MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1202 PM EST SAT JAN 09 2016 VALID JAN 09/1200 UTC THRU JAN 13/0000 UTC ..SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...SHORTWAVE LIFTING FROM THE ARKLATEX TOWARD THE NORTHEASTERN U.S... ...RAPIDLY STRENGTHENING SURFACE CYCLONE MOVING INTO THE LOWER GREAT LAKES... PRELIMINARY PREFERENCE: A NON-12Z NAM MODEL CONSENSUS FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE WATER VAPOR IMAGERY AND THE 500-MB HEIGHT ANALYSIS SHOWED A PRONOUNCED SHORTWAVE MOVING TOWARD THE OZARKS. DOWNSTREAM...NUMEROUS SHOWERS/THUNDERSTORMS HAVE BROKEN OUT ALONG THE EASTERN GULF COAST WITHIN THE INCREASING MOIST AIR MASS. MODELS INDICATE A BROAD BAND OF VORTICITY WILL MIGRATE NORTHEASTWARD UP THE SPINE OF THE CENTRAL APPALACHIANS WITH THE 12Z NAM BEING A HAIR QUICKER WITH THIS PROGRESSION. CONSIDERING THE SURFACE CYCLONE TRACK...ENSEMBLE LOW PLOTS HAVE BEEN RATHER CONSISTENT WITH ONLY SMALL DIFFERENCES AMONG THE MODEL SUITES. GIVEN SPREAD IS ON THE LOWER SIDE...WILL FAVOR A NON-12Z NAM MODEL CONSENSUS. ...ACTIVE NORTHERN STREAM AFFECTING THE DAKOTAS TO NEW ENGLAND... ...SURFACE LOW CROSSING THE GREAT LAKES ON MONDAY/TUESDAY... ...REINFORCING SHOTS OF ARCTIC AIR... PRELIMINARY PREFERENCE: BLEND OF THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: AVERAGE THE NORTHERN STREAM WILL BE RATHER ACTIVE THROUGHOUT THE SHORT RANGE PERIOD AS A SERIES OF VORTICITY MAXIMA SWING ACROSS A LARGE PORTION OF THE NORTHERN TIER. THE MOST SIGNIFICANT FEATURE IS ASSOCIATED WITH A STRONG CLIPPER SYSTEM DIGGING INTO THE UPPER MIDWEST LATE MONDAY. MODELS DO INDICATE A SECONDARY FEATURE TRAILING IN THE WAKE WITH ADDITIONAL UPSTREAM ENERGY LOOMING OVER CENTRAL CANADA. THE SYNOPTIC PATTERN ACROSS THIS REGION IS RESOLVED REASONABLY WELL ALTHOUGH MODELS VARY IN THE TIMING/AMPLITUDE OF EACH INDIVIDUAL SHORTWAVE TRAVERSING THE CYCLONIC FLOW. WILL UTILIZE ENSEMBLE MEANS ALTHOUGH THEY DO EXHIBIT DIFFERENCES AS WELL. ENSEMBLE SPAGHETTI PLOTS INDICATE THE 00Z GEFS MEMBERS ARE MORE AMPLIFIED WITH ITS COLDER SOLUTION. THIS ARTIFACT HAS BEEN NOTED IN BOTH THE 00Z CYCLE AS WELL AS THE 12Z CYCLE FROM YESTERDAY. PLAN ON SPLITTING THE DIFFERENCE BETWEEN THE PAIR OF ENSEMBLE MEANS. ...INITIAL IMPULSE CROSSING THE CA/OR BORDER EVENTUALLY REACHING THE ARKLATEX BY 12/0600Z... PRELIMINARY PREFERENCE: A NON-00Z ECMWF/ECMWF ENSEMBLE MEAN MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE A PRONOUNCED LOBE OF VORTICITY INITIALLY OVER THE CA/OR BORDER WILL GRADUALLY PICK UP FORWARD SPEED AS IT ROUNDS THE BASE OF THE LONGWAVE TROUGH. THROUGH DAY 2 THERE ARE NO SIGNIFICANT DIFFERENCES NOTED UNTIL TIMING UNCERTAINTIES EMERGE BY DAY 3. AT THAT POINT...ENSEMBLE SPAGHETTI PLOTS SHOW SOME SPREAD WHICH WAS NOT EVIDENT IN PREVIOUS MODEL CYCLES. A VAST MAJORITY OF THE 00Z ECMWF ENSEMBLE MEMBERS FAVOR A SLOWER SOLUTION WHICH HAS NO SUPPORT FROM OTHER GUIDANCE. GIVEN THE SPAGHETTIS WERE MOST CLUSTERED IN PREVIOUS DAYS...NOT SOLD IN THIS 00Z ECMWF/ECMWF ENSEMBLE MEAN GROUPING. WPC FAVORS A NON-00Z ECMWF/ECMWF ENSEMBLE MEAN MODEL COMPROMISE. ...SPLIT FLOW AFFECTING THE WEST COAST BY EARLY NEXT WEEK... PRELIMINARY PREFERENCE: BLEND OF THE 06Z GFS/00Z ECMWF FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE A COMPLEX SPLIT FLOW REGIME TAKES SHAPE FOR THE IMMEDIATE WEST COAST FOR EARLY NEXT WEEK. DIFFERENCES ARE MOST NOTABLE WITH THE NORTHERN SPLIT WITH A VARIETY OF SOLUTIONS IN PLAY. OF NOTE...THE 12Z NAM WAS QUICKER WITH THE INITIAL SHORTWAVE WHILE THE 00Z CMC WAS MORE TUCKED TO THE SOUTH. MEANWHILE...THE 12Z GFS MADE A SHIFT IN THE FASTER DIRECTION WHICH STRAYS AWAY FROM THE MORE CLUSTERED ENSEMBLE MEANS. THE MOST MIDDLE GROUND SOLUTIONS AT THIS TIME ARE THE 06Z GFS/00Z ECMWF. FEEL INCLINED TO FOLLOW THIS COMBINATION PENDING FUTURE CHANGES IN THE 12Z SOLUTIONS. ...DEEP UPPER TROUGH ANCHORING THE EASTERN PACIFIC ON TUESDAY... PRELIMINARY PREFERENCE: BLEND OF THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: BELOW AVERAGE AMPLIFIED FLOW STARTS TO TAKE SHAPE ACROSS THE EASTERN PACIFIC TOWARD THE END OF THE PERIOD. SOLUTIONS ARE SCATTERED EVERYWHERE WITH THE 00Z CMC BEING FLATTER AND MORE PROGRESSIVE RELATIVE TO THE SLOWER 00Z UKMET. THERE IS STILL QUITE A BIT OF NOISE IN THE ENSEMBLE SPAGHETTI PLOTS WITH NOT A WHOLE LOT OF TRENDS NOTED IN THE PAST FEW MODEL CYCLES. BEST SOLUTION HERE WOULD BE TO UTILIZE ENSEMBLE MEANS UNTIL THE DETERMINISTIC MODELS COME INTO BETTER AGREEMENT. A 06Z GEFS/00Z ECMWF ENSEMBLE MEANS BLEND WILL BE THE COURSE OF ACTION. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER