Prognostic Meteorological Discussion
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000
FXUS10 KWNH 300418
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1217 AM EDT SUN APR 30 2017

VALID APR 30/0000 UTC THRU MAY 03/1200 UTC

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

00Z MODEL ANALYSIS AND PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...CLOSED LOW CROSSING THE PLAINS ON SUNDAY AND UPPER MISSISSIPPI
VALLEY ON MONDAY/TRAILING FRONT CROSS THE EASTERN STATES TUE....

PREFERENCE: BLEND OF 00Z GFS/12Z ECMWF/18Z GEFS MEAN
CONFIDENCE: AVERAGE

THE ECMWF MEAN/GFS/ECMWF/UKMET ARE FORMING AN INCREASINGLY BETTER
DEFINED CLUSTER OF SOLUTIONS WITH THE EVOLUTION OF THE CYCLONE
MOVING NORTHEAST OUT OF THE PLAINS TOWARDS THE UPPER MS VALLEY.
THE 00Z NAM IS STILL A FEW HOURS SLOW ON DAY 1 BUT PROGRESSES
FASTER ON DAY 2 TO JOIN THE MAJORITY CLUSTER ACROSS THE UPPER MS
VALLEY AND UPPER GREAT LAKES.

THE 00Z NAM FALLS BEHIND AGAIN ON DAY 3/TUE AS IT LINGERS LOWER
HEIGHTS/PRESSURE ACROSS THE GREAT LAKES VS THE OTHER MODELS.  THE
NAM SHOWS A BETTER DEFINED WAVE ALONG A BOUNDARY CROSSING NY
STATE...WHICH WAS MORE AMPLIFIED THAN THE GFS/ECMWF/UKMET...SO
CONFIDENCE IS LOW IN THE NAM.

THE TRIALING COLD FRONT CROSSES THE NORTHEAST/MID
ATLANTIC/SOUTHEAST STATES  EARLY ON TUE.  THE ECMWF WEAKENS THIS
BNDRY FASTER THAN THE GFS/UKMET/SREF MEAN...WHILE THE NAM HAS THE
HIGH AMPLITUDE TROUGH WITH THE FRONT.  AN INTERMEDIATE SOLUTION
CLOSER TO THE 00Z GFS/12Z UKMET/21Z SREF MEAN IS RECOMMENDED UNTIL
BETTER AGREEMENT DEVELOPS.

...PACIFIC FRONTAL SYSTEM TRANSLATING ACROSS THE S CANADIAN
ROCKIES...WITH 700 MB TOUGH/SFC REFLECTION THAT MOVES OUT OF
ALB/SASK ACROSS NORTHERN PLAINS/UPPER MS VALLEY MON/TUES...

PREFERENCE: 00Z GFS...12Z ECMWF...12Z UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 00Z NAM CONTINUES TO BE STRONGER THAN THE REMAINING
DETERMINISTIC AND ENSEMBLE MODEL CONSENSUS ACROSS SWRN CANADA ON
MON MORNING..WITH LOWER 700 MB HEIGHTS EXTENDING INTO NORTHEAST
MT/NORTHERN ND VS THE GFS/ECMWF/UKMET AND RESPECTIVE ENSEMBLE
MEANS.  THIS WAVE DOES WEAKEN IN ALL THE MODELS LATER ON MON AND
MON NIGHT WITH THE WEAKENING WAVE ROTATING UNDER THE BASE OF THE
UPPER MS VALLEY TROUGH...AND THE NAM AGREES WITH THIS IDEA.
BETTER AGREEMENT EXISTS FOR THE MIDDLE ROAD BEST REPRESENTED BY
THE 18Z-00Z GFS/12Z ECMWF/12Z UKMET.


...NEXT WEAK PACIFIC WAVE ENTERING PACIFIC NORTHWEST LATE MON AND
CROSSING N ROCKIES BY TUES MORNING...

PREFERENCE: 18Z GEFS MEAN/00Z GFS/12Z ECMWF BLEND
CONFIDENCE: AVERAGE

A WEAK SHORTWAVE TOPS THE MEAN RIDGE IN THE EASTERN PACIFIC AND
MOVES SOUTHEAST ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES
MONDAY AND THEN INTO THE NORTHERN TO CENTRAL PLAINS AND CENTRAL
ROCKIES TUE...DEVELOPING FURTHER SOUTH ACROSS THE PLAINS AND
ROCKIES AS TUE PROGRESSES.

THE 18Z GFS STOOD OUT BY DEVELOPING A HIGHER AMPLITUDE 700 MB WAVE
CROSSING WY AND THEN INTO NE ON TUE...WITH THE GEFS MEAN AND NOW
THE 00Z GFS SHOWING A LOWER AMPLITUDE SOLUTION..AND THE ECMWF EVEN
LOWER AMPLITUDE THAN THE GEFS MEAN.  THE 12Z UKMET STOOD OUT BY
DEVELOPING A SHARPER 700 MB WAVE IN SOUTHEAST WY THAT PROGRESSES
ACROSS EASTERN CO WHICH CAUSED A SPIKE IN PRECIPITATION.

THE MODELS ARE IN FAVOR OF THE WAVE GRADUALLY AMPLIFYING AS IT
CROSSES CO/CENTRAL PLAINS INTO NM AND THE SOUTHERN PLAINS.  THE
NAM STOOD OUT BY HAVING A MUCH FASTER 700 MB WAVE MOVING OUT OF
THE PLAINS INTO THE LOWER MS VALLEY...WITH GOOD CLUSTERING AMONG
THE 00Z GFS/12Z ECMWF AND THEIR ENSEMBLE MEANS. THEREFORE A BLEND
OF THE 18Z GEFS MEAN/12Z ECMWF/00Z GFS IS RECOMMENDED FOR THIS
SYSTEM.


...PACIFIC CYCLONE OFFSHORE OF THE PACIFIC NORTHWEST MON-WEAKENING
TUE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 18Z GFS/12Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE MODELS SHOW A WEAK CYCLONIC CIRCULATION MONDAY THAT WEAKENS
INTO AN ELONGATED SHEAR AXIS/WARM FRONT ON TUE THAT APPROACHES
VANCOUVER ISLAND.  THE NAM/21Z SREF MEAN/0Z GFS BRING GREATER
PRESSURE FALLS AND STRONG LOW LEVEL CONVERGENCE INTO WA STATE THAN
THE 18Z GFS/ECMWF...WHICH REBUILD A LOW LEVEL RIDGE AND WEAKEN THE
TROUGH AS IT APPROACHES.  RECENT TRENDS HAVE SHOWN MORE MID-LEVEL
RIDGING AHEAD OF THE CLOSED LOW IN THE GULF OF AK. GIVEN THE
12Z-18Z GFS AND 12Z ECMWF ARE IN SYNCH WITH THE TRENDS...THEY
REPRESENT THE PREFERENCE.

WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/

PETERSEN

$$




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