000 FXUS04 KWBC 202157 QPFPFD QUANTITATIVE PRECIPITATION FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 456 PM EST FRI NOV 20 2009 FINAL DAY 1...DAY 2 AND DAY 3 QPF DISCUSSION VALID NOV 21/0000 UTC THRU NOV 24/0000 UTC REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR THE 18Z NAM AND GFS CONTD TO SHOW THE SAME SOLNS THEY HAD ON THEIR RESPECTIVE 12Z RUNS..SO MADE ONLY MINOR CHGS TO THE PRELIM DAY 1 QPF..BASED MSTLY ON RECENT RADAR/SATL IMAGERY/TRENDS. DAY 1... ...NERN U.S.... CLOSED LOW AND ASSOC COLD FRONT WILL BE CLEARING NRN NEW ENGLAND EARLY IN THE PD. EXPECT SOME LGT WRAP-AROUND SHWRS THOUGH TO PERSIST OVER THE OROGRAPHICALLY FAVORED TERRAIN...FROM THE ADIRONDACKS OF NY NEWD UP INTO NWRN MAINE. ...WRN/CNTRL GULF COAST REGION.... SURGE OF DEEP MSTR NWD ACRS THE WRN GULF AHEAD OF S/WV TROF PUSHING EWD ACRS THE SRN PLAINS WILL CONTINUE TO FUEL LOCALLY HEAVY RAINS EARLY IN THE PD ALONG THE S TX COAST...BUT THIS FOCUS OF CONVECTION SHOULD TEND TO SHIFT RATHER QUICKLY OFFSHORE AS A COLD FRONT CLEARS THE REGION. MORE SIGNIFICANT UNCERTAINTY THOUGH WILL UNFOLD FOR THE CNTRL GULF REGION BY THE END OF THE PD AS THE MDLS SHOW A FAIR AMT OF SPREAD REGARDING HOW THE S/WV TROF LIFTS NEWD ACRS THE GULF COAST. THE 12Z GFS CONTINUES TO BE THE MOST PROGRESSIVE WITH THE ENERGY AND ESP THE SFC LOW THAT TRACKS ACRS THE NRN GULF OF MEXICO. THE NAM IS THE SLOWEST...WITH THE 00Z ECMWF AND 12Z GEM GLOB SPLITTING THE DIFF. THE NAM ALSO IS SUFFERING FROM AN EXTREME AMT OF CONVECTIVE FEEDBACK AND SINCE IT ALREADY IS MISHANDLING THE CONVECTION OVER SERN TX AND THE WRN GULF OF MEXICO...HPC OPTED TO DISCOUNT ITS SOLN ENTIRELY. GIVEN THE SOMEWHAT FASTER TREND SEEN IN THE GFS TO ADVECT MOISTURE AND ENERGY NEWD OUT OF THE GULF AND ACRS THE DEEP SOUTH ALONG WITH DECENT RUN TO RUN CONTINUITY...HPC OPTED TO LEAN MORE PROGRESSIVE WITH THIS SYS...WITH A SOLN ESSENTIALLY SPLITTING THE DIFF BETWEEN THE 12Z GFS AND 00Z ECMWF. THE GFS IS LIKELY PULLING ITS HEAVIER QPF A LITTLE TOO QUICK TO THE NORTH CONSIDERING THE AMT OF LOW LVL RIDGING/DRY AIR IN PLACE INITIALLY ALONG THE CNTRL GULF COAST AND WITH THE FACT THE MAIN BAROCLINIC ZONE IS CURRENTLY WELL SOUTH DOWN OVER THE CNTRL GULF OF MEXICO. THIS WILL GRADUALLY MOVE NEWD TWD THE COAST AS SFC LOW PRESSURE BECOMES BETTER ORGANIZED IN RESPONSE TO THE APPROACHING S/WV TROF...BUT THE STRONGEST FORCING IS LIKELY TO STAY ALONG OR JUST OFFSHORE THE GULF COAST INVOF THIS BNDRY AND SO THE HEAVIEST RAINS WERE KEPT SOMEWHAT MORE SUPPRESSED AT LEAST FOR THIS PD. ...WRN U.S.... MODELS ARE VERY SIMILAR HERE IN PROGRESSING FAIRLY HIGH AMPLITUDE UPR TROF EWD ACRS THE WEST COAST AND THRU THE GT BASIN REGION EARLY IN THE DAY 1 PD...WITH A SECOND UPR TROF QUICKLY FOLLOWING AND ARRIVING ALONG THE PAC NW COAST BY THE END OF THE PD. BEST MSTR INFLOW AND UPR DYNAMICS WILL FOCUS INITIALLY OVER THE NRN SIERRA-NEVADA AND INLAND ACRS THE SAWTOOTH/BITTERROOT RANGES OF THE NRN ROCKIES WHERE MDT TO LOCALLY HVY SNOW WILL BE POSSIBLE. THEREAFTER...MDT TO HVY OROGRAPHICALLY DRIVEN RAIN AND SNOW SHOULD IMPACT THE COASTAL RANGES OF WA/OR...INCLUDING THE OLYMPIC PENINSULA AND ALSO SPREADING INTO THE CASCADES AS THE NEXT FRONTAL BAND AND ASSOC UPR SUPPORT ARRIVES. A CONSENSUS OF THE HIGHER-RES 12Z NAM/00Z ECMWF WAS FOLLOWED HERE FOR THE QPF DETAILING. DAYS 2/3... ...PAC NORTHWEST INTO INTER-MOUNTAIN WEST... A STRONG PAC H5 SHRTWV WILL ALREADY BE AFFECTING THE NORTHWEST AT THE START OF THE PD LATE SAT...ACCOMPANIED BY A STRONG CDFNT SWEEPING THROUGH THE REGION SAT NIGHT/SUN. A RATHER PERSISTENT/STRONG ONSHORE FETCH BEHIND THE FNT WILL RESULT IN HEAVY RAINFALL AND MTN SNOWS ACROSS WA/OR THROUGH SUNDAY. HPC HAS INDICATED 1-2 INCHES IN THE HIGHER ELEVATIONS...AND A HALF INCH ACROSS THE LOWER ELEVATION. THE MSTR/INSTABILITY AXIS WILL SHIFT EWD SUNDAY/MONDAY THROUGH THE NRN ROCKIES ACCOUNTING FOR UP TO A HALF INCH OF RAINFALL OR SNOW-LIQUID-EQUIV. ACTIVITY WILL TAPPER OFF FROM W TO E SUN EVENING/MON AS A SHRTWV RIDGE BUILDS BACK OVER THE WEST. YET ANOTHER SYSTEM WILL IMPACT THE NW LATE IN THE PD...BUT THE SIGNIFICANT RAINFALL WILL STILL BE IN B.C. MONDAY AFTERNOON. MODEL GUIDANCE OVERALL IS IN DECENT AGREEMENT AND HPC GENERALLY FOLLOWED THE 00-12Z ECMWF AS A BASE WITH HELP FROM THE ENSEMBLE QPF AND PRISM. ...NRN/CNTRL PLAINS... UPR TROF WILL PROCEED INTO THE PLAINS DAY THREE AND INDUCE SFC CYCLOGENESIS LEE OF THE CNTRL OR NRN ROCKIES...MODELS ARE NOT QUITE SURE YET. REGARDLESS...A BAND OF WAA PRECIP SHOULD DEVELOP ACRS ERN DAKOTAS/MT ON MONDAY AS THE UPR TROF APPROACHES...THEN MORE DYNAMIC PRECIP WILL DEVELOP UNDER THE TROF ON MONDAY FROM CNTRL ROCKIES EWD DEPENDING ON THE SFC CYCLONE EVOLUTION. HPC USED A 12Z ECMWF/ENSEMBLE BLEND HERE. ...CNTRL GULF COAST THROUGH SOUTHEAST AND MID ATLANTIC... TREMENDOUS DIFFERENCES CONTINUE REGARDING THE PROGRESSION OF A SFC WAVE AND UPR ENERGY INVOF NE GULF SPREADING UP THROUGH THE SOUTHEAST AND OFFSHORE MID ATLANTIC. GFS CONTINUES TO BE THE FAST OUTLIER...YET THE TREND IS TO BE MORE PROGRESSIVE THAN BEFORE WITH THE 12Z CAN GLBL/UKMET AND 15Z SREF LENDING SOME SUPPORT TOWARDS A FASTER SOLUTION. MEANWHILE THE 12Z ECMWF HAS TRENDED IN THE OPPOSITE DIRECTION WHILE THE NAM REMAIN SLOW. ALL THIS ADDS TO A HIGHLY UNCERTAIN DEPICTION OF POTENTIALLY MDT RAINFALL FOR A SIZABLE PORTION OF THE SOUTHEAST AND CAROLINAS. HPC HAS CHOSEN TO TAKE AN APPROACH FASTER THAN THE ECMWF...BUT NOT AS FAST AS THE GFS...EVEN THOUGH NONE OF THE DETERMINISTIC MODELS TAKES THIS APPROACH. DRASTIC DIFFERENCES ALSO EXIST UPSTREAM IN THE NORTHEAST/SRN NEW ENG ON MONDAY AS THE FASTER SOLUTION ALLOW PRECIP TO SPREAD NWD...WHILE THE SLOWER SOLUTIONS SHUNT PRECIP OFFSHORE. FOR NOW...HAVE GONE DRY IN THE NORTHEAST. ORRISON/TERRY/SOWKO
