MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1149 AM EST MON FEB 01 2016 VALID FEB 01/1200 UTC THRU FEB 05/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z GUIDANCE EVALUATION INCLUDING MODEL PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MID-LEVEL SHORTWAVE AND SURFACE LOW MOVING INTO SOUTHEAST CANADA ASSOCIATED FRONTAL PASSAGE THROUGH THE EAST COAST TODAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE LITTLE CHANGE WITHIN VERY STRONG AGREEMENT FOR THE REMAINDER OF THIS SYSTEM. CONTINUE TO SUPPORT AN OPERATIONAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. SURFACE LOW TRACKING THROUGH THE SOUTHWEST INTO THE THE SOUTHERN PLAINS MONDAY EVENING NORTHEAST INTO THE GREAT LAKES BY WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/00Z ECMWF AND EITHER 06Z GEFS OR GFS. CONFIDENCE: SLIGHTLY ABOVE AVERAGE LARGE SCALE AGREEMENT CONTINUES TO BE ABOVE AVERAGE WITH THIS SYSTEM AS THE LONG WAVE TROUGH MOVES INTO THE PLAINS. SURFACE LOW PRESSURE NEAR THE FOUR CORNERS REGION CURRENTLY WILL REFORM ACROSS NORTHEAST NM AND SOUTHEAST CO DURING THE DAY TODAY...BEFORE EJECTING EAST INTO KS AND EVENTUALLY NORTHEAST INTO THE GREAT LAKES REGION BY TUESDAY NIGHT. THERE REMAIN SMALL TIMING DIFFERENCES WITH LOCATION/TIMING OF THE PIVOT POINTS/WOBBLES ALONG THE DEFORMATION ZONE FOR SOME LOCALIZED MESOSCALE MAXIMA IN QPF/SNOW TOTALS...BUT THESE WILL VARY WITH SUBTLE INTERNAL DYNAMICS THAT ARE NEAR IMPOSSIBLE TO LOCK DOWN DUE TO RUN TO RUN VARIANCE. THE ECMWF SOLUTION HAS BEEN VERY SOLID WITH VERY LITTLE DIFFERENCE ACROSS THE LAST 2-3 RUNS INCLUDING THE ECENS MEANS IN VERY STRONG AGREEMENT WITH THE OPERATIONAL RUN EVEN THOUGH THERE IS SMALL TO MODERATE SPREAD IN THE ENSEMBLE SPAGHETTI PLOTS/SURFACE LOW CLUSTERS. THE MAIN DIFFERENCE IN THE SPAGHETTI/SURFACE CLUSTER FROM YESTERDAY'S 12Z TO LAST NIGHT'S 00Z IS A FEW MORE GEFS/CMCE MEMBERS CLUSTERING TOWARD THE SLOWER SOUTHWEST...THIS CAN EVEN BE SEEN IN A SLOWING OF THE 06Z GFS PARTICULARLY ACROSS THE UPPER MS VALLEY INTO THE GREAT LAKES AND EVEN MORE DRAMATICALLY WITH THE 12Z RUN AS IT RETAINS THE STRENGTH OF ONE OF THESE INTERNAL PIVOTS AND IS STRONGER WITH THE OCCLUDED SURFACE LOW OVER NW MO AND RETAINING IT AS IT WEAKENS ACROSS IA/S WI THROUGH WED MORNING...OUT OF PHASE WITH OTHER SOLUTIONS MAINLY IN MASS FIELDS BUT ALSO WITH INCREASED LANGUISHING QPF ACROSS NE IA/SE MN/S WI...AS SUCH WOULD FAVOR 06Z GFS OVER 12Z GFS FOR CONSISTENCY/CONTINUITY. THE 00Z UKMET AS STATED IN PRIOR PMDHMD APPEARS SIMILAR BUT IS ON THE NW SIDE OF THE SURFACE CLUSTER LEADING TO A SLIGHT NORTHWEST TREND TO THE TIGHT QPF GRADIENT MAKING IT LESS DESIRABLE GIVEN THE OTHER STRONGER AGREEMENT. SIMILARLY THE 00Z CMC IS ALONG THE OUTER PERIPHERY OF THE CLUSTER BUT ON THE SE SIDE OF THE GUIDANCE. THE 12Z NAM TRENDED A BIT WEAKER (NOW THE WEAKEST...VERY ATYPICAL OF THE NAM) AND SLOWER LOOKING MORE LIKE THE 00Z ECMWF INCLUDING A FURTHER SOUTH TRACK CROSSING SOUTHERN CANADA. UNTIL ABOUT THE LAST RUN OR SO THERE HAD BEEN A DECENT TREND TOWARD CONTINUAL DAMPENING OF THE STRENGTH OF THE WAVE AS A WHOLE AND THE 12Z NAM FALLS INTO THIS POSSIBILITY. ALL CONSIDERED... A BLEND OF THE 12Z NAM/06Z GFS OR GEFS AND 00Z ECMWF WILL BE PREFERRED. AGAIN OVERALL AGREEMENT IS ABOVE AVERAGE...THOUGH THESE INTERNAL DIFFERENCE AS SEEN IN THE 12Z GFS LEAD TO REDUCED CONFIDENCE FOR INTERNAL FEATURES THAT WOULD LEAD TO SIGNIFICANT IMPACT DIFFERENCES. AS SUCH CONFIDENCE IN THE BLEND IN TOTALITY REMAINS SLIGHTLY ABOVE AVERAGE. SHORTWAVE SHEARING THROUGH THE MEAN PACIFIC RIDGE TOWARD THE NORTHWEST TUE REINFORCING THE BASE OF THE CENTRAL U.S. TROF BEFORE SHIFTING EAST INTO THE EASTERN THIRD OF THE U.S BY THURS EVENING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND PRIOR TO 04/12Z NON-ECMWF AFTER CONFIDENCE: ABOVE AVERAGE PRIOR TO 04/12Z AVERAGE AFTER A HIGHLY ELONGATED TROUGH MOVES THROUGH A WELL ESTABLISHED/STRONG MEAN PACIFIC RIDGE MONDAY INTO TUESDAY...AND GENERALLY SHEARS OUT WITH LITTLE IMPACT TO SIGNIFICANT WEATHER...HOWEVER THE SOUTHERN AND CENTRAL ENERGY OF THE WAVE SLIDE ALONG THE EASTERN SIDE OF THE RIDGE TO HELP REINFORCE THE BASE (AND WESTERN SIDE) OF THE LARGER SCALE TROUGH ACROSS THE SOUTHWEST BY TUE EVENING/WED MIDDAY ACROSS NEW MEXICO. MODELS REMAIN IN GOOD AGREEMENT WITH THIS FEATURE. THE 12Z NAM IS A BIT STRONGER AND A FEW HOURS SLOWER AT THE END OF DAY 1 AS IT NEARS THE PACIFIC COAST...THOUGH THE IMPACTS TO SENSIBLE WEATHER AND SURFACE FEATURES APPEAR MINOR. DIFFERENCES IN SOLUTIONS BEGIN TO MANIFEST TOWARD WED NIGHT THURSDAY AS THIS FEATURE AND SOME ENERGY FROM NORTHERN STREAM CONSOLIDATE/REINFORCE THE BASE OF THE TROF...WITH THE ECMWF MOST BROAD AND SLOWER AND THE GFS QUICKLY SHARPENING AND ACCELERATES EAST THOUGH MAINLY AFTER 05/00Z. GENERALLY, A STRONG DOWNSTREAM RIDGE OVER THE BAHAMAS/WESTERN ATLANTIC AS WELL AS A GENERAL POSITIVE TILT WOULD FAVOR A PROGRESSIVE LIFTING OUT OF THE WAVE BUT NOT AT THE LANGUISHING SPEED OF THE BROADER ECMWF. THE ENSEMBLE SPAGHETTI PLOT BARES THIS OUT WITH THE OPERATIONAL 00Z ECMWF MUCH DEEPER/SLOWER AT 05/12Z WHILE THE GFS IS ALREADY WELL IN ADVANCE OF THE BULK OF THE ENSEMBLE MEMBERS. THE 00Z CMC/UKMET AND 12Z NAM ARE MORE MIDDLE GROUND CLOSER TO THE 00Z ECENS MEAN THOUGH JUST A BIT FASTER (WHICH IS EXPECTED GIVEN SLOWER ECMWF ENSEMBLE MEMBERS) TO BEGIN FAVORING THIS BLEND. GIVEN THE 12Z GFS DOES NOT MOVE OUT OF PHASE UNTIL AFTER 05/00Z...WILL INCLUDE IT IN THE BLEND AS NON-ECMWF AFTER 04/12Z AT AVERAGE CONFIDENCE. NEXT DEEPER TROF AND FRONT NEARING THE PACIFIC NORTHWEST COAST WED EVENING AND SETTLING ACROSS THE INTERMOUNTAIN WEST THURS EVENING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z ECMWF BLEND CONFIDENCE: AVERAGE BEFORE 04/00Z...BELOW AVERAGE AFTER. MINUS THE 00Z CMC WHICH IS MUCH MORE CONSOLIDATED AND HAS A DISTINCT DIFFERENCE IN EVOLUTION ACROSS THE WEST BY THE END OF THE FORECAST PERIOD, THE MODELS CONTINUE TO SHOWS A BROADER ALMOST A DUAL TROF STRUCTURE THAT EVENTUALLY PHASES INTO MORE OF A SINGLE TROF. DIFFERENCES GENERALLY ARE RELATED TO TIMING OF THE PHASING AND EVENTUALLY THE DEPTH OF THE AMPLIFICATION AS IT APPROACHES THE WEST COAST. THE 00Z UKMET IS A BIT MORE DECOUPLED WITH SOUTHERN STREAM ENERGY COMPARED TO THE NAM/GFS/ECMWF AND IS A FEW HOURS FASTER IN THE NORTHERN STREAM BRINGING THE QPF/FRONTAL ZONE INTO THE PACIFIC NORTHWEST WED EVENING. THE 00Z ECMWF ENTERS THE WEST COAST A BIT MORE AMPLIFIED THAN MUCH OF THE OTHER GUIDANCE AND WITH DOWNSTREAM SLOWER PROGRESSION OF THE EXITING TROF THAN MOST OTHER GUIDANCE QUICKLY ROLLS UP INTO A DEVELOPING CUT-OFF ACROSS THE SOUTHERN COLORADO RIVER BASIN BY THE END OF THE FORECAST; THIS IS MORE AGGRESSIVE THAN MUCH OF THE ENSEMBLE SOLUTIONS...THOUGH MUCH OF THE GUIDANCE WILL EVENTUALLY HAVE A SIMILAR CUT-OFF THE TIMING IS JUST A SHADE FAST BUT MAY BE ONTO A FASTER TREND WHICH IS SUPPORTED BY A RUN TO RUN COMPARISON OF THE SPAGHETTI ANALYSIS WHILE MORE MEMBERS INDICATING GENERAL TROUGHING THAN FLATTER REGIME. THIS WAS ALSO SUPPORTED BY THE 12Z GFS AND 12Z NAM WHICH TRENDED TOWARD A DEEPER/CUTTING OFF SOLUTION...THOUGH THE NAM IS A BIT FASTER AND SHOWS MORE OF A VERTICAL/PROGRESSIVE AMPLIFICATION THAN A CURLING OF THE FIELD. THE GEFS/ECENS MEANS THOUGH WASHED OUT BY THE OVERALL SPREAD DUE SUPPORT THE OVERALL TIMING OF THE WAVE OF THE ECMWF/GFS BLEND RATHER THAN THE FASTER NAM. AS SUCH WILL CONTINUE TO FAVOR A 12Z GFS/00Z ECMWF BLEND WITH SOME GEFS/ECENS MEAN WEIGHTING TO TAMP OUT THE MORE AGGRESSIVE NATURE OF THE OPERATIONAL ECMWF WHICH SEEMS A BIT TOO DRASTIC OF CHANGE IN CONTINUITY AT THIS TIME FOR FULL WEIGHTING ESPECIALLY WITH DOWNSTREAM (SEE PRIOR SECTION) LIKELY HAVING A SIGNIFICANT IMPACT ON THE EVOLUTION. GIVEN THE SPREAD... CONFIDENCE IS AVERAGE TO SLIGHTLY ABOVE AVERAGE WITH THE LANDFALL OF THE FRONTAL ZONE BUT BECOME BELOW AVERAGE AFTERWARD. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA