EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 219 AM EDT TUE SEP 23 2014 VALID 12Z FRI SEP 26 2014 - 12Z TUE SEP 30 2014 ...OVERVIEW... A BROAD UPPER-LEVEL RIDGE WILL GRADUALLY SETTLE OVER THE OHIO VALLEY...MIGRATING EAST-NORTHEASTWARD FROM THE WEST CENTRAL AND SOUTHERN PLAINS DURING THIS MEDIUM RANGE PERIOD. AND A PACIFIC TROUGH WILL PREVAIL ALONG THE WEST COAST EARLY IN THE PERIOD...THEN MIGRATE ACROSS THE INTERMOUNTAIN WEST INCLUDING THE SOUTHERN ROCKIES BY PERIOD'S END. ...UNCERTAINTY ASSESSMENT... STILL A TROUBLESOME FORECAST FOR THE SOUTHEAST...LOWER MS VALLEY AND OZARKS AFTER DAY 4. THE LINGERING MID-LEVEL DISTURBANCE INVOF THE OZARKS ATTEMPTS TO DRAW UPON THE LOW-LEVEL MOISTURE TAP AND CAPITALIZE ON A WEAKNESS IN THE SOUTHWESTERN PERIPHERY OF THE SURFACE-TO-700 MB LAYER RIDGE PLANTED DOWNSTREAM OVER THE OHIO VALLEY AND DELMARVA. COUPLED WITH A STATIONARY BOUNDARY IN THE NORTHERN GULF OF MEXICO---THE PRESENCE AND PERSISTENT OF THIS SURFACE RIDGE OVER THE EAST CENTRAL STATES AND WESTERN ATLANTIC OCEAN WILL PROVIDE A RATHER CONSISTENT EASTERLY TO NORTHEASTERLY FLOW ACROSS THE SOUTHEASTERN STATES AND INTO THE GULF OF MEXICO. CONCERNING QPF... THE DETERMINISTIC 22/12Z UKMET WOULD BE THE MOST AGGRESSIVE SOLUTION---WITH ITS 1006MB SFC LOW INVOF NORTHEAST MS AT 28/12Z. THE 22/12Z ECMWF AND 22/18Z GFS LIKE THE IDEA OF LOWER PRESSURE DEVELOPMENT IN THE MS DELTA...BUT DELAY THE DEVELOPMENT OF AN ORGANIZED AND 'TRACK-ABLE' SURFACE WAVE A GOOD 24-36 HOURS LATER (INTO THE DAY 6 PERIOD) BEFORE ACCOMPLISHING THE SAME TASK. THIS SUGGESTS SEVERAL THINGS---NAMELY THE EASTERLY FLOW WILL HAVE A PROPENSITY FOR GENERATING WEAK CYCLONIC ALONG THE NORTHERN FRINGES OF THE STATIONARY FRONT AND TWO...THERE WILL BE SOME INTERACTION AND POSSIBLE PHASING WITH RESIDUAL VORTICITY MEANDERING OVER THE LOWER MISSOURI VALLEY DURING THIS CHALLENGING DAY 5 FORECAST. THE SYNOPTIC-SCALE PATTERN ALLOWS FOR IT...AND LEAVES THE WESTERN PORTION OF THE GULF WIDE OPEN FOR ANY SUBTLE WAVE TO MAKE THE NORTHWARD TURN ALONG THE WESTERN PERIPHERY OF THE SURFACE RIDGE. THE PATTERN WILL BE A SLOWLY-EVOLVING ONE. A QUICK LOOK AT THE 00Z CYCLE GUIDANCE AT PRESS TIME---THE GFS/UKMET AND CANADIAN ALL SUGGEST THE SURFACE RIDGE PATTERN ALONG THE EAST COAST REMAINS IN PLACE. ...MODEL PREFERENCES... FOR THE LOWER 48...CAN SEE WHERE A BLEND OF THE 22/12Z ECENS-NAEFS-GEFS WILL WORK SINCE IT KEEPS THE UPPER-LEVEL TROUGH INTACT DURING ITS MIGRATION ACROSS 35N-40N AND MORE IMPORTANTLY---THE UPPER-LEVEL RIDGE PLANTED IN THE EASTERN US. IT DOES NOT RESOLVE THE QPF DIFFERENCES. FOR DAY 3-4 ACROSS THE WEST COAST...THE DETERMINISTIC 22/12Z UKMET...CANADIAN AND 22/18Z GFS WERE TIGHTLY CLUSTERED WITH THE MAJORITY OF THE EC ENSEMBLE MEMBERS--- SIGNALING THE PRESENCE OF A CLOSED 500MB CIRCULATION WITHIN THE BASE OF THE UPPER-LEVEL TROUGH. THE DETERMINISTIC 22/12Z ECMWF SUPPORTS THE DEVELOPMENT OF A NEGATIVE-TILT TROUGH EVOLUTION IN THE SOUTHEASTERN GULF OF ALASKA THROUGH TIME RATHER THAN FOLLOW THE CONSENSUS...STRAYING AWAY FROM ITS OWN PREVIOUS CLOSED LOW SOLUTION THE PREVIOUS TWO CYCLES. THE 22/12Z DETERMINISTIC ECMWF IS THE LEAST LIKELY SOLUTION AND CAN'T IMAGINE IT BLASTING SUCH A STRONG SHORTWAVE INTO AND THROUGH THE SURFACE RIDGE BETWEEN DAY 4-6...UNLESS ITS SOURCE REGION IS THE BAY OF CAMPECHE. DO THINK THE PACIFIC TROUGH HAS LITTLE OPTION BUT TO SLOWDOWN THROUGH TIME AND MY DAY 7 SURFACE GRAPHIC ANTICIPATES THIS TO SOME EXTENT WITH A GRADUAL 'SEEPAGE' OF COOLER CANADIAN AIR ALONG THE EAST SIDE OF THE MONTANA AND WYOMING PORTION OF THE CONTINENTAL DIVIDE. ALONG WITH THE SLOWER PROGRESSION OF THE UPPER-LEVEL TROUGH...A SUCCESSION OF SHORTWAVES EJECTING NORTHEASTWARD OUT OF THE BASE OF THE 500MB TROUGH. THE KEY THOUGH---IS SEPARATION---WITH THE UPPER-LEVEL TROUGH REMAINING LOCKED IN ACROSS THE CENTRAL ROCKIES INTO DAY 7 AND NORTHWEST OF THE BETTER GULF MOISTURE. THE 'OPEN' WESTERN GULF OF MEXICO BEING MORE OF A SUB-SYNOPTIC SCALE MOISTURE SOURCE FOR WEAK EASTERLY WAVE/INVERTED TROUGH MIGRATION ALONG THE SOUTHERN FLANKS OF THE SURFACE RIDGE....ACROSS THE NORTHERN GULF OF MEXICO AND BENDING NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE SURFACE RIDGE. THIS IS ESSENTIALLY WHY I CAN'T PUT MUCH STOCK IN A BLEND OF THE THREE 22/12Z MEANS WITH RESPECT TO DETERMINISTIC QPF ALONG THE SOUTHERN PERIPHERY OF THE SURFACE RIDGE. ...SENSIBLE WEATHER HIGHLIGHTS... THE HIGHEST PROBABILITIES FOR PRECIPITATION WILL CONTINUE TO BE IN THE SOUTHEASTERN QUARTER OF THE NATION AND ALONG THE STATIONARY BOUNDARY. IN THE WEST...HIGHER PROBABILITIES OF PRECIPITATION WILL BE LOCATED ALONG THE NORTHEAST QUADRANT OF THE UPPER-LEVEL TROUGH AND INVOF THE EMBEDDED 500MB CIRCULATION MIGRATING ACROSS THE GREAT BASIN...INTERMOUNTAIN WEST AND CONTINENTAL DIVIDE. THE INFLUENCE OF THE UPPER-LEVEL RIDGE OVER THE OHIO VALLEY AND WESTWARD PROGRESSION OF THE SURFACE RIDGE WILL KEEP THE NORTHERN PLAINS...GREAT LAKES...OHIO VALLEY AND NEW ENGLAND GENERALLY CLEAR/DRY WITH VERY MILD AND/OR PLEASANT DAYTIME HIGHS. VOJTESAK