Prognostic Meteorological Discussion
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FXUS10 KWNH 231627
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1227 PM EDT SUN APR 23 2017

VALID APR 23/1200 UTC THRU APR 27/0000 UTC

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

12Z MODEL EVALUATION WITH PREFERENCES/CONFIDENCE INTERVALS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

DEEP SYSTEM MOVING UP THE EAST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/GFS AND 00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THERE IS FAIRLY GOOD AGREEMENT IN THE GLOBAL GUIDANCE THROUGH THE
FIRST 36 HRS AS THE DEEP UPPER LOW REACHES THE BASE OF ITS CURVE
THROUGH THE SOUTHEAST.  AFTER THIS POINT THE 00Z CMC QUICKLY
BREAKS FROM THE PACK AND RAPIDLY WEAKENS THE UPPER LOW AND
ACCELERATES NORTHEAST AND IS WELL OUT OF THE ENSEMBLE AGREEMENT.
BY 00Z WED...THERE IS FURTHER SPREAD AS THE 00Z UKMET BEGINS TO
BREAK FASTER/WEAKER PARTICULARLY AT 5H-7H LEVELS THAN THE OTHER
GUIDANCE EVEN FASTER THAN THE 12Z GFS WHICH SLOWED SLIGHTLY BUT IS
FASTER THAN THE 12Z NAM/ECMWF AS WELL AS THE 00Z/06Z GEFS MEAN.
OVERALL THOUGH THE SPREAD BETWEEN THE GFS/NAM AND ECMWF IS WELL
WITHIN THE TOLERANCE OF THE TIGHTENING ENSEMBLE SPREAD PROVIDING
SLIGHTLY ABOVE AVERAGE CONFIDENCE IN A BLEND OF THE THREE.


LEADING HEIGHT FALLS/SHORTWAVE CROSSING THE N ROCKIES TODAY WITH
SURFACE LOW IN MT TO SD TODAY INTO MON WEAKENING THROUGH LK
SUPERIOR TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: ABOVE AVERAGE

GOES-WV MOSAIC SHOWS ROBUST SHORTWAVE CURRENTLY OVER N CENTRAL CA
THIS WAVE WILL CONTINUE TO PROGRESS EASTWARD BUT INTERACT WITH
SHORTWAVE ENERGY ACROSS SW CANADA STRETCHING ACROSS THE NORTHERN
ROCKIES AS LEAD HEIGHT FALLS TO INCREASING TROUGHING ACROSS THE
WEST.  THIS SPURS A LEE CYCLONE OVER MT THAT WILL CROSS WY INTO SD
BY EARLY MONDAY...EVENTUALLY WEAKENING INTO THE APEX OF BROAD
SURFACE TROF ACROSS THE WESTERN GREAT LAKES.  THE 12Z NAM TRENDED
TOWARD A DEEPER REFLECTION OF THE NORTHERN STREAM SHORTWAVE WHICH
IN TURN MAINTAINS A STRONGER AND FURTHER NORTH SURFACE LOW ACROSS
N MN BY 00Z TUES.  THE REMAINING GUIDANCE INCLUDING THE 00Z UKMET
(WHICH HAD BEEN A STRONGER OUTLIER LIKE THE NAM YESTERDAY) APPEARS
TO BE IN LINE WITH EACH OTHER AND TIGHTENING ENSEMBLE CLUSTER.  AS
SUCH WILL FAVOR A NON-NAM BLEND AT THIS AT ABOVE AVERAGE
CONFIDENCE.


PAIR OF SHORTWAVES WITH ASSOCIATED SURFACE WAVE APPROACHING NW
COAST MON LEADS TO BROAD AMPLIFYING TROF ACROSS THE INTERMOUNTAIN
WEST TUES BEFORE EMERGING INTO THE CENTRAL PLAINS WED WITH
ACCOMPANYING BROAD ELONGATED SURFACE WAVE THROUGH THE GREAT PLAINS
INTO THE UPPER MIDWEST TUES/WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS AND 00Z ECMWF BLEND
CONFIDENCE: AVERAGE

A PAIR OF VORT CENTERS INTERACT ALONG THE NW PACIFIC COAST MON
WITH FAIRLY GOOD MODEL AGREEMENT WITH ONLY EXCEPTION BEING THE 00Z
CMC WHICH WAS WELL SLOWER THAN THE OTHERWISE TIGHTENING CLUSTER.
AS THE PAIR SHIFT EASTWARD INTO THE ROCKIES THEY FURTHER AMPLIFY
THE BROAD WESTERN TROF AIDING LEE SURFACE CYCLOGENESIS IN THE
TX/OK PANHANDLES BY MON EVENING.  EVENTUALLY BOTH ORIENT INTO A
SHARPER POSITIVE TILT TROF AS THEY EJECT INTO THE PLAINS WED.
THE 00Z CMC CONTINUES TO LAG BUT ALSO BY THIS TIME THE 00Z UKMET
ALSO BECOMES A SLOW AND MORE CLOSED UPPER LOW IN THE BASE OF THE
TROF A CLEAR OUTLIER WITHIN THE ENSEMBLE SPAGHETTI ANALYSIS PLOT.
THE 12Z NAM APPEARS FAIRLY WELL TIMED/PLACED WITH THE INNER
DETAILS OF THIS WAVE...HOWEVER DUE TO INTERACTION WITH THE DEEPER
EXITING LEAD WAVE (SEE SECTION ABOVE) APPEARS TO BE DRAWN DEEPER
FURTHER NORTH LEADING TO A FASTER WEAK SURFACE WAVE LIFTING INTO
THE WESTERN GREAT LAKES WED.   WHILE THIS NAM SOLUTION IS
SUPPORTED SLIGHTLY BY THE 00Z OPERATIONAL ECMWF (PARTICULARLY IN
THE LOWER LEVELS/SFC)...THE 00Z OPERATIONAL EC IS ALSO ON THE
NORTHWEST PERIPHERY OF THE ECENS SURFACE CLUSTER.  THE 12Z GFS
SHOWS LITTLE CHANGE FROM THE 00Z/06Z RUNS PERHAPS A BIT SHARPER
WITH THE TROF ACROSS THE PLAINS ON WED...BUT MATCHES WELL WITH THE
00Z ECENS MEAN/06Z GEFS MEAN.  AS SUCH A BLEND OF THE 12Z GFS/00Z
ECMWF WILL BEST REPRESENT THE ENSEMBLE MEANS AND OVERALL
CONTINUITY FAIRLY WELL.  STILL INTERNAL SMALL SCALE DETAILS REMAIN
QUITE VARIABLE TO HAVE THE HIGHEST CONFIDENCE BUT OVERALL BUT IS
ON THE HIGHER SIDE OF AVERAGE.


SYSTEM APPROACHING THE PACIFIC NORTHWEST TUE NIGHT/WED MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A NARROW AMPLIFIED RIDGE DOMINATES BC BY TUES THOUGH IS SLOWLY
SHIFTING EASTWARD WITH TIME.  STILL THE NEXT WAVE EMERGING FROM
THE PACIFIC LATE TUESDAY/EARLY WED REACHES THE BLOCK AND DEVELOPS
A CYCLONE ALONG THE BC COAST INTO WED BUT ALSO SHEARS A LARGE
PORTION OF THE WAVE UNDER THE RIDGE INTO THE PACIFIC
NORTHWEST...ALSO ESTABLISHING TIGHT HEIGHT PACKING/STRENGTHENING
JET...ALLOWING FOR ADDITIONAL UPSTREAM WAVES TO FOLLOW AS WELL AS
RELOADING THE LARGER SCALE TROF OVER THE WEST LATE WED INTO THURS.
 WHILE THERE ARE SOME SMALL TIMING DIFFERENCES...THE OVERALL
PATTERN APPEARS QUITE STRONGLY AGREED UPON TO HAVE SLIGHTLY ABOVE
AVERAGE CONFIDENCE IN SUGGESTING A GENERAL MODEL BLEND FOR THIS
SYSTEM/FLOW REGIME.


WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/

GALLINA

$$





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