Prognostic Meteorological Discussion
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000 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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