MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 144 AM EST FRI JAN 15 2016 VALID JAN 15/0000 UTC THRU JAN 18/1200 UTC ..SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION - INCLUDING THE NAM/GFS ***SHORTWAVE TROUGH AND SURFACE LOW TRACKING ACROSS THE UPPER MIDWEST AND GREAT LAKES*** PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE SHORTWAVE TROUGH THAT CROSSED THE INTERMOUNTAIN WEST ON THURSDAY IS NOW TRAVERSING THE NORTHERN PLAINS. THIS NORTHERN STREAM FEATURE IS FORECAST TO ACQUIRE A NEGATIVE TILT AS IT CROSSES THE GREAT LAKES BY SATURDAY MORNING. THIS WILL ALSO HAVE A WELL-DEFINED SURFACE LOW THAT WILL TRACK EASTWARD ACROSS MICHIGAN ON FRIDAY NIGHT AND THEN OVER QUEBEC BY SATURDAY NIGHT. THIS LOW WILL ALSO PLAY A ROLE IN KEEPING MUCH OF THE EAST COAST WARM ENOUGH FOR RAIN FOR THIS SYSTEM EXPECTED ALONG THE COAST ON SATURDAY. THE MODEL GUIDANCE REMAINS IN GOOD AGREEMENT WITH THIS LOW, AND THE 00Z UKMET HAS COME CLOSER TO THE MODEL CONSENSUS. ***LOW PRESSURE SYSTEM TRACKING FROM THE GULF OF MEXICO TO THE EAST COAST THROUGH SATURDAY*** PREFERENCE: 00Z GFS/00Z UKMET THROUGH 48 HOURS, THEN GEFS/EC MEAN BEYOND THAT CONFIDENCE: BELOW AVERAGE THE UPPER LEVEL TROUGH AXIS EXITING MEXICO AND EMERGING OVER THE NORTHERN GULF OF MEXICO IS FORECAST TO SPAWN A SURFACE LOW THAT IS FORECAST TO TRACK NEAR THE EAST COAST BY SATURDAY MORNING. THIS SURFACE LOW IS FORECAST TO DEVELOP INTO A NOR'EASTER AS IT PASSES OFFSHORE FROM CAPE COD. SOME OF THIS INTENSIFICATION WILL LIKELY BE RELATED TO THE AFOREMENTIONED ENERGY APPROACHING THE GREAT LAKES REGION AND SOME INTERACTION BETWEEN THE TWO SYSTEMS. THIS REMAINS SOMEWHAT OF A CHALLENGING FORECAST BEYOND 36 HOURS AS THE LOW PASSES BY THE MID-ATLANTIC COAST. THE 00Z ECMWF BECOMES A DEEP OUTLIER WITH RESPECT TO THE SURFACE LOW. THE SPREAD REMAINS QUITE NOTEWORTHY WITH THE SURFACE LOW, WITH THE 00Z NAM HAVING A DUAL LOW STRUCTURE WITH ONE LOW NEAR LONG ISLAND NY AND ANOTHER A FEW HUNDRED MILES TO THE SOUTHEAST BY 12Z SATURDAY. BY 00Z SUNDAY, THE NAM IS STILL MUCH FARTHER WEST THAN THE MODEL CONSENSUS, AND THE GFS ON THE EASTERN SIDE OF THE GUIDANCE. BOTH THE EC AND GFS MEANS ARE NEAR THE MIDDLE GROUND AND ARE CLOSE TO EACH OTHER, MAKING THEM USEFUL PARTS OF THE FORECAST PROCESS BY 48 HOURS AND BEYOND. ***DEEP VORTEX AND UPPER LEVEL LOW OVER SOUTHERN ONTARIO THIS WEEKEND*** PREFERENCE: 00Z GFS/00Z ECMWF COMPROMISE CONFIDENCE: AVERAGE A WELL-DEFINED MID LEVEL VORTEX OVER NORTHERN MANITOBA AT THE START OF THE FORECAST PERIOD FRIDAY MORNING WILL BE A BIG PLAYER IN TERMS OF TEMPERATURES OVER THE NORTH CENTRAL U.S. THROUGH SUNDAY. THIS UPPER LOW WILL HAVE A DEEP LAYER OF COLD AIR WITH IT AND WILL BE ACCOMPANIED WITH AN ARCTIC BLAST ACROSS THE UPPER MIDWEST AND GREAT LAKES REGION WHEN THE DEEP LOW CENTER REACHES NORTHERN MICHIGAN THIS WEEKEND. THE MODELS ARE IN EXCELLENT AGREEMENT THROUGH ABOUT 36 HOURS, AFTER WHICH THE NAM BECOME FARTHER TO THE NORTHWEST THAN THE MODEL CONSENSUS. BOTH THE GFS AND ECMWF HAVE GOOD SUPPORT WITH THEIR ENSEMBLE MEANS, AND THUS A 00Z GFS/00Z ECMWF COMPROMISE CAN BE USED. ***SHORTWAVE TROUGH TRACKING FROM THE PACIFIC NORTHWEST TO THE GULF OF MEXICO*** PREFERENCE: 00Z GFS/00Z GEFS MEAN/00Z UKMET CONFIDENCE: SLIGHTLY BELOW AVERAGE THE CLOSED UPPER LEVEL LOW THAT TRACKED INLAND OVER THE PACIFIC NORTHWEST THURSDAY NIGHT IS EVOLVING INTO AN OPEN WAVE. THE VORTICITY ASSOCIATED WITH THIS SHORTWAVE IS PROGGED TO DROP SOUTHEAST THROUGH THE INTERMOUNTAIN WEST THROUGH FRIDAY AND THEN OVER THE SOUTHERN PLAINS AND THE WESTERN GULF COAST BY SATURDAY, ALONG WITH SOME AMPLIFICATION EXPECTED. THIS IS EXPECTED TO RESULT IN SURFACE CYCLOGENESIS OVER SOUTHERN TEXAS BY SATURDAY MORNING. IN TERMS OF MODEL PERFORMANCE, BOTH THE 00Z ECMWF AND 00Z UKMET SHOW A MORE PRONOUNCED UPPER TROUGH AXIS CROSSING THE GULF OF MEXICO, AND THE ECMWF IS THE SLOWEST DETERMINISTIC SOLUTION. THERE IS GOOD AGREEMENT THAT THE SURFACE LOW WILL TRACK ACROSS THE NORTHERN GULF BEFORE CROSSING THE FLORIDA PENINSULA SUNDAY MORNING, WITH THE CMC BEING FASTER AND FARTHER TO THE NORTH. THE GFS IS NOW RELATIVELY CLOSE TO THE 12 GEFS MEAN, WHICH IS CLOSEST TO THE MODEL CONSENSUS AT THIS TIME. CONFIDENCE REMAINS LIMITED GIVEN THE MASS FIELD MODEL SPREAD. ***UPPER LEVEL TROUGH AND PACIFIC FRONT REACHING THE WEST COAST SATURDAY*** PREFERENCE: 00Z GFS/00Z ECMWF COMPROMISE CONFIDENCE: AVERAGE AFTER TEMPORARY RIDGING OVER THE WEST COAST ON FRIDAY, THE ACTIVE WEATHER PATTERN RETURNS ON SATURDAY WITH A SHORTWAVE TROUGH AND ASSOCIATED COLD FRONT REACHING THE COAST SATURDAY MORNING. THE 00Z UKMET APPEARS TO BE TOO FAST WITH THE PROGRESSION OF THIS ACROSS THE PACIFIC NORTHWEST, AND THE CMC AMONG THE DEEPEST SOLUTIONS. THE 00Z NAM ALSO APPEARS TOO STRONG WITH THE UPPER LEVEL TROUGH. THE 00Z GFS AND 00Z ECMWF ARE CLOSEST TO THE MODEL CONSENSUS AND HAVE BETTER ENSEMBLE SUPPORT, MAKING THEM GOOD CANDIDATES FOR THE MODEL BLEND. ***NEXT UPPER LEVEL TROUGH AND PACIFIC FRONT NEARING THE WEST COAST BY LATE SUNDAY*** PREFERENCE: 00Z GEFS MEAN/00Z GFS/00Z ECMWF COMPROMISE CONFIDENCE: SLIGHTLY BELOW AVERAGE AN EVEN STRONGER LOW PRESSURE SYSTEM AND VORTMAX IS PROGGED TO APPROACH BRITISH COLUMBIA BY SUNDAY EVENING, WITH A TRAILING COLD FRONT REACHING THE PACIFIC NORTHWEST AROUND THE SAME TIME. THE 00Z CMC IS A STRONG OUTLIER BOTH AT THE SURFACE AND ALOFT, BUT LESS SO THAN ITS 12Z RUN. THE 00Z GFS, 00Z GEFS MEAN, AND 00Z ECMWF CLUSTER TOGETHER THE BEST AND THIS MODEL CONSENSUS WILL BE PREFERRED FOR NOW. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... HAMRICK