Prognostic Meteorological Discussion
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000
FXUS10 KWNH 281850
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 PM EDT FRI APR 28 2017

VALID APR 28/1200 UTC THRU MAY 02/0000 UTC

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

12Z MODEL EVALUATION...INCLUDING FINAL MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...COLD FRONT CLEARING THE NORTHEAST EARLY FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

ONLY VERY MODEST MASS FIELD SPREAD IS NOTED WITH THIS SYSTEM. A
GENERAL MODEL BLEND SHOULD SUFFICE.


...UPPER LOW OVER SOUTHERN ALBERTA MOVING SLOWLY EAST ACROSS
SASKATCHEWAN BY SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

ONLY MINOR TIMING/DEPTH DIFFERENCES WITHIN THE MODELS WERE NOTED
WITH THIS SYSTEM AS IT SLOWLY MOVES EAST INTO SASKATCHEWAN BY
SAT...BUT THE MODELS AGREE IN DAMPENING THE ENERGY OUT BY SUN. NO
SIGNIFICANT TRENDS WERE NOTED IN THE 12Z GUIDANCE COMPARED TO
PREVIOUS RUNS...UNTIL PERHAPS MUCH LATER IN THE FORECAST PERIOD AS
THE ENERGY IS SHEARING EAST ACROSS NRN ONTARIO. A GENERAL MODEL
BLEND IS PREFERRED.


...INITIAL TROUGH/HEIGHT FALLS OVER THE HIGH PLAINS TODAY WITH
WEAKENING SURFACE LOW TRACKING EAST FROM KANSAS THIS MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

SURFACE LOW ADJUSTMENTS BY THE 12Z CMC COMPARED TO ITS PREVIOUS
CYCLE ARE IN THE DIRECTION OF THE REMAINING MODELS...THROUGH 00Z
INTO THE KS/MO BORDER TONIGHT. THIS FEATURE BECOMES
INDISTINGUISHABLE BEYOND ABOUT 06Z TONIGHT AND THE LATEST
DETERMINISTIC/ENSEMBLE GUIDANCE NOW SHOWS SIMILARLY WITH THIS
FEATURE.


...AMPLIFYING TROUGH OVER THE INTERMOUNTAIN WEST...
...CLOSED LOW DEVELOPMENT OVER THE FOUR CORNERS REGION FRI/SAT...
...SYSTEM EJECTING ACROSS THE PLAINS/MIDWEST THROUGH SUN/MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z ECMWF/00Z ECMWF MEAN
CONFIDENCE: AVERAGE

THE ECMWF/CMC HAVE GENERALLY BEEN MORE CONSISTENT WITH THE TIMING
OF THE UPPER LOW AS IT REACHES THE PLAINS SUN MORNING BUT THE 00Z
ECMWF/CMC ARE SOUTH OF THE REMAINING GUIDANCE. THE 12Z ECMWF/CMC
ADJUSTED NORTH SLIGHTLY WITH THE MID-LEVEL LOW AND SURFACE LOW
TRACKS BUT NOT TO THE EXTENT OF THE 12Z GFS. THE GFS HAS BEEN
SOMEWHAT INCONSISTENT FROM RUN TO RUN AND THE 12Z GFS HAS ADJUSTED
NORTH FROM PREVIOUS CYCLES...AND LIES ON THE NRN EDGE OF THE
LATEST ENSEMBLE SPREAD. TRENDS IN THE ENSEMBLES HAVE SHOWN A
SLOWER SHIFT TOWARD THE SOUTH ON SUN ACROSS THE CNTRL PLAINS WITH
THE 500 MB LOW AND THE 00Z ECMWF APPEARS TO BE ON THE SRN EDGE OF
THE LATEST ENSEMBLE GUIDANCE. THE 12Z ECMWF MAY BE A HAIR TOO FAR
NORTH GIVEN THE LATEST ENSEMBLE DISTRIBUTION BUT WHEN BLENDED WITH
THE SLOWER/MORE-SOUTH 00Z ECMWF MEAN...A PREFERRED COMPROMISE IS
REACHED.

THERE IS GROWING CONVERGENCE ON THE TIMING OF THE CLOSED LOW
EJECTING OUT THROUGH THE PLAINS INTO THE UPPER MIDWEST WITH EACH
ENSEMBLE CYCLE BUT THE ECMWF MEAN APPEARS TO BE THE MOST
CONSISTENT AND REPRESENTS THE BEST CLUSTERING OF THE LATEST
ECMWF/GEFS/CMC MEMBERS. THE 00Z ECMWF MEAN LIES SLIGHTLY
SOUTH/SLOWER COMPARED TO THE SLIGHTLY MORE NORTHERN 12Z ECMWF AND
THE SIGNIFICANTLY FARTHER NORTH 12Z GFS POSITION ON SUN. FOR
MON...THE 12Z ECMWF/00Z ECMWF ARE RATHER SIMILAR TO ONE ANOTHER.


...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC
NORTHWEST SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE 12Z UKMET ADJUSTED SLIGHTLY FASTER TOWARD THE REMAINING MODEL
CONSENSUS...INCREASING CONFIDENCE IN THE LATEST WELL CLUSTERED
MODEL CONSENSUS.REGARDING THE PROGRESSION OF THE UPPER TROUGH AND
SURFACE LOW THROUGH SWRN CANADA BUT DIFFERENCES ARE MINOR HERE AND
ALMOST NON-EXISTENT ACROSS THE PACIFIC NORTHWEST.


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

OTTO

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