535
FXUS02 KWBC 121846
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 PM 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
NORTHWEST AND BRITISH COLUMBIA 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 15Z NATIONAL HURRICANE CENTER ADVISORY. THIS TRACK WOULD
BRING STRONG WINDS TO EASTERN 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. BUT THE TREND WILL BE TOWARD DRIER CONDITIONS
CONUS-WIDE BY EARLY NEXT WEEK. THE CENTRAL ROCKIES INTO
SOUTH-CENTRAL PLAINS WILL SEE COOL DAYTIME HIGHS LATE THIS WEEK
WHILE AREAS FROM THE PACIFIC NORTHWEST INTO THE 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 EXPECTED DIFFERENCES FOR TIMING AND TRACK BUT OVERALL THE
SOLUTION ENVELOPE IS GRADUALLY NARROWING. THE GEFS MEAN WAS A
GOOD MIDDLE GROUND FROM THE OVERNIGHT GUIDANCE 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, WHICH IS
TIED TO THE TRACK SENSITIVITY OF LEE. THE ENSEMBLE TREND HAS BEEN
TOWARD A STRONGER/DEEPER TROUGH INTO THE GREAT LAKES BY SUNDAY
INTO MONDAY, WHICH SHOULD HELP TO PUSH A FRONT OFF THE COAST IN
THE WAKE OF LEE. FOR PACIFIC FLOW INTO THE PACNW AND BRITISH
COLUMBIA EARLY NEXT WEEK, THE ENSEMBLES HAVE TRENDED A BIT QUICKER
IN RESPONSE TO STRONGER RIDGING OVER THE CENTRAL NORTH PACIFIC
BENEATH HIGH LATITUDE TROUGHING, FAVORING A QUICKER UPPER JET. A
BLENDED MODEL SOLUTION WAS PREFERRED THROUGHOUT THE PERIOD TO
ENCAPSULATE THE LATEST TIMING SHIFTS OVER THE NW AND EAST, BUT
WITH A PREFERENCE TOWARD THE 00Z GFS/06Z GEFS MEAN FOR LEE VS THE
MUCH FARTHER WEST 00Z ECMWF.
..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 TOO LOW TO DEPICT ANY EMBEDDED
SLIGHT RISK AREA (THOUGH TX WOULD BE FAVORED). 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 DUE TO UNCERTAINTY IN
RAINFALL AMOUNTS/RATES. 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, BUT MODEL QPF IS SOMEWHAT LACKLUSTER.
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 WARMING TREND TO OR SLIGHTLY ABOVE NORMAL. THE
EASTERN U.S. SHOULD SEE NEAR TO SOMEWHAT BELOW NORMAL HIGHS ON
MOST DAYS AS NW FLOW DOMINATES BEHIND LEE. HOT WEATHER WITH HIGHS
UP TO 5-10F ABOVE NORMAL MAY PERSIST OVER FAR SOUTHERN TEXAS
THROUGH FRIDAY (WHEN RECORD HIGHS ARE POSSIBLE) 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.
FRACASSO/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