MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1230 PM EDT FRI MAR 17 2017 VALID MAR 17/1200 UTC THRU MAR 21/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE INTERVALS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SHORTWAVE OVER WESTERN GREAT LAKES TODAY DEEPENING THROUGH THE MID-ATLANTIC SAT WITH COASTAL SURFACE LOW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM CONFIDENCE: AVERAGE MULTIPLE CYCLE ENSEMBLE SPAGHETTI ANALYSIS SHOWS AN ACCORDION AFFECT BETWEEN THE TWO SIDES OF THE GUIDANCE PACKAGE: THE GFS/GEFS FAST AND THE ECMWF/ECENS SLOW...AND APPEARS TO HAVE EXPANDED AGAIN WITH THE MOST RECENT CYCLE. THE CONSISTENT TREND IN BOTH CAMPS THOUGH IS CONTINUED WEAKER SOLUTION THAN THE PRIOR CYCLE AS WELL AS LEADING TO SIMILAR EVOLUTION SHAPE/STRENGTH. THE DIFFERENCES RESIDE MAINLY IN THE TIMING/LOADING OF THE TROF AS IT ELONGATES NORTH TO SOUTH BUT ALSO SHIFTS EASTWARD WITHIN THE LARGER SCALE FLOW. THE 00Z ECMWF IS UNLIKE THE BULK OF GUIDANCE IN BEING SLOW AND LOADING THE TROF LATE AND FAVORING THE CENTRAL OR SOUTHERN PORTION OF THE TROF WITH FORCING/STRENGTH...IN SUCH A MANNER THAT THE OPERATIONAL IS EVEN ON THE SLOW SIDE OF THE ECENS MEMBERS MAKING IT LESS FAVORABLE PARTICULARLY LATE MONDAY WHEN THE DIFFERENCES ARE GREATEST. THE GFS HAS BEEN ON FASTER TREND INITIALLY FAVORS THE LEAD PORTION OF THE TROF LEADING TO A STRONGER NORTHWARD INJECTION OF ENERGY WITH THE TROF AS WHOLE AND IS ALSO ON THE NORTHERN SIDE OF THE GEFS SOLUTIONS...THE 12Z RUN HAS TRENDED A BIT FURTHER WEST WITH THE SURFACE LOW BUT CONTINUES TO BE QUITE FAST OVERALL AND THEREFORE LESS PREFERABLE. THE REMAINING GUIDANCE SPLIT PREFERENCE WITH THE 00Z UKMET MATCHING A SLIGHTLY SLOWER REPRESENTATION OF THE 00Z/06Z GEFS MEMBERS/12Z GFS OPS RUN; THE 00Z CMC MATCHING THE ECMWF THOUGH TYPICAL OF THE CMC IS A BIT MORE CONCENTRIC/LESS ELONGATED WITH THE TROF AS A WHOLE. THE 12Z NAM CONTINUES TO BE A NICE REPRESENTATIVE OF BOTH CAMPS IN THE MIDDLE OF THE GUIDANCE...INITIALLY FAVORING THE ECMWF CAMP PARTICULARLY ALOFT THOUGH THE UKMET/GFS AT THE LOWER LEVELS/SFC. AFTER 19/12Z WHEN THE SPREAD IN TIMING ACCELERATES...THE 12Z NAM EVOLUTION SPLITS THE DIFFERENCE IN TIMING AND MORE IN LINE WITH CURRENT PREFERENCE AWAY FROM TYPICAL NEGATIVE BIASES MANIFESTING THE OTHER TWO CAMPS. AS SUCH INITIAL WPC PREFERENCE IS GOING TO BE THE 12Z NAM THOUGH CONFIDENCE IS REDUCED TO AVERAGE GIVEN THE EVOLUTION/SHAPE APPEARS GOOD THOUGH THE TIMING AGREEMENT IS POOR AND MILDLY VARYING WITH EACH CYCLE. SOUTHERN STREAM SHORTWAVE AND SURFACE WAVE ADVANCING TOWARD WA BY EARLY SAT... TRANSLATES ACROSS CANADIAN ROCKIES AND DEEPENS THE SURFACE LOW WITH TRAILING FRONTAL ZONE THROUGH THE NORTHERN TIER SUN INTO GREAT LAKES LATE MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE GOES-WEST WV DENOTES SHORTWAVE IN THE SOUTHERN STREAM BEGINNING TO SHEAR/STRETCH INTO THE PACIFIC NORTHWEST IN ADVANCE OF THE HEIGHT FALLS/JET STREAK WOUNDING THE BASE OF THE NORTHERN PACIFIC DEEP UPPER LOW. GUIDANCE CONTINUES TO BE VERY AGREEABLE IN TIMING/STRENGTH AND PLACEMENT OF THE ENERGY ALOFT AND DEVELOPMENT/EVOLUTION OF THE SURFACE WAVE INTO W WA EARLY SAT MORNING. THE DIFFERENCES REMAIN IN THE PLACEMENT OF AN ARCTIC TROF AND HOW INFLUENTIAL IT IS IN DEEPENING OR KICKING THE WAVE THROUGH THE BOREAL FORESTS OF N SASKATCHEWAN/MANITOBA INTO SUN/MON. THE TRAILING MOISTURE FEED THROUGH THE NORTHERN ROCKIES AND EVENTUAL LEE SURFACE PRESSURE FALLS TIMING AND STRENGTH LOOK QUITE SIMILAR EVEN AS THE FRONTAL ZONE TRACKS THROUGH THE UPPER MIDWEST INTO THE GREAT LAKES. AS SUCH A GENERAL MODEL BLEND IS SUPPORTED THROUGH THE CONUS AT ABOVE AVERAGE CONFIDENCE. DEEP TROF APPROACHING WEST COAST LATE MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE TOWARD THE END OF THE FORECAST PERIOD A LOOSELY ORGANIZED TROF IS PROGRESSIVE ACROSS THE CENTRAL PACIFIC WITH MULTIPLE EMBEDDED SHORTWAVE FEATURES. GIVEN THE BROAD NATURE THERE IS A WEAK WAVE THAT WILL LIFT OUT OF THE SUBTROPICS/TROPICS LATE SUNDAY INTO MONDAY ANGLING TOWARD THE N CA COAST...THE 12Z GFS IS A BIT STRONGER AGGRESSIVE WITH THIS WAVE AND ITS INFLUENCES TO THE WEST COAST THAN THE REMAINING GUIDANCE. HOWEVER...AS THE MEAN TROF ENCROACHES THE 00Z CMC HAS A STRONGER SOUTHEASTWARD ORIENTED TROF. CYCLE TO CYCLE ENSEMBLES SUPPORT CONSISTENCY WITH THE ECENS MEAN THOUGH WITH FAIRLY GOOD AGREEMENT IN THE 00Z UKMET AND 12Z GFS/NAM... THE DIFFERENCES RESIDE WITH THE PLACEMENT/STRENGTH OF SMALLER SCALE INTERNAL WEAK WAVES AND THE INFLUENCE ON THE MOISTURE/WIND FIELDS LOCALLY TO HAVE MUCH CONFIDENCE IN ONE SPECIFIC RUN OVER ANOTHER AT THIS TIME. AS SUCH WILL GRAVITATE PREFERENCE TOWARD THE ENSEMBLE MEANS...WHICH FAIRLY WELL REPRESENTED BY A NON-CMC BLEND. CONFIDENCE IS FAIRLY GOOD ON THE LARGER SCALE BUT WITH LARGE LOCALIZED VARIATION...THE OVERALL CONFIDENCE IS AVERAGE TO SLIGHTLY BELOW AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA