Prognostic Meteorological Discussion
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FXUS10 KWNH 261640
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1240 PM EDT FRI MAY 26 2017

VALID MAY 26/1200 UTC THRU MAY 30/0000 UTC

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

12Z NAM/GFS EVALUATION WITH INITIAL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...CLOSED UPPER LOW ALONG THE NEW ENGLAND COAST MOVING
EAST-NORTHEAST TODAY AND TONIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE LATEST SET OF MODELS...INCLUDING THE 12Z NAM AND 12Z
GFS...REMAIN IN CLOSE AGREEMENT WITH THIS SYSTEM AS IT MOVES AWAY
FROM NEW ENGLAND TODAY AND TONIGHT.


...MID LEVEL SHORTWAVE/WEAK SURFACE FRONT OVER THE MIDDLE MS
VALLEY TRACKING ACROSS THE OH VALLEY/GREAT LAKES LATER
TODAY/TONIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM...12Z GFS BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z NAM AND 12Z GFS SHOW MORE AMPLITUDE WITH THIS SMALL SCALE
FEATURE THAN PREVIOUS MODEL RUNS. GIVEN THE MCV THAT WAS MOVING
FROM EASTERN IA INTO NORTHERN IL AT 16Z...THAT IDEA LOOKS RIGHT
AND THE 12Z RUNS LOOK LIKE A BETTER SOLUTION. THERE ARE MINOR
DIFFERENCES BETWEEN THE TWO MODELS ESPECIALLY TONIGHT...BUT A
BLEND OF THE 12Z NAM AND 12Z GFS SHOULD YIELD A REPRESENTATIVE
FORECAST.


...UPPER LOW MOVING SLOWLY FROM WESTERN MANITOBA INTO THE UPPER
GREAT LAKES ON MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM...12Z GFS...00Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE 5430 METER UPPER LOW OVER WESTERN MANITOBA AT 15Z FRI WILL
LIFT BRIEFLY NORTH TODAY AND TONIGHT...THEN TRACK SLOWLY SOUTHEAST
SAT THROUGH MON TO A POSITION OVER THE UPPER GREAT LAKES. THE
LATEST MODEL RUNS...INCLUDING THE 12Z NAM AND 12Z GFS...AGREE WELL
ON THAT BROAD PICTURE. THE MAIN TREND WITH RECENT MODEL RUNS IS TO
SHOW INCREASE SHORTWAVE ENERGY/VORTICITY MOVING THROUGH THE BASE
OF THE TROUGH OVER THE UPPER MS VALLEY SAT NIGHT...WITH A SECOND
BATCH OF SHORTWAVE ENERGY BEGINNING TO MOVE INTO THE BASE OF THE
UPPER TROUGH ON MON. THE 12Z NAM AND 12Z GFS SHOW THIS THE MOST
EMPHATICALLY OF THE RECENT MODEL RUNS...AND IT WILL BE INTERESTING
TO SEE IF THE 12Z NON-NCEP MODELS EXHIBIT THIS TOO. FOR
NOW...GIVEN THE UNCERTAINTY...A BLEND OF THE 12Z NAM...12Z
GFS...AND 00Z ECMWF IS PROBABLY A GOOD COMPROMISE WITH AVERAGE
CONFIDENCE.


...UPPER TROUGH OVER NORTHERN ROCKIES/INTERMOUNTAIN WEST DIGGING
ACROSS CENTRAL ROCKIES SAT...
...WEAK SURFACE LOW AND FRONTAL BOUNDARY ACROSS THE LOWER/MIDDLE
MS VALLEY SAT NIGHT/SUN...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS...00Z ECMWF
CONFIDENCE: ABOVE AVERAGE

THE MOST RECENT MODEL RUNS...INCLUDING THE 12Z NAM AND 12Z
GFS...REMAIN SIMILAR WITH THE PROGRESSION OF THE UPPER TROUGH FROM
THE NORTHERN ROCKIES/INTERMOUNTAIN WEST TODAY INTO THE CENTRAL
PLAINS SAT NIGHT/SUN. THE UPPER TROUGH WILL HELP INDUCE A WEAK
SURFACE LOW AND FRONTAL BOUNDARY LATE SAT/SAT NIGHT...WHICH BY SUN
SHOULD EXTEND FROM THE SOUTHERN PLAINS ACROSS THE MIDDLE MS
VALLEY. NOT SURPRISINGLY THERE IS MORE SPREAD IN THE MODELS IN THE
SURFACE PATTERN...ALTHOUGH EVEN THERE ON SAT NIGHT THEY ALL HAVE
ONE SURFACE LOW NEAR THE RED RIVER BORDER OF TX/OK AND ANOTHER
OVER THE CENTRAL MS VALLEY. THERE ARE BIGGER DIFFERENCES IN THE
QPF FIELDS OF COURSE. THE 12Z GFS AND 00Z ECMWF AND 00Z GEFS DO
THE BEST JOB OF SHOWING THE PRIMARY PRECIPITATION AXIS ALONG THE
IMPLIED POSITION OF THE SURFACE BOUNDARY...AND THEY ARE PREFERRED.
THE 12Z NAM...00Z CMC...AND 00Z UKMET LOOK MUCH LESS REALISTIC IN
THIS REGARD.


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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