MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 253 AM EDT MON MAY 02 2016 VALID MAY 02/0000 UTC THRU MAY 05/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM/GFS/ECMWF/UKMET/CMC AND FINAL MODEL PREFERENCES ...SHORTWAVES MOVING FROM THE OHIO VALLEY TO THE NORTHEAST ON MONDAY... ...SURFACE LOWS ACROSS THE NORTHEAST/MID-ATLANTIC ON MONDAY... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE A BROAD MID/UPPER-LEVEL TROUGH WILL EXPAND OVER THE EASTERN HALF OF THE NATION MONDAY INTO TUESDAY AS MULTIPLE SHORTWAVES PROGRESS THE REGION. AT THE SURFACE...A FRONTAL BOUNDARY WITH MULTIPLE WAVES OF LOW PRESSURE ALONG IT WILL AFFECT AREAS FROM THE NORTHEAST TO THE LOWER MS VALLEY. MODELS INDICATE ONE SURFACE LOW MOVING FROM THE OHIO VALLEY INTO THE NORTHEAST ON MONDAY WHILE A SECOND SURFACE LOW DEVELOPS FARTHER SOUTH ALONG THE FRONT OVER THE MID-ATLANTIC REGION. WITH THE SURFACE LOW CROSSING THE NORTHEAST...THE GFS APPEARS FARTHER EAST THAN CONSENSUS OFF THE NEW ENGLAND COAST BY MONDAY NIGHT...ALTHOUGH THE 00Z ECMWF HAS MOVED FARTHER EAST AS WELL. THE NAM IS MORE IN LINE WITH THE LOW POSITION SHOWN BY THE UKMET/CMC/12Z ECMWF ENS MEAN. FOR THE SURFACE LOW DEVELOPING OVER THE MID-ATLANTIC MONDAY AFTERNOON...THE GFS AND NAM ARE GENERALLY IN GOOD AGREEMENT WITH THE MODEL CONSENSUS AS THE LOW WEAKENS AND MOVES OFF THE COAST ON TUESDAY. THE NORTHERN OF THE TWO SURFACE LOWS WILL BE MORE SIGNIFICANT PLAYER IN THE WEATHER ACROSS NEW ENGLAND ON MONDAY. GIVEN THE TWO CAMPS OF SOLUTIONS -- THE SLIGHTLY FASTER GFS/ECMWF AND THE SLOWER NAM/UKMET/CMC -- WILL RECOMMEND A GENERAL MODEL COMPROMISE. ...SHORTWAVE ENTERING THE NORTHERN PLAINS/UPPER MIDWEST ON MONDAY... ...COLD FRONT ACROSS THE LOWER MS VALLEY AND SOUTHEASTERN STATES... ...SURFACE LOW DEVELOPING ACROSS THE SOUTHERN MID-ATLANTIC ON WEDNESDAY... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: AVERAGE A MORE SIGNIFICANT SHORTWAVE WILL ENTER THE NORTHERN PLAINS/UPPER MIDWEST MONDAY MORNING BEFORE DIVING SOUTHEASTWARD AND DEEPENING THE LONG WAVE TROUGH ON TUESDAY. THE NAM APPEARS TO BE A LITTLE TO WEAK/FAST WITH THIS SHORTWAVE BY TUESDAY (AND WITH THE SURFACE FRONT ACROSS THE SOUTHEAST)...WHILE THE GFS IS CLOSER IN-LINE WITH THE ECMWF (AND ALSO SUPPORTED BY THE 00Z GEFS MEAN AND 12Z ECMWF ENS MEAN). THE UKMET AND CMC 00Z RUNS HAVE COME IN BOTH SHOWING A SLOWER/MORE AMPLIFIED TROUGH ACROSS THE LOWER MS VALLEY BY WED MORNING RELATIVE TO THE GFS/ECMWF. AS THE FRONT MOVES TOWARD THE EAST COAST...THIS SHORTWAVE WILL INFLUENCE THE DEVELOPMENT OF AN ADDITIONAL WAVE OF LOW PRESSURE ALONG THE SURFACE FRONT ACROSS THE SOUTHERN MID-ATLANTIC BY WEDNESDAY MORNING...WHICH THEN MOVES NORTHEASTWARD OFFSHORE. MODELS ARE INITIALLY IN GOOD AGREEMENT ON THE DEVELOPMENT OF THE LOW BUT SPREAD INCREASES QUICKLY AFTER THE LOW MOVES OFFSHORE. THE NAM APPEARS TO MOVE THE LOW NORTHEASTWARD MORE QUICKLY THAN CONSENSUS...WHILE THE GFS/UKMET/CMC/ECMWF ARE SLOWER. A COMBINATION OF THE GFS AND ECMWF WOULD SEEM TO BEST REPRESENT CONSENSUS AT THIS TIME. ...LOW PRESSURE ACROSS THE GREAT LAKES WED MORNING... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: AVERAGE A STRONG SHORTWAVE WILL DIVE SOUTHEASTWARD FROM THE WESTERN HUDSON BAY TO UPPER GREAT LAKES BY TUESDAY MORNING BEFORE CLOSING OFF INTO AN UPPER-LEVEL LOW. THE ACCOMPANYING SURFACE LOW PRESSURE SYSTEM WILL BRING PRECIPITATION TO THE UPPER GREAT LAKES ON TUESDAY. THE NAM AND GFS BOTH APPEAR ON THE DEEP SIDE WITH THE 500 HPA LOW...ALTHOUGH NOT TO THE POINT OF BEING OUTSIDE CONSENSUS. AT THE SURFACE...THE GFS/NAM/ECMWF/UKMET ARE IN RELATIVELY GOOD AGREEMENT WITH RESPECT TO THE TIMING OF THE COLD FRONT AS IT MOVES ACROSS THE MIDWEST. AS THE LOW PRESSURE SYSTEM BEGINS TO INTERACT WITH THE SYSTEM ALONG THE MID-ATLANTIC/NORTHEAST COASTLINE WED NIGHT/THURS MORNING...IT IS UNCLEAR HOW STRONG THE GREAT LAKES SURFACE LOW WILL REMAIN AS IT ENTERS THE LOWER GREAT LAKES. THE GFS WEAKENS THE GREAT LAKES SFC LOW A LITTLE MORE QUICKLY THAN THE ECMWF/UKMET/CMC...WHILE THE ENSEMBLE MEANS ARE IN BETWEEN. THUS A GFS/ECMWF BLEND APPEARS REPRESENT THE BEST SOLUTION OVERALL. ...DEEP UPPER TROUGH APPROACHING THE WEST COAST ON TUES... ...CLOSED UPPER-LEVEL LOW OFF THE COAST OF CALIFORNIA WED NIGHT/THURS... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: AVERAGE THE NAM/GFS/ECMWF/CMC ARE IN RELATIVELY GOOD AGREEMENT WITH RESPECT TO THE TIMING AND AMPLITUDE OF THE MID/UPPER-LEVEL TROUGH AS IT APPROACHES THE WEST COAST ON TUESDAY...WHILE THE UKMET IS TOO AMPLIFIED. AS THE SYSTEM CLOSES OFF INTO A LOW AT 500 HPA BY WEDNESDAY...THE GFS REMAINS RELATIVELY CLOSE TO THE ECMWF AND CONSENSUS...WHILE THE NAM APPEARS A LITTLE MORE AMPLIFIED WITH THE TROUGH AS THE LOW CLOSES OFF. GIVEN THAT THE 12Z ECMWF ENSEMBLE MEAN/00Z GEFS MEAN BOTH ARE SIMILAR TO THE GFS/ ECMWF...WILL RECOMMEND A BLEND OF THESE TO MODELS AT THIS POINT. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN