227
FXUS02 KWBC 150701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SUN OCT 15 2023
VALID 12Z WED OCT 18 2023 - 12Z SUN OCT 22 2023
..OVERVIEW
THE FORECAST HAS BEEN CONSISTENT WITH THE GENERAL THEME OF A
STRONG MID-LATE WEEK UPPER RIDGE OVER THE WESTERN U.S. SUPPORTING
DOWNSTREAM TROUGH AMPLIFICATION INTO THE EAST BY THE END OF THE
WEEK. HOWEVER GUIDANCE HAS VARIED FOR IMPORTANT TROUGH DETAILS
WITHIN AN OVERALL MULTI-DAY TREND TOWARD A MORE PROGRESSIVE AND
OPEN FEATURE THAT FAVORS LESS PRECIPITATION TO THE WEST OF THE
APPALACHIANS, WITH POTENTIAL BUT STILL UNCERTAIN EAST COAST
SURFACE DEVELOPMENT BY NEXT WEEKEND NOW PROVIDING THE MAIN
POSSIBILITY FOR HEAVIER TOTALS OVER THE NORTHEAST. THE WESTERN
RIDGE SHOULD WEAKEN NOTICEABLY AND DRIFT A LITTLE EASTWARD NEXT
WEEKEND AS A PACIFIC SHORTWAVE AND LEADING FRONT REACH THE WEST
COAST WITH SOME RAINFALL FOR THE PACIFIC NORTHWEST. THE FORECAST
PATTERN WILL FAVOR ABOVE NORMAL TEMPERATURES OVER THE WEST INTO
THE PLAINS MID-LATE WEEK, WITH A MODERATING TREND NEAR THE WEST
COAST NEXT WEEKEND AS THE TROUGH/FRONT ARRIVE. WITH THE EXCEPTION
OF ABOVE NORMAL READINGS OVER NEW ENGLAND, MOST OF THE EAST SHOULD
SEE NEAR TO BELOW AVERAGE HIGHS DURING THE PERIOD.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 12Z/18Z MODELS AND ENSEMBLE MEANS OFFERED A REASONABLE
COMPOSITE OVERALL, REFLECTING THE AFOREMENTIONED TREND TOWARD
KEEPING THE AMPLIFYING CENTRAL INTO EASTERN U.S. UPPER TROUGH OPEN
AND MORE PROGRESSIVE THROUGH LATE WEEK. RECENTLY SOME GFS RUNS
AND GEFS MEMBERS HAVE REPRESENTED THE SOUTHWESTERN SIDE OF THE
SPREAD FOR ANY POTENTIAL ELONGATION OF THE TROUGH, BUT THE 18Z GFS
AND NOW THE NEW 00Z RUN REPRESENT THE ONGOING TREND TOWARD THE
OPEN AND PROGRESSIVE TROUGH THROUGH AT LEAST FRIDAY. AN EMBEDDED
COMPACT UPPER LOW COULD TRACK ACROSS THE NORTHERN TIER BUT IT
SHOULD BE FAIRLY TRANSIENT. THERE IS INCREASING DETAIL
UNCERTAINTY GIVEN THE SPREAD/LOWER PREDICTABILITY FOR HOW PACIFIC
ENERGY WILL ROUND THE WESTERN RIDGE AND FEED INTO THE EASTERN
TROUGH LATE WEEK INTO THE WEEKEND, BUT THERE IS A FAIRLY COMMON
THEME IN THE GUIDANCE FOR LOW PRESSURE TO DEVELOP NEAR THE
NORTHERN MID-ATLANTIC/SOUTHERN NEW ENGLAND BY AROUND
FRIDAY-SATURDAY AND DEEPEN AS IT TRACKS NORTHWARD INTO SUNDAY
WHILE THE CORE OF THE UPPER TROUGH (WITH POSSIBLE LOW) REACHES
EASTERN CANADA/NEW ENGLAND. LATEST CMC RUNS ARE SOMEWHAT ON THE
NORTHERN SIDE OF THE SPREAD WITH THIS SYSTEM BY SUNDAY WHILE THE
12Z ECMWF WAS SOMEWHAT SOUTH. LOW CONFIDENCE FOR SPECIFICS OF
SHORTWAVES FEEDING INTO THE EASTERN TROUGH EXTENDS TO ANY
CORRESPONDING WAVES/FRONTS DROPPING SOUTHEASTWARD OVER THE CENTRAL
U.S. SOLUTIONS FOR THE SHORTWAVE REACHING THE WEST COAST BY NEXT
SUNDAY SHOW BETTER THAN AVERAGE CLUSTERING FOR FORECASTS THAT FAR
OUT IN TIME. A 12Z/18Z OPERATIONAL MODEL BLEND EARLY IN THE
PERIOD AND THEN A TRANSITION TO A COMBINATION OF 18Z GEFS/12Z
ECENS MEANS AND 12Z/18Z MODELS PROVIDED A GOOD INTERMEDIATE
SOLUTION THROUGH THE PERIOD, INCLUDING THE DESIRED MODEL-MEAN
COMPROMISE FOR STRENGTH/TRACK OF THE STORM SYSTEM POTENTIALLY
AFFECTING THE NORTHEAST NEXT WEEKEND.
..WEATHER/HAZARDS HIGHLIGHTS
THE SYSTEM INITIALLY PROGRESSING EASTWARD FROM THE PLAINS SHOULD
SPREAD MOSTLY LIGHT RAINFALL ACROSS PARTS OF THE NORTHERN PLAINS
THROUGH THE MIDWEST. AS THE SUPPORTING UPPER TROUGH AMPLIFIES AND
SHARPENS, RAIN SHOULD EXPAND SOUTHWARD OVER THE EASTERN U.S. WITH
SOMEWHAT HIGHER (BUT LIKELY NOT EXCESSIVE) LOCALIZED TOTALS
POSSIBLE. COVERAGE AND INTENSITY OF RAINFALL, AS WELL AS STRENGTH
OF WINDS, FROM THE MID-ATLANTIC INTO THE NORTHEAST NEXT WEEKEND
WILL DEPEND ON SPECIFICS OF THE DEEPENING SURFACE LOW THAT MAY
AFFECT THE REGION. THE CURRENT MAJORITY GUIDANCE CLUSTER WOULD
SUPPORT THE IDEA OF SOME ENHANCED RAINFALL AND WINDS OVER AT LEAST
THE NORTHEAST, BUT A SLIGHT DIFFERENCE IN LOW TRACK COULD CHANGE
THE PRECIPITATION FORECAST SIGNIFICANTLY. GIVEN THE GUIDANCE
CHANGES OVER THE PAST FEW DAYS FOR EVOLUTION OF THE
CENTRAL-EASTERN U.S. UPPER TROUGH, IT WILL TAKE SOME STABILIZATION
OF THE GUIDANCE OVER COMING RUNS TO GAIN MUCH CONFIDENCE IN NEXT
WEEKEND'S DETAILS. OVER THE NORTHWEST, THE OLYMPIC PENINSULA MAY
SEE SOME RAIN LINGER INTO WEDNESDAY WITH HEAVIEST TOTALS STAYING
FOCUSED OVER VANCOUVER ISLAND. THE UPPER TROUGH/SURFACE FRONT
REACHING THE WEST COAST DURING THE WEEKEND SHOULD EXPAND COVERAGE
OF LIGHT TO PERHAPS LOCALLY MODERATE RAINFALL OVER THE PACIFIC
NORTHWEST AT THAT TIME.
STRONG UPPER RIDGING WILL SUPPORT EXPANSION OF WELL ABOVE NORMAL
TEMPERATURES FROM THE WESTERN U.S. INTO THE PLAINS DURING
WEDNESDAY-FRIDAY. BY NEXT WEEKEND ONE OR MORE FRONTS DROPPING
SOUTHEAST OVER THE CENTRAL U.S. MAY DENT THE EASTERN EXTENT OF THE
VERY WARM TEMPERATURES WHILE THE UPPER TROUGH/FRONT PUSHING INTO
THE WEST COAST SHOULD BRING HIGHS DOWN TO NEAR OR SLIGHTLY BELOW
NORMAL LEVELS OVER THAT REGION. GREATEST ANOMALIES SHOULD BE IN
THE PLUS 15-20F RANGE FOR HIGHS OVER THE NORTHERN ROCKIES INTO
PORTIONS OF THE HIGH PLAINS THURSDAY-SATURDAY. EXPECT THE BEST
POTENTIAL FOR DAILY RECORDS TO BE OVER THE WEST DURING THURSDAY
INTO EARLY SATURDAY, WITH RECORD WARM LOWS TENDING TO BE MORE
NUMEROUS THAN RECORD HIGHS. DURING NEXT WEEKEND THE HIGHS OVER
PARTS OF TEXAS/NEW MEXICO COULD CHALLENGE RECORD HIGHS. FARTHER
EAST, THE GULF COAST AND SOUTHEAST WILL SEE BELOW NORMAL
TEMPERATURES LINGER THROUGH MIDWEEK AND THEN UPPER TROUGHING
AMPLIFYING INTO THE EAST SHOULD EXPAND THE COVERAGE OF MODERATELY
BELOW NORMAL HIGHS OVER THE EAST BY FRIDAY-SUNDAY. NEW ENGLAND
SHOULD BE SOMEWHAT ABOVE NORMAL FROM LATE WEEK INTO SATURDAY
THOUGH.
RAUSCH
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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