE AND SHOWS A CONNECTION LEADING TO AN ELONGATED TROF THAT
DESCENDS INTO THE LOWER CENTRAL GREAT LAKES AND EVENTUALLY UPPER
OHIO VALLEY BY THE END OF THE FORECAST PERIOD.  THE 00Z ECMWF
WHICH HAS THE BIAS OF BEING A BIT SLOWER AND MORE WOUND UP LIVES
UP TO ITS BIAS...AND THEREFORE IS A BIT FURTHER WEST AND LESS
ELONGATED THAT THE 00Z UKMET AND 12Z NAM/GFS.  THIS PLACES THE
ECMWF ON THE WESTERN PERIPHERY OF BEST GUIDANCE INCLUDING
WEST(SOUTHWEST) OF 00Z ECENS MEAN.  AT THE SFC THIS MANIFESTS AS A
FASTER WEAKENING AND TRANSITION ACROSS THE OHIO RIVER VALLEY AND
LEE SIDE CAROLINA DEVELOPMENT BY WED NIGHT.  THE 00Z UKMET IS A
BIT MORE ELONGATED WITH THE TROF SSW TO NNE THAN THE 12Z NAM OR
GFS.  THE 12Z GFS TRENDED A BIT WEST CLOSER TO THE 00Z ECENS MEAN
OVERALL...HOWEVER KEEPS IN GOOD CONTINUITY WITH PRIOR RUNS AS
WELL.  GIVEN THE ECMWF CONTINUES TO SHOW POOR CONTINUITY/CHANGING
APPEARANCE OVER THE PAST FEW DAYS WILL FAVOR A 12Z GFS/NAM AND 00Z
UKMET BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.


CLOSED LOW IN E AZ/W NM MAKING ANTICYCLONIC LOOP ACROSS NW MEXICO
INTO S CA/W AZ BY TUE/WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

REMARKABLE AGREEMENT IN SHAPE/TIMING AND PLACEMENT EXIST WITH THE
DEVELOPING CLOSED LOW AFTER THE ANTICYCLONIC WAVE BREAK IN NM
TODAY THROUGH MUCH OF THE FORECAST TIME PERIOD.  AS THE SYSTEM
LIFTS NORTH THROUGH THE LOWER COLORADO RIVER VALLEY THE 12Z NAM
AND GFS BEGIN TO ELONGATE AND LIFT SLIGHTLY FASTER UNDER INFLUENCE
OF INCREASING SWLY FLOW/DIGGING TROF IN THE PACIFIC NORTHWEST.
THIS IS ONLY NOTICEABLE AFTER 12Z ON THE 28TH...AND AS SUCH THERE
IS LITTLE TO SUGGEST CHANGING A GENERAL MODEL BLEND PREFERENCE AT
THIS TIME.  CONFIDENCE REMAINS VERY HIGH IN THIS BLEND`S
EVOLUTION.


SYSTEM CLIPPING THE PACIFIC NORTHWEST MON NIGHT/TUES WITH TAIL END
OF FRONTAL ZONE THROUGH MT/ND WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

WHILE THERE IS SOME SPREAD WITH THE SHORTWAVE AND SURFACE
REFLECTION IN TIMING WITH THE 00Z CMC/ECMWF FASTER THAN THE UKMET
AND 12Z GFS/NAM.  HOWEVER THE TRAILING EDGE OF THE FRONT CLIPS THE
NORTHWEST AND CROSSES THE NORTHERN US ROCKIES TUES INTO WED WITH
VERY SIMILAR SPEED/SHAPE AND ORIENTATION TO SUPPORT A GENERAL
MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.


TROF DIGGING TOWARD PACIFIC NORTHWEST BY WED EVENING/THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

A MORE CONCENTRIC DEEPER CYCLONE ADVANCES SOUTHEASTWARD TOWARD BC
AND THE PACIFIC NORTHWEST WITH BROAD SWLY FLOW ACROSS WA/OR/N CA
BY THE END OF THE FORECAST PERIOD.  MASS FIELDS ARE REMARKABLY
SIMILAR IN TIMING/STRENGTH AND SHAPE OF THE WAVE TROUGH THE
TROPOSPHERIC COLUMN.  THE 12Z NAM AND 00Z CMC ARE SLIGHTLY DEEPER
BUT WELL WITHIN SPEC TO SUPPORT GENERAL MODEL BLEND AT ABOVE
AVERAGE CONFIDENCE EVEN AT THIS FAR OUT IN TIME.

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

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

GALLINA

$$





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