MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EST THU FEB 23 2017 VALID FEB 23/1200 UTC THRU FEB 27/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS MODEL EVALUATION INCLUDING PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...SOUTHERN STREAM CLOSED LOW FEATURE OVER S FL LIFTING NE/WEAKENING OFF THE SOUTHEAST COAST THROUGH EARLY SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE MODELS NOW IN GENERALLY GOOD ALIGNMENT WITH THE EVOLUTION OF THIS FEATURE. THE 12Z NAM/GFS REMAIN SOLIDLY IN THE FAST/PROGRESSIVE CAMP ALONG WITH THE 00Z UKMET...WITH THE 00Z CMC A BIT SLOWER WITH RESPECT TO THE WAVE AND SURFACE LOW. 00Z ECMWF ALIGNS SIMILARLY BUT IS A BIT FLATTER WITH THE UPPER WAVE. WILL MAINTAIN A GENERAL MODEL BLEND WITH ABOVE AVERAGE CONFIDENCE. ...BROAD LONGWAVE TROF CROSSING THE INTERMOUNTAIN WEST THU/FRI WITH DEVELOPING CLOSED LOW AND SURFACE LOW OVER MIDWEST LATE FRI INTO SAT...AND THROUGH THE CENTRAL GREAT LAKES INTO ONTARIO BY EARLY SUN... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: AVERAGE LATEST IR/WV SAT IMAGERY SHOWING A BROAD LONG WAVE TROUGH ACROSS THE WESTERN CONUS...WITH A WELL DEFINED UPPER SHORTWAVE DIVING ACROSS THE CENTRAL GREAT BASIN. GOOD MODEL AGREEMENT EXISTS IN LIFTING THIS LEAD SHORTWAVE ACROSS THE NORTH CENTRAL ROCKIES INTO THE CENTRAL HIGH PLAINS THROUGH TONIGHT...EVENTUALLY CLOSING OFF OVER THE MID MISSOURI VALLEY BY FRIDAY NIGHT. RESULTANT HEIGHT FALLS WILL RESULT IN RAPID SURFACE CYCLOGENESIS ALONG THE FRONTAL ZONE FROM E KS INTO E IA/IL AND THE WESTERN GREAT LAKES BY FRI NIGHT. AS IS TYPICALLY THE CASE AT THIS TIME RANGE...THE 12Z NAM CONTINUED ITS ABRUPT SHIFT TOWARD THE REMAINDER OF THE GUIDANCE ENVELOPE...AND HAS LOCKED INTO LINE WITH THE MIDDLE OF THE ROAD ECMWF/GFS/GEFS CAMP. THE 00Z CMC REMAINS THE ONLY STRONG OUTLIER AT THIS STAGE...AND ONCE AGAIN TRENDS FROM THE 06Z NAEFS MAY PORTEND TO THE 12Z CMC CATCHING UP TO THE REST OF THE GUIDANCE WITH RESPECT TO HANDLING OF THIS FEATURE. OVERALL...GIVEN GROWING MODEL CONSENSUS AND WITH PREVIOUS MASS FIELD ISSUES LARGELY RESOLVED...A NON-CMC BLEND IS PREFERRED. HOWEVER...FROM AN OPERATIONAL PROSPECTIVE...WEIGHTING HEAVILY FAVORS THE MORE MIDDLE GROUND SOLUTIONS OF THE ECMWF AND THE 12Z NAM...WHICH ALONG WITH THE 12Z NAM PARALLEL IS QUICKLY COMING INTO GOOD ALIGNMENT. SINCE FORECAST CONFIDENCE IS STEADILY GROWING...WILL CHARACTERIZE FORECAST CONFIDENCE AS SLIGHTLY ABOVE AVERAGE. PLEASE REFER TO WPC QPF QPFPFD AND WINTER WEATHER QPFHSD DISCUSSIONS FOR ADDITIONAL DETAILS. ...PAIR OF SHORTWAVES DROPPING ALONG THE WESTERN CANADIAN COAST TOWARD A MORE AMPLIFIED UPPER LOW OFF THE NORTHWEST COAST BY SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 2/3 00Z ECMWF / 1/3 12Z GFS/NAM CONFIDENCE: BELOW AVERAGE WHILE SOME TIGHTENING HAS OCCURRED WITH THE NEW 12Z NAM...A RELATIVELY LARGE SPREAD REMAINS AMONG DETERMINISTIC MODELS WITH RESPECT TO HOW MUCH ENERGY IS SHEARED WEST TOWARD THE DEEP UPPER LOW WELL NORTH OF HAWAII...WITH THE INITIAL WAVE THAT CAN BE SEEN DARKENING IN WV IMAGERY JUST S OF 50N/140W. THE 12Z NAM/GFS...AS WITH THE 00Z SUITE BEFORE IT...CONTINUES A TREND TOWARD A TIGHTER PROXIMITY OF THE WAVES FRI THROUGH EARLY SAT. SO THERE ARE POSITIVE TRENDS TOWARD MORE ENERGY GETTING INCORPORATED WEST TOWARD THE DEEPENING LOW NEAR HAWAII. THIS MANIFESTS IN ALLOWING THE UPPER LOW WEST OF VANCOUVER ISLAND BC AT MIDDAY TODAY TO DIG SOUTH ALONG AND OFFSHORE OF THE PAC NW FRIDAY...TO THE N CA COAST SATURDAY. THE 12Z NAM HAS TRENDED TOWARD THE 00Z ECMWF/UKMET CAMP WITH A SOLUTION THAT FAVORS LAGGING THIS ENERGY A BIT. THE RESULT IS A MORE VIGOROUS/CONCENTRIC VORTICITY MAXIMA WITH THE DIGGING LOW OFF THE CA COAST OVER THE WEEKEND. WILL NOT WEIGHT THE 00Z UKMET AT THIS TIME AS IT BECOMES AN OUTLIER LATE IN THE PERIOD...COMPLETE WITH A SHARP WESTWARD SHIFT OF THE DIGGING LOW BY 00Z/SUN. FOR ITS PART...THE 12Z GFS DID TREND TOWARD THE ECMWF CAMP...BUT IT REMAINS ON THE FAST END OF THE GUIDANCE ENVELOPE BY THE END OF THE PERIOD...DIGGING THE UPPER LOW INTO THE DESERT SOUTHWEST BY SUNDAY. FOR OPERATIONAL UTILITY...A BLEND OF THE ECMWF/NAM/GFS (WEIGHTED IN THAT ORDER) IS PROBABLY SUFFICIENT...AS SPREAD AMONG GEFS/ECENS MEMBERS WILL WASH OUT THE STRONGER CLOSED LOW SOLUTIONS DEPICTED BY EACH OF THE DETERMINISTIC MODELS. HOWEVER...GIVEN CONTINUED ISSUES W/SIGNIFICANT RUN TO RUN VARIABILITY...FORECAST CONFIDENCE REMAINS LOWER THAN AVERAGE. ...NEXT SHORTWAVE DROPPING OUT OF COASTAL BC TO NW WA COAST BY SUN... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE TRAIN OF FAST MOVING BUT STRONG SHORTWAVES CONTINUES INTO THE END OF THE PERIOD...WITH MODELS CONTINUING TO DEPICT SHORTWAVE ENERGY PUSHING OVER TOP THE STRONG ANTICYCLONE DOMINATING THE GULF OF ALASKA...ACROSS THE PACIFIC NORTHWEST SUN/SUN NIGHT. CONSIDERING TIMING ISSUES WITH THE AMPLIFYING UPPER LOW ABOVE...IT IS SURPRISING THAT MODELS ARE IN REASONABLY GOOD ACCORD WITH THIS NEXT SHORTWAVE DROPPING ACROSS THE PAC NW SUN/SUN NIGHT. THE 12Z GFS HAS TRENDED A BIT MORE TOWARDS THE DEEPER ECMWF SOLUTION . THE 00Z UKMET REMAINS MOST WOUND UP BUT HAS SLOWED SLIGHTLY AND IS A BIT WEST OF THE MAIN CLUSTER OF SOLUTIONS. THE 00Z CMC IS A DECENT MIDDLE OF THE ROAD SOLUTION BY SUNDAY NIGHT...IN BETWEEN THE FASTER GFS AND SLOWER ECMWF. HOWEVER...GIVEN THAT IT IS DAY 3...DIFFERENCES ARE RELATIVELY MINOR WITH MASS FIELDS REASONABLY WELL RESOLVED. WILL KEEP A GENERAL MODEL BLEND WEIGHTED TOWARD THE ECMWF AND 12Z GFS AT ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... MONTEFUSCO