EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EDT FRI APR 03 2015 VALID 12Z MON APR 06 2015 - 12Z FRI APR 10 2015 ...OVERVIEW... AN ACTIVE EARLY SPRING MEDIUM-RANGE FLOW PATTERN WILL BE IN PLACE FOR NEXT WEEK AS AN AMPLIFIED...UNSETTLED AND UNSTABLE MID-UPPER LEVEL PACIFIC TROUGH SUPPORTS SEVERAL MODEST SURFACE SYSTEM MIGRATIONS ACROSS THE PLAINS...THE MIDWEST AND EAST CENTRAL COAST OF THE UNITED STATES. ...MODEL PREFERENCES... THE 3/00Z NAEFS/ECENS WERE GENERALLY ACCEPTED AS THE BASELINE FORECAST---ALOFT AND AT THE SURFACE THROUGH DAY 7. THE DETERMINISTIC 3/00Z ECMWF AND GFS HAD THEIR ADVANTAGES IN THE DETAILS ACROSS THE WEST---AS EMBEDDED ENERGY ROTATES THROUGH ITS BASE DURING THE DAY 4-5 TIME FRAME AND MIGRATES EASTWARD INTO A STABLE...DRY BUT CHILLY NORTHEAST SURFACE RIDGE. FOR DAYS 6-7...THE MEANS CHOSEN LIKE THE IDEA OF AN UPPER-LEVEL RIDGE BUILDING SLIGHTLY INTO THE BAHAMAS AND SOUTHEAST COAST---AND SLIGHT BUT NORTHWARD EROSION OF THE SURFACE RIDGE IN THE FAR WESTERN ATLANTIC...AND A SLOWER...MORE AMPLIFIED MID-LEVEL WAVE EJECTING NORTHEASTWARD FROM THE SOUTHERN PLAINS. WILL WATCH THESE KEY AREAS IN THE COMING DAYS. ...UNCERTAINTY ASSESSMENT... THE DAY 3-4 SHORTWAVE MIGRATING THROUGH THE ROCKIES HAS COME INTO MUCH BETTER AGREEMENT---AND THE ECMWF/GFS NOW AGREE WITH RESPECT TO LATITUDE---EJECTING THE MODERATELY-INTENSE 500MB ENERGY ALONG THE NORTH DAKOTA/MANITOBA BORDER. SEVERAL DAYS AGO (4 DAYS ACTUALLY)---THIS SHORTWAVE WAS PROGGED TO MOVE EASTWARD ACROSS SOUTHEAST MONTANA AND 46N LATITUDE. THE DETERMINISTIC GUIDANCE CONTINUES TO WEAKEN/SHEAR THIS WAVE---OVER THE UPPER GREAT LAKES AND SOUTHEAST CANADA---IN RESPONSE TO ITS ENTRY INTO A VERY CONFLUENT FLOW. THE BIGGEST CHANGE IN TRACK---IS WITH LATITUDE. NOW CLOSER TO 50N LATITUDE ACROSS THE NORTH AMERICAN CONTINENT---BUT STILL INTO A CONFLUENT DOWNSTREAM FLOW. WHAT THIS ALLOWS FOR NOW---IS A PACIFIC TROUGH THAT BEGINS TO EXPAND..THEN DIG ACROSS THE GREAT BASIN---AND THE ECMWF...UKMET...GFS AND CANADIAN DETERMINISTIC SOLUTIONS DETAIL 2 DISTINCT SHORTWAVES ---ONE OVER ONE INVOF SRN NEVADA AND A SECOND IMPULSE INVOF PUGET SOUND. THESE ARE APPROXIMATIONS---DETAILED FROM THE 3/00Z DETERMINISTIC GUIDANCE AND THERE ARE SIGNIFICANT (STRENGTH/LAT-LONG) DIFFERENCES AT THE 500 MB LEVEL IN THESE 4 DETERMINISTIC MODEL SOLUTIONS BY THE 9/00Z TIME FRAME. BUT ESSENTIALLY---THE AREAS OF THE WEST MENTIONED AND THEIR SHORTWAVE ENERGY PLACEMENT DOES FIT THIS TROUGH CONFIGURATION. THROUGH TIME...THE RUN-TO-RUN DIFFERENCES (FROM THE DETERMINISTIC RUNS) WILL CREATE TIMING ISSUES...CHALLENGES AND CHANGES DOWNSTREAM EAST OF THE DIVIDE. FOR THIS MEDIUM RANGE FORECAST PACKAGE...THE GUIDANCE PROVIDED THREE SCENARIOS AT 250MBS---WITH SEVERAL JET STREAKS MOVING THROUGH THE EASTERN FLANKS OF THE TROUGH AXIS. HARD TO GO WITH ONLY ONE SOLUTION BEYOND 5---GIVEN THE MULTIPLE JET STREAK SOLUTIONS. IN THIS PACIFIC TROUGH SCENARIO---THE MOST UNCERTAINTY SEEMS TO BE THE ISSUE OF WHEN TO TIME THE EJECTION OF THE PRIMARY SHORTWAVE ENERGY---THE WAVE THAT PULLS INSTABILITY/DYNAMICS OUT ONTO THE PLAINS---AND GENERATES THE MORE WELL-DEFINED SYNOPTIC-SCALE SURFACE FEATURES AND CONCENTRATION OF SENSIBLE WEATHER. NAMELY...ACTIVE SPRING-TIME CONVECTION...STRONG WINDS AND SHARP TEMPERATURE GRADIENTS/CONTRASTS. FOR THIS PACKAGE---THE 3/00Z GEFS BECOMES A QUICKER SOLUTION IN THE NORTHERN STREAM FLOW OVER SOUTH CENTRAL CANADA AND CANADA IN GENERAL---WHEREAS THE NAEFS AND ECENS DEPICT A SLOWER SOLUTION. PAST EXPERIENCE TELLS ME THAT 'SLOWER MAY BE BETTER' WITH THE MIGRATION OF THE LARGER PORTION OF THIS TROUGH...AND SOME INDICATION OF AN UPPER-LEVEL RIDGE IN THE SOUTHEAST US. OPTED TO GO WITH A BLEND OF THE SLOWER MEANS---IF FOR NO OTHER REASON...TO ALLOW FOR MULTIPLE EJECTIONS OF ENERGY FROM THIS POTENT UPPER-LEVEL TROUGH BETWEEN WEDNESDAY NIGHT AND FRIDAY NIGHT ACROSS THE MAJORITY OF THE HIGH PLAINS FROM WYOMING TO WEST TEXAS. THE SECONDARY---BUT NOT THE LEAST IMPORTANT UNCERTAINTY---WILL BE THE DOWNSTREAM PROPAGATION OF THE MORE-ORGANIZED CONVECTION AND EVENTUAL OUTCOME (STRENGTHENING OR WEAKENING) EAST OF THE MISSISSIPPI RIVER. IN THE MEDIUM RANGE---THE ONLY SUBTLE CLUES SEEM TO BE EMBEDDED WITHIN THE SURFACE PATTERN SOLUTIONS. THE FEATURE OF NOTE...WEAKNESS IN THE SURFACE RIDGE ACROSS THE WESTERN ATLANTIC AND EASTERN SEABOARD---WHERE A WELL-DEFINED TROUGH AXIS APPEARS TO EXTEND FROM MISSOURI TO NEW JERSEY. THE MEANS SUGGEST LITTLE SURFACE WAVE REFLECTION MIGRATING ATOP THE SURFACE RIDGE---BUT THE DETERMINISTIC RUNS GENERATE ENOUGH CONVECTIVELY-INDUCED ORGANIZATION TO OCCASIONALLY DOT THIS TROUGH WITH A WEAK SPOT LOW. THOUGHT HERE...THE MEANS PROBABLY SUPPORT THE 'AVERAGE' TRACK FOR DOWNSTREAM SYSTEMS TO MIGRATE---BUT WEAKEN---AS THEY APPROACH THE APPALACHIANS. THIS MAY BE PERHAPS---MEDIUM RANGE SPECULATION---BUT AS WE HAVE SEEN OVER THE PAST 3-4 MONTHS---THIS 'MEDIUM RANGE' INVERTED TROUGH AXIS HAS BEEN ACTIVE AT TIMES ---FROM THE OZARKS TO THE CENTRAL APPALACHIANS. AND IN THIS MEDIUM RANGE PERIOD...THE GULF OF MEXICO IS WIDE OPEN. ...SENSIBLE WEATHER HIGHLIGHTS... AN OPEN GULF LOW-LEVEL MOISTURE SOURCE...AND EJECTING PACIFIC SHORTWAVE ENERGY SPELLS AN ACTIVE...BUT WIDELY VARIABLE PRECIPITATION PATTERN ACROSS THE CENTRAL STATES. BROAD WARM SECTOR RAINFALL/CONVECTION ALONG WITH OVER-RUNNING/WRAP-BACK PCPN INCLUDING SOME ADDITIONAL SNOW POTENTIAL ON THE NRN/NWRN PERIPHERY OF THE OVERALL PCPN SHIELD OVER THE US NRN TIER. VOJTESAK