Prognostic Meteorological Discussion
Issued by NWS

000
FXUS10 KWNH 201654
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1253 PM EDT MON MAY 20 2013

VALID MAY 20/1200 UTC THRU MAY 24/0000 UTC

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

...EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...SLOW-MOVING UPPER LOW ACROSS THE UPPER MIDWEST/NORTHERN
PLAINS...
...EVENTUAL OPEN WAVE TRACKING THROUGH THE OH VALLEY BY MIDDAY
THURSDAY...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z CMC AND THE 06Z GEFS/00Z
ECMWF ENSEMBLE MEANS
FORECAST CONFIDENCE: BELOW AVERAGE

TO BEGIN THE PERIOD...THE 12Z NAM/GFS AND 06Z GEFS/09Z SREF MEANS
INITIALIZED A DEEPER 500-MB CENTER THAN OTHER GUIDANCE.
HOWEVER...THIS IDEA WAS SUPPORTED BY THE 12Z RAOBS ACROSS THE
NORTHERN/CENTRAL PLAINS. AS TIME PROGRESSES ONWARD...THE 12Z NAM
BECOMES QUICKER BY 22/0000Z. LOOKING 24 HOURS FURTHER...THE 00Z
UKMET EVENTUALLY APPEARS FASTER WITH THE CORE OF THE OPEN WAVE
CROSSING THE UPPER GREAT LAKES REGION. AS A WHOLE...THE SPREAD
WITH THE MODELS BECOME MUCH HIGHER BEYOND WEDNESDAY WITH THE 12Z
NAM AND 00Z UKMET/ECMWF PUSHING AHEAD OF WHERE THE ENSEMBLE MEANS
SUGGEST THE PLACEMENT. FURTHER...THE 12Z GFS LOOKED LIKE A
REASONABLE BET EARLY IN THE PERIOD BUT EVENTUALLY DEPICTS A MUCH
SHARPER 500-MB RIDGE/TROF COUPLET WHILE IT ALSO STRUGGLES TO
RESOLVE A WAVE DROPPING DOWN THE WESTERN EDGE OF THE HUDSON BAY.
WPC WILL GO AHEAD AND FAVOR THE 00Z CMC WITH THE ENSEMBLE MEANS TO
COVER THE UNCERTAINTY.


...LINGERING SHORTWAVE ACROSS THE LOWER MID-ATLANTIC EARLY ON...
...WEAKNESS IN THE 500-MB PATTERN OVER THE SOUTHEASTERN U.S...

PRELIMINARY PREFERENCE: A NON-12Z NAM/09Z SREF MEAN MODEL CONSENSUS
FORECAST CONFIDENCE: AVERAGE

THROUGH 24 HOURS INTO THE FORECAST...GUIDANCE ACROSS THE BOARD ARE
IN REASONABLE AGREEMENT WITH THESE UPPER LEVEL FEATURES. BY
22/0000Z...THE 12Z NAM/09Z SREF MEAN QUICKLY SHEAR OUT THE
MID-LEVEL ENERGY EXITING THE DELMARVA PENINSULA. MOVING LATER INTO
THE WEEK...THE SYSTEM ACROSS THE SOUTHEASTERN U.S. BECOMES MUCH
LESS DEFINED AS IT IS ABSORBED BY THE MID-LATITUDE TROF CROSSING
TO THE NORTH. GIVEN A DECENT MODEL CONSENSUS OUTSIDE THE NAM/SREF
MEAN...WILL LEAN TOWARD THIS OTHER SUPPORTING GUIDANCE.


...BROAD CLOSED UPPER LOW AFFECTING MUCH OF THE NORTHWESTERN U.S.
BY MID-WEEK...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: AVERAGE

AS THIS STRONG UPPER LOW DROPS SOUTHWARD FROM THE GULF OF
ALASKA/NORTHEASTERN PACIFIC...IT IS EXPECTED TO GRADUALLY
INTENSIFY ON ITS APPROACH TO THE PACIFIC NORTHWEST COAST. AS THE
SYSTEM MOVES INLAND...THERE IS SOME MODEL SPREAD IN TERMS OF
PLACEMENT/STRENGTH. THROUGH WEDNESDAY MORNING...THE 12Z NAM/09Z
SREF MEAN ARE THE DEEPEST ALOFT WITH THEIR 540-DM CENTER DEPICTED.
WITH REGARDS TO PLACEMENT...THE 12Z NAM/09Z SREF MEAN ARE THE
FURTHEST NORTH/WEST WITH A LOW CENTER NEAR THE OLYMPICS ON
23/0000Z WHILE THE 00Z CMC IS ALL THE WAY TO SOUTH ACROSS
EAST-CENTRAL OR. TOWARD THE END OF THE FORECAST CYCLE...THE 12Z
GFS APPEARS TO HAVE TRENDED AWAY FROM THE 06Z GEFS SOLUTION WHICH
WAS OFF TO THE NORTH/WEST. THIS BRINGS THE GFS IDEA MORE IN LINE
WITH THE 00Z ECMWF/ECMWF ENSEMBLE MEAN. THUS...THE RECOMMENDATION
WILL BE A 12Z GFS/00Z ECMWF MODEL 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...

RUBIN-OSTER

$$