Prognostic Meteorological Discussion
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FXUS10 KWNH 281907
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
306 PM EDT THU MAY 28 2015

VALID MAY 28/1200 UTC THRU JUN 01/0000 UTC

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

12Z MODEL EVALUATION INCLUDING FINAL MODEL PREFERENCES

MODEL INITIALIZATION ERRORS DO NOT APPEAR TO BE SUFFICIENTLY LARGE
TO IMPACT THEIR FORECASTS OF LARGE-SCALE FEATURES.


NEW ENGLAND SHORTWAVE AND COLD FRONT EXITING BY FRIDAY AFTERNOON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z OPERATIONAL MODELS
CONFIDENCE: ABOVE AVERAGE

VERY GOOD MODEL AGREEMENT EXISTS WITH THE EVOLUTION OF THE
WEAKENING SHORTWAVE AND ASSOCIATED COLD FRONT OVER NEW ENGLAND


SURFACE LOW CROSSING THE NORTHERN GREAT PLAINS INTO GREAT
LAKES/ONTARIO
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~
PREFERENCE: BLEND OF 12Z OPERATIONAL MODELS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A SURFACE LOW IS DEVELOPING IN MONTANA IN RESPONSE TO THE
DEEPENING NORTHERN STREAM TROF OVER SASKATCHEWAN.  GOOD CLUSTERING
OF THE OPERATIONAL MODELS EXIST WITH THE EVOLUTION OF THE SURFACE
AS IT MOVES ACROSS THE ONTARIO. THE 12Z NAM/GFS HAVE SHIFTED EVER
SO SLIGHTLY SOUTH AND EAST ALOFT AND AS SUCH THE SURFACE
REFLECTION IS A BIT WEAKER AND FURTHER WEST AS COMPARED TO THEIR
PRIOR RUNS. EVENTUALLY CONSOLIDATING INTO A MUCH DEEPER LOW OVER
WESTERN QUEBEC BY SATURDAY MORNING 30/06Z.  THIS TREND HAS BEEN
FOLLOWED BY THE 12Z ECMWF/12Z UKMET.  THE 12Z CANADIAN REMAINS A
BIT SLOWER BUT STILL A VIABLE SOLUTION.



SHORTWAVE EJECTING FROM THE CENTRAL ROCKIES INTO THE PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z GFS/12Z GEFS MEAN/00Z ECMWF ENSEMBLE MEAN
CONFIDENCE: AVERAGE

THE MAIN SHORTWAVE CURRENTLY LOCATED NEAR YELLOWSTONE SHIFTS
SOUTHEAST DAMPENING OUT AS IT PROGRESSES...WHILE ANOTHER WEAK
SHORTWAVE EJECTS OUT OF THE BASE OF THE POSITIVELY TILTED AND
FILLING TROF IN NORTHEAST NEW MEXICO TODAY.  A WEAK SURFACE LOW
DEVELOPS ALONG THE COLORADO FRONT RANGE THIS EVENING INTO THE
CENTRAL GREAT LAKES BY FRIDAY NIGHT/SATURDAY MORNING LEAVING A
TRAILING WEAK FRONTAL BOUNDARY THAT WILL REMAIN THE FOCUS OF
SENSIBLE WEATHER FOR THE SHORT RANGE. THE 12Z NAM INITIALLY LOOKS
IN LINE WITH OTHER GUIDANCE UNTIL OVER DEEPENING OF A SURFACE LOW
IN IOWA SATURDAY MORNING...LIKELY IN RESPONSE TO CONVECTIVE
FEEDBACK AND SHOULD NOT BE PREFERRED AFTER THIS TIME PERIOD.
SIMILARLY...THE 12Z ECMWF ALSO HAS A CONVECTIVE FEED BACK ANOMALY
THAT PRESENTS ITSELF AT 29/06Z OVER CENTRAL TEXAS AND LIFTS IT
NORTHWEST WITH A STRONGER SURFACE INFLECTION.  THIS HAS ALLOWED A
STRONGER SOLUTION A THE SURFACE AND SHOULD BE USED WITH CAUTION.
THE 12Z UKMET IS FAST WITH THE EJECTION OF THE NEARLY ALL OF THE
TROF ENERGY THROUGH SATURDAY LEAVING A SOLUTION THAT IS TOO FLAT
FOR THE REST OF THE WEEKEND. AS SUCH A BLEND OF THE 12Z GFS ALONG
WITH THE 12Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN IS PREFRERRED
DUE MAINLY TO RUN TO RUN CONTINUITY.



UPPER LEVEL LOW OVER BRITISH COLUMBIA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE OPERATIONAL AND ENSEMBLE GUIDANCE ARE IN VERY GOOD AGREEMENT
WITH THE VERY SLOW PROGRESSION SOUTHEAST OF THE CUT-OFF LOW OVER
BRITISH COLUMBIA THROUGH SATURDAY NIGHT 30/18Z.  AFTER THAT TIME
PERIOD...THE STRONGER UPSTREAM FLOW BECOMES HIGHLY INFLUENTIAL AND
BEGIN TO MOVE THE OPENING LOW TOWARD THE EAST. THE 12Z CMC HAS
COME INTO BETTER AGREEMENT WITH THE INITIAL PREFERENCE AS IT HAS
SLOWED COMPARED TO THE 12Z UKMET WHICH STILL REMAINS A BIT TOO
FAST IN THE INITIAL EJECTION OF SHEARING ENERGY.   AT THE 12Z GFS
LOOKS IN LINE WITH PRIOR GUIDANCE AND IS PREFERRED ALONG WITH THE
00Z ECMWF SOLUTION AS GOOD REPRESENTATIVES OF THE 00Z ECMWF
ENSEMBLE MEAN...THOUGH THE SPREAD IN SOLUTIONS REDUCES CONFIDENCE
TOWARD THE END OF THE PERIOD.


WEAKENING PACIFIC CUT-OFF LOW PROGRESSING TO CENTRAL U.S. PACIFIC
COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~
PREFERENCE: BLEND OF 12Z GFS/12Z ECMWF/12 UKMET
CONFIDENCE:  AVERAGE

WELL DEFINED CUT-OFF UPPER LOW NEAR 40N150W...WOBBLES IN DAY 1 BUT
BEGINS TO MOVE EAST AND SLOWLY FILL EVENTUALLY BEGINNING TO OPEN
UP AS IT AFFECTS THE U.S. WEST COAST BY DAY 3 WITH A SLIGHT
NEGATIVE TILT ORIENTATION.  THE 12Z CMC HAS COME INTO BETTER
AGREEMENT THOUGH REMAINS A BIT STRONGER AND SLOWER BOTH ALOFT AND
AT THE SURFACE. THE 12Z NAM ALSO APPEARS TOO FAST IN ITS SOLUTION.
 THE 12Z GFS IS A BIT WEAKER AND FILLS THE SURFACE LOW MORE THAT
THE 12Z ECMWF/12 UKMET BUT ALL ARE IN GENERAL AGREEMENT WITH
06Z/12Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN GIVING MODERATE
CONFIDENCE IN THIS BLEND.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

GALLINA

$$





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