MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 252 PM EDT MON APR 24 2017 VALID APR 24/1200 UTC THRU APR 28/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH PREFERENCES/CONFIDENCE INTERVALS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ DEEP SYSTEM MOVING UP THE EAST COAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-NAM BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z NAM IS FAST WITH THE TROPICAL ORIGIN LOW AS IT SWINGS BACK TOWARD THE CAROLINA COAST MERGING WITH THE COASTAL SURFACE WAVE THAT IS DIRECTLY UNDER THE UPPER LOW. THIS FAST NATURE KEEPS THE SOLUTION ON THE NORTHERN/FASTER SIDE OF THE GUIDANCE...AND THEREFORE IS LESS PREFERABLE. AS THE SYSTEM CONSOLIDATES AND VERTICALLY STACKS ON LATE TUESDAY THERE IS SOME DISAGREEMENT ON THE DEVOLUTION AS THE SYSTEM LIFTS TOWARD LONG ISLAND/SE NEW ENGLAND...POSSIBLY INFLUENCED BY THE UPSTREAM EVOLUTION OVER THE GREAT LAKES. THE ENSEMBLE TREND THERE HAS BEEN FOR SLOWER INCREASING RIDGING...WHICH IS BEST REPRESENTED BY THE 00Z ECMWF/ECENS MEAN AND CMC...THE FASTER WEAKENING SOLUTIONS BEST REPRESENTED BY THE GFS TAKE A DRAMATIC RIGHT TURN SE OF NEW ENGLAND THURSDAY WHICH SEEMS A BIT DRAMATIC GIVEN THE ENSEMBLE TRENDS AND WHILE THE 00Z ECMWF/ECENS MEAN SHOW THE NEGATIVE BIAS OF RETAINING A VERY STRONG/WOUND UP UPPER LOW...THIS COMBINED WITH THE WEAKER AND SLIGHTLY EASTWARD 00Z CMC MAY BE A NICE COMPROMISE TO ACCOUNT FOR THE TRENDS WHILE KEEPING SOME CONTINUITY AND INCLUSION OF THE EASTWARD TURNING POSSIBILITY. A NON-NAM BLEND IS SUPPORTED THROUGH 26/12Z TRANSITIONING TO A 00Z ECMWF/CMC BLEND AFTERWARD. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE PRIOR TO 26/12Z BUT FALLING TO AVERAGE GIVEN THE CHANGE/SPREAD FOR DAY 3. 19Z UPDATE: SLIGHT EASTWARD ADJUSTMENTS BY THE ECMWF/CMC INDICATES BETTER OVERALL ALIGNMENT WITH THE GFS/UKMET SINCE BOTH SHIFTED SLIGHTLY WEST WITH THERE 12Z RUNS. STILL FAVOR THE DEEPER SOLUTIONS OF THE ECMWF/CMC BUT OVERALL A NON-NAM BLEND COULD BE SUPPORTED THROUGH THE DURATION OF THE EVENT AFTER 26/12Z. BROAD TROF IN THE WEST AMPLIFYING TO BROAD POSITIVE TILT TROF ACROSS PLAINS WED WITH SURFACE LOW/ELONGATED SURFACE TROF TRACKING OUT OF TX/OK PANHANDLES INTO UPPER MIDWEST/GREAT LAKES THURS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF (12Z GEFS/00Z ECENS IF DESIRED) CONFIDENCE: SLIGHTLY BELOW AVERAGE WV LOOP SHOWS THE DUAL SHORTWAVE FEATURES OVER THE NORTHWEST STATES CURRENTLY WITH THE UNDERCUTTING JET STREAK INFLUENCED WAVE ENTERING NV WITH THE OLDER MORE CONSOLIDATED CENTER JUST OFF THE WA COAST. IN THE SHORT TERM THE SPACING BETWEEN THE TWO WILL EXPAND BROADENING THE LARGER SCALE TROF AND SPURRING THE INITIAL SURFACE LOW ACROSS THE TX/OK PANHANDLE WITH INVERTED SURFACE TROF EXTENDING TO THE REFLECTION OF THE PRIOR EXITING WAVE ENTERING THE UPPER MIDWEST LATER TODAY(WHICH IS NOW WELL AGREED UPON WITHIN THE GUIDANCE). EVENTUALLY THE LEAD WAVE ELONGATES AND ACTS AS THE PIVOT DRAWING THE OLDER CONSOLIDATED WAVE THROUGH THE ROCKIES DEEPENING THE UPPER TROF ACROSS THE SOUTHERN PLAINS WED. THE TREND HAS BEEN FAVORING THE A SLOWER/DEEPENING UPSTREAM WAVE THOUGH THE SPACING BETWEEN THE WAVES CONTINUES TO BE THE GREATEST UNCERTAINTY. THE GFS HAS BEEN FAST TO PRESS/SHEAR THE LEAD WAVE FURTHER EAST AND NORTH WHICH IS GENERALLY AWAY FROM THE ENSEMBLE TRENDS INCLUDING A MAJORITY OF THE 06Z GEFS MEMBERS. HOWEVER...THE 12Z GFS SEEMS TO HAVE RESPONDED IN TURN SLOWING AS WELL; WHILE STILL A BIT FURTHER EAST THAN THE ECMWF/ECENS MEAN OR FASTER (NORTH) OF THE GEFS MEAN IT IS MORE IN LINE WITH THE OVERALL TREND/WPC PREFERENCE AND COULD BE INCLUDED PERHAPS A SLIGHTLY LOWER WEIGHTING IN THE PREFERENCE. THE 12Z NAM ON THE OTHER HAND IS LIKE THE 00Z UKMET SUGGESTING A STRONG WOUND UP AND MUCH FURTHER SOUTHERLY SOLUTION BEFORE SWINGING THE SHORTWAVE NORTH THROUGH THE MID-MS VALLEY. THIS MAY BE TOO AGGRESSIVE OF A CHANGE TO JUMP TOO PARTICULARLY AS THE 00Z UKMET HAS BEEN MUCH SLOWER BEING AN OUTLIER AND HAS SHIFTED FASTER TO COMPROMISE TOWARD A COMMON SOLUTION PRESENTED IN THE ENSEMBLE SUITE... CLOSEST TO THE 00Z ECMWF. THE 00Z CMC HAS SOME COMPROMISE OVERALL WITH THE ECMWF/ECENS PARTICULARLY IN TIMING THOUGH IT...LIKE THE UKMET/NAM IS A BIT MORE WOUND UP LIFTING NORTH AND IN DOING SO BENDS WESTWARD BECOMING A WESTERN MEMBER OF THE ENSEMBLE CLUSTER OVERALL. AS SUCH WPC PREFERENCE IS THE 00Z ECMWF HEAVY WEIGHTING WITH THE 12Z GFS INCLUDING SOME 06Z GEFS/00Z ECENS MEAN TO ACCOUNT FOR THE LARGE REMAINING SPREAD IN POSSIBILITIES. CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE IN THIS BLEND/PREDICTABILITY OF PATTERN. 19Z UPDATE: BOTH UKMET/CMC SHIFTED TOWARD THE ECMWF SOLUTION THOUGH BOTH REMAIN A BIT MORE WOUND UP AND THEREFORE TRACK A BIT WEST OF THE ECMWF/00Z ECENS MEAN. THE 12Z ECMWF SHOWS LITTLE CHANGE REMAINING THE MOST MIDDLE GROUND AND A BIT FLATTER THAN THE UKMET/CMC/NAM THOUGH IS A BIT FASTER AND FURTHER NORTH THAN THE ECENS MEAN. THE 12Z GEFS MEAN LIKE THE FAVORABLE 06Z ENSEMBLE SUPPORTS THE ECENS MEAN/ECMWF MORE THAN THE 12Z GFS ITSELF. WITH LARGE SPREAD BUT GOOD AGREEMENT IN THE ENSEMBLES...WILL FAVOR THE 12Z ECMWF AS WPC PREFERENCE BUT AT SLIGHTLY BELOW AVERAGE CONFIDENCE. SYSTEM MOVING INTO THE WEST WEDNESDAY RELOADING LARGE SCALE TROF IN INTERMOUNTAIN WEST THURS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE STRONG BUT DRIFTING EASTWARD BLOCKING PATTERN OVER WESTERN CANADA FORCES SHORTWAVE ENERGY TO EITHER REINFORCE CYCLONE TO THE WEST OVER THE EASTERN GULF OF AK OR UNDERCUT THE RIDGE INTO THE PACIFIC NORTHWEST BY WED. EVENTUALLY THE STRONG JET AND NUMEROUS EMBEDDED SHORTWAVES WILL FURTHER EXPAND THE LARGE SCALE TROF THAT DOMINATES THE CENTRAL AND WESTERN PORTION OF THE CONUS BY 00Z FRIDAY. OVERALL THE GUIDANCE IS QUITE AGREEABLE THOUGH OBVIOUSLY SMALLER SCALE EMBEDDED WAVE TIMING DIFFERENCES LEAD TO SMALLER SCALE VARIABILITY TO WX ACROSS THE INTERMOUNTAIN WEST. AS SUCH A GENERAL MODEL BLEND IS SUPPORTED AT ABOVE AVERAGE CONFIDENCE THROUGH THIS FORECAST PERIOD. 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