EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1156 AM EDT FRI MAR 31 2017 VALID 12Z MON APR 03 2017 - 12Z FRI APR 07 2017 OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... THE PREVAILING LARGE-SCALE FLOW DEPICTED BY GUIDANCE SHOWS SPLIT-FLOW ENTERING THE MEDIUM RANGE PERIOD/DAYS 3-7, WITH ONE SIGNIFICANT SHORTWAVE TROUGH EXITING THE SOUTHERN PLAINS, WHILE A COMPLEX UPPER TROUGH FORMS UPSTREAM, WITH THE EVOLUTION AND DETAIL OF THIS TROUGH A MAJOR SOURCE OF UNCERTAINTY FOR THE DAY-TO-DAY DETAILS FROM THE CENTRAL U.S. EASTWARD STARTING DAY 5/WED, ALTHOUGH THE OUTCOME OF THIS TROUGH PROBABLY INVOLVES A CYCLONE TRACKING FROM THE OH VALLEY TO NEW ENGLAND TOWARD THE END OF NEXT WEEK, WITH POTENTIALLY SIGNIFICANT WEATHER. FOR DAYS 3-4/MON-TUE, THE 06Z GFS IS CLOSEST OVERALL TO THE MODEL CONSENSUS AND THEREFORE PREFERRED, INCLUDING THE LOW MOVING FROM THE LOWER MISSISSIPPI VALLEY TOWARD THE OH VALLEY, AS WELL AS THE LOW NEAR HUDSON BAY, OF WHICH THE 00Z ECMWF IS MOST DISTANT FROM THE MODEL CONSENSUS, AND THUS NOT RECOMMENDED. CONFIDENCE IS NEAR TO SLIGHTLY BELOW AVERAGE THROUGH DAY 4, WHICH IS SUPPORTED BY THE LARGER THAN USUAL SPREAD SEEN WITHIN THE ENSEMBLES. FOR DAY 5/WED AND BEYOND, MODELS GENERALLY AGREE ON A HIGH AMPLITUDE UPPER TROUGH OR CLOSED LOW FORMING OVER THE GREAT LAKES/OH VALLEY, ALTHOUGH WITH HIGHLY UNCERTAIN DETAILS DUE TO THE COMPLEXITY AND POTENTIAL INTERACTION OF MULTIPLE STREAMS EMBEDDED WITHIN OR SURROUNDING THE TROUGH. IN FACT, THE SPREAD IS SO HIGH AND RUN-TO-RUN CHANGES SO SIGNIFICANT, THAT CHOOSING A MODEL OR CLUSTER OF MODELS IS DIFFICULT AT BEST AND ACCOMPANIED BY VERY LOW CONFIDENCE. IT EVEN APPEARS THAT THE MOST RECENT GUIDANCE MAY BE NO BETTER THAN YESTERDAY'S GUIDANCE. THEREFORE, WHILE THE 06Z GFS APPEARS TO BE A GOOD STARTING POINT FOR DAYS 3/4, THE PREFERENCES FOR DAY 5 AND BEYOND ARE WPC CONTINUITY, ACCOMPANIED BY VERY LOW CONFIDENCE. SENSIBLE WEATHER HIGHLIGHTS... THERE IS A LARGER THAN USUAL SPECTRUM OF POSSIBILITIES. MODERATE TO HEAVY PRECIPITATION IS QUITE POSSIBLE FOR THE CENTRAL GULF COAST NORTHEASTWARD MON-TUE, WITH ANOTHER AXIS MAY EXTEND ACROSS THE OH VALLEY, AS A SHORTWAVE TROUGH PROGRESSES ACROSS THE REGION. IF THE 06Z GFS/00Z ECMWF ARE CORRECT, THE EFFECTS ACROSS THE SOUTH AND EAST WILL BE MORE NOTICEABLE THAN IF THE 00Z GFS IS CORRECT, WHICH PLACES GREATER EMPHASIS FOR HEAVY PRECIPITATION ACROSS THE OH VALLEY. FOR DAY 5/WED AND BEYOND, A SIGNIFICANT CYCLONE APPEARS MORE LIKELY TO TRACK FROM THE MIDDLE MISSISSIPPI VALLEY TOWARD NEW ENGLAND BY DAY 7/FRI THAN A WEAK CYCLONE, ALTHOUGH CONFIDENCE IS VERY LOW. THE 06Z GFS MOVES QUICKLY TOWARD THE NORTHWEST AND DEEP EDGES OF THE GUIDANCE OVER IOWA ON DAY 5, AND THUS WAS NOT USED, WHILE THE 00Z ECMWF IS EMBEDDED WITHIN THE MIDDLE OF A VERY LARGE ENSEMBLE MEMBERSHIP, AND 00Z GFS WEAKER AND FARTHER EAST THAN MOST SOLUTIONS. THUS, THESE SOLUTIONS WERE NOT USED. INSTEAD, RELIED UPON THE PREVIOUS WPC FORECAST THAT IS NEAR THE OVERNIGHT MODEL CONSENSUS. HEAVY PRECIPITATION AND STRONG WINDS ARE LIKELY IF A STRONG CYCLONE FORMS. HOWEVER, GIVEN THE COMPLEXITY OF THE TROUGH AND POTENTIAL INTERACTIONS FROM THE NORTHERN STREAM OVER CANADA, CONFIDENCE IS VERY LOW FOR ANY PARTICULAR OUTCOME. JAMES