MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1208 PM EST TUE DEC 01 2015 VALID DEC 01/1200 UTC THRU DEC 05/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS MODEL EVALUATION INCLUDING INITIAL FORECAST PREFERENCE AND CONFIDENCE MID-ATLANTIC COASTAL DEVELOPMENT MOVING TOWARD NOVA SCOTIA BY WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON GFS BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE FAIRLY SOLID AGREEMENT EXISTS WITH THE DEVELOPMENT OF THE MID-ATLANTIC COASTAL LOW AS IT TRACKS UP THE NORTHEAST U.S. SEABOARD TONIGHT. 12z GFS CONTINUES TO BE A BIT OF AN EASTWARD OUTLIER COMPARED TO THE REST OF THE MODEL GUIDANCE. WILL STAY WITH THE PREVIOUS PREFERENCE OF A NON-GFS BLEND. DEEP CLOSED LOW EJECTING FROM THE CENTRAL PLAINS TO THE NORTHEAST INCLUDING SURFACE REFLECTIONS: ACROSS MIDWEST INTO THE GREAT LAKES THRU WED. MID-ATLANTIC COASTAL DEVELOPMENT SHIFTING TO NOVA SCOTIA BY THU. SOUTHERN APPALACHIAN LOW DEVELOPING EARLY WED MOVING INTO NEW ENGLAND BY THURS. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-UKMET BLEND CONFIDENCE: AVERAGE MODELS CONTINUE TO SOLIDIFY TOWARD A COMMON SOLUTION FOR THE UPPER LOW AS WELL AS THE SURFACE LOW MOVING THROUGH THE UPPER MIDWEST BEFORE SHIFTING EAST WHILE WEAKENING...AS WELL AS THE SURFACE CYCLOGENESIS OVER THE SOUTHERN APPALACHIANS THROUGH THE SHORT RANGE. THE 00Z UKMET GENERALLY WAS FURTHER WEST WITH THE SOUTHERN APPALACHIAN SURFACE LOW...MAKING IT LESS DESIRABLE. THE 00Z UKMET ALSO BECOMES A BIT SLOWER AND STRONGER/WOUND UP ON DAY 3 OVER NOVA SCOTIA. THE 12Z GFS IS ALSO ON THE STRONG SIDE WITH THE SURFACE LOW...WHILE BEING THE MOST PROGRESSIVE SOLUTION ON DAY 3 TO THE NORTHEAST OF THE WELL CLUSTERED 12Z NAM/00Z ECMWF AND 00Z CMC. SPREAD INCREASES BY THE END OF DAY 3 BUT BY THAT TIME ANY SURFACE LOW WILL BE WELL REMOVED FROM THE MAINE. PREFER TO GO WITH A NON-UKMET SOLUTION. SHALLOW PROGRESSIVE WAVE ENTERING BC WED MORNING AND AFFECTING THE NORTHERN TIER AND GREAT LAKES BY FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON GFS BLEND CONFIDENCE: BELOW AVERAGE ANOTHER PACIFIC SHORTWAVE IMPULSE CROSSES INTO BRITISH COLUMBIA TUES NIGHT WHICH WILL MOVE THROUGH THE MEAN RIDGE AXIS DOWNSTREAM AND CLIP THE NORTHERN TIER STATES THROUGH THURS WITH FAIRLY STRONG AGREEMENT IN THE TIMING OF THE WAVE. THE 12Z NAM/00Z ECMWF/00Z CMC AND 00Z UKMET ARE ALL WELL CLUSTERED WITH A SHARP TROUGH OVER SOUTH CENTRAL CANADA BY 48 HOURS WITH GOOD AGREEMENT ON STRENGTH AND TIMING. THE 12Z GFS IS SLOWER AND MORE POSITIVELY TILTED WHILE ALSO NOT AS DEEP WITH THE WAVE. THE 12Z GFS ALSO HAS MUCH MORE ENERGY SAGGING SOUTHWARD BACK TOWARD THE CENTRAL ROCKIES WHICH LOOKS OUT OF PLACE COMPARED TO THE REST OF THE MODEL GUIDANCE. SPAGHETTI PLOTS SHOW MORE SUPPORT FOR THE CONSENSUS OF THE NON GFS SOLUTIONS SO WILL GO WITH THAT PREFERENCE INITIALLY. SOUTHERN STREAM SHORTWAVE ENERGY TRAVERSING THE FOUR CORNERS/S PLAINS/LOWER MS VALLEY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE GIVE THE WEAKNESS LEFT BY THE EJECTING UPPER LOW...WEAK SOUTHERN STREAM AND INCONSISTENT SHEDDING OF NORTHERN STREAM ENERGY FROM THE WAVE CURRENTLY OVER THE PACIFIC NORTHWEST...EVOLUTION OF THE LINGERING TROF ACROSS THE SOUTHERN TIER OF THE U.S. REMAINS IN HIGH FLUX WITH A LARGE SPREAD. THE ENSEMBLE SPAGHETTI PLOT SHOWS EACH ENSEMBLE SUITE GENERALLY CLUSTERS WELL WITH THEIR OWN...BUT GOOD AMOUNT OF DIFFERENCES EXISTS BETWEEN EACH MODEL. THERE APPEARS TO BE 2 CLUSTERS OF SOLUTIONS WITH THE HANDLING OF THIS ENERGY. THE 12Z NAM/12Z GFS ARE IN GOOD AGREEMENT WITH THE ENERGY IN AN EAST-WEST ORIENTATION ACROSS THE SOUTHERN PLAINS AND LOWER MS VALLEY IN 24 HOURS. THE 00Z NON NCEP GUIDANCE IS WELL CLUSTERED WITH A SOLUTION THAT IS SLOWER AND FURTHER NORTH WITH THE ENERGY STRETCHED OUT FROM THE SOUTHWEST U.S. TO THE CENTRAL PLAINS. BY 48 HOURS THE MODEL SOLUTION LOOK MORE SIMILAR ACROSS THE BOARD WITH THE NCEP GUIDANCE ONLY SLIGHTLY FURTHER SOUTH AND EAST. PREFER TO GO WITH A GENERAL MODEL COMPROMISE GIVEN THAT THE DIFFERENCES GENERALLY DISSIPATE AFTER ABOUT 24 HOURS. DEEPER/STRONGER WAVE APPROACHING THE WEST COAST THURSDAY... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-UKMET BLEND CONFIDENCE: AVERAGE THERE IS SOLID AGREEMENT WITH THE TIMING/STRENGTH OF THE BASE OF THE LARGE UPPER LEVEL TROF EMANATING FROM THE LARGE GULF OF ALASKA LOW BY 03/12Z. DIFFERENCES REMAIN RELATED TO THE STRENGTH OF THE LEADING VORT LOBE WHICH LEADS TO DIFFERENCES IN TIMING OF THE REFLECTED SURFACE LOW RIDING OUT OF THE DEEP SOUTHWESTERLY FLOW. THE 12Z NAM TRENDED FASTER AND WEAKER WITH THE 12Z GFS ON THE FAST SIDE AS WELL. THE 00Z UKMET/00 ECMWF ARE STRONGER AND DEEPER WITH THE WAVE BUT THE 00Z UKMET IS BY FAR THE OUTLIER CARRYING THE SHORTWAVE ENERGY MUCH FURTHER SOUTH THAN ANY OTHER MODEL. PREFER TO GO WITH A NON UKMET BLEND AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... KREKELER