MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1135 PM EST WED JAN 07 2015 VALID JAN 08/0000 UTC THRU JAN 11/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...ARCTIC SHORTWAVE TROUGH SURGING THROUGH THE MIDWEST/GREAT LAKES/NORTHEAST THURS/FRI... ...REINFORCING ARCTIC COLD FRONT CROSSING THE EASTERN U.S.... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE EMBEDDED WITHIN DEEP LAYER AND LARGE SCALE CYCLONIC FLOW IMPACTING MUCH OF EASTERN NORTH AMERICA...ANOTHER WELL-DEFINED SHORTWAVE WILL CROSS THE UPPER MIDWEST BY LATE THURS AND PIVOT THROUGH THE GREAT LAKES AND NORTHEAST THURS NIGHT AND FRI. THIS WILL DRIVE A REINFORCING SHOT OF ARCTIC AIR INTO THE EASTERN U.S. BY THE END OF THE WEEK. THERE IS MINIMAL SPREAD FROM A MASS FIELD PERSPECTIVE WITH THIS NEXT SYSTEM...AND SO A GENERAL MODEL COMPROMISE WILL BE PREFERRED. ...SHORTWAVE TROUGH DROPPING SOUTHEAST INTO THE UPPER MIDWEST/UPPER GREAT LAKES BY SUN... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: THE MODELS SUGGEST YET ANOTHER SHORTWAVE TROUGH EMBEDDED WITHIN THE ARCTIC STREAM IMPACTING THE UPPER MIDWEST AND THE UPPER GREAT LAKES REGION BY SAT NIGHT AND SUN. THIS ENERGY WILL DRIVE ANOTHER COLD FRONT INTO REGION BY THE END OF THE PERIOD. THE 12Z UKMET IS A BIT SLOWER THAN THE MULTI-MODEL CONSENSUS WITH THIS NEXT SYSTEM. THE REMAINING MODELS ARE FAIRLY WELL CLUSTERED WITH THE TIMING OF THE IMPULSE...BUT THE 00Z NAM IS A BIT STRONGER THAN THE CONSENSUS. THE STRONGER MODEL CLUSTERING OVERALL FAVORS A BLEND OF THE 00Z GFS AND 12Z ECMWF...AND SO THIS WILL BE PREFERRED. ...SLOW-MOVING UPPER LOW LIFTING ACROSS WESTERN MEXICO... ...ENERGY SHEARING EAST INTO THE SOUTHERN PLAINS... ...INVERTED SURFACE TROUGH NEAR THE WESTERN GULF COAST... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: BELOW AVERAGE A BROAD CLOSED LOW AND ASSOCIATED TROUGH LINGERING ACROSS BAJA CA IS FORECAST TO LIFT NORTHEAST OVER THE NEXT COUPLE OF DAYS AND THEN GRADUALLY SHIFT EAST TOWARD THE SOUTHERN PLAINS AND SHEAR OUT. THIS ENERGY WILL BE INSTRUMENTAL IN FOSTERING AN INVERTED TROUGH OVER THE WESTERN GULF COAST AREA JUST EAST OF THE TX COASTLINE. THE 00Z GFS ANS 12Z ECMWF ARE A LITTLE FASTER TO SHEAR OUT THE SOUTHERN STREAM ENERGY COMPARED TO THE SLOWER AND RELATIVELY STRONGER 00Z NAM/12Z GEM AND 12Z UKMET SOLNS. THE ENSEMBLE MEANS LED BY THE GEFS MEAN/SREF MEAN AND ECENS MEAN ALL FAVOR THE FLATTER AND RELATIVELY MORE PROGRESSIVE GFS/ECMWF CAMP. WILL THEREFORE FAVOR A GFS/ECMWF BLEND ATTM. CONFIDENCE HOWEVER IS LIMITED. ...SOUTHERN STREAM SHORTWAVE TROUGH ARRIVING IN THE SOUTHWEST LATE FRI... PREFERENCE: 00Z GFS CONFIDENCE: AVERAGE THE MODELS DEPICT SPLIT FLOW ACROSS THE EASTERN PACIFIC AND SUGGEST A WELL-DEFINED SOUTHERN STREAM SHORTWAVE TROUGH ARRIVING ACROSS SOUTHERN CA BY LATE FRI AND ADVANCING INTO THE SOUTHWEST ON SAT. THE 12Z GEM IS A STRONG AND SLOW OUTLIER WITH THIS SYSTEM. THE 12Z ECMWF GRADUALLY BECOMES MORE SHEARED AND WEAKER THAN ANY OTHER SOLN AS IT TRAVERSES THE SOUTHWEST ON SAT. THE 12Z UKMET AND 00Z NAM/00Z GFS SOLNS SPLIT THE DIFF. THE LATEST GEFS MEAN AND ECENS MEAN TEND TO FAVOR THE 00Z GFS OVERALL...AND SO WILL FAVOR THE 00Z GFS. ...NORTHERN STREAM SHORTWAVE TROUGH SKIRTING THE PACIFIC NORTHWEST ON FRI... PREFERENCE: NON-GEM CONSENSUS CONFIDENCE: AVERAGE A WEAK NORTHERN STREAM SHORTWAVE TROUGH COMING IN OFF THE PACIFIC WILL SHEAR ACROSS THE PACIFIC NORTHWEST LATE FRI AND SAT. THE 12Z GEM IS A STRONGER OUTLIER SOLN WITH THIS FEATURE. THE REMAINING MODELS ARE REASONABLY WELL CLUSTERED WITH THIS SPECIFIC SHORTWAVE...SO A NON-GEM CONSENSUS WILL BE PREFERRED. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON