MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 206 PM EST WED FEB 22 2017 VALID FEB 22/1200 UTC THRU FEB 26/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION INCLUDING PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...SOUTHERN STREAM CLOSED LOW EVOLUTION FROM THE FL PANHANDLE TO THE FL KEYS TODAY... ...FEATURE WEAKENING AND LINGERING OFF THE SOUTHEAST COAST THROUGH EARLY SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE MID TO LATE MORNING WV IMAGERY CONTINUES TO FEATURE AN EVOLVING CLOSED UPPER LOW ALONG AND JUST OFFSHORE OF THE EASTERN GULF COAST. EMBEDDED IN THE UPPER LOW AXIS IS A LOBE OF VORTICITY ORIENTED JUST SOUTH OF THE FLORIDA PANHANDLE. IT IS THIS FEATURE THAT WILL BECOME DOMINANT...FORCING THE SURFACE LOW SE ACROSS SOUTH FL TODAY...EVENTUALLY WOBBLING ALONG AND NORTH OF THE STRAIT OF FLORIDA TO A POSITION NEAR THE NW BAHAMAS LATE TONIGHT...MEANDERING THERE IN WAIT FOR THE MAIN VORT FEATURE TO BOTTOM OUT THROUGH THE MEAN TROUGH AND START TO FILL THROUGH THU. FROM THURSDAY NIGHT ON...THE WEAKENING WAVE LIFTS NORTHEAST TOWARD BERMUDA FROM FRI INTO EARLY SAT. OVERALL...THE GUIDANCE REMAINS IN GOOD AGREEMENT WITH THE OVERALL SYNOPTIC PATTERN...WITH SMALL DIFFERENCES WITH SPECIFIC DETAILS SUCH AS EXACT POSITION OF THE SURFACE LOW AS IT WOBBLES OFF THE FL COAST. THE 12Z NAM AND THE 12Z NAM PARALLEL EACH TRENDED A BIT QUICKER WITH THE FILLING UPPER TROUGH FRI/SAT...AND IS ALSO A BIT MORE PROGRESSIVE WITH THE ASSOCIATED SURFACE LOW...WHICH IS A TREND TOWARD THE REST OF THE GUIDANCE. THE NAM SOLUTION NOW MESHES REASONABLY WELL WITH THE 12Z GFS...ALTHOUGH THE NAM SOLUTION IS A BIT STRONGER FRIDAY NIGHT/EARLY SATURDAY. THE 00Z ECMWF AND 00Z CMC ARE EACH SLIGHTLY WEAKER/FASTER WITH THE SURFACE LOW...WITH THE 00Z UKMET ESSENTIALLY IN BETWEEN THE TWO SOLUTIONS. THE 06Z NAEFS HAS TRENDED TOWARD THE NCEP MODEL CONSENSUS...WHICH COULD PORTEND TO THE 12Z CMC TRENDING TOWARD THE CONSENSUS SOLUTION AS WELL. GIVEN THE 12Z TRENDS FROM NAM/GFS...A GENERAL MODEL BLEND CAN NOW BE SUPPORTED AT ABOVE AVERAGE CONFIDENCE. 19Z UPDATE: NO MAJOR CHANGES IN THE 12Z SUITE OF MODELS WITH HANDLING OF THIS FEATURE. WILL MAINTAIN A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. ...SHORTWAVE LIFTING OUT OF NORTHERN ROCKIES INTO THE UPPER MIDWEST.... ...ASSOCIATED SURFACE LOW TRACKING ACROSS THE GREAT LAKES TONIGHT AND CLIPPING N NEW ENGLAND THU NIGHT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE LATE MORNING WV IMAGERY SHOWS THE ELONGATED SHORTWAVE ENERGY SWINGING ACROSS THE DAKOTAS...SUPPORTING A WEAK SURFACE REFLECTION THAT WILL CONTINUE TO LIFT ACROSS THE UPPER MIDWEST THROUGH TODAY. THE 12Z NAM CONTINUED TO LEAN TOWARDS A MORE PROGRESSIVE SOLUTION WITH THIS SYSTEM...IN LINE WITH THE 00Z ECMWF SOLUTION. THE 12Z GFS LIKEWISE TRENDED FASTER/FLATTER ALOFT TOWARDS THE CONSENSUS SOLUTION...AS DID THE 00Z CMC. THE 00Z UKMET IS SLIGHTLY MORE AMPLIFIED INITIALLY...BUT OVERALL DIFFERENCES ARE MINOR. OVERALL...THE TRENDS/WV MOSAIC SETUP CONTINUE TO SUPPORT A FLATTER AND FASTER EVOLUTION...AND MODEL GUIDANCE IS INDEED TRENDING IN THIS DIRECTION. WILL FAVOR A GENERAL MODEL CONSENSUS AT JUST ABOVE NORMAL CONFIDENCE. 19Z UPDATE: MODELS CONTINUE TO TREND TOWARDS A GENERAL MODEL CONSENSUS WITH THIS FEATURE. 12Z UKMET...LIKE THE 12Z NAM IS A BIT STRONGER WITH THE UPPER VORTICITY MAXIMA TONIGHT AND EARLY THU...BUT MATCH UP WITH THE REST OF GUIDANCE TEMPORALLY AND WITH MASS FIELDS. 12Z LAGS A BIT BEHIND THE REMAINING GUIDANCE WITH THE SURFACE FEATURE...BUT AGAIN OVERALL DIFFERENCES ARE MINOR. WILL CONTINUE PREVIOUS GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. ...BROAD LONGWAVE TROF CROSSING THE INTERMOUNTAIN WEST THU/FRI... ...DEVELOPING CLOSED LOW OVER MIDWEST LATE FRI INTO SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GEFS/ECMWF CONFIDENCE: AVERAGE LATEST WV IMAGERY FEATURES SEVERAL PERTURBATIONS ROUNDING THE BASE OF A POSITIVELY TILTED UPPER TROUGH...WHICH IS IN THE PROCESS OF COMING ASHORE WEST COAST. JUST UPSTREAM...A STRONGER PIECE OF SHORTWAVE ENERGY IS DIGGING SOUTH OFFSHORE OF THE WA/OR COASTLINE. THIS FEATURE WILL CARVE OUT A MORE BROAD UPPER TROUGH ACROSS THE INTERMOUNTAIN WEST BY EARLY THURSDAY MORNING....WITH A STRONGER/MORE CONCENTRIC UPPER LOW EVENTUALLY SETTING UP ACROSS THE MIDWEST BY FRIDAY MORNING. ON THE HEELS OF THE RESULTANT HEIGHT FALLS...INCREASINGLY NEGATIVE TILT/HIGHLY DYNAMIC DIFFLUENCE WILL RESULT IN RAPID SURFACE CYCLOGENESIS OF THE SURFACE WAVE ALONG A FRONTAL ZONE EXTENDING FROM WESTERN KS INTO THE MID MISSISSIPPI VALLEY. THE SURFACE LOW IS EXPECTED TO THEN FOLLOW THE FRONTAL ZONE OUT OF WEST-CENTRAL KS INTO SOUTHERN IA BY FRIDAY MORNING. PLEASE REFER TO THE WPC QPFPFD AND QPFHSD (HEAVY SNOW/QPF DISCUSSIONS)...AS WELL AS LOCAL NATIONAL WEATHER SERVICE OFFICE PRODUCTS FOR MORE LOCATION SPECIFIC INFORMATION ON ASSOCIATED SNOW...WIND AND OTHER HAZARDS. AS FOR MODEL DETAILS...THE 12Z NAM/GFS HAVE CONTINUED THEIR GRADUAL TREND TOWARD THE ECMWF SOLUTION....THOUGH BOTH MODELS AND THEIR RESPECTIVE PARALLEL SOLUTIONS...REMAIN DISPLACED A BIT TO THE NORTH WITH THE SURFACE LOW AND DEFORMATION ZONE...MORE SO WITH THE NAM AND NAM PARALLEL. THE 00Z UKMET AND CMC TRENDED INCREMENTALLY FASTER BUT ARE STILL LAGGING AND SLOW WITH THE UKMET BEING THE BIT DEEPER/SLOWER OF THE TWO. THE 00Z ECMWF FAVORED TOWARD A TRIPLE POINT SOLUTION INTO THE GREAT LAKES BY FRIDAY NIGHT/EARLY SAT...THE 12Z GFS CONTINUES TO DEPICT A STRONGER SURFACE/OCCLUDED LOW SOLUTION...AN IDEA TO WHICH THE 00Z NAM...AND INTERESTINGLY THE 06Z NAEFS BOTH TRENDED. IT REMAINS TO BE SEEN IF THE 12Z CMC FOLLOWS SUIT. CONFIDENCE IS AGAIN INCREMENTALLY INCREASED...BUT REMAIN ABOUT AVERAGE. WILL CONTINUE TO WEIGHT THE ECMWF/ECENS HEAVIER IN THE BLEND OVERALL AS PREFERENCE...BUT WILL MIX IN A LITTLE OF THE 12Z GFS TO ACCOUNT FOR THE TREND TOWARD A STRONGER SURFACE LOW AND TIGHTENING BAROCLINIC ZONE. 19Z UPDATE: THE 12Z ECMWF...LIKE MOST OF THE REST OF THE AVAILABLE 12Z GUIDANCE...HAS TRENDED SLIGHTLY SOUTH...AND A BIT MORE PROGRESSIVE DAY 1/DAY 2. HOWEVER...IT IS SLOWER THAN THE PREFERRED BLEND AS THE SYSTEM SLOWS/TAKES ON A NEGATIVE TILT DAY 3. THE 12Z CMC SLOWED FURTHER...AND IS ON THE SLOW END OF THE GUIDANCE ENVELOPE FOR DAY 2.5 AND DAY 3...AS PER ITS BIAS. 12Z UKMET REMAINED ON THAT SAME SLOW END OF GUIDANCE AND IS A BIT STRONGER WITH THE PARENT UPPER LOW THROUGH SATURDAY. 12Z GEFS/ECMWF ARE ESSENTIALLY A MIDDLE GROUND SOLUTION AT THIS TIME AND FOR THAT REASON...HAVE STEERED THE BLEND IN THAT DIRECTION AT AVERAGE CONFIDENCE. ...PAIR OF SHORTWAVES FALLING DROPPING ALONG THE WESTERN CANADIAN COAST TOWARD A MORE AMPLIFIED UPPER LOW OFF THE NORTHWEST COAST BY SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z ECENS CONFIDENCE: BELOW AVERAGE MODELS CONTINUE TO SHOW ADDITIONAL SHORTWAVE ENERGY SETTLING SOUTH OVER TOP OF THE UPPER RIDGE OVER AK...DROPPING DOWN ALONG AND JUST OFF THE PAC NW COAST FRI/FRI NIGHT. THE SECOND...STRONGER SHORTWAVE TRACKS ALONG THE BC COAST INTO THE COASTAL WATERS OFFSHORE WA/OR BY SAT NIGHT. WHILE THE ENSEMBLE SPAGHETTI PLOTS SHOW INCREASING CONVERGENCE TOWARD A COMMON SOLUTION OVER THE PAST FEW CYCLES...THERE REMAINS IMPORTANT DETAIL DIFFERENCES. FOR EXAMPLE...THE ECMWF IS QUITE AGGRESSIVE IN SHEDDING THE BULK OF ENERGY WEST TO THE UPPER LOW IN COMPARISON TO 12Z NAM/00Z CMC/UKMET SHEDDING SOME. THE 12Z GFS SHEDDING NO ENERGY PREFERRING TO SWING THE SHEARED WAVE INTO THE PACIFIC COAST AND GREAT BASIN BY FRI/SAT. THIS ALSO LEAVES THE ECMWF HAVING LESS INTERACTION BETWEEN THE TWO WAVES...AND THEREFORE A BIT CLOSER TO THE COAST WITH THE SECOND CLOSING OFF WAVE. WILL GO WITH A BLEND OF THE 06Z GEFS AND THE 00Z ECMWF...WHICH IS A GOOD REPRESENTATION OF THE CONSENSUS SOLUTION AMONG ENSEMBLE SPAGHETTI HEIGHTS AT THIS TIME. CONFIDENCE IS SLIGHTLY BELOW AVERAGE AS THERE ARE MANY MOVING PARTS AND INTERACTIONS THAT ARE KEYED ON TIMING DIFFERENCES...SO THE PREDICTABILITY IS A BIT TOO LOW TO HAVE TREMENDOUS CONFIDENCE AT THIS TIME. 19Z UPDATE: 12Z ECMWF HAS COME A LITTLE CLOSER INTO ALIGNMENT TOWARD THE GFS SOLUTION WITH THE INITIAL SHORTWAVE LATE FRI/SAT. HOWEVER...SIGNIFICANT DIFFERENCES REMAIN. THE 12Z CMC HAS TRENDED TOWARD THE MORE SHEARED TO THE WEST IDEA OF THE 00Z ECMWF...AND HAS BEEN DISREGARDED FOR NOW. WILL CONTINUE WITH A GENERAL ECENS/12Z GFS BLEND. FORECAST CONFIDENCE REMAINS BELOW NORMAL...AGAIN WITH SO MANY FEATURES/INTERACTIONS TO DIAGNOSE IN THIS PERIOD. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... MONTEFUSCO