706
FXUS02 KWBC 120659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT TUE SEP 12 2023
VALID 12Z FRI SEP 15 2023 - 12Z TUE SEP 19 2023
...POTENTIAL FOR HURRICANE LEE TO BRING RAINFALL AND STRONG WINDS
TO PARTS OF NEW ENGLAND...
...HEAVY RAINFALL THREAT FOR THE SOUTH-CENTRAL ROCKIES/PLAINS
LIKELY TO TAPER OFF AFTER LATE THIS WEEK...
..OVERVIEW
GUIDANCE CONTINUES TO SHOW A STRONG UPPER RIDGE BUILDING INTO THE
WEST WHILE TROUGHING AMPLIFIES INTO THE EAST-CENTRAL U.S. DURING
THE FRIDAY-SUNDAY TIME FRAME. THE WESTERN RIDGE SHOULD GRADUALLY
WEAKEN AND DRIFT EASTWARD AS NORTH PACIFIC INTO CANADA FLOW DRIFTS
SOUTHWARD WITH TIME, POSSIBLY BRINGING THE SOUTHERN PERIPHERY OF A
MEAN TROUGH INTO THE FAR NORTHWESTERN U.S. EARLY NEXT WEEK. AT
THE SAME TIME A WEAK UPPER LOW MAY APPROACH CALIFORNIA. SOME
TROUGHING SHOULD LINGER OVER THE EAST BUT IN WEAKER FASHION BY
NEXT TUESDAY. MEANWHILE SOLUTIONS DISPLAY TYPICAL SPREAD BUT ARE
GRADUALLY COMING CLOSER TOGETHER FOR THE SPEED AND TRACK OF
HURRICANE LEE THAT SHOULD PROGRESS NORTHWARD OVER THE WESTERN
ATLANTIC THIS WEEK AND REACH A POSITION CLOSE TO THE SOUTHERN TIP
OF NOVA SCOTIA BY LATE SATURDAY PER THE 03Z NATIONAL HURRICANE
CENTER ADVISORY. THIS TRACK WOULD BRING STRONG WINDS TO NEW
ENGLAND AND SIGNIFICANT RAINFALL TO PARTS OF MAINE. INITIAL
WESTERN U.S./PLAINS SHORTWAVE ENERGY ALONG WITH EASTERLY LOW LEVEL
FLOW OVER PARTS OF THE SOUTHERN PLAINS WILL HELP TO GENERATE AREAS
OF RAIN AND THUNDERSTORMS OVER PARTS OF THE CENTRAL-SOUTHERN
ROCKIES/PLAINS LATE THIS WEEK FOLLOWED BY A DRIER TREND. THIS
ENERGY AND NORTHERN STREAM FLOW FEEDING INTO THE EAST-CENTRAL U.S.
TROUGH, ALONG WITH A LEADING FRONT, MAY GENERATE SOME AREAS OF
RAINFALL OVER THE CENTRAL/EASTERN U.S. THE CENTRAL ROCKIES INTO
SOUTH-CENTRAL PLAINS WILL SEE COOL DAYTIME HIGHS LATE THIS WEEK
WHILE AREAS FROM THE PACIFIC NORTHWEST INTO NORTHERN HIGH PLAINS
WILL SEE ABOVE NORMAL HIGHS THROUGH THE WEEKEND FOLLOWED BY A
COOLING TREND FROM WEST TO EAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
REGARDING HURRICANE LEE, MODEL AND ENSEMBLE GUIDANCE CONTINUES TO
SHOW SOME MEANINGFUL DIFFERENCES FOR TIMING AND TRACK BUT OVERALL
THE SOLUTION ENVELOPE IS GRADUALLY NARROWING. FOR THE FORECAST
BASED ON 12Z/18Z GUIDANCE, THE 12Z ECMWF/UKMET WERE GENERALLY THE
CLOSEST TO THE PAST COUPLE NATIONAL HURRICANE CENTER ADVISORIES.
MODELS WILL LIKELY CONTINUE TO SHUFFLE AROUND SOME IN COMING RUNS.
FARTHER WEST THERE ARE STILL SOME MEANINGFUL DETAIL DIFFERENCES
WITH EXACTLY HOW THE AMPLIFYING EAST-CENTRAL U.S. TROUGH WILL
AMPLIFY. LATELY THERE HAS BEEN A FAIR NUMBER OF SOLUTIONS
SUGGESTING AN INITIAL SOUTHERN CANADA UPPER LOW MAY WOBBLE INTO
THE GREAT LAKES, AND THE LATEST GEFS MEAN/12Z CMCENS ARE HINTING
AT THAT IDEA OR WITH A LOW TRACK JUST A BIT NORTHWARD. THE
ECMWF/ECMWF MEAN THROUGH 12Z KEEP THE TROUGH OPEN AND MORE
PROGRESSIVE. AT THIS TIME PREFER AN INTERMEDIATE IDEA OF SHOWING
AN UPPER LOW BUT WITH A TRACK SLIGHTLY NORTH OF THE GREAT LAKES.
THE NEW 00Z ECMWF SHOWS SOME TRENDS TOWARD THE OTHER GUIDANCE.
FOR PACIFIC FLOW PROGRESSING INTO CANADA AND NORTHERN TIER U.S.,
THE 18Z/00Z GFS RUNS ARE EXTREME VERSUS OTHER SOLUTIONS FOR UPPER
ENERGY CONTINUING ALONG THE U.S.-CANADIAN BORDER BY NEXT
MONDAY-TUESDAY. THE 00Z GFS STRAYS WEST OF CONSENSUS FOR THE
UPPER LOW APPROACHING CALIFORNIA EARLY NEXT WEEK.
IN ORDER TO COME UP WITH THE BEST STARTING POINT FOR FEATURES OF
INTEREST, THE UPDATED FORECAST STARTED WITH A BLEND OF 12Z
ECMWF/GFS/UKMET EARLY IN THE PERIOD AND THEN TRANSITIONED TOWARD A
LATE-PERIOD BLEND OF 60 PERCENT TOTAL WEIGHT OF THE 18Z GEFS AND
12Z ECENS/CMCENS MEANS WITH 40 PERCENT INPUT FROM THE 12Z
ECMWF/GFS.
..WEATHER/HAZARDS HIGHLIGHTS
THE DAY 4 EXCESSIVE RAINFALL OUTLOOK THAT COVERS FRIDAY-FRIDAY
NIGHT MAINTAINS A MARGINAL RISK AREA OVER PARTS OF THE
CENTRAL/SOUTHERN PLAINS, WITH ONLY SOME ADJUSTMENTS TO REFLECT THE
LATEST ARRAY OF PLAUSIBLE GUIDANCE. INITIAL WESTERN U.S./PLAINS
SHORTWAVE ENERGY AND EASTERLY LOW LEVEL UPSLOPE FLOW OVER SOME
AREAS, ALONG WITH A FRONT DROPPING INTO THE CENTRAL PLAINS, SHOULD
CONTRIBUTE TO RAIN AND THUNDERSTORMS FROM THE CENTRAL PLAINS INTO
PARTS OF TEXAS. SIGNALS CONTINUE TO BE FAIRLY DIFFUSE WITH
RESPECT TO EXACTLY WHERE THE BEST FOCUS OF HIGHEST RAINFALL TOTALS
WILL BE, SO CONFIDENCE REMAINS TO LOW TO DEPICT ANY EMBEDDED
SLIGHT RISK AREA. THE DAY 5 ERO (SATURDAY-SATURDAY NIGHT) DEPICTS
A SLIGHT RISK AREA OVER DOWNEAST MAINE AND VICINITY, ALONG WITH A
MARGINAL RISK TO THE WEST, REFLECTING THE POTENTIAL FOR HEAVY
RAINFALL IN ASSOCIATION WITH LEE BASED ON THE CURRENT FORECAST
TRACK. CURRENTLY NO OTHER RISK AREAS ARE DEPICTED IN THE DAY 5
OUTLOOK. AREAS OF INTEREST FOR MONITORING INCLUDE SOUTHERN TEXAS
(SOME LINGERING MOISTURE AND INSTABILITY BUT INCONSISTENT GUIDANCE
SIGNALS FOR RAINFALL) ALONG WITH THE TENNESSEE VALLEY AND
SURROUNDING AREAS (WIDE RANGE OF GUIDANCE QPFS AND MIXED SIGNALS
FOR MOISTURE ANOMALIES OVER THE REGION).
SOME RAIN/THUNDERSTORMS SHOULD CONTINUE OVER PARTS OF THE SOUTHERN
ROCKIES/PLAINS AND PERHAPS THE SOUTH BEYOND EARLY SATURDAY BUT
LIKELY WITH LESS COVERAGE AND LIGHTER TOTALS. MEANWHILE A FRONT
SETTLING OVER THE FLORIDA PENINSULA MAY PRODUCE ONE OR MORE DAYS
OF RAIN OVER THAT REGION. OVER NEW ENGLAND, EXPECT ANY LINGERING
RAIN FROM THE MIDWEEK SYSTEM TO DEPART ON THURSDAY. CONTINUE TO
MONITOR NATIONAL HURRICANE CENTER PRODUCTS REGARDING THE TRACK OF
HURRICANE LEE AND POTENTIAL EFFECTS ON NEW ENGLAND AND THE
CANADIAN MARITIMES BY LATE WEEK AND THE WEEKEND. UNCERTAINTY WITH
DETAILS FOR THE UPPER TROUGH EVOLVING OVER THE EASTERN HALF OF THE
COUNTRY DURING THE WEEKEND AND EARLY NEXT WEEK KEEPS CONFIDENCE
LOW FOR WHAT THE SURFACE PATTERN MAY LOOK LIKE ALONG WITH ANY
AREAS OF RAINFALL, THOUGH INTO FRIDAY OR SO A FRONT REACHING THE
UPPER MIDWEST COULD PRODUCE SOME AREAS OF MOSTLY LIGHT RAIN.
A WAVY COLD FRONT PROGRESSING FROM THE MIDWEST THROUGH THE EAST
MAY PRODUCE SOME AREAS OF RAINFALL OF VARYING INTENSITY OVER THE
COURSE OF THE PERIOD. THE FLORIDA PENINSULA SHOULD BE FAIRLY WET
THROUGH THE PERIOD DUE TO A PERSISTENT FRONT OVER THE AREA. A
LITTLE MEASURABLE RAINFALL COULD REACH THE NORTHERN PACIFIC
NORTHWEST EARLY NEXT WEEK AS A FRONT MOVES IN.
CLOUDS AND RAINFALL FROM THE CENTRAL ROCKIES INTO SOUTH-CENTRAL
PLAINS WILL KEEP DAYTIME HIGHS UP TO 10-15F OR SO BELOW NORMAL ON
FRIDAY BEFORE A WARM TREND TO OR SLIGHTLY ABOVE NORMAL. THE
EASTERN U.S. SHOULD SEE NEAR TO SOMEWHAT BELOW NORMAL HIGHS ON
MOST DAYS. HOT WEATHER WITH HIGHS UP TO 5-10F ABOVE NORMAL MAY
PERSIST OVER FAR SOUTHERN TEXAS THROUGH FRIDAY BEFORE A COOLER
TREND. THE UPPER RIDGE BUILDING INTO THE WEST WILL SUPPORT HIGHS
10F OR MORE ABOVE NORMAL OVER THE PACIFIC NORTHWEST FROM LATE WEEK
THROUGH THE WEEKEND, WITH A BROADER AREA OF MORNING LOWS 5-15F
ABOVE NORMAL ACROSS THE WEST. SOME OF THIS WARMTH SHOULD EXTEND
INTO THE NORTHERN HIGH PLAINS SATURDAY ONWARD WHILE THE PACIFIC
NORTHWEST WILL LIKELY TREND COOLER EARLY NEXT WEEK, REACHING NEAR
NORMAL BY NEXT TUESDAY AS A PACIFIC FRONT APPROACHES/ARRIVES.
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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