177
FXUS61 KOKX 232053
AFDOKX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
353 PM EST MON NOV 23 2009
SYNOPSIS
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.
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
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.
SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/
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.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
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.
AVIATION /20Z MONDAY THROUGH SATURDAY/
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.
MARINE
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.
HYDROLOGY
LESS THAN A QUARTER INCH OF PRECIP REGIONWIDE TONIGHT AND TUESDAY.
A MORE SIGNIFICANT QUANTITATIVE PRECIPITATION EVENT IS POSSIBLE
THURSDAY NIGHT INTO FRIDAY.
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
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