MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 203 PM 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: NON-UKMET BLEND 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. THE 12Z UKMET/CMC/ECMWF ALL SLOWED A BIT TOWARD THE 12Z GFS TREND HOWEVER...ALL REMAINS A BIT WEAKER THAN THE GFS WITH THE 12Z UKMET REMAINING ON THE NW SIDE OF THE PACKING AND THE 12Z CMC A BIT SLOW AND SOUTH BUT MUCH BETTER THAN ITS 00Z RUN TOWARD THE REMAINING CLUSTER. THIS LEFT THE 12Z NAM A BIT EAST OF THE BEST PACKING AT 36HRS BUT ONLY THE 12Z GFS REMAINED VERY STRONG WITH THE DYING OCCLUSION BEFORE TRANSFERRING TO THE NEW LOW/TRIPLE POINT. THE MAIN OUTLIER SEEMS TO BE THE 12Z UKMET BEING NW LEADING TO A DIFFERENT TRACK DIFFERENCE IN PLACEMENT OF THE QPF AXIS AS WELL AS TRACKING FURTHER NORTH AWAY FROM THE CLUSTER OVER S CANADA BY THURSDAY AS WELL AS MUCH HIGHER SWATH OF QPF ALONG THE COLD FRONT DUE TO A STRONGER WEAK SURFACE WAVE ALONG IT OVERNIGHT THURSDAY MORNING MOVING THROUGH THE MID-ATLANTIC/CAROLINAS. AS SUCH WILL BLEND A NON-UKMET SOLUTION... WITH HIGH CONFIDENCE SYNOPTICALLY. INTERNAL DIFFERENCES/MAXIMA THAT WILL OCCUR BUT ARE GENERALLY BLENDED OUT (SUCH AS THE STRONGER 12Z GFS SOLUTION) DO LEAD TO SOME LOCALIZED LOWER CONFIDENCES...SO OVERALL CONFIDENCE REMAINS SLIGHTLY ABOVE AVERAGE IN THIS BLEND. 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 12Z GFS/CMC/ECMWF BLEND AFTER CONFIDENCE: ABOVE AVERAGE PRIOR TO 04/12Z SLIGHTLY ABOVE 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. 19Z UPDATE: THE 12Z UKMET/CMC/ECMWF CONTINUED TO SUPPORT AN OPERATIONAL MODEL BLEND THROUGH 04/12Z. THE 12Z ECMWF TRENDED FASTER TOWARD BETTER AGREEMENT WITH THE 12Z GFS. THE 12Z CMC REMAINED THE MOST CENTRAL AND CONSISTENT OF THE GUIDANCE BUT TRENDED TOWARD A BROADER TROF WHICH LOOKS BETTER TO ORIGINAL THINKING. THE 12Z UKMET HOWEVER DID TREND FASTER AND ALONG WITH THE 12Z NAM IS SLIGHTLY OUT OF PHASE FASTER...WHICH WAS NOT SUPPORTED BY THE 12Z GEFS WHICH LOOKS LIKE A DEEPER AND SLIGHTLY SLOWER 00Z ECENS MEAN OR MIDDLE GROUND BETWEEN THE GFS/ECMWF. AS SUCH WILL FAVOR A 12Z ECMWF/CMC/GFS BLEND AFTER 04/12Z AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. NEXT DEEPER TROF AND FRONT NEARING THE PACIFIC NORTHWEST COAST WED EVENING AND SETTLING ACROSS THE INTERMOUNTAIN WEST THURS EVENING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-UKMET BLEND BEFORE 04/00Z 12Z ECMWF/GFS/CMC AFTER CONFIDENCE: SLIGHTLY ABOVE 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. 19Z UPDATE: WITH BETTER DOWNSTREAM AGREEMENT (FASTER SOLUTION) AS WELL AS A SLIGHTLY LESS AMPLIFIED WAVE ENTERING THE WEST COAST ON WED NIGHT...THE ECMWF'S STRONGER FASTER CUT-OFF LOW IS DELAYED BY ABOUT A DAY AND DEVELOPS TOWARD THE FOUR CORNERS AFTER THE FORECAST PERIOD...THIS IS IN LINE WITH THE 12Z GFS/NAM AND A DRAMATIC SHIFT IN THE 12Z CMC WHICH LOOKS LIKE A GOOD MIDDLE GROUND WITHIN THE ENSEMBLE SUITE. THE 12Z UKMET REMAINS VERY FAST ENTERING THE WEST COAST AND THEREFORE IS LESS AMPLIFIED AND PROGRESSIVE BY THE END OF DAY 3. OVERALL THE TIMING/PLACEMENT OF THE FRONT/WAVE IS IN FAIRLY GOOD AGREEMENT TO ABOUT 04/00Z WHEN THE MODEL SPREAD INCREASES AND CONFIDENCE DEGRADES. AS SUCH WILL SUPPORT A NON-UKMET BLEND PRIOR TO 04/00Z AT SLIGHTLY ABOVE AVERAGE CONFIDENCE AND CMC/GFS/ECMWF AFTERWARD BUT AT BELOW AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA