AFDOKX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW YORK NY 1043 PM EDT SUN APR 17 2011 .SYNOPSIS... LOW PRESSURE TRACKS SLOWLY NORTHEAST THROUGH SOUTHEASTERN CANADA THROUGH MONDAY NIGHT...WITH AN ASSOCIATED TROUGH OF LOW PRESSURE CROSSING THE TRI-STATE TONIGHT...AS HIGH PRESSURE BUILDS INTO OUR SOUTH. A COLD FRONT CROSSES THE AREA MONDAY NIGHT...THEN STALLS OUT TO OUR SOUTH INTO WEDNESDAY...AS CANADIAN HIGH PRESSURE BUILDS IN ACROSS SOUTHEASTERN CANADA AND THE NORTHEASTERN UNITED STATES. TWO STORM SYSTEMS IMPACT THE REGION LATE THIS WEEK...THE FIRST FROM WEDNESDAY NIGHT INTO THURSDAY AND THE SECOND FROM FRIDAY NIGHT INTO NEXT SUNDAY. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... APPROACHING SHORTWAVE TROUGH WILL BRING SOME SCATTERED SHOWERS ACROSS THE FORECAST AREA THIS EVENING. SHOULD SEE DECENT CLEARING IN THE WAKE OF THE SHORTWAVE LATE TONIGHT...SO TEMPERATURES WILL FALL OFF OVERNIGHT...BUT THE BOUNDARY LAYER SHOULD REMAIN SUFFICIENTLY WELL MIXED TO ALLOW FOR ANYTHING BEYOND MODEST RADIATIONAL COOLING. MAV/MET GUIDANCE WERE FAIRLY CLOSE...AND CONSISTENT WITH THIS REASONING...SO USED A BLEND FOR LOWS. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... THE FIRST PART OF MONDAY SHOULD BE DRY...THEN A PASSING COLD FRONT MONDAY AFTERNOON/MONDAY NIGHT COUPLED WITH A WEAK SHORTWAVE MOVING THROUGH IN THE LOW TO MID LEVELS SHOULD PROMOTE INCREASING CHANCE OF SHOWERS FROM NW TO SE FROM MONDAY AFTERNOON INTO MONDAY EVENING (RESTRICTED LIKELY POPS TO NORTHERN TIER CLOSEST TO BEST IMPACT FROM PASSING SHORTWAVE)...WITH POPS TAPERING TO SLIGHT CHANCE LATE MONDAY NIGHT. USED A BLEND OF 2/3 MET/MAV BLEND AND 1/3 MIXING DOWN FROM 900 HPA - PER BUFKIT SOUNDINGS - FOR HIGHS MONDAY...AND A BLEND OF 2/3 MAV/MET BLEND AND 1/3 NAM 2-METER TEMPERATURES FOR LOWS MONDAY NIGHT - NAM 2-METER TEMPERATURES FAIR PRETTY WELL IN THESE SHALLOW LOW LEVEL POST-FRONTAL COLD ADVECTION CASES. TUESDAY INTO WEDNESDAY WILL FEATURE A FRONTAL BOUNDARY STALLED TO THE S...WITH SW FLOW ALOFT...WITH SHORTWAVES PASSING ALOFT...AND DEVELOPING LOW LEVEL WARM ADVECTION AS SOUTHERLY FLOW SETS UP IN THE UPPER PART OF THE BOUNDARY LAYER...WITH AN EASTERLY FLOW AT THE SURFACE - CLASSIC OVER RUNNING PATTERN. HAVE TIMED THE BEST POPS TUESDAY INTO WEDNESDAY WITH THE PROJECTED PASSAGE OF A SHORTWAVE TROUGH LATE TUESDAY AFTERNOON AND TUESDAY EVENING (LIKELY POPS N TIER WITH BETTER FORCING). WEDNESDAY WILL SEE STEADIER RAIN GIVE WAY TO LIGHT RAIN/DRIZZLE FROM S TO N AS 850 WARM FRONT LIFTS TO THE N WHILE SFC WRM FRONT STAYS TO THE S. FOR TEMPERATURES TUESDAY-WEDNESDAY BLENDED AVAILABLE GUIDANCE WITH NAM 2-METER TEMPERATURES TO REFLECT IMPACT OF COLD AIR DAMMING (WITH SFC HIGH BUILDING OVER SE CANADA)...AND PRECIPITATION INTO THE DAMMING HIGH - NAM 2-METER TEMPERATURES GENERALLY PERFORM FAIRLY WELL IN THIS SCENARIO. EXPECT BELOW NORMAL HIGHS AND LOWS SLIGHTLY ABOVE NORMAL AS A RESULT. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... ANOTHER PAC STORM SYSTEM IS FORECAST TO TRACK ACROSS THE GREAT LAKES AT THE ONSET OF THE PERIOD SENDING A MODERATE COLD FRONT ACROSS THE AREA. GLOBAL MODELS STILL IN SOME DISAGREEMENT WITH THE MAGNITUDE OF THE PARENT LOW AND TIMING OF THE COLD FRONT. THAT BEING THE CASE...WE ARE STILL LOOKING AT A COLD FRONTAL PASSAGE WED NIGHT. ONLY LOOKING AT SHOWERS WITH MARGINAL INSTABILITY AND THE BEST UPPER SUPPORT PASSING TO THE NW OF THE FORECAST AREA. RIDGING BOTH ALOFT AND THE SURFACE TRANSLATES EAST FOR THE END OF THE WEEK WITH A BRIEF SHOT OF DRY...SEASONABLE WEATHER. YET ANOTHER PAC STORM SYSTEM IS FORECAST TO TRACK NE ACROSS THE GREAT LAKES NEXT WEEKEND...FIRST IMPACTING THE AREA WITH OVERRUNNING RAINS FRI NIGHT INTO SAT AND THEN POSSIBLE CONVECTION ALONG AND AHEAD OF THE TRAILING COLD FRONT SAT NIGHT. THE GFS CONTINUES TO BE STRONGER...MORE AMPLIFIED WITH THESE LOWS VERSUS THE ECMWF...WHICH IS FLATTER AND SOMEWHAT MORE PROGRESSIVE. NEXT WEEKEND THE DIFFERENCES BECOME QUITE APPARENT AS THE GFS SENDS A MODERATE COLD FRONT ACROSS THE AREA SAT NIGHT...WHILE THE ECMWF STALLS A WEAK FRONT ACROSS THE AREA WITH LIGHT OVERRUNNING PRECIPITATION CONTINUING INTO SUN. THE GFS AT THIS TIME IS AN OUTLIER WITH THE GLOBAL MODEL ENSEMBLE. THIS WOULD SEEM REASONABLE WITH THE NEARLY ZONAL FLOW. && .AVIATION /03Z MONDAY THROUGH FRIDAY/... A TROUGH MOVES THROUGH THE AREA BY 06Z WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. TERMINALS WILL REMAIN VFR. WINDS SHIFT TO THE WEST TO NORTHWEST BEHIND THE TROUGH AND A BRIEF GUST TO 20 KT WILL BE POSSIBLE. WILL BE A BRIEF PERIOD OF GUSTS AND UNCERTAIN OF OCCURRENCE SO NOT INCLUDED IN THE TERMINALS. AFTER THE TROUGH MOVES THROUGH CONDITIONS WILL REMAIN VFR. DURING MONDAY WESTERLY WINDS GRADUALLY SHIFT TO SOUTHWEST...AND ALONG THE COAST SEA BREEZE INFLUENCES WILL BE LIKELY AFTER 16Z. GUSTS WILL BECOME POSSIBLE AT KJFK. SOME UNCERTAINTY WITH DEVELOPMENT OF THE SEA BREEZE INFLUENCES. OUTLOOK FOR 00Z TUESDAY THROUGH FRIDAY... MONDAY NIGHT...VFR WITH SCATTERED SHOWERS. TUESDAY THROUGH WEDNESDAY NIGHT...PERIODS OF SUB-VFR LIKELY IN SHOWERS. GUSTY WINDS/LLWS POSSIBLE. THUNDER ALSO POSSIBLE AHEAD OF A COLD FRONT. THURSDAY...VFR WITH GUSTY NORTHWESTERLY WINDS. FRIDAY...VFR. && .MARINE... WINDS ON THE SOUND...NEW YORK HARBOR AND BAYS HAVE DIMINISHED BELOW ADVISORY LEVELS WITH LIMITED MIXING OF LOW LEVEL JET WINDS UP TO 40 KT. SURFACE TROUGH WILL BE MOVING THROUGH THE WATERS THROUGH 06Z AND WINDS WILL BE LIMITED WITH THE TROUGH PASSAGE. SO WILL TAKE DOWN THE SMALL CRAFT ADVISORY. FOR THE OCEAN WATERS....WINDS STILL GUSTING TO AROUND 25 KT AND SEAS REMAIN ABOVE 5 FT...SO WILL CONTINUE THE ADVISORY THROUGH MONDAY WITH SEAS EXPECTED TO GRADUALLY FALL. WITH EASTERLY FLOW DEVELOPING BY LATE TUESDAY...THERE IS SOME POTENTIAL FOR SEAS TO STAY UP ON THE COASTAL OCEAN WATERS THROUGH WEDNESDAY. AS FOR WINDS FROM MONDAY-WEDNESDAY...FOR NOW FORECAST TO STAY BELOW SCA LEVELS...BUT THIS IS NOT A CERTAINTY...AS ANY WAVE OF LOW PRESSURE WHICH COULD RIDE ALONG A STALLED OUT BOUNDARY TO OUR SOUTH COULD INCREASE THE PRESSURE GRADIENT JUST ENOUGH TO BRING WINDS FROM JUST BELOW SCA LEVELS TO SCA LEVELS IN THIS TIME FRAME. && .HYDROLOGY... RIVERS IN PASSAIC AND BERGEN COUNTIES ARE FORECAST TO REMAIN IN FLOOD OVERNIGHT. REFER TO THE LATEST AREAL FLOOD ADVISORY AND RIVER FLOOD WARNING FOR DETAILS. A FLOOD WARNING HOWEVER REMAINS IN EFFECT FOR SPOTS ALONG THE CONNECTICUT...STILL AND PASSAIC RIVERS IN ADJACENT HYDROLOGIC SERVICE AREAS...BUT WITHIN THE OFFICE/S COUNTY WARNING AREA. PLEASE SEE WWW.WEATHER.GOV/NYC FOR MORE INFORMATION. LESS THAN A TENTH OF AN INCH OF QPF IS EXPECTED FROM ANY SHRA/TSRA THIS EVENING. THERE IS THE POTENTIAL FOR UP TO A HALF AN INCH OF RAINFALL FROM LATE MONDAY NIGHT INTO WEDNESDAY...WITH LOCALLY HIGHER AMOUNTS POSSIBLE. GIVEN THE LONG DURATION THIS PRECIPITATION IS EXPECTED TO BE SPREAD OVER...LIMITED HYDROLOGIC IMPACT IS EXPECTED. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...NONE. NY...NONE. NJ...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT MONDAY FOR ANZ350-353-355. && $$