318
FXUS02 KWBC 151832
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
231 PM 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 WITH VARIABLE PRECIPITATION CHANCES FROM THE PLAINS
TO THE APPALACHIANS WITH POTENTIAL BUT STILL UNCERTAIN EAST COAST
SURFACE LOW 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 GUIDANCE IS IN DECENT AGREEMENT ON THE BROADER DETAILS THROUGH
MOST OF THE MEDIUM-RANGE PERIOD, WHICH LOOKS TO CONTINUE AN
AMPLIFIED PATTERN FEATURING MEAN LONG-WAVE TROUGHING OVER THE
CENTRAL-EASTERN U.S. AND A RIDGE TO THE WEST. AS ONE SHORTWAVE
DEPARTS THE EAST COAST, MORE UPSTREAM SHORTWAVE ENERGY DROPPING
SOUTHWARD OVER THE PLAINS IN THE MEAN FLOW WILL REINFORCE THE
TROUGHING IN THE EAST. THE GFS HAS BEEN CONSISTENT RUN-TO-RUN WITH
SOME OF THIS ENERGY DROPPING FURTHER SOUTHWARD OVER TEXAS WHILE
THE 00Z CMC IS LESS AGGRESSIVE, KEEPING THIS ENERGY FURTHER NORTH,
WITH THE 00Z ECMWF IN BETWEEN THE OTHER SOLUTIONS. ANOTHER TREND
ACROSS THE GUIDANCE HAS BEEN FOR A BIT LESS AMPLIFICATION AS
ADDITIONAL UPSTREAM ENERGIES DO NOT DEEPEN THE LONG-WAVE TROUGH AS
FAR SOUTH INTO THE GULF MID- TO LATE PERIOD COMPARED TO EARLIER
RUNS. IN THIS CASE, THE 00Z ECMWF IS STILL ON THE MORE AGGRESSIVE
SIDE OF THE ENVELOPE WITH A LARGER DEGREE OF RUN-TO-RUN
VARIABILITY IN THE GFS, WHICH HAS TRENDED LESS AMPLIFIED IN THE
00Z/06Z RUNS THAN THE ECMWF AFTER SHOWING A DEEPER, CLOSED LOW
DEVELOPING OVER THE SOUTHEAST IN PREVIOUS RUNS. THIS WILL HAVE
IMPLICATIONS ON THE POTENTIAL FOR SUBSEQUENT COASTAL LOW
DEVELOPMENT AS THE TROUGH AXIS SHIFTS EASTWARD ALONG THE EAST
COAST, AS THE 06Z GFS FOR EXAMPLE HAS TRENDED FASTER AND FURTHER
NORTHWARD BY THE END OF THE PERIOD, FAVORING SURFACE LOW
DEVELOPMENT FURTHER NORTHWESTWARD AND INLAND IN TANDEM WITH AN
UPPER-LEVEL CLOSED LOW DEVELOPING IN THE VICINITY OF THE LOWER
GREAT LAKES/INTERIOR NORTHEAST/SOUTHEASTERN CANADA. THE ECMWF HAS
BEEN MORE CONSISTENT IN TAKING A SURFACE LOW NORTHWARD ALONG THE
COAST. THE VARIED SOLUTIONS HAVE AN IMPACT ON PRECIPITATION
CHANCES THROUGH THE PERIOD, WITH DRIER CONDITIONS WITH SOUTHWEST
EXTENT OVER THE PLAINS/MISSISSIPPI VALLEY IN THE 00Z CMC COMPARED
TO THE ECMWF AND THE 00/06Z GFS. THE ECMWF ALSO FAVORS HIGHER
RAINFALL CHANCES ALONG THE COAST OF THE NORTHEAST WITH THE COASTAL
LOW AS COMPARED TO THE INTERIOR NORTHEAST IN THE GFS. OTHERWISE,
ALTHOUGH THERE ARE SOME TIMING DIFFERENCES, THE GUIDANCE IS IN
AGREEMENT THAT AN UPSTREAM TROUGH APPROACHING THE WEST COAST
SHOULD BEGIN TO BREAK DOWN THE RIDGE OVER THE WEST BY NEXT
WEEKEND.
THE UPDATED WPC FORECAST USES A COMPOSITE BLEND OF THE
DETERMINISTIC GUIDANCE (00Z ECMWF/CMC/UKMET AND 06Z GFS) EARLY IN
THE PERIOD, FAVORING THE 00Z ECMWF WHICH FALLS IN THE MIDDLE OF
THE SOLUTIONS WITH RESPECT TO THE EVOLUTION OF THE TROUGHING OVER
THE CENTRAL-EASTERN U.S. A CONTRIBUTION FROM THE 00Z ECENS/GEFS
MEANS IS ADDED TOWARDS THE END OF THE PERIOD AS RUN-TO-RUN
VARIABILITY AMONG ALL THE GUIDANCE, PARTICULARLY THE GFS,
INCREASES FOR THE EASTERN TROUGH AS WELL AS THE SYSTEM UPSTREAM
ALONG THE WEST COAST. THE CONTRIBUTION FOR THE GFS IS SPLIT
BETWEEN THE 00Z AND 06Z RUNS LATE TO BETTER CAPTURE THE
UNCERTAINTY IN THE EVOLUTION OF THE PATTERN AS THIS VARIABILITY
INCREASES.
..WEATHER/HAZARDS HIGHLIGHTS
AN INITIAL SYSTEM PROGRESSING EASTWARD ACROSS THE PLAINS SHOULD
SPREAD MOSTLY LIGHT RAINFALL ACROSS PARTS OF THE NORTHERN PLAINS
THROUGH THE MIDWEST. AS UPSTREAM SHORTWAVE ENERGY AMPLIFIES AND
SHARPENS THE UPPER TROUGH, RAIN SHOULD EXPAND SOUTHWARD OVER THE
EASTERN U.S. WITH SOMEWHAT HIGHER (BUT LIKELY NOT EXCESSIVE)
LOCALIZED TOTALS POSSIBLE, PARTICULARLY FOR THE TENNESSEE
VALLEY/SOUTHERN APPALACHIANS. 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. A COMPOSITE BLEND OF THE
CURRENT GUIDANCE WOULD FAVOR RAINFALL AND WINDS OVER AT LEAST THE
NORTHEAST, BUT VARIABLE DIFFERENCES IN THE DEVELOPMENT AND TRACK
OF THE SURFACE LOW(S) 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 AND INTO THE NORTHERN ROCKIES
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.
PUTNAM/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page