949
FXUS61 KBOX 240107
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
907 PM EDT WED JUL 23 2008
SYNOPSIS
A SLOW MOVING COLD FRONT WILL BRING HEAVY RAINFALL AND POSSIBLE
FLOODING TO PORTIONS OF SOUTHERN NEW ENGLAND THROUGH THURSDAY
EVENING. A SECOND COLD FRONT WILL APPROACH LATE THIS WEEKEND WITH
ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS POSSIBLE. UNSETTLED
WEATHER WILL REMAIN ACROSS THE REGION THROUGH EARLY NEXT WEEK.
NEAR TERM /UNTIL 4 AM THURSDAY MORNING/
THREAT OF SEVERE THUNDERSTORMS SEEMS TO BE DIMINISHING SLIGHTLY.
CURRENT PLAN IS TO KEEP THE THUNDERSTORM WATCH IN EFFECT UNTIL 10 PM.
WILL REEVALUATE THIS WATCH IN THE NEXT 30 MINUTES.
VERY HEAVY RAINFALL CONTINUES WITH THESE SHOWERS AND THUNDERSTORMS...
WITH LOCALIZED URBAN OR FLASH FLOODING LIKELY.
SHORT TERM /4 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/
ANOMALOUS LATE JULY PATTERN WITH UPPER LOW AMPLIFYING ACROSS GT
LAKES AND ACQUIRING SOME NEGATIVE TILT. SLOW MOVING COLD FRONT WILL
BE FOCUS FOR VERY HEAVY RAINFALL...BUT LOCALLY HEAVY RAIN ALSO
POSSIBLE EAST THE BOUNDARY AS WE ARE WITNESSING CURRENTLY IN HIGH
PWAT AIRMASS.
GFS/NAM/ECMWF AND ALL GEFS ENSEMBLE MEMBERS IN REASONABLE AGREEMENT
ON AXIS OF HEAVIEST RAIN SETTING UP ACROSS OUR W ZONES...ESPECIALLY
CT VALLEY AND BERKSHIRES. AMOUNTS DIFFER BUT GENERAL LOCATION IS
SIMILAR SO WE HAVE ENOUGH CONFIDENCE TO ISSUE FLOOD WATCH FOR W
ZONES AND EXTENDING IT EWD TO S NH...ORH COUNTY AND RI/CT BORDER.
HIGHEST CONFIDENCE OF FLOODING RAINS WILL BE OVER CT VALLEY AND
BERKSHIRES.
NAM INDICATING UP TO 10 INCHES ACROSS W ZONES WHILE GFS/ECMWF SHOW
UP TO 5 INCHES. GEFS ENSEMBLES SHOW LOW LEVEL JET +4SD FOR 24H
PERIOD WHICH SUGGEST PERSISTENT INFLOW AND INTENSE LOW LEVEL
CONVERGENCE ALONG FRONTAL BOUNDARY. GIVEN SLOW MOVEMENT OF
FRONT...WE CANT COMPLETELY RULE OUT LOCALIZED 8" WITH WIDESPREAD
2-5" AMOUNTS IN WATCH AREA...HIGHEST CT VALLEY AND BERKSHIRES.
FURTHER EAST IN THE COASTAL PLAIN...OUR BEST ESTIMATE IS FOR 1-2".
WE FOCUSED HIGHEST POPS IN W ZONES...THEN DECREASING TO THE EAST.
GIVEN HIGH AMPLITUDE PATTERN MUCH OF THE RAIN MAY REMAIN WEST OF
CAPE/ISLANDS THROUGH THU AND WE HAVE JUST CHC POPS HERE.
SEVERE WEATHER ALSO REMAINS A CONCERN LATE TONIGHT AND THU GIVEN
VERY STRONG LOW LEVEL WIND FIELD PRODUCING A HIGHLY SHEARED
ENVIRONMENT. INSTABILITY WILL BE LIMITED...BUT ANY STORMS WILL HAVE
TO MONITORED VERY CLOSELY. ANY STORMS STAY DEVELOP WILL HAVE
POTENTIAL TO BECOME SUPERCELLS.
SURF ZONE...WE ISSUED HIGH SURF ADVISORY FOR THU/THU NIGHT DUE TO
INCREASING SOUTH WIND WAVE. SEAS WILL BUILD TO 8 FT OFFSHORE
RESULTING IN A HIGH RISK OF RIPS ON SOUTH FACING BEACHES.
LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/
MODELS SHOWING LESS CONTINUITY THIS AFTERNOON...LENDING TO LESS
CONFIDENCE TO THIS PORTION OF THE FORECAST...ESPECIALLY FROM MONDAY
ONWARD. LEANED TOWARD THE GFS AND ECMWF ENSEMBLES FOR THIS PORTION
OF THE FORECAST.
ONE THING THAT APPEARS TO SHOW SOME CONTINUITY IS THE LONG WAVE
UPPER LEVEL TROUGH THAT IS EXPECTED TO REMAIN ALONG THE EASTERN U.S.
THROUGH AT LEAST TUESDAY.
THURSDAY NIGHT...FRONT MOVES SLOWLY ACROSS THE REGION WITH LIKELY TO
CATEGORICAL SHWRS/TSTMS. MODELS HAVING DIFFICULTY WITH THE TIMING OF
THIS SYSTEM...THOUGH APPEARS THAT THE FRONT WILL WORK INTO EASTERN
MA BY 12Z. WITH HIGH PW VALUES CONTINUING...WILL ALSO SEE MORE HEAVY
RAINFALL AS WELL.
FRIDAY...COLD FRONT SWINGS OFFSHORE...THEN STALLS S OF THE REGION IN
THE GENERAL SW UPPER FLOW AS HIGH PRES REMAINS STALLED OVER THE
WESTERN ATLC. SOME LEFTOVER SHOWERS WILL END OVER EASTERN MA IN THE
MORNING. DEWPTS WILL DROP A BIT...BUT REMAIN IN THE LOWER-MID 60S AS
HIGHS HEAD TO THE LOWER TO MID 80S. WILL ALSO REMAIN DRY FRI NIGHT
SATURDAY...NEXT FRONT BEGINS TO APPROACH AROUND THE CUTOFF UPPER LOW
OVER QUEBEC. TIMING IS SUSPECT AS MODELS SHOWING SOME SPREAD AT THIS
POINT...BUT HAVE INCLUDED CHANCE POPS FROM W-E DURING THE DAY.
DEWPTS HEAD BACK UP WITH THE CONTINUED SW FLOW. CURRENT TIMING
SUGGESTS BEST SHOT OF SHWRS/TSTMS WILL OCCUR DURING THE NIGHTTIME
HOURS...BUT NOT A WHOLE LOT OF CONFIDENCE.
SUNDAY THROUGH TUESDAY...AT THIS POINT...APPEARS THAT THE FRONT
SLOWS TO A CRAWL AS IT CROSSES THE REGION OVER THIS WEEKEND...THEN
WILL PUSH JUST OFF THE COAST ON MONDAY. HAVE CARRIED CHANCE POPS
THROUGH MONDAY...THOUGH STILL HAVE NOT A LOT OF CONFIDENCE WITH THE
TIMING OF THIS SYSTEM.
WEDNESDAY...APPEARS THAT IT WILL BE A DRY DAY WITH HIGH PRES TRYING
TO PUSH E OUT OF THE GREAT LAKES. HOWEVER...LOW CONFIDENCE DUE TO
THE VERY AMPLIFIED UPPER PATTERN IN PLACE.
AVIATION /01Z THURSDAY THROUGH MONDAY/
TONIGHT...
A MIXTURE OF MVFR/IFR CONDITIONS WERE OBSERVED ACROSS SOUTHERN NEW
ENGLAND THIS EVENING. CONDITIONS WILL DETERIORATE TO IFR/LIFR ACROSS
THE REGION OVERNIGHT. IN ADDITION...PERIODS OF HEAVY SHOWERS AND
EMBEDDED THUNDERSTORMS WILL CONTINUE...ESPECIALLY ACROSS THE
INTERIOR. SOME OF THE STRONGER STORMS WILL PRODUCE BRIEF GUSTY
SURFACE WINDS.
THURSDAY...
MVFR/IFR CONTINUE WITH PERIODS OF HEAVY SHOWERS AND EMBEDDED
THUNDERSTORMS. THE HEAVY SHOWERS WILL RESULT IN BRIEF VLIFR/LIFR
CONDITIONS ALONG WITH GUSTY WINDS.
OUTLOOK...THURSDAY NIGHT THROUGH MONDAY...
THU NIGHT...EXPECT IFR FOR ALL LOCATIONS WITH SHRA/SCT TSRA. SOME
SHRA WILL HAVE HEAVY RAINFALL. MAY SEE SOME SLOW IMPROVEMENT OVER
THE CT VALLEY AFTER MIDNIGHT.
FRI...CONDITIONS GRADUALLY IMPROVING TO VFR...LINGERING MVFR-IFR
CONDITIONS POSSIBLE CAPE AND ISLANDS.
SAT...VFR EARLY. CONDITIONS LOWERING TO MVFR-IFR IN SCT SHRA/TSRA
FROM W-E DURING THE DAY.
SUN AND MON...IFR AM/MVFR PM SCT SHRA/TSRA AND FOG PATCHES S COAST
EACH DAY.
MARINE
SOUTHERLY WINDS WILL INCREASE LATE TONIGHT AND THU AS LOW LEVEL JET
DEVELOPS. LOW LEVEL INVERSION WILL LIMIT MIXING BUT 40-50 KTS JUST
ABOVE THE SURFACE SHOULD ALLOW FOR G25 KTS. UNDERCUT WNAWAVE
GUIDANCE AS IT IS EXHIBITING ITS HIGH BIAS IN SOUTH FLOW. SWAN
OUTPUT LOOKED MUCH BETTER WITH SEAS BUILDING TO 8 FEET THU ON OUTER
WATERS.
OUTLOOK...THURSDAY NIGHT THROUGH MONDAY...
THURSDAY NIGHT AND FRIDAY...EXPECT SCA FOR HAZARDOUS SEAS EXPECTED
WITH BUILDING SOUTHERLY SWELL. WIND GUSTS TO 25 KT POSSIBLE THU
NIGHT. UNDERCUT WNA GUIDANCE SLIGHTLY GIVEN LOW LEVEL INVERSION AND
AN OVERFORECAST BIAS ON THE S SWELLS.
SATURDAY AND SUNDAY...SCA FOR HAZARDOUS SEAS WILL CONTINUE WITH
BUILDING S-SW SWELL EXPECTED AHEAD OF THE NEXT APPROACHING COLD
FRONT...MAINLY ON THE SOUTHERN WATERS.
MONDAY...WINDS SHIFT TO W AND DIMINISH. LEFTOVER SEAS WILL REMAIN
CLOSE TO SMALL CRAFT CRITERIA ON THE SOUTHERN OUTER WATERS.
HYDROLOGY
QPF AMOUNTS WILL VARY ACROSS OUR REGION. MAX AMOUNTS EXPECTED OVER
CT VALLEY AND BERKSHIRES WITH 2-5 INCHES AND LOCALLY 8 INCHES POSSIBLE
THROUGH THURSDAY NIGHT. AMOUNTS DECREASE TO THE EAST WITH GENERALLY
1-2 INCHES ACROSS THE COASTAL PLAIN...AND LESS ACROSS THE CAPE AND
ISLANDS. FLOOD WATCH HAS BEEN ISSUED DUE TO THIS THREAT.
URBAN AND POOR DRAINAGE FLOODING LIKELY ALONG WITH RIVER AND SMALL
STREAM FLOODING...HIGHEST RISK CT VALLEY AND BERKSHIRES.
BOX WATCHES/WARNINGS/ADVISORIES
CT...FLOOD WATCH THROUGH LATE THURSDAY NIGHT FOR CTZ002>004.
MA...FLOOD WATCH THROUGH LATE THURSDAY NIGHT FOR MAZ002>004-008>012-
026.
HIGH SURF ADVISORY FROM 8 AM THURSDAY TO 8 AM EDT FRIDAY FOR
MAZ020-023-024.
NH...FLOOD WATCH THROUGH LATE THURSDAY NIGHT FOR NHZ011-015.
RI...HIGH SURF ADVISORY FROM 8 AM THURSDAY TO 8 AM EDT FRIDAY FOR
RIZ006>008.
MARINE...SMALL CRAFT ADVISORY FROM 8 AM TO 6 PM EDT THURSDAY FOR
ANZ231>234-250.
SMALL CRAFT ADVISORY FROM 10 AM TO 6 PM EDT THURSDAY FOR
ANZ236.
SMALL CRAFT ADVISORY FROM 1 AM TO 6 PM EDT THURSDAY FOR ANZ235-
237.
SMALL CRAFT ADVISORY UNTIL 6 PM EDT THURSDAY FOR ANZ254-255.
SYNOPSIS...KJC/EVT
NEAR TERM...BELK
SHORT TERM...KJC
LONG TERM...EVT
AVIATION...EVT/FRANK
MARINE...KJC/EVT
HYDROLOGY...BELK/KJC
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