EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1111 AM EST TUE MAR 07 2017 VALID 12Z FRI MAR 10 2017 - 12Z TUE MAR 14 2017 ...PATTERN OVERVIEW AND MODEL EVALUATION... THE LARGE SCALE PATTERN WAS FAIRLY CONSISTENT AMONGST GUIDANCE WITH NEARLY FLAT/ZONAL FLOW TO SLIGHT RIDGING IN THE WEST AND A TROUGH IN THE EAST...HOWEVER DIFFERENCES IN THE TIMING AND AMPLITUDE OF THE SHORTWAVES MOVING THROUGH THE PACIFIC NORTHWEST, THE GREAT LAKES AND WHETHER OR NOT A WAVE DEVELOPS ALONG THE SOUTHEAST COAST BY THE END OF THE FORECAST PERIOD KEEPS CONFIDENCE LOW ON THE SPECIFICS WITH EACH FEATURE. A SIGNIFICANT FOCUS OF THE FORECAST WILL BE ON THE EVOLUTION OF EASTERN U.S. LOW PRESSURE DURING THE WEEKEND. SUPPORTING ENERGY IS FORECAST TO REACH THE PACIFIC NORTHWEST COAST AROUND THE START OF THE PERIOD EARLY FRIDAY AND THEN HEAD INTO THE EASTERN U.S. MEAN TROUGH. THE WEAK NATURE OF THIS ENERGY AND THE FACT IT IS EMBEDDED WITHIN PROGRESSIVE FLOW WOULD TEND TO SUPPORT BELOW AVERAGE PREDICTABILITY SEVERAL DAYS OUT IN TIME. THIS IS REFLECTED BY CURRENT MODEL AND ENSEMBLE SPREAD AS WELL AS MEANINGFUL RUN TO RUN TRENDS WITH THE LATITUDE OF THE SURFACE SYSTEM. LATEST TRENDS HAVE GENERALLY BEEN TOWARD A MORE SUPPRESSED/SOUTHERN TRACK. HOWEVER THE FACT THAT THE SHORTWAVE ENERGY IS HEADING INTO A MEAN TROUGH KEEPS THE DOOR OPEN FOR A SLIGHTLY STRONGER SHORTWAVE AND REVERSAL OF THE TREND. THUS AN INTERMEDIATE SOLUTION SEEMS MOST REASONABLE. LATE IN THE MEDIUM RANGE PERIOD...DETERMINISTIC GUIDANCE...ESPECIALLY THE GFS...CONTINUES TO FLIP-FLOP WITH THE EVOLUTION OF SHORTWAVE ENERGY POSSIBLY PROGRESSING SOUTHEASTWARD OUT OF THE PACIFIC NORTHWEST ON SUNDAY AND POTENTIAL ASSOCIATED SURFACE CYCLONE DEEPENING OVER THE CENTRAL PLAINS ON MONDAY. THE WPC DAY 3-7 FORECAST BEGAN WITH AN INITIAL COMBINATION OF THE THE 00Z ECWMF/GFS/CMC AND GEFS/ECMWF ENSEMBLE MEANS...WITH SLIGHTLY MORE WEIGHT GIVEN TO THE PREVIOUS WPC FORECAST AND THE ECMWF/ECMWF ENSEMBLE MEAN SINCE THEY HAVE BEEN MORE CONSISTENT WITH THE LARGE SCALE FLOW PATTERN OVER THE PAST FEW MODEL CYCLES. ...WEATHER HIGHLIGHTS... MUCH OF THE THE NORTHERN TIER STATES WILL REMAIN VERY CHILLY INTO THE WEEKEND ONCE AN ARCTIC AIRMASS PLUNGES THROUGH THE REGION AND SETTLES IN OVER THE CENTRAL AND EASTERN U.S. MANY LOCATIONS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL HAVE MAXIMUM TEMPERATURES RANGING 10 TO 20 DEGREES COOLER THAN SEASONAL AVERAGES...AND IN SOME INSTANCES... NEARLY 25 DEGREES COOLER. AFTERNOON HIGHS WILL GENERALLY BE IN THE SINGLE DIGITS AND TEENS. BELOW NORMAL TEMPERATURES EXPECTED TO REACH AS FAR SOUTH AS THE TENNESSEE VALLEY AND CAROLINAS ON SUNDAY. THUNDERSTORMS...MODERATE TO HEAVY RAIN...AND ACCUMULATING SNOW...WILL BE POSSIBLE AS MOISTURE ADVECTION INCREASES AHEAD OF SURFACE CYCLONE EXPECTED TO DEEPEN ALONG THE LEADING COLD FRONT AND TRACK FROM THE SOUTHERN PLAINS TO THE MID-ATLANTIC COAST THIS WEEKEND. EMBEDDED AREAS OF MODERATE TO HEAVY PRECIPITATION WILL BE POSSIBLE WITH AN UPSTREAM SHORTWAVE AND SURFACE LOW POTENTIALLY DEEPENING OVER THE CENTRAL PLAINS ON MONDAY...BUT THE DETAILS OF THE FORECAST REMAIN UNCERTAIN. NEARLY CONTINUOUS ONSHORE FLOW COMBINED WITH A SERIES OF SHORTWAVE ENERGY PASSING THROUGH WILL KEEP MUCH OF THE PACIFIC NORTHWEST IN AN ACTIVE WET PATTERN. PERIODS OF HEAVY RAIN AND MOUNTAIN SNOW TO THE FAVORED TERRAIN OF THE PACIFIC NORTHWEST AND NORTHERN ROCKIES IS FORECAST FOR THE END OF THE WORK WEEK AND THIS WEEKEND. MUCH OF THE DESERT SOUTHWEST...CENTRAL GREAT BASIN AND THE SOUTHERN ROCKIES WILL REMAIN FAIRLY DRY AND WARM OVER THE NEXT SEVERAL DAYS. IN FACT... WARMER THAN AVERAGE TEMPERATURES ARE EXPECTED FROM THE SOUTHWEST TO THE SOUTHEAST WITH DAILY HIGHS RANGING FROM THE 60S TO MID-TO-UPPER 80S. A FEW LOCATIONS MAY REACH OR EXCEED DAILY TEMPERATURE RECORDS. CAMPBELL/RAUSCH/GERHARDT