Prognostic Meteorological Discussion
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FXUS10 KWNH 301844
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 PM EDT SUN APR 30 2017

VALID APR 30/1200 UTC THRU MAY 04/0000 UTC

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

12Z MODEL ANALYSIS WITH PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...CLOSED LOW CROSSING THE PLAINS ON SUNDAY AND UPPER MISSISSIPPI
VALLEY ON MONDAY/TRAILING FRONT CROSSING THE ATLANTIC COAST MON
NIGHT...

PREFERENCE: NON-NAM BLEND OF 12Z MODELS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z GLOBAL ECMWF...CMC...AND UKMET ARE CLOSE TO THE STRONG
MODEL CONSENSUS SEEN IN THEIR 00Z RUNS AND THE 12Z GFS...SHOWING A
WELL DEFINED CLUSTER OF SOLUTIONS AS THE CYCLONE MOVES NORTHEAST
FROM THE PLAINS INTO THE UPPER MS VALLEY ON MONDAY. THE 12Z NAM IS
CLOSE TO THIS SOLUTION AS WELL...HOWEVER IT SHOWS LESS
PRECIPITATION WITHIN THE FRONTAL BAND AS IT MOVES ACROSS THE OHIO
VALLEY AND THE GREAT LAKES REGION MON AND MON NIGHT. THE 12Z NAM
FALLS SLIGHTLY BEHIND THE OTHER SOLUTIONS WITH THE PROGRESSION OF
THE UPPER LOW TUE INTO WED AS IT MOVES FROM THE GREAT LAKES ACROSS
NEW ENGLAND...SHOWING ITS TYPICAL TENDENCY TO MAINTAIN A TIGHTER
UPPER CIRCULATION CENTER. THIS IS A FAIRLY MINOR DISCREPANCY AS
THE SYSTEM IS EXITING THE UNITED STATES...BUT A BLEND OF THE 12Z
MODELS EXCLUDING THE NAM LOOKS BEST.


...PACIFIC FRONTAL SYSTEM CROSSING THE SOUTHERN CANADIAN
ROCKIES...WITH 700 MB TOUGH/SURFACE REFLECTION THAT MOVES OUT OF
ALBERTA/SASKATCHEWAN ACROSS NORTHERN PLAINS/UPPER MISSISSIPPI
VALLEY MON/TUE...

PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z NAM MOVED CLOSE TO THE GENERAL MODEL CONSENSUS. IN
ADDITION THE REMAINDER OF THE 12Z MODELS REMAINED CONSISTENT WITH
THEIR PREVIOUS SOLUTIONS. ASIDE FROM FINE DETAILS...THE 12Z SUITE
OF MODELS AGREE WELL WITH REGARD TO THIS FEATURE THROUGH TUE. A
GENERAL BLEND OF THE 12Z MODELS SHOULD WORK WELL.


...WEAK PACIFIC WAVE ENTERING PACIFIC NORTHWEST LATE
MON...CROSSING NORTH ROCKIES TUE...AND DIGGING INTO THE
CENTRAL/SOUTHERN PLAINS TUE NIGHT/WED...

PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE

A WEAK SHORTWAVE TOPS THE MEAN RIDGE IN THE EASTERN PACIFIC AND
MOVES SOUTHEAST ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES
MON THROUGH TUE...THEN PROGRESSES INTO THE CENTRAL AND SOUTHERN
PLAINS TUE NIGHT/WED. THERE IS STILL A DECENT AMOUNT OF SPREAD IN
THE 12Z SUITE OF MODELS BY TUE NIGHT AND WED AS THE PATTERN
AMPLIFIES AND THE SYSTEM DEVELOPS. THE 12Z GFS...12Z UKMET...AND
12Z ECMWF SPLIT THE VORTICITY MAXIMA BETWEEN THE MAIN UPPER TROUGH
CENTERED OVER THE SOUTHERN PLAINS AND A TRAILING SHORTWAVE FURTHER
NORTH-NORTHWEST OVER THE NORTHERN PLAINS. THE 12Z NAM IS RATHER
ALONE NOW IN SHOWING MORE CONCENTRATED ENERGY IN THE MAIN TROUGH.
THE 12Z CMC IS SOMETHING OF COMPROMISE BETWEEN THESE TWO GROUPS.
THE DIFFERENCES SHOWN IN THE MASS FIELDS OF VARIOUS MODEL
SOLUTIONS WILL MANIFEST THEMSELVES MOST IMPORTANTLY IN FRONTAL
DEVELOPMENT AND QPF FIELDS TUE NIGHT/WED. THEY DIFFER WITH RESPECT
TO WHERE THE HEAVIEST PRECIPITATION WILL OCCUR AND HOW MUCH THERE
WILL BE. AT THIS POINT A COMPROMISE OF THE 12Z MODELS IS PROBABLY
THE BEST WAY TO GO...BUT THE MODEL SPREAD YIELDS ONLY AVERAGE
CONFIDENCE IN THE FORECAST.


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

MCDONNAL

$$





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