MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 151 AM EST THU DEC 01 2016 VALID DEC 01/0000 UTC THRU DEC 04/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z GUIDANCE EVALUATION INCLUDING MODEL PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SHORTWAVE AMPLIFYING IN THE SOUTHWEST FRI WITH A CLOSED 700 MB LOW FORMING AND DRIFTING SOUTH INTO NORTHWEST MEXICO SAT AND POSSIBLY TURNING EAST ON SUN...SPURRING RETURN FLOW/WEAK SURFACE REFLECTION OVER NE MEXICO/ TEXAS/ GULF COAST... PREFERENCE: 00Z GFS/00Z ECMWF BLEND CONFIDENCE: AVERAGE THE MODELS FORECAST THE 700-500 MB TROUGH TO DRIFT SOUTH ACROSS CA/NV WITH A 700 MB CLOSED LOW FORMING IN AZ 12Z FRI. THE GFS/NAM/UKMET/ECMWF TAKE THIS LOW SOUTH INTO NORTHWEST MEXICO BY 12Z SAT AND THEN DIFFERENCES DEVELOP BY 12Z SUN WITH THE NAM AND ECMWF BRINGING THE LOW FURTHER EAST THAN THE GFS/00Z GEFS MEAN. THE UKMET AND 00Z ECMWF TRENDED A LITTLE FASTER IN BRINGING THE LOW EAST...SIMILAR TO WHAT WE SAW THE LAST COUPLE OF NIGHTS. THE ENSEMBLE SPAGHETTI PLOTS STILL SHOW MORE 12Z ECMWF MEMBERS THAN GEFS MEMBERS IN MOVING THE 500 MB TROUGH FASTER EAST ON SUNDAY...BUT THE GAP IS STARTING TO LESSEN FROM YESTERDAY. THE SURFACE RESPONSE TO THE UPPER TROUGH IS A TROUGH OR WEAK WARM FRONT ALONG THE TX GULF COAST. THE 21Z SREF MEAN IS WEAKER THAN THE NAM/GFS/UKMET/ECMWF SO THE LEAST WEIGHTING IS RECOMMENDED ON THE 21Z SREF MEAN SOLUTION. ...GREAT LAKES/NORTHEAST COASTAL LOW AND ASSOCIATED FRONTS... PREFERENCE: MODEL CONSENSUS CONFIDENCE: ABOVE AVERAGE THE MODELS HAVE COME INTO BETTER AGREEMENT ON THE LOW FORECAST TO BE NEAR THE NH COAST 12Z THU AND THEN NEAR THE MAINE COAST DURING THE DAY TO REACH NEW BRUNSWICK BY 00Z FRI. A TRAILING BNDRY REMAINS OVER NORTHERN NEW ENGLAND AS THE SECONDARY WAVE ROTATES ACROSS THE REGION WITH A BROAD TROUGH ACROSS THE NORTHEAST BY 12Z SAT...WEAKENING AND PULLING OFFSHORE SUNDAY. MINOR MASS DIFFERENCES EXIST WITH NO REASON TO SUGGEST ONE PARTICULAR SOLUTION OVER ANOTHER. A GENERAL MODEL BLEND SHOULD COVER THE UPPER LOW, SURFACE REFLECTIONS IN ONTARIO/QUEBEC AND COASTAL DEVELOPMENT IN NEW ENGLAND INCLUDING THEIR DEPTH/STRENGTH. ...SHORTWAVE CROSSING SOUTHWEST CANADA FRI INTO SAT WITH SHORTWAVE MOVING ACROSS THE NORTHERN PLAINS SAT AND UPPER MS VALLEY/UPPER LAKES SUN... PREFERENCE: MODEL CONSENSUS CONFIDENCE: ABOVE AVERAGE A STRONG 150+ KT JET STREAK APPROACHES AND REACHES VANCOUVER ISLAND ON SAT. THE WAVE DOWNSTREAM FROM THE JET MAX WILL BEGIN TO AMPLIFY ACROSS THE SOUTHERN CANADIAN/NORTHERN U.S. ROCKIES AND SUPPORT A WEAK SURFACE DEVELOPMENT IN THE LEE ACROSS SW SASKATCHEWAN. WHILE THERE REMAIN SUBTLE DIFFERENCES MOSTLY IN STRENGTH/DEPTH OF THE SHORTWAVE...THE DETERMINISTIC GFS/ECMWF/UKMET/NAM MODELS ARE IN ABOVE AVERAGE AGREEMENT IN TIMING/PLACEMENT AND STRENGTH TO HAVE ABOVE AVERAGE CONFIDENCE IN A MODEL BLEND FOR THIS FEATURE INTO THE WEEKEND. THE PROBLEM SOLUTION IS THE 21Z SREF MEAN...WHICH IS MUCH FLATTER WITH THE WAVE AND OUT OF PHASE WITH THE MODELS AND 12Z ECMWF MEAN AND 18Z GEFS MEAN. THE SREF MEAN IS THE LOWEST PROBABILITY OUTCOME AND SHOULD BE GIVEN THE LEAST WEIGHTING. ...WEAK LOW AMPLITUDE 700 MB WAVE AND ASSOCIATED MODEST SURFACE COLD FRONT COMING INTO THE PACIFIC NORTHWEST SAT NIGHT.... THE MODELS START TO BUCKLE THE CONFLUENT FLOW WITH A LOW AMPLITUDE WAVE FORMING AT 700 MB WITH A WEAK SURFACE REFLECTION IN THE FORM OF A TROUGH OR WEAK COLD FRONT COMING INTO THE PACIFIC NORTHWEST BY EARLY SUN. THE GFS IS A FEW HOURS FASTER THAN THE 0Z ECMWF AND THE UKMET AND ECMWF ENSEMBLE MEAN SO THE ODDS FAVOR A SLIGHTLY SLOWER MOTION THAN THE 00Z GFS AND NAM INDICATES. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... PETERSEN