MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1250 AM EDT MON MAR 13 2017 VALID MAR 13/0000 UTC THRU MAR 16/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... ...SHORTWAVE QUICKLY EXITING THE NEW ENGLAND COAST... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: HIGH MODEST HEIGHT FALLS PULLING AWAY FROM THE NEW ENGLAND COAST ARE WELL AGREED UPON BY RECENT MODEL GUIDANCE. THUS...A GENERAL MODEL COMPROMISE IS RECOMMENDED. ...LEAD HEIGHT FALLS CURRENTLY PUSHING THROUGH THE CENTRAL PLAINS... ...EVOLVING NEGATIVELY-TILTED TROUGH LIFTING FROM THE CAROLINAS TO NEW ENGLAND ON TUESDAY... ...RAPIDLY STRENGTHENING COASTAL LOW AFFECTING THE EASTERN SEABOARD ON TUESDAY/WEDNESDAY... ...NORTHERN STREAM UPPER LOW/ATTENDANT SURFACE CYCLONE... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF FORECAST CONFIDENCE: AVERAGE A COMBINATION OF ACTIVE JET STREAMS COUPLED WITH INTENSE SURFACE CYCLOGENESIS OFF THE EASTERN SEABOARD WILL SET THE STAGES FOR A HEAVY SNOWFALL EVENT FROM THE MID-ATLANTIC INTO NEW ENGLAND. FIRST...WATER VAPOR IMAGERY TONIGHT SHOWS A DECENT CYCLONIC SWIRL MOVING THROUGH EASTERN NEB WITH THE SHORTWAVE CONTINUING TO DIG ON ITS APPROACH TO THE CAROLINAS ROUGHLY 24 HOURS FROM NOW. ON THE QUICKER SIDE OF THE GUIDANCE WERE THE 12Z CMC/GFS-PARALLEL...PARTICULARLY BY 14/0600Z. THESE NOTED DIFFERENCES SEEM TO BE SOMEWHAT OFFSET BY SOME ADJUSTMENTS MADE AS THE SHORTWAVE ABRUPTLY LIFTS NORTHWARD ALONG THE DELMARVA TO LOWER NEW ENGLAND COAST. CONSIDERING THE COASTAL LOW TRACK...THERE IS STILL SOME SPREAD WHICH REMAINS ALTHOUGH IT HAS REDUCED RELATIVE TO RECENT MODEL CYCLES. THE CENTER OF THE ENSEMBLE CLUSTER GENERALLY CROSSES THE INFAMOUS 40N/70W BENCHMARK AROUND 15/0000Z WITH A FEW CAMPS EVIDENT. THE ECMWF MEMBERS CONTINUE TO BE SLOWER AND DISPLACED SLIGHTLY TOWARD THE SOUTHWEST OF THE QUICKER GEFS ENSEMBLES. WHILE INCONSISTENT RUN TO RUN...THE CMC ENSEMBLES SEEMS TO SIT SOMEWHERE IN BETWEEN THIS PAIR. CONSIDERING THE TRACK DEPICTED BY INDIVIDUAL DETERMINISTIC SOLUTIONS...THE 12Z CMC/UKMET PAINT THE TRACK CLOSEST TO THE COAST WHICH IS ON THE FAR WEST SIDE OF THE 90-MEMBER ENSEMBLE SPREAD. TO SOME EXTENT...THE 00Z NAM MIMICS THIS SOLUTION WHILE STRENGTHENING LOW LIFTS TOWARD COASTAL MA BY 15/0000Z. WHILE THE 00Z GFS/12Z GFS-PARALLEL AND 12Z ECMWF DO DIFFER...THEY HAVE BEEN REASONABLY CONSISTENT ON A RUN-TO-RUN BASIS. AS SUCH...WILL RESPECT THAT AND INCORPORATE THEIR SOLUTIONS INTO THE BLEND. UNTIL ADDITIONAL GUIDANCE ARRIVES...THE PREFERENCE WILL BE AN EQUAL BLEND OF THE 00Z GFS/12Z ECMWF. REGARDING THE NORTHERN STREAM UPPER LOW SWINGING FROM THE GREAT LAKES TO THE MID-ATLANTIC THE NEXT COUPLE OF DAYS...THE ECMWF AND A VAST MAJORITY OF ITS ENSEMBLE MEMBERS HAVE BEEN MORE AMPLIFIED COMPARED TO OTHER GLOBAL MODELS. THIS HAS REMAINED IN THE FORECAST THE PAST FOUR MODEL CYCLES WHICH SUGGESTS ITS AT LEAST BEEN CONSISTENT. THE MORE NORTHWARD SOLUTION SHOWN BY THE 00Z GFS IS AGREED UPON BY THE LATEST 00Z NAM. FOR NOW WILL JUST SPLIT BETWEEN THE PAIR OF SCENARIOS. THE BLEND WILL BE THE SAME AS THE ABOVE COASTAL SYSTEM. ...WEAK SHORTWAVE TROUGH CROSSING THE GULF OF CA/SEA OF CORTEZ BY MID-WEEK... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE A CLOSED 582-DM MID-LEVEL RIDGE INITIALLY ANCHORED OVER THE SOUTHWESTERN U.S. WILL ADVANCE EASTWARD IN RESPONSE TO WEAK HEIGHT FALLS COMING OUT OF THE EASTERN PACIFIC. THERE ARE TIMING DIFFERENCES WITH THE 00Z NAM A BIT AHEAD OF THE REST OF THE PACK. GIVEN THE FACT MOST OF THE UNCERTAINTY IS ON THE MESOSCALE COMBINED WITH A LIMITED INFLUENCE ON THE SENSIBLE WEATHER...WILL LEAN TOWARD A GENERAL MODEL COMPROMISE HERE. ...AMPLIFYING TROUGH AFFECTING THE PACIFIC NORTHWEST/UPPER INTERMOUNTAIN WEST BY WEDNESDAY/THURSDAY... ...APPROACHING SURFACE LOW/PACIFIC FRONTS... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/18Z GEFS MEAN FORECAST CONFIDENCE: AVERAGE MEAN RIDGING ACROSS THE WESTERN U.S. WILL REMAIN IN PLACE THROUGH 14/1200Z BEFORE UPSTREAM HEIGHT FALLS TRACK INTO THE PACIFIC NORTHWEST BY THE FOLLOWING DAY. LIKE YESTERDAY...THE 12Z CMC CAME IN QUICKER WITH THE ADDITIONAL MID-LEVEL FORCING AS IT TRACKS INTO SOUTHERN BRITISH COLUMBIA BY WEDNESDAY AFTERNOON. ADDITIONALLY...THE 12Z ECMWF HAS CONTINUED TO BE FASTER WITH THE OVERALL EVOLUTION WHICH INCLUDES THE TIMING OF THE INCOMING PACIFIC FRONT. WHILE LARGE-SCALE SPREAD SEEMED ON THE LOWER SIDE BASED ON EVALUATION OF THE ENSEMBLE SPAGHETTI PLOTS...THERE ARE PLENTY OF DIFFERENCES COMPARING DETERMINISTIC SOLUTIONS FROM ONE ANOTHER. WILL STICK CLOSER TO THE 00Z GFS/18Z GEFS MEAN HERE UNTIL FURTHER GUIDANCE ARRIVES. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER