Prognostic Meteorological Discussion
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000
FXUS10 KWNH 271837
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
237 PM EDT SAT MAY 27 2017

VALID MAY 27/1200 UTC THRU MAY 31/0000 UTC

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

12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

WEAK MID LEVEL SHORTWAVE/SURFACE LOW TRACKING INTO THE MID
ATLANTIC TODAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

12Z NAM AND GFS CONTINUE TO BACKUP TO THE 00Z ECMWF/UKMET/CMC FOR
STRONG AGREEMENT WITH THE WEAK SHORTWAVE/SURFACE REFLECTION
CROSSING THE CENTRAL MID-ATLANTIC TODAY.  AS SUCH A GENERAL MODEL
BLEND REMAINS PREFERENCE AT INCREASED CONFIDENCE (SLIGHTLY ABOVE
AVERAGE.

BOTH THE 00 UTC NAM AND GFS ARE A LITTLE SLOWER THAN THEIR 12 UTC
RUNS WITH THE SURFACE LOW AS IT TRACKS EAST FROM THE OH VALLEY
INTO THE MID ATLANTIC REGION SAT MORNING.  THERE ARE SOME SLIGHT
TIMING DIFFERENCES WITH THIS SYSTEM AS THE LOW STARTS TO MOVE OFF
OF THE VA/NC COAST...BUT OVERALL...THE LATEST DETERMINISTIC
GUIDANCE IS IN GENERALLY GOOD AGREEMENT.


UPPER LOW MOVING SLOWLY FROM WESTERN MANITOBA INTO THE UPPER GREAT
LAKES ON MON/TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND THRU 30/00Z
            12Z GFS/ECMWF BLEND AFTERWARD
CONFIDENCE: SLIGHTLY ABOVE AVERAGE THRU 30/00Z
            SLIGHTLY BELOW AVERAGE THEREAFTER

UPPER LOW ACROSS CANADIAN PRAIRIE WILL SHIFT SE AND EXPAND AS IT
GOES THROUGH BINARY INTERACTION/ABSORPTION OF SHORTWAVE ENERGY ON
THE WESTERN SIDE CURRENTLY OVER N SASKATCHEWAN SWINGS AROUND THE
SW SIDE TODAY INTO EARLY SUNDAY INTO THE DAKOTAS/MN.   OVERALL
THIS INTERACTION IS BECOMING BETTER AGREED UPON THROUGH 29/12Z.

AS THE TROF SWINGS UNDER THE BASE...THE MCV AND ASSOCIATED SURFACE
LOW (SEE SECTION BELOW) WILL LIFT NORTH INTO THE EASTERN SIDE OF
THE EXPANDING UPPER LOW...MON INTO TUES.  GIVEN ISSUES WITH THE
UKMET BEING A BIT TOO WOUND UP WITH MESOSCALE FEEDBACK...LEADS TO
AN UNSTABLE EVOLUTION OF THE UPPER LOW AFTERWARD.

THE LARGE SPREAD IN GUIDANCE STARTS TO MANIFEST LATE TUESDAY AS A
STRONG/COMPACT SHORTWAVE OVER NUNAVUT STARTS TO BE INFLUENCED WITH
MUCH OF THE GUIDANCE DRAWING IT SOUTHWARD INTO THE WESTERN SIDE OF
THE UPPER LOW.  THE 00Z CMC IS THE ONLY GUIDANCE THAT WEAKENS THIS
UPPER LOW IN FAVOR OF THE COLDER CORE SYSTEM TO ITS NW (TYPICAL OF
ITS BIAS).  THE 12Z NAM AND UKMET ARE BOTH A BIT AGGRESSIVE
DRAWING THE ENTIRE CONSOLIDATED WAVE SOUTH (UKMET A BIT FASTER DUE
TO AFOREMENTIONED ISSUES)...WHILE THE 12Z GFS/ECMWF ARE MORE TAME
SHEARING SMALLER PIECES SOUTH WITH THE GFS OUTPACING THE ECMWF AT
A TYPICAL ARRANGEMENT.   AS SUCH A NON-UKMET BLEND CAN BE FAVORED
THROUGH 30/12Z AT SLIGHTLY ABOVE AVERAGE CONFIDENCE...THOUGH
SHIFTING TOWARD A 12Z GFS/00Z ECMWF BLEND AT AVERAGE CONFIDENCE
THEREAFTER.

19Z UPDATE: THE UKMET IS A BIT BETTER BUT REMAINS QUITE ROBUST AND
FAST DRAWING THE SHORTWAVE OUT OF NUNAVUT INTO THE DAKOTAS.  THE
12Z CMC CONTINUES TO FAVOR THE ARCTIC WAVE OVER THE WEAKENING CORE
OF THE UPPER LOW...BUT DOES NOT WEAKEN IT AS FAST AS ITS 00Z
RUN...AND MUCH CLOSER TO THE NAM.   THE 12Z ECMWF MUCH LIKE THE
GFS IS DEVOLVING THE UPPER LOW ACROSS ONTARIO TUESDAY BUT DRAWS A
MORE WOUND UP SHORTWAVE OUT OF NUNAVUT.  WOULD TREND TO FAVOR
GOING TO THE ENSEMBLE MEANS TOWARD TUESDAY...THOUGH AS STATED
BEFORE AFFECTS ARE MAINLY NORTH OF CONUS.  AS SUCH WILL KEEP
INITIAL PREFERENCE OF NON-UKMET THROUGH 30/00Z AND GFS/ECMWF BLEND
AFTERWARD THOUGH CONFIDENCE IS REDUCED SLIGHTLY DUE TO INCREASING
TIMING SPREAD ON TUESDAY.


SHORTWAVE EJECTING FROM ROCKIES TODAY SWINGING THROUGH OH VALLEY
SUN/MON BEFORE LIFTING THROUGH NEW ENGLAND MON...WEAK SURFACE LOW
AND FRONTAL BOUNDARY ACROSS THE LOWER/MIDDLE MS VALLEY SAT
NIGHT/SUN AND INTO MI/EASTERN GREAT LAKES SUN/MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND
CONFIDENCE: AVERAGE

GOES-WV/IR DENOTES MCS AHEAD OF TRAILING SHORTWAVE TROF CURRENTLY
OVER S WY...THE GUIDANCE APPEARS IN FAIRLY GOOD AGREEMENT WITH THE
TIMING/STRENGTH OF THE TRAILING SHORTWAVE AS IT CROSSES THE PLAINS
AN OHIO VALLEY TODAY AND SUNDAY.  HOWEVER...THE PRECURSORY
SHORTWAVE IS A DIFFERENT STORY.  THE UKMET CONTINUES TO RAPIDLY
DEVELOP THIS COMPLEX WITH UPSCALE ENHANCEMENT THAT SEEMS QUITE
AGGRESSIVE OVERALL AND IS NOT SUPPORTED ATTM.   THE 12Z NAM IS A
BIT STRONG WITH THIS WAVE AS WELL BUT THAT SEEMS ON PAR WITH THE
HIGHER RESOLUTION OF THE MODEL ITSELF...THOUGH WITH THAT STATED IT
IS QUITE PROGRESSIVE WITH THE WAVE COMPARED TO THE ENSEMBLE MEAN
(12Z GFS AND 00Z ECMWF/CMC SOLUTIONS).   ADDITIONALLY...THE
STRONGER REFLECTION DELAYS THE TRAILING MEAN TROF ACROSS THE OH
VALLEY AND UPPER MID-ATLANTIC/WESTERN NEW ENGLAND INTO MONDAY.  AS
SUCH WOULD SUGGEST FAVORING A 12Z GFS AND 00Z ECMWF/CMC BLEND.
GIVEN THE COMPLEXITY IN THE MESOSCALE TO SYNOPTIC
SCALE...ENVIRONMENTAL PARAMETERS FOR UPSCALE GROWTH TOWARD A NAM
SOLUTION STILL REMAIN PLAUSIBLE TO HAVE ONLY AVERAGE CONFIDENCE IN
THE SLIGHTLY SLOWER/FLATTER SOLUTIONS (PARTICULARLY GIVEN THE
SYSTEM IS ALREADY A BIT FASTER THAN PROGGED).

19Z UPDATE: WHILE THE 12Z UKMET HAS TRENDED A BIT SLOWER AND
WEAKER TOWARD THE REMAINING GUIDANCE...IT IS STILL MUCH TOO DEEP.
THE 12Z ECMWF/CMC BOTH TRENDED A BIT DEEPER AND FASTER EVEN MORE
SO THAN THE 12Z GFS BRINGING THE 12Z NAM IN PLAY.   AS SUCH WILL
FAVOR A NON-UKMET BLEND AT AVERAGE CONFIDENCE.


UPPER TROUGH APPROACHING THE NORTHWEST TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

DEEP UPPER LOW IS FORECAST TO TRACK INTO THE SOUTHERN GULF OF AK
TOWARD TUESDAY...IN ITS WARM SECTOR...A SHORTWAVE SHIFTS EASTWARD
TOWARD THE NW US COAST LOWERING HEIGHTS AND EVENTUALLY WINDING UP
TO A POTENTIALLY CLOSE OFF 00Z WED AS SUGGESTED BY THE 00Z ECMWF.
INTERESTINGLY...THE 00Z ECMWF IS ALSO THE FASTEST PIECE OF
DETERMINISTIC GUIDANCE...AN UNUSUAL PLACE. THE 12Z NAM TRENDED
FASTER TO BE BETTER ALIGNED IN TIMING WITH THE ECMWF THOUGH IS A
BIT MORE ELONGATED N-TO S LIKE THE GFS/CMC.  OVERALL THE
DIFFERENCES ARE FAIRLY SMALL FOR THE END OF DAY 3 TO CONTINUE TO
SUPPORT A GENERAL MODEL BLEND.  STILL THE DIFFERENCES ARE ALSO
LARGE ENOUGH TO HAVE ONLY AVERAGE CONFIDENCE IN THIS BLEND.

19Z UPDATE: THE 12Z ECMWF TRENDED A BIT LESS WOUND UP...SHAPED AND
TIMED WELL WITH THE GFS/NAM.  THE 12Z UKMET/CMC ALSO MATCH WELL TO
CONTINUE A GENERAL MODEL BLEND...BUT WITH BETTER AGREEMENT
CONFIDENCE IS INCREASED TO SLIGHTLY ABOVE AVERAGE GIVEN THE
AGREEMENT AT DAY 3.

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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