EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1158 AM EDT FRI MAR 14 2014 VALID 12Z MON MAR 17 2014 - 12Z FRI MAR 21 2014 ...AN ACTIVE 'LATE-WINTER LIKE' PATTERN FOR THE EASTERN HALF OF THE NATION NEXT WEEK... ...OVERVIEW... THE TRANSITION FROM A SPLIT-FLOW IN THE WEST TO ONE THAT IS MORE PROGRESSIVE IN NATURE IS THE THEME TODAY. AND THAT TRANSITION HAS A FEW DETAILS THAT WILL COME TO THE FORE FRONT. A SURE SIGN OF SPRING SEEMS 'TO EMERGE' WHEN/HOW THE GLOBAL MODEL SOLUTIONS FIND LITTLE IN COMMON WITH EACH OTHER ONE DAY...AND THEN THERE BECOMES A 'NEED' FOR ADJUSTMENTS EMBEDDED WITHIN THE FLOW PATTERN--THE NEXT DAY. ADDING VALUE/MORE DETAIL...AND THE IMPLICATIONS TURN INTO A POSITIVE...IS WHAT SPRING FORECASTING AND CHALLENGE IS ALL ABOUT. TODAY'S FORECAST AND FOLLOWING DISCUSSION HOPE TO RELAY THOSE ADJUSTMENTS AND HIGHLIGHT THE DIFFERENCES. ...MODEL PREFERENCES... THE 14/00Z ECENS...GEFS AND NAEFS MEANS LOOKED TO BE IN SOLID AGREEMENT THROUGH DAY 4 WITH THE 2 SYSTEMS (DISCUSSED YESTERDAY). ONE IN THE EAST...ONE IN THE PLAINS. ALONG THE WEST COAST...A PROGRESSIVE APPROACH TO THE INFLUX OF ONSHORE FLOW...ESPECIALLY IN BRITISH COLUMBIA AND DOWNSTREAM INTO THE GREAT BASIN AND WEST-FACING PORTIONS OF THE CONTINENTAL DIVIDE IS A THIRD FEATURE OF THIS MEDIUM RANGE FORECAST AND TRANSITION PERIOD. OVERALL...WITH PREFERENCES AND CONTINUITY IN MIND...TODAY'S WPC GRAPHICS--SURFACE AND 500 MB---UTILIZED A BLEND OF THE 14/00Z ECENS/GEFS MEANS WITH THE DETAILS OF THE INDIVIDUAL DAILIES PREFERRING A BLEND OF THE DETERMINISTIC 14/00Z ECMWF FOR BOTH SYSTEMS AND THE PROGRESSIVE OUTCOME IN THE WEST. THE 14/00Z GEFS/ECENS MEANS COMPRISE A MAJOR PART THE BLEND THROUGH DAY 4...THEN TAPERING OUT OF A GEFS-BASED/GFS-BASED SOLUTION AFTER DAY 4...DUE TO ITS FASTER SOLUTION...NEGATIVE-TILT SCENARIO AND FRONTAL PROGRESSION THROUGH APPALACHIA AND THE EASTERN SEABOARD DAYS 6-7. ...14/00Z CYCLE UNCERTAINTY ASSESSMENTS... IN THE EAST...THE DIFFERENCE WITH THIS 14/00Z CYCLE VS PREVIOUS CYCLES--AND AN 'ACTIVE' EAST COAST PATTERN VS A BUT COLD/DRY ONE--REVOLVE AROUND THE OUTCOME OF A SHORTWAVE THAT TRACKS THROUGH THE BASE OF THE UPPER-LEVEL TROUGH ANCHORED ACROSS THE EASTERN HALF OF NORTH AMERICA. PREVIOUS SOLUTIONS--AND ALL MODELS WERE GUILTY OF THIS--TOOK THE KEY SHORTWAVE DEEP INTO THE SOUTHERN PLAINS (A FEW CYCLES EVEN PINCHED A CLOSED LOW OFF OVER NORTHERN MEXICO). THIS EMBEDDED DETAIL IN THE GENERAL FLOW PATTERN IS THE CULPRIT AND THE 'NEED' FOR ADJUSTMENT PERTAINS MAINLY WITH P-TYPE (THE IMPLICATION IS A MAJOR ONE). IN THE CENTRAL PLAINS...THE DIFFERENCES ARE TIED TO THE TIMING AND 'SHEARING OUT' OR LACK THEREOF...OF A PACIFIC NORTHWEST/NORTHERN ROCKIES SHORTWAVE ACROSS THE CENTRAL HIGH PLAINS. IT'S SPRING! BUT THE DIFFERENCES ARE NOT PERPLEXING OR DIFFICULT ENOUGH TO NOT BE ABLE TO 'WEED THROUGH THEM' AND DECIPHER. 1) THE EAST AND ITS FLAT WAVE EXITING THE OUTER BANKS...DAY 3. THIS WAVE CONTINUES TO QUICKLY MIGRATE OUT FROM THE OUTER BANKS INTO THE WESTERN ATLANTIC. THIS WAVE RIDES ALONG THE LEADING EDGE OF THE 'NEWLY-LAID OUT" CANADIAN AIRMASS...WHICH IS A VERY COLD ONE FOR MID-MARCH AND STRETCHED OUT INTO A MAJOR PORTION THE CANADIAN MARITIMES. NO SURPRISES THERE FOR P-TYPE CHALLENGES DAY 3 INTO EARLY DAY 4. HOWEVER...SENSIBLE WEATHER IMPLICATIONS NOW FOCUS AND REMAIN FIXED UPON THE COMPLEXITIES SURROUNDING A SECONDARY WAVE IN THE SOUTHEAST THAT IS ANTICIPATED TO MIGRATE ACROSS THE SOUTHERN APPALACHIANS...SOUTHEAST AND PIEDMONT. THIS WAVE GENERATES AN OVER-RUNNING EVENT ACROSS THE MID-ATLANTIC STATES AND NORTHEAST DAY 4-5. AND THIS 'CLEAN-UP' WAVE IN THE LONGWAVE PATTERN ON DAY 4 OVER THE EASTERN PORTION OF THE NORTH AMERICAN CONTINENT WILL DRIVE ACROSS THE COLD...CANADIAN AIRMASS IN PLACE (FROM THE CANADIAN MARITIME TO THE NORTHEAST AND SOUTHWARD TO THE DELMARVA AND MASON-DIXON LINE TO THE NC/VA STATE LINE). THIS IS THE WAVE THAT AT ONE TIME WAS GOING TO BE A CLOSED CUTOFF IN NORTHERN MEXICO. 2) OVER THE NORTHERN ROCKIES AND INTO PLAINS...DAYS 4-5. THE ENSEMBLE CLUSTERING IS GOOD THROUGH 19/12Z (MID-POINT DAY 5) WITH THE PRIMARY SURFACE CYCLONE FIXED INVOF LAKE MICHIGAN AND MIGRATING INTO SOUTHERN ONTARIO DAY 6. THE DIFFERENCES INCLUDE: THE NAEFS/GEFS MEANS TAKING ON A TAD MORE OF A NEGATIVE-TILT ORIENTATION OVER THE UPPER OHIO VALLEY AND NORTHERN MID-ATLANTIC REGION DAY 6-7 AS THE CYCLONE SWINGS THROUGH THE GREAT LAKES. THE IMPLICATION--LIMIT THE WARM ADVECTION ACROSS THE NORTHEAST AND SOUTHERN NEW ENGLAND AHEAD OF ITS ATTENDANT COLD FRONT. COMPARED TO THE ECENS MEAN SOLUTION...THEY (THE GEFS/NAEFS) ARE TOO FAST. SECONDARY TO THIS CYCLONE AND STORM TRACK OUTCOME...THE LEAD ENERGY EXITING THE NORTHERN HIGH PLAINS IS ANOTHER SET OF DIFFERENCES WITH IMPLICATIONS. THIS IS MORE OF A P-TYPE AND WIND IMPLICATION OVER THE DAKOTAS...THE UPPER-HALF OF THE MISSOURI VALLEY AND THE CENTRAL HIGH PLAINS. ...SENSIBLE WEATHER HIGHLIGHTS...WINTER RETURNS! UNSEASONABLY COLD HIGH PRESSURE OVERSPREADING THE NORTHEAST QUARTER OF THE NATION SUGGESTS MORE WINTER-LIKE CONDITIONS...INCLUDING CONSIDERABLE SNOW ACCUMULATION AND LOCAL ICE/SLEET ACCUMULATION ACROSS THE NORTHERN/NORTHWEST PERIPHERY OF THE SURFACE WAVES MIGRATING ALONG THE EAST COAST AND WITHIN THE CANADIAN AIRMASS. THE INFUSION OF COLD CANADIAN AIR ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST (I-90/I-94 TO I-70 CORRIDORS) WILL LIKELY DELIVER ANOTHER ROUND OF WINTER-LIKE CONDITIONS IN THE DAY 4-5 CENTRAL US CYCLONE'S DEFORMATION PRECIPITATION SHIELD. AHEAD OF THE FRONT...WILD TEMPERATURE SWINGS...NOT UNUSUAL IN MARCH...WITH WARM BUT WINDY CONDITIONS. IN THE WEST...WELCOMED SPRING RAINFALL AND HIGH-ELEVATION SNOW IS A LIKELY CONCLUSION IN THIS PROGRESSIVE PATTERN. VOJTESAK