Issued by NWS Upton, NY
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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --000 FXUS61 KOKX 232053 AFDOKX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW YORK NY 353 PM EST MON NOV 23 2009 .SYNOPSIS...-- Changed Discussion --HIGH PRESSURE OVER THE CANADIAN MARITIMES MOVES EAST...ALLOWING A BROAD AREA OF LOW PRESSURE TO MOVE UP THE US EAST COAST. THIS LOW PASSES EAST OF CAPE COD TUESDAY AFTERNOON. WEAK HIGH PRESSURE BUILDS IN WEDNESDAY. DEEPENING LOW PRESSURE APPROACHES FROM THE WEST WEDNESDAY NIGHT. A POTENTIALLY STRONG COASTAL LOW MAY IMPACT THE REGION THURSDAY THROUGH SATURDAY NIGHT...WITH HIGH PRESSURE RETURNING SUNDAY AND MONDAY.-- End Changed Discussion --&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...-- Changed Discussion --WEAK SYNOPTIC SCALE LIFT OVER MOST OF THE AREA THIS AFTERNOON. THERE IS VERY LITTLE INSTABILITY IN THE LOW LEVELS WHERE MOISTURE IS ABUNDANT HOWEVER. GIVEN THESE WEAK AND RELATIVELY SHALLOW DYNAMICS...EXPECT THE MAIN P-TYPE TO BE DRIZZLE FOR MOST OF TONIGHT. RADAR IMAGERY AND SURFACE OBS INDICATING THAT THERE IS A LOT OF VIRGA ACROSS THE REGION. IT WILL TAKE AWHILE LONGER FOR THE COLUMN TO MOISTEN COMPLETELY...AND EXCEPT FOR EASTERN LONG ISLAND...IT WILL BE AT LEAST A FEW HOURS BEFORE STEADY RAINS BEGIN TO FALL. THE 00Z EC INITIALIZED THE BEST IN TERMS OF PRECIP DISTRIBUTION. THIS WAS THE MODEL OF CHOICE FOR THE PREVIOUS FORECAST. WITH LITTLE CHANGE IN THE LARGE SCALE FEATURES THIS FORECAST IS LARGELY SIMILAR. MINOR TWEAKS MADE TO TIMING OF PRECIP ONSET...AND TO LOWER QPF IN GENERAL GIVEN DRIZZLE. OVERNIGHT LOWS SHOULD END UP WARMER THAN LAST NIGHT WITH SOLID CLOUD COVER AND NE WINDS INHIBITING ANY RADIATIONAL COOLING.-- End Changed Discussion --&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...-- Changed Discussion --THE PREFERRED LOW TRACK TAKES THE WEAK SYSTEM EAST OF CAPE COD BY LATE AFTERNOON TUESDAY. THE FLOW IN GENERAL WEAKENS A BIT...BUT DOES NOT REALLY CHANGE FROM NORTHEASTERLY. THERE IS ALSO NO APPRECIABLE COLD FRONT TO SCOUR OUT LOW LEVEL MOISTURE. THEREFORE...SKIES WILL PROBABLY REMAIN CLOUDY INTO AT LEAST EARLY WEDNESDAY DESPITE HIGH PRESSURE. THIS WILL HELP KEEP TEMPS A FEW DEGREES BELOW FULLY MIXED VALUES...WITH HIGHS IN THE LOW 50S. WEAK HIGH PRESSURE PASSES OVERHEAD WEDNESDAY...WITH WHAT IS LIKELY TO BE THE BEST WEATHER DAY OF THE WEEK. HIGHS EXPECTED TO APPROACH 60...ESPECIALLY IF PARTLY CLOUDY SKIES PREVAIL. POTENT COLORADO LOW SETS THE STAGE FOR AN ACTIVE END OF THE WEEK. THE PARENT LOW LOOKS TO TAKE A ST. LAWRENCE/GREAT LAKES TRACK INTO EASTERN CANADA. A SECONDARY COLD LOW ALOFT DIVES IN BEHIND THE INITIAL TROUGH AND ALLOWS IT BECAME NEGATIVELY TILTED AND SPAWN A COASTAL LOW LATE THURSDAY AFTERNOON. THE EC DEVELOPS THE SURFACE LOW JUST EAST OF THE 40/70 BENCHMARK...WHILE THE GFS IS MUCH FARTHER WEST WITH A DOUBLE BARRELED SFC LOW OVER NYC/LI. BOTTOM LINE IS LOTS OF MODEL UNCERTAINTY AT THIS POINT.-- End Changed Discussion --&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...-- Changed Discussion --A DEEPENING NORTHERN STREAM CLOSED UPPER LOW CONTINUES TO BECOME NEGATIVELY TILTED OVER THE OH VALLEY AND LOWER GREAT LAKES THANKSGIVING NIGHT. SPOTTY PRECIP OVER THE AREA INITIALLY IN THE EVENING SHOULD BECOME MORE WIDESPREAD DURING THE NIGHT AS THE CLOSED LOW APPROACHES AND INDUCES SECONDARY LOW DEVELOPMENT NEARBY...AS WELL AS THE DEVELOPMENT OF AN INVERTED TROUGH NW OF INCIPIENT LOW PRESSURE E OF THE VA CAPES. THE SECONDARY LOW WILL RAPIDLY DEEPEN AS IT LIFTS NE FROM THE LOCAL AREA INTO EASTERN NEW ENGLAND ON FRI...WITH A BRISK W FLOW TAKING HOLD IN THE AFTERNOON AFTER SOME MORNING RAINFALL...AND LASTING INTO SAT. POTENTIAL FOR STRONG WINDS MEETING ADVISORY CRITERIA EXISTS ON SAT IF INGREDIENTS OF STRONG COLD AIR ADVECTION...TIGHT PRESSURE GRADIENT AND LARGE PRESSURE RISES TO THE REAR OF THE LOW MESH. CYCLONIC FLOW AND ADDITIONAL MID LEVEL DISTURBANCES ROTATING AROUND THE LOW WILL PRESENT LOW CHANCES FOR RAIN SHOWERS...POSSIBLY SOME SNOW SHOWERS AS WELL LATE FRI NIGHT INTO EARLY SAT MORNING NORTH/WEST OF NYC. BRISK W FLOW SHOULD LESSEN ON SUNDAY AS A WEAK HIGH PRESSURE RIDGE SLIDES ACROSS...FOLLOWED BY ANOTHER CHANCE OF SHOWERS WITH AN APPROACHING FRONTAL SYSTEM ON MON.-- End Changed Discussion --&& .AVIATION /20Z MONDAY THROUGH SATURDAY/...-- Changed Discussion --WIDESPREAD MVFR CEILINGS THE REMAINDER OF THIS AFT. CEILINGS TO DROP BELOW 2 KFT BY 20Z. ANY LIGHT RAIN/DRIZZLE WILL BE SPOTTY WITH BRIEF EPISODES OF MVFR VSBYS...BUT PRIMARILY AFTER 00Z. DIFFICULT FORECAST TOWARD 00Z AS CEILINGS APPROACH IFR. CEILINGS WILL BE RIGHT AROUND THE UPPER END OF THE IFR CATEGORY OR LOW END OF THE MVFR CATEGORY. WINDS TO REMAIN FROM THE NORTHEAST...020 TO 050...THROUGH THE PERIOD WITH SPEEDS 10 TO 15 KT. GUSTS UP TO 20 KT NYC TERMINALS THROUGH 20Z. TAF COMMENTS (FORECASTER INSIGHT ON TIMING, CONFIDENCE, TRENDS AND GROUND OPS) KEWR...AFTER 00Z...PREVAILING MVFR...BUT THERE IS A CHANCE FOR IFR CONDITIONS WITH CEILINGS RIGHT AROUND THE 1 KFT. KEWR HOURLY WIND FORECAST ALL WIND DIRECTIONS ARE TRUE...ADD 13 DEGREES FOR MAGNETIC 23/18Z 03012KT 23/19Z 03012KT 23/20Z 03011KT 23/21Z 03011KT 23/22Z 03011KT 23/23Z 03011KT 24/00Z 03011KT 24/01Z 03011KT 24/02Z 03011KT 24/03Z 03011KT 24/04Z 03010KT 24/05Z 03010KT KJFK...AFTER 23Z...PREVAILING IFR...BUT THERE IS A CHANCE FOR MVFR CONDITIONS WITH CEILINGS RIGHT AROUND THE 1 KFT. KLGA...AFTER 00Z...PREVAILING MVFR...BUT THERE IS A CHANCE FOR IFR CONDITIONS WITH CEILINGS RIGHT AROUND THE 1 KFT. KTEB...AFTER 00Z...PREVAILING MVFR...BUT THERE IS A CHANCE FOR IFR CONDITIONS WITH CEILINGS RIGHT AROUND THE 1 KFT. KHPN...AFTER 23Z...PREVAILING IFR...BUT THERE IS A CHANCE FOR MVFR CONDITIONS WITH CEILINGS RIGHT AROUND THE 1 KFT. KSWF...AFTER 00Z...CEILINGS WILL VARY BETWEEN IFR AND MVFR...AMENDMENTS LIKELY. KISP...AFTER 00Z...CEILINGS WILL VARY BETWEEN IFR AND MVFR...AMENDMENTS LIKELY. KBDR...AFTER 00Z...CEILINGS WILL VARY BETWEEN IFR AND MVFR...AMENDMENTS LIKELY. KGON...AFTER 23Z...CEILINGS WILL VARY BETWEEN IFR AND MVFR...AMENDMENTS LIKELY. OUTLOOK 18Z TUESDAY THROUGH FRIDAY... TUESDAY AFT-WED...VFR. WEDNESDAY NIGHT THROUGH THURSDAY...SUB VFR POSSIBLE IN LIGHT RAIN. FRIDAY...SUB VFR POSSIBLE IN SHOWERS. SNOW POSSIBLY MIXING IN NORTH AND WEST OF THE NYC TERMINALS AT NIGHT. SATURDAY...VFR CEILINGS IN STRONG COLD ADVECTION/CYCLONIC FLOW.-- End Changed Discussion --&& .MARINE...-- Changed Discussion --STRONG NE FLOW RESULTING IN SMALL CRAFT ADVISORY CONDITIONS ON ALL WATERS. SLOW MOVING HIGH COUPLED WITH A WEAK ATLANTIC STORM TRACK WILL KEEP THIS WIND REGIME IN PLACE THROUGH AT LEAST TUESDAY MORNING. AS THE LOW PULLS AWAY...LONG ISLAND SOUND AND PROTECTED BAYS WILL BE THE FIRST TO DROP BELOW SCA CRITERIA. LOWER CONFIDENCE ON OCEAN SEAS FALLING BELOW 5 FT BY LATE IN THE DAY TUESDAY. THE SMALL CRAFT MAY NEED TO BE EXTENDED HERE. SUB SCA ON ALL WATERS BY WEDNESDAY. SCA CONDITIONS ARE LIKELY THANKSGIVING NIGHT INTO FRI MORNING IN STRENGTHENING S-SW FLOW ASSOCIATED WITH DEVELOPING LOW PRESSURE. GALES ARE LIKELY ESPECIALLY ON THE OCEAN FROM FRI AFTERNOON INTO SAT EVENING...AS THE LOW RAPIDLY DEEPENS WHILE LIFTING NE FROM THE LOCAL AREA INTO EASTERN NEW ENGLAND AND THE CANADIAN MARITIMES. LINGERING SCA CONDITIONS SHOULD THEN FOLLOW FOR SAT NIGHT.-- End Changed Discussion --&& .HYDROLOGY...-- Changed Discussion --LESS THAN A QUARTER INCH OF PRECIP REGIONWIDE TONIGHT AND TUESDAY. A MORE SIGNIFICANT QUANTITATIVE PRECIPITATION EVENT IS POSSIBLE THURSDAY NIGHT INTO FRIDAY.-- End Changed Discussion --&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...NONE. NY...NONE. NJ...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST TUESDAY FOR ANZ330-335-338- 340-345-350-353-355. && $$ SYNOPSIS...BS NEAR TERM...BS SHORT TERM...BS LONG TERM...BG AVIATION...DW MARINE...BG/BS HYDROLOGY...BS
