Prognostic Meteorological Discussion
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FXUS10 KWNH 241833
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT SAT SEP 24 2016

VALID SEP 24/1200 UTC THRU SEP 28/0000 UTC

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

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

DEEP CYCLONE MOVING NEAR THE US/CANADIAN BORDER
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/UKMET/ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

MODELS CONTINUE TO CONVERGE ON A COMMON SOLUTION WITH THE UPPER
LOW AND ASSOCIATED SURFACE LOW TRACKING ACROSS THE NORTHERN TIER
AND NORTHERN GREAT LAKES.  MINUS THE 00Z CMC (A BIT TOO SLOW AND
FURTHER NORTH)...THE ENSEMBLE SUITE SHOWS VERY STRONG AGREEMENT
THROUGH 60HRS (27/00Z).  SMALL DIFFERENCES IN TIMING/STRENGTH OF
INTERNAL SHORTWAVES AS WELL AS AMPLITUDE OF DOWNSTREAM RIDGE LEAD
TO THE LARGER MODEL SPREAD WED.   THE 00Z UKMET PER ITS BIAS IS A
BIT STRONGER AND FASTER WITH INTERNAL WAVES AND LEADS TO EARLIER
STALLING/PIVOTING ACROSS LAKE SUPERIOR THEN AS A
STRONGER/CONCENTRIC COMPARED TO AVERAGE CLOSED LOW DESCENDS ACROSS
LAKE MICHIGAN.  THE 00Z ECMWF COMES OFF A DRAMATIC CHANGE FROM
YESTERDAY`S 12Z RUN WITH A MUCH MORE REASONABLE/CENTRIC SOLUTION
TO THE DEEP CYCLONE.  THIS HAS SIMILARITIES TO THE UKMET IT IS
SLOWER/STRONGER WITH INTERNAL WAVES AND STARTS A SOUTHERLY OR
SSE-LY TRACK BUT AFTER THE UKMET LATER ON WED.  HOWEVER...THE
ECMWF SHOWS SIMILARITIES TO THE MORE CONSISTENT GFS/GEFS SOLUTIONS
MAKING IT OVERALL QUITE PREFERENTIAL AT THIS TIME.

THE 12Z NAM CONTINUES TO BE A BIT DIFFUSE WITH OVERALL UPPER LOW
BUT QUITE STRONG/CONSOLIDATED WITH INTERNAL SHORTWAVE
FEATURES...IT IS ALSO THE MOST AGGRESSIVE MODEL IN BREAKING DOWN
THE DOWNSTREAM RIDGE ALLOWING FOR A FASTER EASTWARD PROGRESSION
COMPARED TO THE REST OF THE GUIDANCE...THOUGH ONLY STEPPING
FORWARD OF THE ECMWF/GFS/ENSEMBLE MEAN SURFACE LOW IN THE
AFTERNOON OF WED.   THE 12Z GFS HAS SLOWED A BIT RESOLVING A
STRONGER INTERNAL SHORTWAVE/DEEPER OCCLUSION WEST OF THE 06Z
GFS/GEFS SOLUTIONS AND WEST OF THE NAM VERY NEAR THE 00Z ECMWF.
OVERALL CONFIDENCE CONTINUES TO INCREASE AS THE DIFFERENCES
CONTINUE TO SMALLER SCALE INTERNAL RUN TO RUN VARIATIONS...A BLEND
OF THE 12Z GFS/00Z ECMWF IS PREFERRED TOUGH CANNOT FULLY DISCOUNT
THE 00Z UKMET OR 12Z NAM (09Z SREF) WHICH COULD PROVE USEFUL
(PARTICULARLY BEFORE 72HRS).  CONFIDENCE IS SLIGHTLY ABOVE AVERAGE
IN THIS BLEND.

19Z UPDATE: A SLIGHT WEAKENING IN THE 12Z UKMET ALLOWED FOR A
SLIGHTLY SLOWER PIVOT OVER THE NORTHERN GREAT LAKES AND WHILE IT
REMAINS SLIGHTLY FASTER IT IS NOW MUCH CLOSER TO EARLIER/INITIAL
PREFERENCE.  THE 12Z ECMWF SHOWED THIS SLIGHT SOUTHWARD SHIFT AS
WELL MATCHING VERY WELL WITH THE UKMET.  THE 12Z CMC ALSO SHIFTED
TOWARD THE CONSENSUS BUT STILL REMAINS ON THE WESTERN SIDE OF THE
GUIDANCE.  ALL IN ALL THE TIGHTENING OF THE SOLUTIONS SUPPORTS
LESS NAM/SREF BLENDING TOO...LEADING TO A 12Z GFS/UKMET/ECMWF
BLEND WITH INCREASED CONFIDENCE...STILL SLIGHTLY ABOVE AVERAGE.


DEVELOPING CLOSED LOW IN NM SUNDAY RETROGRADING TROUGH NW MEXICO
INTO S CA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

MODELS APPEAR TO HAVE SETTLED ON A GENERAL CONSENSUS OF
PLACEMENT/STRENGTH AND TIMING WITH RESPECT TO THE ANTICYCLONIC
WAVE BREAKING EVENT ACROSS THE FOUR CORNERS REGION SAT
NIGHT/SUNDAY MORNING.  THE 00Z CMC IS A BIT WEAKER AND SLOWER AND
THE 00Z UKMET IS A BIT STRONGER AND SOUTHWEST TYPICAL OF
TRADITIONAL PLACEMENT IN ENSEMBLE/DETERMINISTIC CLUSTER...AS SUCH
WILL SUPPORT AN OPERATIONAL MODEL BLEND AT ABOVE AVERAGE
CONFIDENCE IN THE MASS FIELDS.

19Z UPDATE: MASS FIELDS REMAIN FAIRLY ALIGNED THOUGH SOME SPREAD
REMAINS IN THE QPF SOLUTIONS...AS SUCH PLEASE REFER TO
QPFPFD/EXCESSIVE RAINFALL OUTLOOK FOR ADDITIONAL
DETAILS/PREFERENCES FOR HAZARDS.


UPPER TROUGH/FRONT CLIPPING THE PACIFIC NORTHWEST EARLY TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A BROAD TROF IN THE EASTERN GULF OF ALASKA STARTS TO BREAK DOWN
THE RIDGING ACROSS THE NORTHWEST/WESTERN CANADA  WITH SOLID MODEL
AGREEMENT WITH THE PLACEMENT OF THE FRONTAL ZONE INTO CENTRAL BC
WITH A LEADING SFC WAVE MAKING LANDFALL SUNDAY.  THE BASE OF THE
TROF BEGINS TO LIFT NORTHEAST ON MONDAY AND TUESDAY WITH SOME
DIFFERENCES IN TIMING/CONSOLIDATION OF THE WAVE... THE UKMET IS A
BIT FAST WHILE THE NAM/GFS ARE SLOWER BUT ALSO STRONGER THAN THE
ELONGATED/SHEAR ZONE THAT SAGS TOWARD VANCOUVER ISLAND/PACIFIC
NORTHWEST TUESDAY MORNING.  THE SURFACE WAVE REMAINS FAR ENOUGH
NORTH FOR LITTLE IMPACT TO THE PAC NW...WITH AN EVENTUAL WEAK
FRONTAL PASSAGE LATE TUESDAY/00Z WED WITH LIMITED SENSIBLE WEATHER
DIFFERENCES.   THOUGH THERE IS SOME DIFFERENCES WITH THIS
SECONDARY SURFACE WAVE MOVING INTO CANADA MONDAY AND LARGER SPREAD
AS THE ENERGY CROSSES THE CANADIAN ROCKIES...THE AFFECTS IN THE
CONUS ARE MINOR TO SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE
CONFIDENCE.

19Z UPDATE: THE 12Z ECMWF TRENDED A BIT DEEPER AND SLOWER WITH THE
UPPER LEVEL WAVE BUT KEEPS A SIMILAR TRACK WITH THE SFC WAVE AND
THEREFORE STILL FAIRLY NORTH OF THE PAC NW.  ALL CONSIDERED WILL
CONTINUE THE GENERAL MODEL BLEND DUE TO THE LIMITED SPREAD AND
SENSIBLE WX IMPACTS.


SOUTHERN EDGE OF DEEP TROF/UPPER LOW EXITING NEW ENGLAND SUNDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

EXCELLENT MODEL AGREEMENT EXISTS WITH TIGHT HEIGHT CLUSTERING AND
INTERNAL SHORTWAVE FEATURES AFFECTING NEW ENGLAND/UPPER
MID-ATLANTIC TODAY INTO TOMORROW BEFORE SHIFTING AWAY MONDAY.
ONLY THE 12Z NAM BEING A BIT FASTER BREAKING DOWN THE UPSTREAM
RIDGING DIFFERS BY THE VERY END OF THE PERIOD.  THIS IS A MINOR
DIFFERENCE WITH LITTLE IMPACT WITH THIS SYSTEM TO MAINTAIN A
GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.


LINGERING MID-LEVEL LOW IN SOUTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

MODELS CONTINUE VERY GOOD AGREEMENT WITH RESPECT TO THE LINGERING
MID-LEVEL ENERGY REMAINING  ACROSS THE SOUTHEAST.  A SLOW SE DRIFT
WILL CONTINUE INTO WESTERN FL PANHANDLE SUN INTO MONDAY BEFORE THE
SMALL AREA OF RIDGING TO THE NORTH IS SQUEEZED PRESSING THE
REMAINS SOUTH INTO THE EASTERN GULF.  ONLY THE 12Z NAM DIFFERS
FROM THE MAIN GUIDANCE AFTER MONDAY...REFOCUSING THE CENTER OF THE
WAVE FURTHER SOUTH TOWARD W CUBA BY THE END OF THE PERIOD... THIS
IS GENERALLY MINOR AND WILL CONTINUE TO FAVOR A GENERAL MODEL
BLEND AT ABOVE AVERAGE CONFIDENCE.


...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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