EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EDT TUE MAR 21 2017 VALID 12Z FRI MAR 24 2017 - 12Z TUE MAR 28 2017 ...OVERVIEW/GUIDANCE EVALUATION/PREFERENCES... AT THE START OF THE PERIOD...FRIDAY MORNING...SPLIT FLOW WILL BE IN PLACE WITH A COMPACT UPPER LOW SPINNING OVER THE SOUTHERN/CENTRAL HIGH PLAINS. CURRENT FORECAST 500-MB HEIGHT ANOMALIES ARE ROUGHLY ONE SIGMA BELOW CLIMATOLOGY WITH SUCH DEPARTURES DIMINISHING AS THE UPPER LOW GRADUALLY OPENS UP ACROSS THE OH VALLEY/LOWER GREAT LAKES BY THE END OF THE WEEKEND. MULTI-DAY COMPARISONS OF THE GUIDANCE SHOW A SLOWING TREND IN THE SOLUTION ENVELOPE WITH THE 00Z CMC/UKMET BEING THE SLOWEST OF THE BUNCH. THE PREVIOUS FOUR RUNS OF THE GFS HAS BEEN FAIRLY CONSISTENT WITH THE PLACEMENT OF THE UPPER LOW/SURFACE REFLECTION WHILE THE 00Z ECMWF TRENDED AHEAD OF THE PACK. ALL OF THESE DIFFERENCES ARE DRIVEN BY UPSTREAM TIMING ISSUES WITH PLENTY OF ENSEMBLE SPREAD NOTED. COMPARISONS OF RECENT ENSEMBLE SPAGHETTI PLOTS SHOW MANY ECMWF MEMBERS ON THE QUICKER SIDE WHICH DOES REFLECT ON THE FASTER DOWNSTREAM PROGRESSION. IT DOES APPEAR THIS IS QUITE THE REPEATABLE SYNOPTIC PATTERN AS THE NEXT BAND OF HEIGHT FALLS REACH THE SOUTHERN HIGH PLAINS BY LATE SUNDAY...PREVIOUSLY VACATED BY THE OH VALLEY/GREAT LAKES SYSTEM. EVENTUALLY THIS FEATURE IS FORECAST TO LIFT INTO THE MO VALLEY BY EARLY NEXT WEEK WHERE IT TOO WILL BEGIN TO SHEAR. LIKEWISE...THERE IS EVEN A TRAILING SYSTEM WHICH IS EXPECTED TO MOVE THROUGH THE FOUR CORNERS REGION BY MONDAY/TUESDAY. WHILE THERE IS SOME VARIABILITY IN PLACEMENT AND INTENSITY...GLOBAL ENSEMBLE MEANS ARE IN STRONG AGREEMENT OF THIS THIRD SYSTEM ENTERING THE FOUR CORNERS REGION/SOUTHERN HIGH PLAINS. THE FORECAST WAS BASED ON SOME OF THE OVERNIGHT CONTINUITY...20 PERCENT...TO CAPTURE THE 12Z ECMWF/ECMWF ENSEMBLE MEAN COMBINATION AS THEY WERE SLOWER WITH THE INITIAL UPPER LOW EXITING THE SOUTHERN/CENTRAL PLAINS. OTHERWISE...GENERALLY TOOK A BALANCE OF THE 06Z GFS/00Z ECMWF MODEL SUITES WITH INCREASING USE OF THEIR ENSEMBLE MEANS BY DAY 5/SUNDAY AS MODEL SPREAD BEGAN TO INCREASE. STILL KEPT ABOUT 20 PERCENT OF THE DETERMINISTIC SOLUTIONS INTO DAY 6/MONDAY GIVEN SOME CONFIDENCE IN THE PLACEMENT OF INDIVIDUAL FEATURES BEFORE MOVING TO ALL ENSEMBLE MEANS TO CONCLDUE THE PERIOD. ...SENSIBLE WEATHER/HIGHLIGHTS... OUT AHEAD OF THE CLOSED LOW MOVING OUT OF THE SOUTHERN/CENTRAL HIGH PLAINS...WELL ABOVE NORMAL TEMPERATURES ARE EXPECTED WITHIN THE EXPANSIVE WARM SECTOR. FORECAST TEMPERATURE ANOMALIES ON FRIDAY ARE EXPECTED TO BE IN THE 10 TO 20 DEGREE ABOVE AVERAGE RANGE FROM THE MIDDLE MS VALLEY TO THE OH VALLEY. BY THE WEEKEND AND INTO EARLY NEXT WEEK...A TIGHT TEMPERATURE GRADIENT SETS UP AS A BACK DOOR COLD FRONT SWEEPS SOUTHWARD FROM NEW ENGLAND DOWN INTO THE MID-ATLANTIC. ON SATURDAY...HIGHS MAY REACH THE 70S ACROSS NORTHERN VA WHILE READINGS STAY IN THE MID/UPPER 40S ACROSS SOUTHERN NY. REGARDING THE PRECIPITATION THREAT...HEAVY RAINFALL AND BOUTS OF SEVERE WEATHER ARE POSSIBLE FROM THE ARKLATEX AND OZARKS DOWN INTO THE CENTRAL GULF COAST. A SEPARATE THREAT OF MODERATE TO LOCALLY HEAVY RAINFALL WILL BE LIKELY ALONG THE WEST-EAST FRONTAL ZONE EXTENDING FROM THE MIDDLE MS VALLEY TO THE OH VALLEY. THIS SHOULD GENERALLY BE IN MORE OF AN OVERRUNNING FASHION. DEPENDING ON THE QUALITY OF MOISTURE RETURN FROM THE GULF OF MX...EXPECT ANOTHER ROUND OF CONVECTION ACROSS THE SOUTHERN/CENTRAL PLAINS LATER IN THE PERIOD IN RESPONSE TO THE NEXT BAND OF HEIGHT FALLS. RUBIN-OSTER