AFDOKX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW YORK NY 416 PM EDT FRI JUL 8 2011 .SYNOPSIS... A FRONTAL BOUNDARY WILL REMAIN OVER THE AREA THIS EVENING...THEN SLOWLY PUSH OFFSHORE TONIGHT. LOW PRESSURE DEVELOPING OVER THE DELMARVA WILL PUSH ALONG THE FRONT AND JUST SOUTH OF THE REGION TONIGHT. HIGH PRESSURE WILL THEN BUILD IN FROM THE GREAT LAKES FOR THE WEEKEND...AND THEN SLIDE EAST ON MONDAY. A COLD FRONT WILL MOVE ACROSS ON TUESDAY...FOLLOWED BY CANADIAN HIGH PRESSURE FOR THE REST OF THE WEEK. && .NEAR TERM /UNTIL 6 AM SATURDAY/... SEVERE THUNDERSTORM WATCH IN EFFECT FOR ENTIRE REGION THROUGH 9 PM. MARGINAL TO MODERATE INSTABILITY...COMBINED WITH 35-40KT DEEP LAYER SHEAR AND APPROACHING SHORTWAVE ENERGY HAS SET THE ENVIRONMENT. HEAVY RAINFALL AND DAMAGING WINDS WILL BE MAIN THREAT WITH ANY SEVERE STORMS...WITH LARGE HAIL POSSIBLE IN ROTATING STORMS. DUE TO THE SLOW-MOVING NATURE OF THESE STORMS AND ABUNDANT MOISTURE OVER THE AREA...FLASH FLOODING WILL BE POSSIBLE. A FLASH FLOOD WATCH HAS BEEN ISSUED FOR THE NEW YORK CITY METRO AREA...NORTHEAST NEW JERSEY AND THE LOWER HUDSON VALLEY UNTIL 2 AM. SLOW-MOVING COLD FRONT DRAPED OVER THE AREA WILL SLOWLY PUSH OFFSHORE TONIGHT. MODELS AGREE THAT LOW PRESSURE DEVELOPING OVER THE DELMARVA WILL BECOME MORE ORGANIZED AS IT TRACKS ALONG THE FRONT. DURING THE LATE EVENING HOURS...500MB TROUGH WILL APPROACH THE REGION FROM THE WEST AND SHARPEN...CAUSING THE 500 MB JET TO INCREASE TO 40-50KT. PW WILL STILL BE CLOSE TO 2 INCHES...RESULTING IN A CONTINUED POSSIBILITY OF THUNDERSTORMS WITH HEAVIER RAINFALL AND GUSTY WINDS. THE COLD FRONT WILL PUSH OFFSHORE BY SATURDAY MORNING. POPS GRADUALLY DECREASE FROM NW TO SE LATE TONIGHT AS SHOWER/TSTM ACTIVITY TRENDS OFFSHORE. MAV/MET GUIDANCE BLENDED FOR LOW TEMPS...WHICH WILL RANGE FROM THE LOW 60S OVER NORTHERN SECTIONS TO THE UPPER 60S OVER THE NYC METRO. THERE IS A MODERATE RIP CURRENT RISK AT THE OCEAN BEACHES THROUGH THIS EVENING. && .SHORT TERM /6 AM SATURDAY THROUGH SATURDAY NIGHT/... THE FRONT PUSHES OFFSHORE SATURDAY AS HIGH PRESSURE OVER SOUTHERN CANADA DROPS INTO THE REGION. COULD BE SOME LEFTOVER SHOWERS OR THUNDERSTORMS EARLY SATURDAY MORNING...BUT ANY REMAINING ACTIVITY WILL MOVE OFFSHORE DURING THE MORNING. SKIES WILL CLEAR THROUGHOUT THE DAY AND REMAIN SO THROUGH SATURDAY NIGHT. DOWNSLOPE COMPONENT TO WIND FLOW SATURDAY WILL SUPPORT ABOVE- NORMAL HIGHS...RANGING FROM THE MID 80S TO 90. GOOD RADIATIONAL COOLING LIKELY SATURDAY NIGHT...WITH TEMPS DROPPING INTO THE MID 50S OVER INTERIOR AREAS AND THE PINE BARRENS. TEMPS CLOSE TO NYC WILL REMAIN AROUND 70 OVERNIGHT. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... SUNDAY...REGION ON THE EASTERN SIDE OF A LONGWAVE RIDGE SETTING UP IN THE CENTRAL U.S WITH QUASI-ZONAL FLOW ALOFT. AT THE SURFACE...HIGH PRESSURE WILL STILL HOLD STRONG IN THE AREA...SETTLING OFFSHORE BY THE END OF THE DAY TO DEPICT A BERMUDA HIGH SCENARIO. WARMER AIR ADVECTS IN WITH SOUTHWEST WINDS LOW LEVELS VEERING TO MORE WESTERLY ALOFT. 850 MB TEMPS REACH AROUND 15 DEGREES C WITH AGREEMENT BETWEEN ECMWF...NAM...AND CMC. GFS IS SEVERAL DEGREES WARMER. VERY WARM AND HUMID CONDITIONS WILL BE IN PLACE LOOKING AT THE RESULTING SURFACE TEMPS AND INCREASE IN LAYER PW. LAYER PW INCREASES TO NEAR 1.5 INCHES. FOR MONDAY...FLOW ALOFT TURNS MORE WNW DOWNSTREAM OF AN UPPER LEVEL TROUGH ONTARIO CANADA. AT THE SURFACE...BERMUDA HIGH SET UP REMAINS IN PLACE. BETTER MODEL AGREEMENT INCLUDING THE GFS FOR 850 MB TEMPS REACHING 17 TO 18 DEGREES C. MODELS ALSO SHOW INCREASING RH IN THE 1000 TO 700 MB LAYER...SO MORE CLOUDS CAN BE EXPECTED. THIS MAKES SENSE AS THERE WILL BE A SMALLER SCALE SHORTWAVE RIDING ALONG THE NORTHERN FRINGE OF THE RIDGE AND INTO THE REGION BY AFTERNOON. PERHAPS...EVEN ENOUGH FORCING TO ALLOW FOR SOME ISOLATED SHOWERS AND THUNDERSTORMS TOWARDS INTERIOR LOCATIONS. LAYER PW VALUES INCREASE TO BETWEEN 1.5 AND 2 INCHES. MAX TEMPS CLOSER TO MOSGUIDE SUNDAY THROUGH TUESDAY WITH UPPER 80S TO NEAR 90 WESTERN LOCATIONS AND NEAR CITY AND COOLER TOWARDS THE COAST. FOR MONDAY NIGHT AND TUESDAY...THE STRONG UPPER LEVEL TROUGH WILL BE MOVING INTO QUEBEC AND INTO NORTHERN NEW ENGLAND. DOWNSTREAM EFFECTS OF THIS ARE A 50 TO 60 METER DECREASE IN 500 HPA HEIGHT...AND THEREBY COLDER TEMPERATURES ALOFT. THIS INCREASES INSTABILITY THROUGHOUT THE COLUMN. THE AMOUNT OF INSTABILITY REALLY DEPENDS ON THE TIMING OF THIS COLDER AIR ALOFT AND DAYTIME WARMING AT THE SURFACE. SURFACE COLD FRONT WILL BE APPROACHING AND MOVING INTO THE REGION DURING THIS TIMEFRAME. MUCAPE COULD VARY FROM 500 TO MORE THAN 1500 J/KG WITH SOME SPATIAL VARIATIONS BETWEEN THE LAND AND MARINE AREAS. ALTHOUGH WITH A WNW FLOW ALOFT...THIS HAS BEEN MORE FAVORABLE WITH MORE WIDESPREAD CONVECTION FOR CLIMATOLOGY. THE BULK SHEAR IS FORECAST TO BE 25-35 KT BETWEEN 0 AND 6 KM ABOVE SFC SO A STRONG TO SEVERE THUNDERSTORM WILL BE POSSIBLE WITH HEAVY RAIN ALSO POSSIBLE WITH THE HIGH PW VALUES. THE MODELS ARE IN SOME DISAGREEMENT WITH THE TOTAL QPF...WITH GFS HAVING THE MOST AND CMC AND ECMWF HAVING VERY LITTLE QPF. STILL FORECAST SIDES MORE WITH GFS AND ITS ENSEMBLE WHICH FOCUSES THE QPF BETWEEN 18Z TUESDAY AND 06Z WEDNESDAY. COLD FRONT MOVES OFFSHORE TUESDAY NIGHT AS SHOWERS AND THUNDERSTORMS TAPER OFF. UPPER LEVEL TROUGH AXIS WILL BE SHIFTING EAST OF THE AREA TUESDAY NIGHT AS WELL...TAKING BEST DYNAMIC FORCING WITH IT. WANTED TO KEEP MENTION OF THE CHANCE OF SHOWERS AND THUNDERSTORMS A LITTLE INTO THE EVENING TO COVER THE EXTRA FORCING ALOFT FROM PVA...BUT THIS MAY TREND TO END EARLIER WITH LATER FORECASTS. THEREAFTER WEDNESDAY THROUGH REST OF LONG TERM...HIGH PRESSURE BUILDS IN FROM THE GREAT LAKES. 850MB TEMPS WILL BE NEAR 10 TO 11 DEGREES C. WNW FLOW ALOFT WILL TRANSITION TO MORE WESTERLY BY END OF NEXT WEEK WITH UPPER LEVEL RIDGING BUILDING IN. LAYER PW VALUES DECREASE TO NEAR 0.5 AND THEN SLIGHTLY INCREASE BY END OF NEXT WEEK. MAX TEMPS WILL BE CLOSER TO NORMAL. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... A WEAK FRONT WASHES OUT OVER THE REGION THIS AFTERNOON...WITH WAVES OF LOW PRESSURE MOVING SOUTH OF THE REGION TONIGHT. GENERALLY VFR CONDS EXPECTED THROUGH THIS AFTERNOON ACROSS WESTERN TERMINALS...EXCEPT IN SHRA/TSRA. PATCHY IFR/MVFR CIGS ACROSS COASTAL TERMINALS WITH BANDS OF MARINE STRATUS/FOG PARTIALLY EVIDENT. STRATUS/FOG MAY BECOME MORE WIDESPREAD ACROSS EASTERN TERMINALS THAN DEPICTED THIS EVENING IF CONVECTION DOES NOT MATERIALIZE. CONVECTIVE COVERAGE INCREASING JUST WEST OF THE TERMINALS...AND EXPECT IT TO BE FAIRLY WIDESPREAD BY 20-22Z ACROSS WESTERN TERMINALS...MOVING INTO EASTERN TERMINALS THIS EVENING. EXPECT WIDESPREAD CONVECTION TO COME TO AN END TONIGHT FROM NW TO SE. WILL BE AMENDING TAFS TO GIVE MORE PRECISE TIMING ON CONVECTION. WITH ANY STRONGER STORM LOCALIZED MVFR-IFR CONDITIONS ARE POSSIBLE IN HEAVY RAINS. DAMAGING WINDS AND LARGE HAIL POSSIBLE AS WELL. ALL TERMINALS ARE UNDER A SVR TSTSM WATCH TIL 9PM. CCFP CONFIDENCE/COVERAGE LOOKS GOOD. WIND GENERALLY FROM A LIGHT ESE THIS AFTERNOON INTO EVENING AHEAD OF WAVE...BECOMING LIGHT N LATE TONIGHT. MVFR STRATUS/FOG LIKELY ACROSS EASTERN TERMINALS AND POSSIBLY ACROSS WESTERN TERMINALS IN LIGHT WINDS AND ABUNDANT LOW-LEVEL MOISTURE LATE TONIGHT. CONDS IMPROVING TO VFR SATURDAY MORNING...IN NW FLOW. NY METRO ENHANCED AVIATION WEATHER SUPPORT... DETAILED INFORMATION...INCLUDING HOURLY TAF WIND COMPONENT FCSTS CAN BE FOUND AT: HTTP:/WWW.ERH.NOAA.GOV/ZNY/N90 (LOWER CASE) KJFK FCSTER COMMENTS: AMENDMENTS LIKELY TO REFLECT THUNDERSTORMS. KLGA FCSTER COMMENTS: AMENDMENTS LIKELY TO REFLECT THUNDERSTORMS. KEWR FCSTER COMMENTS: AMENDMENTS LIKELY TO REFLECT THUNDERSTORMS. KTEB FCSTER COMMENTS: AMENDMENTS LIKELY TO REFLECT THUNDERSTORMS. KHPN FCSTER COMMENTS: AMENDMENTS LIKELY TO REFLECT THUNDERSTORMS. KISP FCSTER COMMENTS: AMENDMENTS LIKELY TO REFLECT THUNDERSTORMS. OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY... SATURDAY MORNING...BECOMING VFR. SATURDAY AFTERNOON-MONDAY...VFR. MONDAY NIGHT-TUESDAY...CHANCE OF MVFR OR LOWER LATE MONDAY NIGHT/TUESDAY MORNING WITH LOW STRATUS/FOG...THEN SUB-VFR POSSIBLE WITH SHRA/TSRA LATER IN THE DAY AHEAD OF A COLD FRONT. WEDNESDAY...VFR. && .MARINE... GENERALLY QUIET WITH RESPECT TO WINDS/WAVES...BUT CONVECTION COULD PRODUCE LOCALLY GUSTY WINDS THIS EVENING AND EARLY TONIGHT. S SWELL GENERATED BY HIGH PRESSURE OFF THE S COAST WILL SPREAD NORTHWARD TODAY INTO SAT...AND WAVEWATCH INDICATES 5 FT OCEAN SEAS POSSIBLE SAT AFTERNOON. AT THIS TIME EXPECT CURRENT 7 FT SEAS OFF THE NC COAST TO DECAY TO JUST UNDER 5 FT BEFORE THEY REACH OUR COASTAL WATERS. SEAS ARE EXPECTED TO DROP BELOW 5 FT OVER ALL WATERS BY SUNDAY MORNING. SUB SCA CONDITIONS CONTINUE WITH OCEAN WATERS SE OF MONTAUK APPROACHING 5 FT BY TUESDAY AFTERNOON AHEAD OF COLD FRONT. GUSTS UP TO MOSTLY 20 KT AHEAD OF COLD FRONT AND THEN UP TO 25 KT IN SOME OCEAN LOCATIONS BEHIND COLD FRONT TUESDAY NIGHT AND EARLY WEDNESDAY. OTHERWISE...SUB SCA CONDITIONS EXPECTED. && .HYDROLOGY... A FLASH FLOOD WATCH HAS BEEN ISSUED FOR THE LOWER HUDSON VALLEY...NORTHEAST NEW JERSEY AND THE NEW YORK CITY METRO AREA UNTIL 2 AM. SHOWERS AND THUNDERSTORMS WILL CONTINUE OVER THE REGION THIS EVENING. STORMS HAVE BEEN RELATIVELY SLOW-MOVING SO FAR...AND WITH POTENTIAL TRAINING LOCAL AREAS COULD SEE MULTIPLE STORMS THIS EVENING AND EARLY TONIGHT. STORMS WITH HEAVIER RAINFALL MAY PRODUCE 1 TO 2 INCHES OF RAINFALL PER HOUR. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...NONE. NY...NONE. NJ...NONE. MARINE...NONE. && $$ SYNOPSIS...KCS