Prognostic Meteorological Discussion
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895
FXUS10 KWNH 290417
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1216 AM EDT SAT APR 29 2017

VALID APR 29/0000 UTC THRU MAY 02/1200 UTC

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

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

...CLOSED LOW DEVELOPMENT OVER THE FOUR CORNERS REGION TONIGHT
EJECTING ACROSS THE PLAINS/UPPER MIDWEST THROUGH SUN/MON SPURRING
DEEP SURFACE CYCLONE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM AND 12Z ECMWF/CMC BLEND
CONFIDENCE: AVERAGE

THE 12Z ECMWF/ECENS MEAN SHIFTED A BIT FASTER THAN YESTERDAY`S 00Z
RUN TOWARD A GROWING TIGHTER CONSENSUS DENOTED IN THE 12Z ENSEMBLE
SPAGHETTI ANALYSIS; THOUGH IT WAS A SMALL ADJUSTMENT AND THE 12Z
RUN APPEARS TO REPRESENT THE MIDDLE OF THE CLUSTER QUITE WELL
THROUGHOUT THE DURATION OF THE EVOLUTION OF THE UPPER LOW AND
SURFACE REFLECTION FROM THE SOUTHERN PLAINS INTO THE WESTERN GREAT
LAKES BY THE END OF THE FORECAST PERIOD.  WHILE THE
ENSEMBLE/DETERMINISTIC GUIDANCE IS TIGHTENING TOWARD A GENERAL
MODEL PREFERENCE/NATIONAL MODEL BLEND SOLUTION...THERE REMAIN SOME
DETAILS THAT KEEP THE 12Z ECMWF/ECENS MEAN AS WPC PREFERENCE.

THE 12Z UKMET IS INITIALLY WELL TIMED WITH THE ECMWF BUT ALSO
DEVELOPS AN UNSTABLE INNER CORE/WOBBLE TO THE UPPER LOW (NOTED BY
LOADING THE EASTERN SIDE OF THE CLOSED LOW 01/12Z MONDAY...THIS
NEGATIVELY AFFECTS A DEEP OCCLUSION OVER THE UP OF MI WHILE THE
REMAINING GUIDANCE IS BEGINNING TO FILL AND SHIFT FOCUS FURTHER
NORTHEAST INTO ONTARIO BY 12Z TUES.  THE 00Z GFS TRENDED A BIT
SLOWER INITIALLY BUT CONTINUES TO BE ON THE FASTER SIDE OF THE
GUIDANCE LEADING TO A LARGE WOBBLE/OCCLUSION ACROSS KS BREAKING
FROM ITS CONTINUITY.  AFTER THIS LARGE WOBBLE...LIKE THE UKMET IS
AN UNBALANCED UPPER LOW FAVORING A FASTER (NORTH AND EAST)
SOLUTION COMPARED TO THE ECMWF/WPC DAY PREFERENCE...THOUGH OVERALL
THE 00Z RUN FURTHER TIGHTENS THE OVERALL PACKING/SOLUTION SUITE.

THE 00Z NAM SHIFTED A BIT FASTER OVERALL AND TRENDED TOWARD A MORE
COMMON SOLUTION WITH THE 12Z ECMWF THOUGH REMAINS ON THE SLOWER
END OF THE GUIDANCE (BEST DEMARCATED AT 01/12Z). ANOTHER MINOR
DIFFERENCE IS A SLIGHT EASTWARD SHIFT OF THE TRIPLE POINT SURFACE
LOW INTO THE CENTRAL MS RIVER VALLEY BY LATE SUN INTO MON...THIS
KEEPS THE TRAILING COLD FRONT ACROSS THE OH/TN VALLEYS ACROSS THE
SOUTHEAST A SHADE FASTER THAN THE ECMWF...WHICH IS LIKELY A
POSITIVE IN THE BLEND KNOWING THE ECMWF SLOW BIAS. THE 12Z CMC
ONLY NEGATIVE IS A SLIGHT FASTER EVOLUTION TOWARD A CLOSED LOW
ALOFT ALLOWING FOR A FASTER SURFACE OCCLUSION THAT IS A BIT WEST
WITHIN THE ENSEMBLE SURFACE CLUSTER...BUT THIS QUICKLY RESOLVES
ITSELF AS IT FILLS IN FAVOR OF THE NEW TRIPLE POINT LOW.   AS SUCH
BOTH THE NAM/CMC COULD BE INCLUDED IN THE PREFERENCE HELPING TO
STABILIZE SOME SMALL VARIATION THAT WILL CONTINUE TO OCCUR FROM
RUN TO RUN.  AS SUCH A 00Z NAM AND 12Z ECMWF/CMC BLEND WEIGHTED
TOWARD THE ECMWF PROVIDES SOME INCREASED CONFIDENCE THOUGH AVERAGE
OVERALL.


...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC
NORTHWEST SAT TRANSLATING ACROSS THE S CANADIAN ROCKIES SPURRING
LEE SURFACE WAVE THAT SLIDES OUT OF ALB/SASK ACROSS N TIER LATE
MON/TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: ABOVE AVERAGE

THE REMAINS SOLID MODEL AGREEMENT IN THE TIMING/PLACEMENT OF THE
SHORTWAVE ENTERING CENTRAL BC EARLY SUNDAY WITH ASSOCIATED SURFACE
WAVE/COLD FRONT AFFECTING THE PACIFIC NORTHWEST.  AFTER LANDFALL
ON MONDAY...THE WAVE OVER TOPS THE MEAN RIDGE AND SLIDES SOUTHEAST
ALONG THE SPINE OF THE CANADIAN ROCKIES TOWARD THE DEEP CLOSED LOW
OVER THE MIDWEST.  THE 12Z UKMET AND 00Z NAM CONTINUE TO BE THE
DEEPER REPRESENTATIONS WITHIN THE GUIDANCE SUITE...AND WHILE THE
UKMET REMAINS A BIT MORE TEMPERED AS IT SHEARS INTO THE NW SIDE OF
THE DEEP CYCLONE...THE 00Z NAM REMAINS QUITE STRONG AND DISTORTS
THE UPPER LEVEL HEIGHT PATTERN QUITE SUBSTANTIALLY MAKING IT A
CLEAR OUTLIER WITHIN THE ENSEMBLE SUITE.   AS SUCH WILL SUPPORT A
NON-NAM SOLUTION AT ABOVE AVERAGE CONFIDENCE GIVEN THE REMAINING
TIGHT AGREEMENT.


...NEXT WEAK PACIFIC WAVE ENTERING PACIFIC NORTHWEST LATE MON
STARTING TO AMPLIFY OVER N ROCKIES TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/GFS AND 12Z ECMWF BLEND
CONFIDENCE: AVERAGE

A WEAK SHORTWAVE BREAKS OFF FROM DEEPER UPPER LOW OVER THE AK
PENINSULA EARLY MONDAY AND TRANSLATES ACROSS THE MEAN RIDGE IN THE
SE GULF OF AK...WITH THE VERY FAR SE EXTENTS OVER TOPPING THE MEAN
RIDGE LEADING TO A WEAK SURFACE REFLECTION THAT APPROACHES THE
JUAN DE FUCA/OLYMPIC PENINSULA 00Z TUES.  THE 00Z NAM/GFS BOTH ARE
MUCH WEAKER WITH THE WAVE WHILE THE 12Z CMC AND UKMET ARE MOST
ROBUST...WHILE THE 00Z ECMWF IS STRONGER ALOFT...IT IS WEAKER AT
THE SURFACE AS A COMPROMISE TO BOTH CAMPS.  THE PATTERN WITH THE
MEAN RIDGE FAVORS THE WEAKER SOLUTIONS OF THE NAM/GFS AND
ECMWF...AND THIS FURTHER COMPOUNDS AS THE SHORTWAVE ADVANCES
THROUGH THE COLUMBIA PLATEAU AND STARTS TO AMPLIFY ON THE LEE OF
THE RIDGE BY 12Z TUESDAY ACROSS THE SNAKE RIVER PLAIN. BY THIS
TIME THE UKMET IS FAST AND LESS AMPLIFIED...THE CMC IS SLOW BOTH
CONTINUE TO BE UNFAVORED.  THE NAM/GFS ARE A BIT MORE STRETCHED
NORTH TO SOUTH AND ECMWF A BIT MORE COMPACT SLIGHTLY FASTER...BUT
OVERALL THE DIFFERENCES ARE SMALL A BLEND OF THE 00Z NAM/GFS AND
THE 12Z ECMWF SHOULD SUFFICE AT AVERAGE CONFIDENCE.


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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