EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 145 AM EST TUE FEB 21 2017 VALID 12Z FRI FEB 24 2017 - 12Z TUE FEB 28 2017 ...OVERVIEW... THE ERN PAC/WRN U.S. CONTINUES TO BE AN AREA OF HIGH FCST SENSITIVITY FOR SPECIFIC DETAILS WITHIN AN OVERALL MEAN TROUGH ALOFT DOWNSTREAM FROM A STRONG NERN PAC RIDGE. ISSUES WITHIN THIS REGION WILL THEN HAVE AN IMPACT ON THE REMAINDER OF THE LOWER 48 WHERE MEAN FLOW SHOULD EVOLVE TOWARD A SWLY ORIENTATION. MEANWHILE THERE ARE STILL DETAIL UNCERTAINTIES FOR A STRONG SYSTEM TRACKING NEWD FROM THE MIDWEST FRI ONWARD. ...MODEL EVALUATION/PREFERENCES... AFTER GUIDANCE HAD APPEARED TO START THE PROCESS OF CONVERGING TOWARD A COMMON SOLN FOR THE EVOLUTION OF ERN PAC/WEST COAST ENERGY ALOFT BY THE WEEKEND... 12Z/18Z MODEL RUNS ADJUSTED TOWARD TAKING NWRN NOAM ENERGY AND WRAPPING UP A FAIRLY DEEP SYSTEM JUST OFF THE WEST COAST. MANY OF THESE MODELS ALSO INCORPORATED ENERGY FROM A CLOSED LOW FARTHER OFFSHORE. GIVEN THE DIFFICULTY THAT GUIDANCE HAS IN RESOLVING DETAILS OF FLOW IN THIS KIND OF PATTERN IT WOULD NOT BE SURPRISING FOR FURTHER CHANGES TO OCCUR IN THE FCST. ALSO THERE IS STILL WIDE SPREAD IN ENSEMBLE MEMBERS BY DAY 5 SUN. SOME MEMBERS LOOKED MORE SIMILAR TO THE LATEST OPERATIONAL CLUSTER WHILE OTHERS REPRESENTED THE QUICKER EJECTING SOLNS THAT WERE THE MAJORITY 24-36 HRS AGO. THIS DIVERGENCE LED TO A 12Z SUN FCST THAT HAD ENSEMBLES RANGING ANYWHERE FROM RIDGE TO TROUGH OVER THE INTERIOR WEST/ROCKIES. OVER SOME AREAS SPREAD ACTUALLY DAMPENED OUT A LITTLE BY DAYS 6-7 MON-TUE AS AGREEMENT IMPROVED TOWARD A POSITIVELY TILTED MEAN TROUGH SETTING UP OVER THE WEST WITH SOME EJECTING ENERGY SUPPORTING A WAVE THAT REACHES THE MIDWEST/UPR MS VLY BY NEXT TUE. CONFIDENCE IS NOT VERY HIGH THAT CURRENT CONSENSUS WILL VERIFY BUT THESE MODEL RUNS PROVIDED ENOUGH OF A COMMON SIGNAL TO INCORPORATE A PORTION OF THE OPERATIONAL MODEL EVOLUTION WITH THE WEAKER ENSEMBLE MEANS AS THE BEST OPTION FOR THE DETERMINISTIC FCST UPDATE. THE 00Z GFS/UKMET/CMC AT LEAST MAINTAIN A REASONABLE DEGREE OF CONTINUITY. FOR THE SYSTEM TRACKING NEWD FROM THE MIDWEST AN AVG AMONG THE 18Z GFS/GEFS MEAN AND 12Z ECMWF/ECMWF MEAN PROVIDED THE MOST STABLE SOLN FOR TRACK AND TIMING. IN VARYING WAYS UKMET/CMC RUNS HAVE TENDED TO DEVIATE MORE FROM THE MAJORITY CLUSTER THOUGH THEY ILLUSTRATE SOME OF THE LINGERING DETAIL UNCERTAINTIES WITH THE SUPPORTING ENERGY ALOFT. AS THE TRAILING COLD FRONT HEADS TOWARD/INTO NEW ENGLAND... ONE TREND OF NOTE FROM YDAY IS TOWARD SOMEWHAT MORE POTENTIAL THAT FLOW COULD TAP SOME OF THE MSTR ASSOC WITH A FEATURE TRACKING FROM THE GULF OF MEXICO ACROSS THE FL PENINSULA AND INTO THE ATLC DURING THE SHORT RANGE TIME FRAME. CONSIDERATIONS OVER AREAS OF INTEREST LED TO STARTING WITH A BLEND OF THE 18Z GFS/12Z ECMWF AND THEIR MEANS FOR DAYS 3-5 FRI-SUN WITH A TRANSITION MOSTLY TO THE MEANS THEREAFTER AS OPERATIONAL RUNS DIVERGED MORE GREATLY WITH SOME DETAILS. ...WEATHER HIGHLIGHTS/THREATS... THERE ARE PERSISTENT UNCERTAINTIES WITH SPECIFICS BUT IN PRINCIPLE THE FCST IS STILL ON TRACK FOR THE STORM TRACKING NEWD FROM THE MIDWEST FRI INTO THE WEEKEND. YDAYS SPC OUTLOOK MAINTAINED A FOCUS ON AN AREA OVER AND AROUND INDIANA AS BEST POTENTIAL FOR SEVERE CONVECTION IN THE FRI-FRI NIGHT PERIOD. CONSULT LATEST SPC PRODUCTS FOR UPDATED INFO. SNOW TO THE NW OF THE SFC LOW TRACK MAY BE HVY AT TIMES WHILE THERE MAY ALSO BE AREAS OF MDT-HVY RAIN AHEAD OF THE COLD FRONT CROSSING THE EAST. HOW MUCH ATLC MSTR MAY REACH NEW ENGLAND BY SAT-SAT NIGHT WILL HAVE TO BE MONITORED. SOME LOCATIONS MAY SEE STRONG WINDS. ALONG THE WEST COAST THE LATEST EVOLUTION SFC/ALOFT SHOWN IN MOST GUIDANCE HAS INCREASED THE POTENTIAL FOR A PERIOD OF HEAVIER RAIN/HIGHER ELEV SNOW FOCUSED OVER CALIFORNIA... MOST LIKELY DURING THE WEEKEND... WITH A PERIOD OF STRONG WINDS ALSO A PSBL THREAT. SOME MSTR WILL EXTEND INTO FAVORED TERRAIN OF THE INTERIOR WEST/ROCKIES. THEN BEYOND THE ROCKIES ONE OR MORE AREAS OF PCPN MAY DEVELOP WITH THE AID OF IMPULSES EMBEDDED WITHIN FLOW ALOFT THAT SHOULD BE TURNING SWLY AS WELL AS A WAVY FRONT GRADUALLY LIFTING NWD OVER THE CNTRL-ERN STATES. NRN AREAS MAY SEE SOME WINTRY PCPN TYPES WITH RAIN FARTHER S. ON FRI MUCH OF THE ERN U.S. SHOULD SEE TEMPS 15-30F ABOVE NORMAL WITH WARMTH HANGING ON INTO SAT ALONG THE EAST COAST. EXPECT SOME LOCATIONS TO SEE RECORD WARM VALUES FOR MAX/MIN READINGS. IN SPITE OF A SIGNIFICANT COOLING TREND... TEMPS SHOULD ONLY DROP TO NEAR OR SLIGHTLY BELOW NORMAL LEVELS BRIEFLY BEFORE REBOUNDING ABOVE NORMAL AGAIN EARLY NEXT WEEK. THE WARMING TREND SHOULD START ON SUN OVER THE SRN PLAINS. MUCH OF THE WEST AND INTO THE N-CNTRL PLAINS WILL LIKELY SEE BELOW NORMAL TEMPS WITH SOME LOCATIONS SEEING MINUS 10-15F OR SO ANOMALIES ONE OR MORE DAYS. RAUSCH