EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT FRI OCT 21 2016 VALID 12Z MON OCT 24 2016 - 12Z FRI OCT 28 2016 ...OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT... THE BEGINNING OF NEXT WEEK WILL FEATURE A HIGH-AMPLITUDE SYNOPTIC PATTERN WITH MEAN UPPER TROUGHING ACROSS THE WEST COAST AND NORTHEASTERN U.S...RESPECTIVELY. SANDWICHED IN BETWEEN THESE NEGATIVE HEIGHT ANOMALIES WILL BE AN EXPANSIVE RIDGE ENCOMPASSING MUCH OF THE CENTER OF THE COUNTRY. MOVING FORWARD IN TIME...THE DEEP UPPER LOW OFF THE PACIFIC NORTHWEST COAST GRADUALLY WEAKENS WITH SHEARING IMPULSES TRACKING THROUGH ALBERTA/SASKATCHEWAN. MEANWHILE...RESIDUAL NORTHWESTERLY FLOW IS EXPECTED OVER NEW ENGLAND AS THE UPPER TROUGH MOVES OFFSHORE. BY MID-WEEK...A MODEST PERTURBATION IN THE FLOW WILL TRACK FROM THE CENTRAL PLAINS INTO THE UPPER GREAT LAKES CARRYING A THREAT FOR HEAVY RAINFALL IN RESPONSE TO THE DEEPENING SURFACE CYCLONE. THIS SYSTEM SHOULD EVENTUALLY BECOME ABSORBED BY AMPLIFICATION IN THE NORTHERN STREAM OVER THE GREAT LAKES BY LATE IN THE FORECAST. WHILE UNCERTAIN GIVEN CONSIDERABLE MODEL SPREAD...GENERAL RIDGING SHOULD TAKE SHAPE ALONG THE MEXICAN BORDER OVER CA/AZ/NM WITH PRONOUNCED TROUGHING TOWARD 130W. SUCH A SCENARIO IS NOT SET IN STONE GIVEN CONSIDERABLE RUN-TO-RUN VARIABILITY NOTED IN RECENT SOLUTIONS. MULTI-DAY COMPARISONS INDICATE A MARKED SLOWING TREND...PARTICULARLY DURING THE PAST TWO CYCLES RELATIVE TO THE ONES PRECEDING IT. ALL SIGNS IN THE LATEST GUIDANCE DO SHOW MEAN RIDGING SETTING UP ACROSS THE SOUTHWESTERN U.S. AND FOUR CORNERS REGION DURING THE DAY 5-7...OCTOBER 26-28 TIME FRAME. OF COURSE AS MENTIONED PREVIOUSLY...RUN-TO-RUN CONTINUITY IS POOR WITH SOME RECENT SOLUTIONS FAVORING AMPLIFICATION IN THE NORTHERN STREAM CARRYING SHORTWAVE ENERGY INTO NORTHERN NM BY 28/1200Z. AN ENSEMBLE APPROACH WOULD BE BEST GIVEN THIS ASSESSMENT. LONGWAVE TROUGHS WILL BE PRESENT OVER THE EASTERN PACIFIC/WEST COAST, AS WELL AS, THE CANADIAN MARIATIMES AND THE U.S. EAST COAST...WITH A RIDGE OVER THE ROCKIES AND THE SURROUNDING PLAINS. THE RECENT TREND OF THE RIDGE BECOMING MORE AMPLIFIED AS THE WEEK PROGRESSES HAS CONTINUED WITH THE CURRENT MODEL SOLUTIONS, WHICH INCREASED CONFIDENCE. THE ECWMF SUGGESTS A SPLIT FLOW PATTERN BY THE END OF DAY 5 (WEDNESDAY) OVER THE MIDWEST/MISSISSIPPI VALLEY,WHEREAS THE REST OF THE DETERMINISTIC AND ENSEMBLE MEANS SHOW A SHORTWAVE LIFTING THROUGH THE MIDWEST/UPPER MIDWEST...WHICH HAS HAD A STRONGER SIGNAL DURING THE PAST FEW RUNS. WITH THAT IN MIND, CHOSE TO FOLLOW A SIMILAR APPROACH TO THE PREVIOUS FORECAST ON MODEL PREFERENCE. DAYS 3 THROUGH 5 (MONDAY THROUGH WEDNESDAY) CONSISTED OF A BLEND OF THE 00Z ECWMF AND ITS ENSEMBLE MEAN AND THE 06Z GFS AND ITS ENSEMBLE MEAN. FOR THURSDAY, THE ECWMF WAS REPLACED WITH A HEAVIER WEIGHTING OF THE 06Z GFS AND FOR FRIDAY, A HEAVIER WEIGHTING OF THE ENSEMBLE MEANS. WITH THE UPPER TROUGH DIGGING FURTHER SOUTH, PORTIONS OF CENTRAL AND SOUTHERN CALIFORNIA WILL LIKELY HAVE MEASURABLE RAINFALL. ...WEATHER HIGHLIGHTS/THREATS... THE BELOW NORMAL TEMPERATURES SHOULD BE CONFINED TO THE WEST AND EAST COASTS...RESPECTIVELY...GIVEN NEGATIVE HEIGHT ANOMALIES ANCHORING THESE REGIONS. HOWEVER...SUCH ANOMALIES WILL AT BEST BE 5 DEGREES BELOW CLIMATOLOGY GIVEN THE COLDEST AIR MASS REMAINS NORTH OF THE CANADIAN BORDER. MILD CONDITIONS SHOULD BE THE MORE PREVALENT WEATHER STORY FROM THE CENTRAL GREAT BASIN AND FOUR CORNERS REGION EASTWARD TO THE MS RIVER VALLEY. THE PERSISTENCE OF MEAN RIDGING OR GENERAL ZONAL FLOW WILL MAINTAIN ABOVE NORMAL READINGS WITH ANOMALIES POSSIBLY APPROACHING THE 10 TO 15 DEGREE RANGE. THE PRIMARY REGIONS OF RAINFALL DURING THE PERIOD WILL BE FROM THE CENTRAL PLAINS INTO THE GREAT LAKES IN RESPONSE TO THE ADVANCING AREA OF LOW PRESSURE. ELSEWHERE...THE PERSISTENT OF UPPER TROUGHING ACROSS THE EASTERN PACIFIC WILL MAINTAIN MID-LEVEL SOUTHWESTERLY FLOW FROM NORTHWESTERN CA UP INTO THE PACIFIC NORTHWEST. THIS SHOULD KEEP THE REGION WET WITH MUCH OF THE ACTION OVER THE FAVORED UPSLOPE TERRAIN WHERE MANY INCHES OF RAIN IS POSSIBLE. THERE IS A POTENTIAL FOR INCREASINGLY WET CONDITIONS ACROSS CENTRAL/SOUTHERN CA VERY LATE IN THE PERIOD DEPENDING ON THE POSITION OF THE OFFSHORE TROUGH. RUBIN-OSTER/RAUSCH/CAMPBELL