MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1148 PM EST SUN FEB 21 2016 VALID FEB 22/0000 UTC THRU FEB 25/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...ELONGATED SHORTWAVE EXITING THE LOWER NEW ENGLAND COAST BY 22/1200Z... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: HIGH QUASI-ZONAL FLOW ACROSS THE EASTERN THIRD OF THE COUNTRY WILL CARRY AN ELONGATED LOW-AMPLITUDE SHORTWAVE THROUGH THE MID-ATLANTIC DURING THE OVERNIGHT HOURS. MODEL HAVE A GOOD HANDLE DURING THIS SHORT PERIOD OF TIME TO AFFORD A GENERAL MODEL COMPROMISE. ...SOUTHERN STREAM JET ENERGY TRAVERSING THE GULF COAST... ...ASSOCIATED WAVY FRONTAL BOUNDARY... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE LEFT EXIT REGION DYNAMICS ALONG A SUBTROPICAL JET HAS HELPED IGNITE A BROAD AXIS OF SHOWERS AND THUNDERSTORMS FROM NORTHEASTERN TX INTO THE LOWER MS VALLEY. THE PARENT MID-LEVEL SHORTWAVE CURRENTLY OVER TX WILL RACE EASTWARD THE NEXT 24 HOURS WITH GRADUAL SHEARING NOTED. MODELS HANDLE THIS FEATURE AS WELL AS THE QUASI-STATIONARY SURFACE BOUNDARY QUITE WELL THROUGHOUT DAY 1. AS SUCH...A GENERAL MODEL COMPROMISE IS WARRANTED HERE. ...SHARP HEIGHT FALLS DIGGING THROUGH THE FOUR CORNERS REGION LATE MONDAY... ...CLOSED LOW BARRELING FROM THE SOUTHERN PLAINS TO THE OH VALLEY ON TUESDAY/WEDNESDAY... ...STRENGTHENING SURFACE LOW/ATTENDANT BOUNDARIES... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF FORECAST CONFIDENCE: AVERAGE WELL ADVERTISED AMPLIFICATION TAKES PLACE OVER THE WESTERN U.S. AS A POTENT JET STREAK TRACKS THROUGH THE CENTRAL GREAT BASIN. THIS HIGH AMPLITUDE PATTERN EVOLVES AS A SHARP AXIS OF SHORTWAVE ENERGY DIVES SOUTHEASTWARD FROM WA/OR TOWARD THE FOUR CORNERS REGION. BY 23/0000Z...THE 12Z CMC BEGINS TO LAG THE CONSENSUS WITH THE TRACK OF THE LEADING SHORTWAVE THROUGH NM. THE GENERAL TREND IN MULTI-DAY SPAGHETTI PLOTS IS TO BE A BIT QUICKER WHICH THE ECMWF SUITE HAS BEEN SUGGESTING FOR MANY MODEL CYCLES NOW. AS THE SYSTEM STRENGTHENS ACROSS THE SOUTHERN HIGH PLAINS...THE GUIDANCE SHOW SURFACE WAVE DEVELOPMENT ACROSS NORTH TX BY EARLY TUESDAY. ENSEMBLE LOW SCATTER PLOTS SUGGEST THE 00Z NAM IS TOO QUICK WITH ITS INITIAL CYCLONE TRACK. THIS CONTINUES FORWARD AS THE SYSTEM MOVES THROUGH THE LOWER MS VALLEY WITH GENERAL LOW TRACK AGREEMENT EXCEPT FOR THE FASTER 00Z NAM AND SLOWER 12Z CMC. THE ROBUST SYSTEM CONTINUES TO DEEPEN WHILE LIFTING THROUGH TN VALLEY AND EVENTUALLY INTO THE LOWER GREAT LAKES BY THE END OF THE PERIOD. THERE ARE TIMING DIFFERENCES IN SPITE OF THE GENERAL SYNOPTIC AGREEMENT. THE OVERALL FORECAST IS OF HIGHER CONFIDENCE THAN YESTERDAY BUT THERE ARE STILL MANY DETAILS TO IRON OUT. ONE LOOK AT THE SURFACE LOW PLACEMENT AT 72 HOURS INTO THE FORECAST SHOWS REASONABLE LOW SPREAD OVER THE UPPER OH VALLEY. THE 00Z NAM/GFS AND 12Z ECMWF ARE IN ALIGNMENT WITH THE ENSEMBLE MEANS WHILE THE 12Z CMC/UKMET DIVERGE MORE SIGNIFICANTLY. GIVEN THE 00Z NAM HAD ISSUES EARLY ON...WILL REMOVE IT IN FAVOR OF A 00Z GFS/12Z ECMWF BLEND. ...INITIAL NORTHERN STREAM SHORTWAVES CROSSING THE UPPER MIDWEST/GREAT LAKES... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF WITH THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: BELOW AVERAGE SPLIT FLOW ACROSS THE CONUS WILL ALLOW A SERIES OF NORTHERN STREAM SHORTWAVES TO TRACK FROM CENTRAL CANADA DOWN INTO THE MIDDLE MS VALLEY. THERE IS DECENT MODEL AGREEMENT THROUGH 24/0000Z WITH THE TRACK OF THE STRONGER OF THE FEATURES TRAVERSING THE UPPER MIDWEST. SOME OF THESE ENERGETICS ARE EXPECTED TO PINCH OFF AND INTERACT WITH THE SOUTHERN STREAM CLOSED LOW. THERE ARE PLENTY OF DIFFERENCES AT THIS POINT SO WILL LEAN MORE HEAVILY ON THE PREFERENCE IN THE SOUTHERN STREAM ALONG WITH SOME ENSEMBLE SUPPORT GIVEN THE UNCERTAINTY. THE CURRENT THOUGHT IS TO BLEND THE GFS/ECMWF SUITES UNTIL FURTHER GUIDANCE ARRIVES. ...MORE SIGNIFICANT HEIGHT FALLS SLIDING THROUGH THE DAKOTAS BY 24/1800Z... PRELIMINARY PREFERENCE: BLEND OF THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: BELOW AVERAGE ON THE HEELS OF THE INITIAL SYSTEMS TRACKING DOWN INTO THE MIDDLE MS VALLEY...AN EVEN MORE AMPLIFIED NORTHERN STREAM SHORTWAVE DIGS INTO THE NORTHERN PLAINS BY WEDNESDAY EVENING. THERE IS A HIGH AMOUNT OF SPREAD WITH THIS FEATURE AS NOTED IN THE 540-DM SPAGHETTI PLOTS. WHILE MODELS AGREE ON THE LONGWAVE TROUGH PLACEMENT EXTENDING FROM THE MIDDLE MS VALLEY TO THE CENTRAL APPALACHIANS...EMBEDDED SHORTWAVES VARY GREATLY. GIVEN THE NOTED SPREAD...THE RECOMMENDATION IS A BLEND OF THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS. ...WEAK IMPULSE APPROACHING WESTERN WA/VANCOUVER ISLAND LATE TUESDAY... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE A WEAK SHORTWAVE IS EXPECTED TO APPROACH A STOUT WESTERN U.S. RIDGE BY TUESDAY NIGHT. THERE HAVE BEEN GENERAL WEAKENING TRENDS EVALUATING THE PAST FEW MODEL CYCLES. AT THIS POINT THERE IS SUFFICIENT AGREEMENT WITH DIFFERENCES PRIMARILY WITHIN THE NOISE OF TYPICAL DAY 2 SPREAD. A GENERAL MODEL COMPROMISE APPEARS REASONABLE HERE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER