MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1115 AM EST THU FEB 09 2017 VALID FEB 09/1200 UTC THRU FEB 13/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ LOW LIFTING OUT OF MID-ATLANTIC COAST TOWARD NOVA SCOTIA EARLY FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-UKMET BLEND CONFIDENCE: ABOVE AVERAGE THE DEEPENING SFC LOW OFF THE MID-ATLANTIC WILL CONTINUE TO LIFT OFFSHORE OF THE SOUTHEAST COAST OF NEW ENGLAND AS IT APPROACHES THE EAST COAST OF NOVA SCOTIA TOMORROW MORNING. THERE IS VERY TIGHT MODEL AGREEMENT AT THIS POINT AS EACH MODEL SUITE SHIFT SLOWLY FROM THEIR TYPICAL BIAS POSITIONS TO A MORE COMMON SOLUTION. THE GFS/GEFS REMAINS SLIGHTLY FASTER...THE ECMWF/CMC SLOWER. THE 12Z NAM FITS NICELY WITHIN THE OVERALL TIGHT AGREEMENT. ONLY THE 00Z UKMET CONTINUES TO BE SLIGHTLY MORE DISPLACED COAST-WARD AND SLOWER...DUE TO THE FACT IT RESOLVES A LOW ABOUT 6-12 MB DEEPER THAN THE REST OF THE DETERMINISTIC SUITE. AS SUCH A NON-UKMET BLEND IS SUPPORTED AT ABOVE AVERAGE CONFIDENCE. SHORTWAVE AND ASSOCIATED SURFACE WAVE ENTERING PACIFIC NORTHWEST TODAY THAT SPURS CLIPPER LOW THAT TRACKS ALONG THE US/CANADIAN BORDER ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE WV LOOP SHOWS A IMPRESSIVE BAROCLINIC SHIELD DEVELOPING WITH EMBEDDED SOUTHERN STREAM SHORTWAVE WEST OF THE MOUTH OF THE COLUMBIA RIVER CURRENTLY... A WEAK SURFACE REFLECTION AND FRONTAL ZONE EXTEND SOUTHWARD FROM IT. THIS WAVE WILL TRANSLATE NORTHEASTWARD AND CROSS THE NORTHERN ROCKIES TONIGHT. THIS WILL SPUR LEE SFC PRESSURE FALLS FOR A WEAK BUT FAST MOVING CLIPPER SYSTEM THAT TRACKS JUST NORTH OF TH US/CANADIAN BORDER INTO THE GREAT LAKES BY EARLY SAT. EVENTUALLY THIS LOW WILL FADE IN FAVOR OF COASTAL REDEVELOPMENT OVER GEORGES BANK BY SAT EVENING. THERE CONTINUES TO BE BETTER AGREEMENT WITH THE GLOBAL MODELS AND THEIR ASSOCIATED ENSEMBLE SOLUTIONS WITH THE 12Z GFS AND 00Z ECMWF MOST CENTRAL AND WELL AGREED UPON THROUGH THE LOWER ATMOSPHERE/SURFACE. THE 00Z CMC GENERALLY LAGS THE UKMET IS GENERALLY A BIT FASTER AND DEEPER CROSSING NORTHERN NEW ENGLAND. THE 12Z NAM LOOKS QUITE SIMILAR IN TRACK BUT THERE IS SOMETHING JUST NOT QUITE RIGHT IN THE MIDDLE ATMOSPHERE MASS FIELDS THAT APPEARS SPURIOUS TO KEEP IT FROM INCLUSION AT THIS TIME. AS SUCH A 12Z GFS/00Z ECMWF BLEND SHOULD SUFFICE AT SLIGHTLY ABOVE AVERAGE CONFIDENCE GIVEN THE TIGHT AGREEMENT AND FAIRLY STRONG CONTINUITY. REMAINING NORTHERN PORTION OF UPPER LOW IS SWEPT UP BY NEXT WAVE...THAT COMBINED TRACK ACROSS THE NORTHERN TIER BY SUN WITH ASSOCIATED SURFACE WAVE ALONG THE BORDER ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z UKMET BLEND CONFIDENCE: AVERAGE MODEL CONSENSUS REMAINS FAIRLY STRONG WITH RESPECT TO THE GENERAL EVOLUTION OF THE REMAINING INNER CORE TO THE UPPER LOW AS IT UNFOLDS TOWARD THE SOUTH AS IT APPROACHES THE COAST FRIDAY. A DEGREE OF COMPLEXITY IS ADDED TO THE SITUATION AFTER 12Z FRI AS THE SHORTWAVE SPLITS, WITH ONE LESS AMPLIFIED PIECE OF ENERGY EJECTING QUICKLY INTO THE INTERIOR NORTHWEST, AND ANOTHER DIGGING SOUTHWARD ALONG THE WEST COAST AND AMPLIFYING. THE NORTHERN STREAM PORTION IS KICKED ALONG BY A FAIRLY POTENT SHORTWAVE SHEARING ALONG THE ENTIRE AK PENINSULA/BC COAST EVENTUALLY CONSOLIDATING WITH THE NORTHERN SPLIT ACROSS THE CANADIAN/N US ROCKIES LATE SAT. THESE HEIGHT FALLS GENERATE ANOTHER SURFACE WAVE THAT TRACKS NEARLY IDENTICAL TO THE PRIOR SURFACE WAVE BEFORE STARTING TO COMBINE WITH SOUTHERN STREAM SURFACE WAVE (OUT OF THE E CO FROM HEIGHT FALLS AT BASE OF THIS UPPER LEVEL WAVE) ACROSS THE CENTRAL/EASTERN GREAT LAKES INTO NEW ENGLAND/MID-ATLANTIC BY 00Z MON. THE 00Z ECMWF/UKMET/CMC HAVE JOINED THE GFS AND NAM IN SHOWING A SLIGHTLY STRONGER INITIAL SHORTWAVE AND INCREASED UPSTREAM INTERACTION WITH APPROACHING GULF OF AK WAVE BEFORE THE SEPARATION OF STREAMS OCCUR. THIS RESULT IN MAINTAINING A STRONGER OCCLUDED LOW/OCCLUDED FRONT THAT SWINGS BACK THROUGH THE PACIFIC NORTHWEST AS A COLD FRONT INTO FRIDAY PROVIDING MUCH HIGHER CONFIDENCE AND AGREEMENT IN THE EARLY PERIODS OF THE FORECAST IN THE PACIFIC NORTHWEST STATES. AS THE ENTIRE WAVE SHIFTS ACROSS THE INTERMOUNTAIN WEST...ENSEMBLE SPAGHETTI PLOTS SHOW A DISTINCT BIFURCATION OF THE SOLUTIONS WITH THE ECMWF/ECENS MEMBERS UNCHARACTERISTICALLY PROGRESSING FASTER. THE 00Z ECMWF INDICATES A FASTER DECOUPLING WITH THE LOW IN THE SOUTHWEST AS WELL AS A STRONGER UPPER LEVEL FLOW (JET STRUCTURE) THAN THE REST OF THE GUIDANCE PACKAGE (WITH SOME EXCEPTION OF THE UKMET WHICH IS TYPICALLY A BIT STRONGER). THIS RESULTS IN THE ECMWF SUPPORTING A STRONGER PLAINS SURFACE WAVE THIS EQUALLY FAST AND FAVORS IT WHEN THE SURFACE STREAMS MERGE IN THE MID-ATLANTIC/EASTERN GREAT LAKES BY 00Z MON. THE 12Z GFS AND 00Z UKMET ARE IN THE SLOWER CAMP COMPARED TO THE ECMWF BUT ON THE LEADING EDGE OF THAT ENSEMBLE GROUPING SHOWING SOME WEAK CONNECTION TO THE SOUTHWEST SYSTEM BUT LESSER SO THAN THE SLOWEST 12Z NAM/00Z CMC. WILL FAVOR A 12Z GFS/00Z UKMET BLEND AT AVERAGE CONFIDENCE. SOUTHERN PORTION OF UPPER TROF MOVES INTO CALIFORNIA SATURDAY MORNING THEN CLOSES OFF ACROSS THE SOUTHWESTERN U.S ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE AS DISCUSSED ABOVE, AS THE SHORTWAVE SPLITS INTO TWO PARTS OFF THE NORTHWEST U.S. COAST, THE SOUTHERN OF THE TWO COMPONENT WAVES WILL DIVE SOUTHEASTWARD ALONG THE WEST COAST AS IT UNDERGOES AMPLIFICATION WITH SOME INTERACTION WITH LINGERING SUBTROPICAL SHORTWAVE ENERGY. THE 00Z UKMET/CMC ARE BOTH QUITE WEAK WITH THE INNER CORE OF THE WAVE AS IT DROPS INTO THE LOWER COLORADO BASIN...BOTH EVENTUALLY CONSOLIDATE A DEEPER LOW BUT LESSER SO COMPARED TO THE TIGHT ECMWF/NAM AND GFS. AS NOTED BEFORE THE ECMWF SEVERS ITS NORTHERN STREAM CONNECTION EARLIER AND THEREFORE IS A BIT SLOWER/WOUND UP AND SOUTH AND WEST OF THE 12Z GFS/NAM INITIALLY BUT NOT SIGNIFICANTLY ENOUGH TO REMOVE IT FROM A PREFERENCE. BY THE END OF DAY 3...THE 12Z NAM SHOWS SOME OF ITS NEGATIVE DAY 3 BIAS OF VERY DEEP/SLOW WOUND UP UPPER LOWS...WHICH RESULTS IN A FURTHER SOUTH SOLUTION LEADING TO IT STICKING OUT WITHIN THE SPAGHETTI ANALYSIS. STILL OVERALL THE WARM CONVEYOR BELT MOISTURE STREAM AND QPF/SNOWS ACROSS THE HIGHER TERRAIN OF THE SOUTHWEST INTO THE CO ROCKIES APPEARS FAIRLY COMPARABLE BUT PLEASE REFER TO THE QPFPFD AND QPFHSD FOR ADDITIONAL DETAILS/MODEL SPECIFICS. THIS LEADS TO SLIGHTLY ABOVE AVERAGE CONFIDENCE IN THE 12Z GFS AND 00Z ECMWF BLEND. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA