Prognostic Meteorological Discussion
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FXUS10 KWNH 261843
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
243 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 MODEL EVALUATION WITH 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 12Z SUITE OF MODELS REMAIN CONSISTENT WITH PREVIOUS RUNS AND
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 THE OTHER 12Z MODELS...ALTHOUGH THE 12Z UKMET IS
CLOSE. THE WEAK MCV THAT WAS MOVING ACROSS NORTHERN IL AT 18Z
SUGGESTS THAT THE GREATER AMPLITUDE SHOWN IN THE 12Z NCEP MODELS
IS A BETTER WAY TO GO. THERE ARE MINOR DIFFERENCES BETWEEN THE NAM
AND GFS...SPECIFICALLY THE 12Z NAM PRESERVES THE WAVE THROUGH
TONIGHT WHEREAS THE 12Z GFS WEAKENS IT RATHER QUICKLY. THERE IS A
GOOD CHANCE THAT THE NAM IS KEEPING THE WAVE TOO LONG AND THE GFS
IS WEAKENING IT TOO QUICKLY...THEREFORE 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: NON 12Z UKMET MODEL BLEND
CONFIDENCE: AVERAGE

THE 5450 METER UPPER LOW OVER WESTERN MANITOBA AT 18Z FRI WILL
LIFT BRIEFLY NORTH TODAY AND TONIGHT...THEN TRACK SLOWLY SOUTHEAST
SAT THROUGH MON TO A POSITION OVER THE UPPER GREAT LAKES. THE 12Z
MODEL RUNS AGREE WELL ON THAT BROAD PICTURE. THE MAIN TREND WITH
RECENT MODEL RUNS IS TO SHOW INCREASED 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...12Z
GFS...12Z ECMWF...AND 12Z CMC ALL SHOW THIS WELL. BETWEEN THESE
MODELS...THOUGH...THERE ARE DIFFERENCES IN THE DETAILS LIKE VIGOR
AND SPEED OF THE SHORTWAVE. GIVEN THAT UNCERTAINTY...A BLEND OF
THE 12Z MODELS THAT EXCLUDES THE UKMET 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...12Z ECMWF
CONFIDENCE: ABOVE AVERAGE

THE 12Z MODEL RUNS 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 12Z ECMWF
AND 12Z GEFS PROBABLY DO THE BEST JOB OF SHOWING THE PRIMARY
PRECIPITATION AXIS ALONG THE IMPLIED POSITION OF THE SURFACE
BOUNDARY...AND THEY ARE PREFERRED. THE 12Z CMC HAS MOVED CLOSER TO
THAT IDEA. THE 12Z NAM DOES NOT SHOW THIS ESPECIALLY WELL...AND
THE 12Z UKMET AGAIN LOOKS WELL OVERDONE. A BLEND OF THE 12Z GFS
AND 12Z ECMWF SHOULD YIELD THE BEST 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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