Prognostic Meteorological Discussion
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FXUS10 KWNH 251650
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1250 PM EDT TUE APR 25 2017

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

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

12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES/CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...CONSOLIDATING CYCLONE MOVING UP THE EAST COAST THROUGH THU...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z NAM BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE ENSEMBLE SCATTER LOW PLOTS HAVE SHOWN A GRADUAL TREND TO THE
NORTH OVER THE PAST 3-4 12/00Z CYCLES...AND WHILE THERE ARE SOME
MINOR PLACEMENT DIFFERENCES WITH THE SURFACE AND MID-LEVEL LOW
TRACKING NEAR THE NEW ENGLAND COAST...THE BIGGEST DIFFERENCE MAY
BE WITH THE PLACEMENT OF THE 500 MB LOW BY 00Z/28 WITH THE 12Z NAM
DISPLACED FARTHER OFFSHORE COMPARED TO THE REMAINING MODEL
GUIDANCE. OUTSIDE OF THE 12Z NAM...GOOD MODEL AGREEMENT EXISTS
WITH THIS SYSTEM.


...SURFACE CYCLONE REACHING THE PACIFIC NORTHWEST TODAY/TONIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


...LOW AMPLITUDE SHORTWAVE REACHING THE PACIFIC NORTHWEST WED
MORNING AND REACHING THE SRN/CNTRL PLAINS FOR THU NIGHT...
...WEAK SURFACE LOW TRACKING INTO THE MIDWEST ON FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE MODELS SHOW MINOR DIFFERENCES WITH THIS SYSTEM AS IT KICKS OUT
INTO THE PLAINS REGARDING MID-LEVEL HEIGHTS AND THE SURFACE LOW
WEAKENING FROM THE SRN PLAINS TOWARD THE MISSISSIPPI VALLEY.
DESPITE MODEL DIFFERENCES...ENSEMBLE SPAGHETTI HEIGHTS AND SCATTER
LOW PLOTS DO NOT SHOW ANY DETERMINISTIC RUN TO BE AN OUTLIER AND
THERE IS BROAD ENOUGH AGREEMENT WITH THIS SYSTEM TO RECOMMEND A
GENERAL MODEL COMPROMISE.


...SHORTWAVE DROPPING INTO DEVELOPING LARGE SCALE TROUGH ACROSS
THE INTERMOUNTAIN WEST FRI/SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND
CONFIDENCE: BELOW AVERAGE

ENSEMBLE SPAGHETTI HEIGHTS SHOW MODEST SPREAD EVOLVING ACROSS THE
WRN U.S. THROUGH FRI WITH LARGE DIFFERENCES SEEN IN THE 552 DAM
HEIGHT. THE PREFERENCE FOR NOW WILL BE TO STAY TOWARD THE MIDDLE
OF THE SPREAD...WITH THE 12Z GFS A BIT DEEPER ACROSS THE SOUTHWEST
REGARDING THE MID-LEVEL TROUGH AND THE 00Z ECMWF A BIT
NORTH/WEAKER. A GFS/ECMWF BLEND IS PREFERRED GIVEN THE BLENDS
PLACEMENT IN THE MIDDLE OF THE ENSEMBLE SPREAD BUT CONFIDENCE IS
LOW GIVEN THE BROAD NATURE OF THIS SYSTEM.


...SYSTEM MOVING NORTHWARD THROUGH THE PLAINS INTO SE CANADA ON
THU...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF BLEND
CONFIDENCE: AVERAGE

A PORTION OF THIS SYSTEM IMPACTS THE N-CNTRL U.S. TUE NIGHT INTO
WED WITH A 500 MB VORT CENTER AND CORRESPONDING 850 MB LOW. WHILE
THE 12Z NAM APPEARS REASONABLE WITH ITS PLACEMENT...IT IS
DISPLACED SLIGHTLY WEST OF THE ENSEMBLE MEANS 12Z/26...WHILE THE
00Z UKMET/CMC ARE SIGNIFICANTLY SLOWER/WEAKER WITH THE 500 MB
REFLECTION BY 00Z/27. ENSEMBLE SPAGHETTI HEIGHT SUPPORT A BLEND OF
THE 12Z NAM/GFS AND 00Z ECMWF HERE.

FARTHER SOUTH...A NEGATIVELY TILTED SHORTWAVE IS FORECAST TO SWING
ACROSS THE MISSISSIPPI VALLEY WED NIGHT AND THE DISTANCE BETWEEN
THIS FEATURE AND THE CLOSED LOW HAS IMPACTS FOR LATER IN THE
FORECAST. WHILE THE 00Z UKMET/CMC SHOW POORLY WITH RESPECT TO THE
BETTER ENSEMBLE CONSENSUS ACROSS THE N-CNTRL U.S. BY 00Z/27...THE
NAM SHOWS SOME BROAD SUPPORT FOR THE UKMET/CMC. HOWEVER...THE
BETTER ENSEMBLE CLUSTERING IS NEARER TO THE 12Z GFS AND 00Z ECMWF
WITH THE EVOLUTION OF THE UPPER SYSTEM AND SURFACE COLD FRONT
MOVING THROUGH THE OHIO VALLEY INTO THE MID-ATLANTIC REGION FOR
THU/FRI.


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

OTTO/MCDONNAL

$$





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