MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1220 AM EDT SAT MAR 26 2016 VALID MAR 26/0000 UTC THRU MAR 29/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION INCLUDING PREFERENCE AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ BROAD LONGWAVE TROF WITH EMBEDDED SHORTWAVES IN W NEB AND DIGGING ACROSS GREAT BASIN TO SHARPEN/PHASE ACROSS CENTRAL PLAINS AND SHIFT ACROSS OHIO VALLEY MONDAY INTO NEW ENGLAND TUES. ASSOCIATED SURFACE TROF/FRONT FROM ONTARIO TO SOUTHERN PLAINS WITH DEVELOPING CENTRAL LOW IN THE GREAT LAKES/OHIO VALLEY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF/CMC CONFIDENCE: SLIGHTLY BELOW AVERAGE COMPLEX UPPER LEVEL PATTERN WITH FOUR SIGNIFICANT SHORTWAVES WITH DIFFERENT TIMING/SPACING WITH THEIR INTERACTION IS LEADING TO THE LARGE SPREAD IN MODEL AND ENSEMBLE MEMBER SOLUTIONS. THE LEAD SHORT WAVE ACROSS NEB AND EJECTING WAVE CURRENTLY IN CO/NM LIFT NORTHEAST AND EVOLVE TO FAIRLY ROBUST SURFACE REFLECTION ALONG THE ELONGATED FRONTAL ZONE FROM ONTARIO TO THE SOUTHERN PLAINS ALREADY IN PLACE...BUT SHEAR INTO THE GREAT LAKES WITH GOOD MODEL SUPPORT AND AGREEMENT THROUGH AT LEAST 36HRS. THE SPREAD BEGINS TO INCREASE AFTER THIS TIME DUE TO TIMING/STRENGTH INTERACTIONS WITH THE TIMING/STRENGTH AS THE SHORTWAVE CURRENTLY IN THE WESTERN PORTION OF THE LONGWAVE TROF IN THE GREAT BASIN EJECTS INTO THE PLAINS SUNDAY MORNING AND BEGINS TO SHORTEN THE OVERALL TROF WAVELENGTH AND SHIFT EAST; INFLUENCES OF AMPLIFICATION OF NORTHERN STREAM SHORTWAVE OUT OF SASKATCHEWAN LEAD COMPOUND TIMING/SHAPE DIFFERENCES OF THE OVERALL TROF MOVING THROUGH THE GREAT LAKES AND OHIO VALLEY BY MONDAY...AS WELL AS THE SURFACE LOW POSITION/TRACK THROUGH THE GREAT LAKES/OHIO RIVER VALLEY AND POTENTIAL COASTAL SURFACE REDEVELOPMENT ON TUES. GIVEN ALL THE INTERPLAY OF THESE WAVES AND THE RESULTANT SURFACE AND LOWER LEVEL PATTERN/LOWS INDIVIDUAL MODEL CONTINUITY IS QUITE RANDOM...THOUGH ECENS MEAN HAS BEEN THE LEAST VARIANT THROUGH THE LAST FEW DAYS. AS SUCH HAVE BEEN FAVORING SOLUTIONS CLOSER TOWARD THE ECENS MEAN. THE OPERATIONAL ECMWF HAS ALSO SHOWN THE RUN TO RUN VARIATION...AND THOUGH THE 12Z ECMWF IS A BIT DEEPER ALOFT...IT IS VERY NEAR THE BEST OVERALL CLUSTERING IN THE ENSEMBLE PLOTS IN FACT NEAR THE LEADING EDGE OF ECENS MEMBERS NEARER TOWARD A SECONDARY CLUSTER OF GEFS AND CMCE MEMBERS. ON THE OTHER HAND...THE 00Z GFS REMAINS FASTER IN TIMING BOTH WITH THE NORTHERN STREAM SHORTWAVE AS WELL AS PHASING SOUTHERN STREAM SHORTWAVE ENERGY RESULTING INCLUDES A FURTHER NORTH SURFACE LOW. THIS MATCHES THE TREND SEEN WITH THE 18Z GEFS SHOWING SIGNS OF BETTER AGREEMENT TOWARD THE 12Z ECENS MEAN AND 12Z ECMWF SOLUTIONS BUT STILL QUITE A BIT SPREAD OVERALL. THE 00Z NAM SHOWED SOME POSITIVE TRENDS TOWARD THE ECMWF SOLUTION AS WELL. BY 36HRS THE SURFACE LOW IN THE IOWA HAS TRENDED WEAKER AND AFTERWARD THE LOW IS VERY NEAR THE CENTER OF THE ECENS SURFACE LOW CLUSTER EVEN THOUGH IT REMAINS A BIT WEST/NORTH OF THE MEAN AND 12Z ECMWF ITSELF. AT THIS POINT IT BUILDS CONFIDENCE TOWARD THE ECMWF SOLUTION BUT GIVEN IT IS FURTHER NORTH AND WEST AS WELL AS MORE CONSOLIDATED ALOFT (NOT ELONGATED N-S LIKE MUCH OF THE GUIDANCE) WILL NOT INCLUDE IN THE BLEND TO KEEP/STRENGTHEN THE SIGNAL THAN WASH IT OUT IN AVERAGING PROCESS. THE 12Z CMC IS MOST IN AGREEMENT WITH THE 12Z ECMWF/ECENS MEAN OVERALL WITH SOME SLOWNESS ALOFT...A NICE MIDDLE GROUND BETWEEN THE ECMWF/NAM. THE 12Z UKMET IS VERY WEAK IN THE NORTHERN STREAM AND THEREFORE A BIT MORE DECOUPLED AND WHILE IN GOOD TIMING WITH THE SHORTWAVE CROSSING THE OHIO VALLEY...IT IS GENERALLY SOUTH AND WEAKER HAVING NO NORTHERN SHORTWAVE INFLUENCE. ADDITIONALLY THE UKMET DEEPENS A SHORTWAVE IN THE SUBTROPICAL STREAM ACROSS THE SOUTH/SOUTHEAST EVENTUALLY DEVELOPING A ROBUST COASTAL LOW WELL SOUTH AND EAST OF THE MAIN CLUSTER. AS SUCH WILL PREFER A BLEND OF THE 12Z CMC/ECMWF BUT GIVEN THE HIGH VARIABILITY AND LARGE SPREAD CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE. UPPER TROUGH/FRONT APPROACHING THE PACIFIC NORTHWEST BY LATE SAT EVOLVING TO A DEEP CLOSED LOW DEVELOPING OVER THE WEST MON INTO TUES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE A PROGRESSIVE UPPER TROUGH AND ASSOCIATED FRONT ADVANCING THROUGH THE GULF OF AK WILL DIG SHARPLY SOUTHEASTWARD SAT AND SUN INTO THE PACIFIC NORTHWEST AS STRONG HEIGHT RISES/RIDGING DEVELOPS SOUTHEAST OF THE ALEUTIANS AND THEN MOVES INTO THE GULF OF AK THROUGH THE PERIOD. THE RIDGE AMPLIFICATION WILL LEAD TO DEVELOPMENT OF A ROBUST CLOSED LOW OVER THE WEST BY LATE MON AND TUES. THIS WILL RESULT IN A BROAD AND DEEPENING AREA OF LOW PRESSURE ACROSS MUCH OF THE INTERMOUNTAIN REGION BY THE END OF THE PERIOD. OVERALL ONLY VERY SMALL DIFFERENCES IN PLACEMENT/STRENGTH OF INTERNAL SHORTWAVES TO THE LARGE UPPER LOW SEEM TO EXIST BY THE END OF THE FORECAST PERIOD...BUT GIVEN LACK OF PREDICTABILITY OF THIS SMALL SCALE INTERACTIONS AND THE OVERALL SHAPE/TIMING/PLACEMENT OF THE UPPER LOW AND BROAD SURFACE LOW IN THE INTERMOUNTAIN WEST... AN OPERATIONAL MODEL BLEND WILL BE PREFERRED AT ABOVE AVERAGE CONFIDENCE. IT WAS NOTED THAT THERE ARE SOME QPF DIFFERENCES ACROSS THE WEST EVEN THOUGH THE MASS FIELDS ARE ALIGNED...PLEASE REFER TO QPFPFD FOR ADDITIONAL INFORMATION. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA