Prognostic Meteorological Discussion
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FXUS10 KWNH 240424
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1123 PM EST MON JAN 23 2017

VALID JAN 24/0000 UTC THRU JAN 27/1200 UTC

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

00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

CLOSED LOW LIFTING ACROSS THE MID-ATLANTIC/COASTAL NEW ENGLAND AND
ASSOCIATED STRONG SURFACE LOW LIFTING NORTHEAST ALONG THE COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

SMALL INTERNAL DIFFERENCES REMAIN WITH RESPECT TO THE UPPER LOW
AND EXACT PLACEMENT OF THE OCCLUDED SURFACE LOW AND TRIPLE POINT
AS THE SYSTEM LIFTS ALONG THE COAST.  THE 00Z NAM AND 12Z UKMET
ARE A BIT CLOSER TO THE COAST AT LEAST INITIALLY AND THE 00Z
GFS/12Z CMC  ARE A BIT FURTHER OFFSHORE BEFORE THE MAIN WAVE WITH
THE 12Z ECMWF MOST CENTRAL BUT ALL IN ALL THIS IS MILD OR WEAK
SPREAD FOR SUCH A LARGE/STRONG SYSTEM TO FAVOR ONE OVER ANOTHER
PARTICULARLY AS WE HAVE SEEN THESE SMALL RUN TO RUN ADJUSTMENTS
FOR THE LAST FEW DAYS/CYCLES.  AS SUCH A GENERAL MODEL BLEND IS
SUPPORTED WITH HIGHER WEIGHTING TO THE TRADITIONALLY BETTER
VERIFYING MODELS OF THE ECMWF/GFS.  STILL THESE INTERNAL RUN TO
RUN VARIATIONS LEAD TO SOME DOUBT OVERALL THAT CONFIDENCE STILL
ONLY REMAINS AT SLIGHTLY ABOVE AVERAGE.


LONGWAVE TROUGH/SURFACE LOW OVER THE WEST EJECTING OUT INTO THE
PLAINS WITH ENERGY LIFTING NORTHEAST INTO THE GREAT LAKES REGION
BY WED.  ATTENDANT COLD FRONT ADVANCING THROUGH THE EASTERN U.S.
THROUGH THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

WV LOOP INDICATES EASTERN SIDE OF THE BROAD LONGWAVE TROF IS
BEGINNING TO CONSOLIDATE/WIND UP ACROSS WY UNDER INCREASING
DIFFLUENT FLOW AND SPURRING LARGE SURFACE PRESSURE FALLS IN THE
LEE OF THE ROCKIES.  BETTER SAMPLING OF THE OVERALL PATTERN HAS
LEAD TO INCREASED CONVERGENCE OF MODEL SOLUTIONS THROUGH THE
MIDWEST INTO THE GREAT LAKES.  THERE WERE SOME NOTED THERMAL
DIFFERENCES BETWEEN THE GFS AND ECMWF PARTICULARLY ACROSS NE
NEB/IA BUT THE 00Z GFS HAS COOLED A BIT MORE TO HAVE SOME
INCREASED CONFIDENCE IN KEEPING WITHIN ANY BLEND.  OTHERWISE THE
MASS FIELDS SEEM TO JIVE WELL UNTIL WED NIGHT/THURSDAY AS THE
SYSTEM GROWS UP SCALE WITH THE NORTHWESTERN SIDE OF THE PRECEDING
DEEP WAVE...INTO THE NEW CENTROID OF CIRCULATION IN THE MID-LEVELS
ACROSS THE ONTARIO/QUEBEC BORDER.  THIS IS WERE THE WEAKER CMC
BECOMES FASTER AND REDUCES THE SURFACE AND LOWER LEVEL WAVE FASTER
ACROSS THE GREAT LAKES WED INTO THURS.  THE 00Z NAM AS IT IS KNOWN
TO DO IS THE MOST STUBBORN TO WIND DOWN THOUGH IS ACCOMPANIED BY
THE ECMWF AND LESSER SO THE UKMET/GFS.  AS SUCH A NON-CMC BLEND
WILL BE PREFERRED THOUGH MORE WEIGHTING WILL BE GIVEN TO THE 00Z
NAM/12Z ECMWF.  CONFIDENCE IS FAIRLY GOOD GIVEN THE LARGE SCALE OF
THE SYSTEM WITH SMALLER MESO-SCALE FEATURES HAVING IMPACT...AND IS
SLIGHTLY ABOVE AVERAGE IN THE BLEND.


SURFACE LOW DROPPING SOUTH DOWN OFF THE WEST COAST THROUGH TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE INNER CORE ALONG THE WESTERN SIDE OF THE LONGWAVE TROF AND
ASSOCIATED SURFACE CYCLONE CAN BE SEEN IN GOES-WV FILLING AND
TRACKING ALONG THE CA COAST ATTM.  MODELS SHOW STRONG ENOUGH
SIMILARITY WITH RESPECT TO THIS WAVE/SFC LOW TO SUPPORT GENERAL
MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.


SHORTWAVE DROPPING ACROSS THE UPPER MIDWEST/GREAT LAKES THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS AND 12Z ECMWF/UKMET BLEND
CONFIDENCE: AVERAGE

IN THE WAKE OF THE BROAD TROF TRANSLATING ACROSS THE MIDDLE OF THE
CONTINENT... A VAST POSITIVE TILT TROF DOMINATES THE PATTERN WITH
SMALLER EMBEDDED SHORTWAVES WITHIN IT.  AT THE NORTHERN SIDE OF
THE TROF...AN ELONGATED BUT ILL-DEFINED WAVE WILL DESCEND OUT OF
CANADA SHORTENING THE WIDTH OF THE TROF FROM SE ONTARIO TO THE
FOUR CORNERS BY THE END OF THE FORECAST PERIOD.  THE 00Z NAM/12Z
CMC BOTH ARE A BIT SLOWER IN THE WEST WITH A BIT MORE
AMPLIFICATION WITH SOME OF THE EMBEDDED SHORTWAVES CROSSING THE
GREAT LAKES...WHILE THE GFS/UKMET/ECMWF ARE A BIT MORE IN LINE
WITH COMMON AXIS/ORIENTATION.  THE 00Z GFS DID INDICATE A
SHARPER/NARROW WESTERN BASE HAVING A MUCH MORE WOUND UP MID-LEVEL
VORT CENTER THAN THE UKMET/ECMWF BUT ENSEMBLE SPREAD SUPPORTS BOTH
A BROADER WAVE LIKE THE UKMET/ECMWF AS WELL AS THE TIGHTER GFS.
AT THIS POINT FEEL FOCUS/IMPORTANCE ON ORIENTATION/TIMING OF THE
TROF THAN THE EXACT DEPTH...PARTICULARLY GIVEN THE LACK OF
QPF/SENSIBLE WEATHER WITH IT.  CONFIDENCE IN THIS BLEND IN ONLY
AVERAGE GIVEN THESE WESTERN DEPTH DIFFERENCES THAT REMAIN.


SHORTWAVE APPROACHING THE WEST COAST LATE WED/EARLY THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A NARROW BUT ELONGATED TROF WILL EXTEND FROM THE GULF OF AK TO
ABOUT 40N BY 12Z WED WITH AN ACCOMPANYING COLD FRONT.  DOWNSTREAM
AN EQUALLY NARROW RIDGE WILL CONTINUE TO AMPLIFY INTO SW CANADA
AND ALLOW THE TROF ENERGY TO UNDERCUT THE RIDGE BY THURSDAY
MORNING BRINGING LIGHT SHOWERS. THE 12Z CMC IS A BIT SLOWER MAINLY
IN THE BASE OF THE TROF (MORE IMPACTING PORTION OF THE TROF)
COMPARED TO OTHERWISE GOOD MODEL AGREEMENT THROUGH 12Z THURSDAY.
AS SUCH A NON-CMC BLEND IS SUPPORTED AT SLIGHTLY ABOVE AVERAGE
CONFIDENCE.  AFTER THURSDAY  THERE IS INCREASED MODEL DIFFERENCE
HOW THE ENERGY ENTERS THE WESTERN "BASE" OF THE ELONGATED POSITIVE
TILT TROF.  PLEASE SEE SECTION ABOVE ADDITIONAL DETAILS.

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

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

GALLINA

$$





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