Prognostic Meteorological Discussion
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428
FXUS10 KWNH 010438
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1236 AM EDT SUN MAY 01 2016

VALID MAY 01/0000 UTC THRU MAY 04/1200 UTC

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

==================================================
00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES
==================================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==================================================

...FRONTAL ZONE AND SHORTWAVES EJECTING FROM THE SOUTHWEST AND
PLAINS TOWARD THE EAST COAST...
...NORTHERN STREAM SHORTWAVE SETTLING INTO THE MEAN LONGWAVE
TROUGH BASE OVER THE PLAINS/SOUTHEAST...

PREFERENCE: BLEND OF 12Z UKMET/ECMWF...TRENDING TOWARD THE 12Z
ECMWF ENSEMBLE MEAN AFTER 03/12Z

THOUGH THERE ARE A NUMBER OF SHORTWAVES...THE FLOW OVER THE
CENTRAL AND EASTERN U.S. IS MORE BROADLY CHARACTERIZED BY A STORM
TRACK TAKING IMPULSES OUT OF THE SOUTHWEST AND THE PLAINS TOWARD
THE EAST COAST. A MEAN LONGWAVE TROUGH AXIS REMAINS ESTABLISHED
OVER THE CENTRAL U.S. THROUGH DAY 3...AS NORTHERN AND SOUTHERN
STREAM WAVES CONVERGE DOWNSTREAM OF A NORTHERN ROCKIES RIDGE. THE
FIRST NOTEWORTHY SHORTWAVE AND SURFACE LOW REFLECTION ARE HANDLED
SIMILARLY BY MOST OF THE MODELS...TRACKING TOWARD THE MID ATLANTIC
BY MONDAY AND THEN TOWARD THE COAST OF NEW ENGLAND MONDAY NIGHT.
THE GFS/ECMWF/UKMET COULD BE USED WITH CONFIDENCE. THE NAM WAS
DECENT IN THE UPPER LEVELS...BUT ITS SURFACE LOW TRACK IS SOUTH OF
THE RATHER STEADY MODEL CONSENSUS.

BACK FARTHER WEST...THE GFS FALLS OUT OF FAVOR...AS SPAGHETTI
PLOTS SHOW IT TO BE SEVERELY UNDERPLAYING THE AMOUNT OF POSITIVELY
TILTED TROUGHING THAT IS LIKELY TO EXTEND BACK UNDERNEATH THE
RIDGE POSITION IN THE CENTRAL HIGH PLAINS/ROCKIES. SOME OF THIS
MAY BE RELATED TO THE GFS EJECTING ENERGY FROM THE SOUTHWEST U.S.
TOO QUICKLY ON DAY 1/2...WHILE ALSO UNDERPLAYING THE SMALL BUT
PRONOUNCED SHORTWAVE THAT WILL DROP OUT OF CANADA BY MONDAY
MORNING. UNFORTUNATELY...THE OTHER OPERATIONAL MODELS HAVE NOT
INSPIRED MUCH CONFIDENCE EITHER...WITH AN ARRAY OF SOLUTIONS...BUT
THE ECMWF/UKMET HAVE GENERALLY DONE A BETTER JOB OF BEING PATIENT
WITH THE SOUTHWEST ENERGY AND MAINTAINING A BETTER SEMBLANCE OF
THE NORTHERN STREAM ENERGY. STILL...WITH LITTLE CONFIDENCE IN THE
DETAILS...WE RECOMMEND TRENDING TOWARD ENSEMBLE MEANS BY DAY
3...AND ESPECIALLY THE ECMWF ENSEMBLE MEAN.


...DEEP UPPER TROUGH APPROACHING THE WEST COAST ON TUES...

PREFERENCE: BLEND OF THE OPERATIONAL MODELS...EXCLUDING THE 12Z
UKMET

THE MODELS AGREE IN DEVELOPING A FULL-LATITUDE TROUGH OVER THE
EASTERN PACIFIC OCEAN...AND THIS WILL APPROACH THE WEST COAST ON
TUESDAY. THE GUIDANCE IS IN RELATIVELY GOOD AGREEMENT AND HAS
SHOWN SOME STABILITY FROM RUN TO RUN. THE MAIN ODDITY IS THE 12Z
UKMET WHICH DEPICTED A SHARP SHORTWAVE TROUGH AT THE BASE OF THE
LARGER SCALE TROUGH BY LATE TUESDAY. THIS FEATURE IS ABSENT IN THE
OTHER MODELS. WE ALSO NOTE THAT THE GFS THERMAL FIELDS IN THE MID
LEVELS ARE SLIGHTLY COOLER THAN CONSENSUS OVER CA/OR...BUT NOT SO
MUCH AS TO REMOVE IT FROM THE PREFERENCE.


...DEEP GREAT LAKES TROUGH DEVELOPING MON/TUE...

PREFERENCE: BLEND OF 00Z NAM/12Z ECMWF

THE PATTERN TRENDS TOWARD A DEVELOPING OMEGA BLOCK THAT SPANS THE
ENTIRE U.S. BY DAY 3 INTO THE MEDIUM RANGE PERIOD. THIS WILL
INCLUDE A CLOSED LOW DIGGING IN AND FEEDING INTO THE BROAD MEAN
WEAKNESS/TROUGH OVER THE GREAT LAKES AND EASTERN U.S. TUESDAY.
MODELS ARE PRETTY AGREEABLE ON THE LARGE SCALE...THOUGH THE 12Z
UKMET AND GFS WERE A BIT QUICK. THE 00Z NAM AND 12Z ECMWF ARE
BETTER SUPPORTED...ESPECIALLY AT SURFACE...BUT ENSEMBLE SURFACE
LOW PLOTS SEEN OVER MULTIPLE MODEL CYCLES. THE 00Z GFS TRENDED
TOWARD THE NAM/ECMWF...AND COULD NEARLY BE INCLUDED IN THE
PREFERENCE...ALTHOUGH THE GFS IS STILL JUST SLIGHTLY FASTER.

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

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

BURKE
$$





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