EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1132 AM EDT FRI APR 24 2015 VALID 12Z MON APR 27 2015 - 12Z FRI MAY 01 2015 ...OVERVIEW... THE DOMINANT FOCUS OF THE MEDIUM RANGE FCST IN TERMS OF COMBINED SENSIBLE WEATHER IMPACTS AND UNCERTAINTY WILL BE ON THE EVOLUTION OF CLOSED LOW ENERGY EJECTING FROM THE SRN HIGH PLAINS AND NRN STREAM SHORTWAVES FLOWING INTO AN EASTERN CONUS MEAN TROUGH. IMPORTANT DETAILS ARE OF THE TYPE THAT CAN BE DIFFICULT TO RESOLVE VERY FAR IN ADVANCE BUT WILL HAVE SIGNIFICANT INFLUENCE ON SENSIBLE WEATHER. UPSTREAM... THERE IS FAIR AGREEMENT THAT A WESTERN CONUS MEAN RIDGE SHOULD GRADUALLY BUILD TOWARD THE PLAINS OR AT LEAST EAST OF THE DIVIDE AS AN EPAC UPPER TROUGH DIGS SLOWLY TOWARD THE WEST COAST. GUIDANCE SHOWS INCREASING DIVERGENCE FOR SHORTWAVE DETAILS THAT WILL INFLUENCE TIMING/SWD EXTENT OF NWRN CONUS PRECIP. ...GUIDANCE EVALUATION AND PREFERENCES... ENSEMBLE AGREEMENT IS GOOD IN THE CENTRAL/EASTERN STATES THROUGH ABOUT TUE... WITH MUCH MORE SPREAD OFF THE PAC NW COAST. FOR WED-FRI... THE UNCERTAINTY IN FCST DETAILS INCREASES FAIRLY RAPIDLY GIVEN THE MODEL/ENSEMBLE SPREAD IN HOW NRN PLAINS/MS VLY ENERGY MAY INTERACT WITH THE SRN PLAINS FEATURE. THE APPROACH OF ONE OR MORE UPSTREAM SHRTWVS FURTHER COMPLICATES THE FCST MID-LATE PERIOD. THUS FAR THE GEFS/ECMWF MEANS HAVE BEEN THE MOST STABLE GUIDANCE SOURCES OVERALL WITH THE TRACK/TIMING OF ASSOC LOW PRES FROM THE GULF COAST INTO THE WRN ATLC... WITH ONLY TYPICAL RUN TO RUN VARIATIONS. 00Z MODELS HAPPENED TO CLUSTER FAIRLY WELL NEAR THE GA COAST UNTIL ABOUT LATE WED -- 00Z/30 -- BEFORE THEY DIVERGE. 06Z GFS WENT ITS OWN WAY. 00Z GFS OFFERED THE BEST AGREEMENT WITH THE ENSEMBLE MEANS AND OVERNIGHT CONTINUITY WHILE THE 00Z ECMWF SHOWED ITS TYPICAL SLOWER/DEEPER BIAS... BUT WAS WITHIN THE ENSEMBLE SPREAD. PREFERRED AN ENSEMBLE COMPROMISE TAKING THE LOW OFF THE NC COAST AND THEN E OF SE NEW ENGLAND... WITH ROOM TO MOVE IN ANY DIRECTION. BLOCKY PATTERN WOULD CERTAINLY SUPPORT A SLOWER AND PERHAPS WRAPPED UP SOLUTION SO ANYTHING IS ON THE TABLE... COMPLICATED BY NORTHERN STREAM ENERGY IN SE CANADA THAT MAY DIVE INTO THE NORTHEAST... ALLOWING A SYSTEM TO ITS EAST TO GET TUGGED WESTWARD. SHRTWV DETAIL DIFFS WITHIN THE TROUGH OFF THE NWRN COAST BECOME APPARENT ALREADY BY DAY 4/TUE. 00Z GFS RUN WAS NOTICEABLY SLOWER THAN MOST OTHER SOLNS WITH A LEADING SHRTWV. 06Z WAS QUICKER BUT STILL LAGGED A BIT. MODEST COMPROMISE OFFERED A GOOD STARTING POINT. THEREAFTER... RECENT ECMWF RUNS HAVE BEEN QUICKER THAN THE ENSEMBLES TO BRING HEIGHT FALLS INTO THE PAC NW AMID INCREASING ENSEMBLE SPREAD. WITH GOOD AGREEMENT AMONG THE GEFS/ECENS MEMBERS ON A SLOWER SOLUTION... OPTED TO TREND TOWARD THEM WHICH ALSO FIT THE BILL IN THE EAST. ...SENSIBLE WEATHER HIGHLIGHTS... HEAVY PRECIP POSSIBLE ALONG THE GULF COAST EARLY/MID-WEEK... COMBINATION OF UPPER LOW ENERGY EJECTING FROM THE SOUTHERN PLAINS... SFC FRONTAL BOUNDARY... AND LOW PRESSURE TRACKING ALONG THE GULF COAST INTO THE ATLANTIC SHOULD FAVOR A LARGE AREA OF MODEST RAIN AND SOME AREAS OF HEAVY PRECIP FROM PORTIONS OF THE SRN HALF OF THE ROCKIES OR HIGH PLAINS THROUGH THE SOUTHEAST AND CENTRAL/NORTHERN FLORIDA. SOME AREAS LIKELY TO BE AFFECTED HAVE ALREADY RECEIVED SIGNIFICANT RAINFALL TOTALS OVER RECENT WEEKS. CONSULT SPC OUTLOOKS FOR LATEST INFO REGARDING SEVERE WEATHER THREATS... CURRENTLY INDICATED OVER THE SRN PLAINS EARLY IN THE PERIOD. COVERAGE AND INTENSITY OF PRECIP OVER THE CENTRAL/NORTHERN PARTS OF THE EAST IS MUCH MORE UNCERTAIN AND DEPENDENT ON DIFFICULT TO RESOLVE ASPECTS OF MULTIPLE FEATURES ALOFT. TEMPERATURES SHOULD AVERAGE NEAR TO BELOW CLIMO AMID LOWER THAN AVERAGE HEIGHTS AND NORTH/NORTHEASTERLY FLOW. MEANWHILE THE PATTERN FARTHER WWD WILL SUPPORT MULTIPLE EPISODES OF LGT TO PERHAPS LOCALLY MDT PRECIP OVER THE PAC NW AND VICINITY. THE MOST NOTABLE EXTREMES IN TEMPS WILL BE FROM THE CENTRAL-SOUTHERN HIGH PLAINS INTO THE SOUTHEAST WHERE CLOUDS/PCPN SHOULD HOLD DAYTIME HIGHS TO 5-20F BELOW AVERAGE ONE OR MORE DAYS... AND FROM THE WEST INTO THE NORTHERN PLAINS WHERE SOME LOCATIONS MAY SEE READINGS UP TO 10-20F ABOVE AVERAGE. FRACASSO/RAUSCH