MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 238 PM EDT SUN APR 16 2017 VALID APR 16/1200 UTC THRU APR 20/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING FINAL MODEL PREFERENCES AND CONFIDENCE ...MID-LEVEL CIRCULATION SHEARING ACROSS THE GULF COAST... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE A WEAKENING MID LEVEL SHORTWAVE NEAR THE CENTRAL GULF COAST WILL EAST AND GRADUALLY SHEAR OUT TOWARD THE FL PENINSULA OVER THE NEXT DAY OR SO. A GENERAL MODEL COMPROMISE WILL BE PREFERRED WITH THIS SYSTEM GIVEN MINIMAL MASS FIELD SPREAD. ...SHORTWAVE ENERGY/MID LEVEL TROUGH CROSSING THE GREAT LAKES/NORTHEAST THROUGH MON... ...COLD FRONT ADVANCING EAST THROUGH OH VALLEY/NORTHEAST... PREFERENCE: BLEND OF THE 12Z NAM/GFS/ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE A PAIR OF SHORTWAVE TROUGHS INVOLVING THE UPPER MIDWEST AND ALSO SASKATCHEWAN WILL PROGRESSIVE EAST AND TEND TO CONSOLIDATE OVER THE NORTHEAST BY LATER MON BEFORE THEN CROSSING INTO SOUTHEAST CANADA. THIS WILL DRIVE A SURFACE LOW CENTER NEAR LAKE HURON OFF TO THE EAST ACROSS NORTHERN NEW ENGLAND ALONG WITH A TRAILING COLD FRONT THAT WILL CROSS THE OH VALLEY AND SWEEP THROUGH THE NORTHEAST BY LATE MON. A SECONDARY AREA OF LOW PRESSURE CLIPPING FAR NORTHERN MN TODAY WILL GRADUALLY DAMPEN OUT TONIGHT IN LIEU OF THE LEAD LOW PRESSURE CENTER BECOMING DOMINANT. THE 12Z CMC AND 12Z UKMET ARE BOTH A LITTLE TOO SLOW IT APPEARS WITH THE DOMINANT LOW CENTER...AS THE 12Z NAM/GFS/ECMWF ALL SUGGEST A SOMEWHAT MORE PROGRESSIVE SOLUTION. THERE TENDS TO BE A BIT MORE ENSEMBLE SUPPORT FOR THE FASTER CAMP...SO A BLEND OF THE NAM/GFS AND ECMWF WILL BE PREFERRED. ...SHORTWAVE/CLOSED LOW REACHING THE NORTHERN CA COAST TODAY... ...CROSSING THE NORTHERN PLAINS/UPPER MIDWEST BY TUES... PREFERENCE: BLEND OF THE 12Z GFS/UKMET/ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE PROGRESSIVE MID-LATITUDE FLOW WILL USHER IN A STRONG SHORTWAVE INTO NORTHERN CA/SOUTHWEST OR COAST BY SUN EVE. THIS ENERGY WILL QUICKLY TRAVERSE THE INTERMOUNTAIN WEST AND STREAK EAST ACROSS THE DAKOTAS MON NIGHT AND THE UPPER GREAT LAKES REGION ON TUES. THE MODELS ARE IN VERY GOOD AGREEMENT WITH THEIR MASS FIELDS UNTIL ABOUT 48 HOURS WHEN THE 12Z CMC BECOMES A MODESTLY SLOW OUTLIER WITH ITS SURFACE LOW. THE 12Z NAM MEANWHILE BEGINS TO THEN TRACK ITS SURFACE LOW A BIT FARTHER NORTH AND FASTER AHEAD OF THE REMAINING GUIDANCE AS IT LIFTS INTO SOUTHERN ONTARIO. THE STRONGER MODEL CLUSTERING FAVORS A 12Z GFS/UKMET/ECMWF BLEND AT THIS POINT...AND SO THIS WILL BE THE PREFERENCE. ...LEAD SHORTWAVE TRAVERSING THE GREAT BASIN TUES... ...ENERGY PROGRESSING OVER THE NORTHERN PLAINS WED... ...SURFACE LOW DEVELOPING OVER THE CENTRAL PLAINS WED... ...LONGWAVE TROUGH APPROACHING THE WEST COAST WED... PREFERENCE: BLEND OF THE 12Z NAM/UKMET/ECMWF CONFIDENCE: AVERAGE LATE IN THE PERIOD...A RATHER EXTENDED LONGWAVE TROUGH BEGINS TO TAKE SHAPE OVER THE EASTERN PACIFIC AND APPROACHES THE WEST COAST BY THE END OF THE PERIOD. A LEAD SHORTWAVE AHEAD OF THIS LARGER SCALE TROUGH WILL ARRIVE ACROSS THE WEST COAST EARLY TUES AND QUICKLY CROSS THE INTERMOUNTAIN WEST BEFORE ADVANCING OVER THE NORTHERN PLAINS ON WED. THIS WILL DRIVE CYCLOGENESIS IN THE LEE OF THE ROCKIES WITH LOW PRESSURE ADVANCING EAST ACROSS THE CENTRAL PLAINS THROUGH WED. THE 12Z CMC IS LIKELY TOO PROGRESSIVE WITH ITS LEAD SHORTWAVE PROGRESSION ACROSS THE WEST AND OVER THE PLAINS...AND APPEARS TOO FAST WITH ITS SURFACE LOW PROGRESSION AS A RESULT OVER THE PLAINS. THE 12Z CMC IS LIKELY TOO SLOW THOUGH WITH THE LONGWAVE TROUGH OFF THE WEST COAST. THE 12Z GFS APPEARS TO BE A BIT TOO STRONG WITH THE ENERGY EJECTING OUT OVER THE PLAINS WITH A SURFACE LOW CENTER A TAD TOO DEEP. STRONGER MODEL CLUSTERING OVERALL GENERALLY FAVORS THE 12Z UKMET AND 12Z ECMWF AT THIS POINT WITH THE LEAD ENERGY AND THE OFFSHORE TROUGH. THE 12Z NAM ALSO FAVORS THE UKMET/ECMWF CAMP... AND WITH DECENT ENSEMBLE SUPPORT FROM THE LATEST GEFS MEAN AND ECENS MEAN... BLEND OF THE NAM/UKMET/ECMWF SOLUTIONS WILL BE PREFERRED. ...BROAD TROUGH OVER THE WESTERN GULF OF MEXICO/LOWER MS VALLEY... PREFERENCE: NON-12Z NAM CONSENSUS CONFIDENCE: SLIGHTLY ABOVE AVERAGE A SOUTHERN STREAM TROUGH GRADUALLY DEEPENS AND BROADENS OUT OVER THE LOWER MS VALLEY AND THE WESTERN GULF OF MEXICO BY TUES IN RESPONSE TO VORT ENERGY THAT AMPLIFIES EJECTING ACROSS THE RIO GRANDE VALLEY MON AND MON NIGHT. THE 12Z NAM OVERALL APPEARS THE MOST INTENSE WITH ITS VORT ENERGY COMPARED TO THE REMAINING GUIDANCE. THE MODELS HOWEVER ALL AGREE THAT A BROAD UPPER TROUGH WILL EVOLVE REGARDLESS OF THE EXACT DETAILS OF THE EJECTING VORT ENERGY. A NON-NAM CONSENSUS WILL BE PREFERRED FOR NOW. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON