Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 050603 CCA AFDOKX AREA FORECAST DISCUSSION...CORRECTED NATIONAL WEATHER SERVICE NEW YORK NY 1259 AM EST THU MAR 5 2015 .SYNOPSIS... A COLD FRONT MOVES THROUGH THE REGION LATE TONIGHT...WITH WAVES OF LOW PRESSURE TRACKING ALONG IT INTO THURSDAY. CANADIAN HIGH PRESSURE BUILDS IN THURSDAY NIGHT...THEN SLIDES TO OUR SOUTH THROUGH FRIDAY NIGHT. A SERIES OF WEAK COLD FRONTS CROSS THE REGION THIS WEEKEND INTO EARLY NEXT WEEK. && .NEAR TERM /THROUGH TODAY/...
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PCPN HAS BECOME MUCH BETTER ORGANIZED IN THE LAST COUPLE OF HOURS WITH A STEADY RAIN MOVING IN FROM THE SW...IMPACTING MOST AREAS WITH THE EXCEPTION OF THE FAR INTERIOR OF THE LOWER HUDSON VALLEY AND SRN CT. DUAL POL RADAR DATA SHOWS A MIXED PCPN PHASE AT ABOUT 4000 TO 5000 FT. IT WILL TAKE SEVERAL MORE HOURS OF VERTICAL COOLING BEFORE A TRANSITION TO SNOW OCCURS. COLD FRONT REMAINS JUST NORTH OF THE LOWER HUDSON VALLEY. 00Z NAM WRF HAS TRENDED A BIT SLOWER WITH THE COLD AIR WORKING IN WHICH MAY DELAY THE CHANGEOVER AN HOUR OR TWO. SEVERAL WAVES WILL FORM ALONG THIS FRONTAL ZONE...WHICH WILL BE SUPPORTED BY A VERY INTENSE UPPER LEVEL JET...BETWEEN 200 AND 215 KT. UPPER LEVEL DIVERGENCE INCREASES OVERNIGHT INTO THURSDAY WITH THIS JET. TIGHT BAROCLINIC ZONE ALSO SETS UP AS COLD AIR FILTERS IN OVERNIGHT BEHIND THE FRONT. AS THE COLDER AIR FILTERS IN FROM THE NORTHWEST BEHIND THE FRONT...PRECIPITATION TRANSITIONS TO A RAIN...SLEET..AND SNOW MIX FROM NORTHWEST TO SOUTHEAST INITIALLY OVERNIGHT. FEEL THE ENTIRE AREA WILL BE ALL SNOW BY 07-08Z. SNOW...MODERATE TO POSSIBLY HEAVY AT TIMES...IS THEN EXPECTED THROUGH AT LEAST MID MORNING ACROSS SOUTHERN ZONES. THE SNOWFALL WILL BE A BIT LIGHTER ACROSS THE INTERIOR ZONES AS THE BEST FRONTOGENESIS AND LIFT WILL RESIDE ACROSS THE SOUTHERN PORTION OF THE REGION. THE SNOW BEGINS TO TAPER OFF FROM NORTHWEST TO SOUTHEAST DURING THE AFTERNOON AND EVENING. OVERALL MODELS HAVE COME INTO BETTER AGREEMENT WITH THE GFS..EURO...CMC...CMC REGIONAL...UKMET...GEFS...AND SREF ALL INDICATE AT LEAST MODERATE SNOW ACROSS SOUTHERN ZONES FROM JUST AFTER 06Z TO AROUND 18Z THURSDAY. THE NAM APPEARS TO BE AN OUTLIER AS IT SUPPRESSES MUCH OF THE SNOW SOUTH OF THE REGION AFTER 12Z. THE 18Z NAM DID SHIFT THE AXIS A BIT FURTHER NORTH HOWEVER COMPARED TO ITS 12Z RUN. LARGE SCALE SYNOPTIC LIFT SUPPORTS SNOW CONTINUING LONGER THAN THE NAM IS SHOWING AND THIS THINKING IS MORE IN LINE WITH THE REST OF THE GUIDANCE. THE FIRST PORTION OF THE SNOW WILL SEE LOWER SNOW TO LIQUID RATIOS...BUT AS THE COLUMN COOLS SIGNIFICANTLY EARLY THURS MORNING...EXPECT RATIOS TO INCREASE A BIT. DUE TO INCREASED CONFIDENCE HAVE ADDED MANHATTAN...BRONX...HUDSON... AND EASTERN ESSEX INTO THE WINTER STORM WARNING...AND REPLACED THE REST OF THE WATCH WITH ADVISORIES FOR ALL BUT NORTHERN NEW LONDON WHERE NO HEADLINE IS IN EFFECT. ROCKLAND AND NORTHERN WESTCHESTER INTO AN ADVISORY. SNOWFALL ACCUMULATIONS OF 4 TO 7 INCHES IN THE WARNING AND 2 TO 5 INCHES IN THE ADVISORY AREA. SOME UNCERTAINTIES STILL EXIST INCLUDING THE NORTHERN EXTENT OF THE SNOW...ESPECIALLY DURING THE DAY ON THURSDAY. IF ANY NORTH SHIFT NORTH OCCURS...TOTALS COULD BE A BIT HIGHER THAN FORECAST. ON THE OTHER HAND...IF A SOUTH SHIFT OCCURS...TOTALS COULD END UP LOWER. TEMPERATURES WILL BEGIN TO FALL OVERNIGHT...EVENTUALLY BELOW FREEZING BEFORE 08Z. EXPECT TEMPERATURES FALLING INTO THE 20S THURSDAY MORNING AND REMAINING IN THE LOW TO MIDDLE 20S DURING THE DAY.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM FRIDAY/... HIGH PRESSURE BUILDS IN FROM THE WEST THURSDAY NIGHT. SKIES WILL CLEAR FROM WEST TO EAST. WINDS SHOULD DIMINISH LATE AND WITH DRY CONDITIONS...EXPECTING AN UNSEASONABLY COLD NIGHT WITH TEMPERATURES FALLING INTO THE SINGLE DIGITS FOR MOST LOCATIONS AND LOWER TO MIDDLE TEENS IN THE NYC METRO. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... HIGH PRESSURE RIDGE AXIS WILL BE RIGHT OVER US ON FRIDAY...AND IT WILL SLOWLY SHIFT OFFSHORE LATE IN THE DAY INTO FRIDAY NIGHT. THIS HIGH PRESSURE SYSTEM HAS CANADIAN ORIGINS...AND WITH PLENTY OF SNOWPACK TO THE WEST...IT WON`T HAVE MUCH OF A CHANCE TO MODERATE BEFORE IT ARRIVES HERE. AFTER A RECORD TO NEAR-RECORD COLD START...DAYTIME TEMPS WILL ONLY RECOVER INTO THE MID 20S...ABOUT 20 DEGREES BELOW NORMAL. A FAST FLOW ALOFT FOR THE WEEKEND THROUGH WEDNESDAY LEADS TO DIFFERENCES AMONG THE GLOBAL MODELS REGARDING THE TIMING OF WEAK FRONTS/TROUGHS PASSING THROUGH HERE. THIS RELATIVELY FLAT FLOW WILL AT LEAST KEEP THE ABNORMALLY COLD AIR WE`VE BEEN EXPERIENCING LOCKED UP TO OUR NORTH. SO WITH THE GIVEN UNCERTAINTY OF THE SURFACE FEATURES...WILL GO CLOSE TO WPC GUIDANCE FOR THIS PERIOD. THIS KEEPS MOST OF THE REST OF THE LONG TERM PERIOD DRY. JUST A SLIGHT CHANCE OF LIGHT SNOW NORTH OF THE CITY SATURDAY NIGHT WHERE MOISTURE AND LIFT WILL BE BETTER AS LOW PRESSURE PASSES WELL TO THE NORTH. THE ONLY OTHER CHANCE OF PCPN WILL ARRIVE ON MONDAY AS ANOTHER SYSTEM PASSES WELL TO THE NORTH. THIS ONE APPEARS TO HAVE MORE MOISTURE WITH IT...SO HAVE SLIGHT CHC POPS FOR THE ENTIRE AREA. PCPN TYPE MOST LIKELY SNOW TO START...THEN MIXING WITH RAIN BEFORE CHANGING TO RAIN IN THE AFTERNOON. WITH THE VERY COLD AIR STAYING NORTH...HIGH TEMPERATURES WILL GRADUALLY MODERATE FROM THE MID 30S ON SATURDAY TO THE UPPER 40S ON WEDNESDAY...WHICH IS NORMAL. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... PERIODS OF LIGHT TO LOCALLY MODERATE RAIN WILL CONTINUE AS LOW PRES TRACKS FROM THE GULF COAST AND MOVES OFF THE MID-ATLANTIC LATE TONIGHT THROUGH THURSDAY MORNING. MVFR TO IFR CONDS EXPECTED IN RAIN AND FOG. BASED ON LATEST SFC OBS AND GUIDANCE...THE COLD AIR IS TAKING A BIT LONGER TO ARRIVE THAN PREVIOUSLY FORECAST. THE TRANSITION TO THE WINTRY MIX WILL OCCUR FROM 07-09Z...AND THEN THE TRANSITION TO ALL SNOW WILL OCCUR AFTER 09Z. IT IS ALSO POSSIBLE THAT THE CHANGEOVER MAY TAKE PLACE AN HOUR OR 2 LATER THAN THIS. MODERATE SNOW THEN EXPECTED THROUGH THE AFTERNOON...TAPERING OFF LATE IN THE DAY. IFR/LIFR CONDS IN THE HEAVIEST SNOW...GRADUALLY IMPROVING TO MVFR IN THE AFTERNOON...AND THEN TO VFR LATE. EXPECTED RUNWAY ACCUMULATIONS: KJFK/KISP...6-8 INCHES. KLGA/KEWR/KTEB/KHPN/KBDR/KGON...4-6 INCHES. KSWF...2-3 INCHES. W-NW AT 10 KT OR LESS THROUGH DAYBREAK...AND THEN NW WINDS INCREASE TO 10-15 KT WITH GUSTS UP TO 20 KT BY DAYBREAK. NW WINDS DIMINISH TO 10 KT OR LESS LATE IN THE DAY. .OUTLOOK FOR 06Z FRIDAY THROUGH MONDAY... .LATE TONIGHT-FRIDAY...VFR. .SAT/SUN...VFR. .MON...VFR. GUSTY NW WINDS. && .MARINE... SCA CONDITIONS ARE EXPECTED TO CONTINUE ACROSS THE OCEAN WITH THE REMAINING WATERS BELOW SCA THROUGH THURSDAY. WINDS ARE MARGINAL ON THE OCEAN WATERS...ESPECIALLY TONIGHT WHEN THEY LIKELY STAY BELOW. SEAS HOWEVER WILL BE ABOVE SCA LEVELS. WINDS INCREASE ON THURSDAY AND WILL CONTINUE THROUGH THE DAY WITH SEAS AROUND 5 FEET OVER THE OCEAN. SCA CONDITIONS MAY CONTINUE INTO THURSDAY NIGHT SO THE ADVISORY MAY NEED TO BE EXTENDED FURTHER. A PERIOD OF SUB SCA CONDITIONS FOR FRIDAY AND FRIDAY NIGHT EXPECTED AS A HIGH PRESSURE RIDGE APPROACHES AND PASSES THROUGH THE WATERS. THE RETURN SW FLOW INCREASES ON SATURDAY...WITH SCA CONDITIONS DEVELOPING ON THE OCEAN DURING THE MORNING AND LASTING INTO SATURDAY EVENING. A LACK OF STRONG SURFACE FEATURES THEREAFTER THROUGH MONDAY WILL PROMOTE SUB-SCA CONDITIONS. HAVE GONE BELOW WAVEWATCH GUIDANCE FOR SOME OF THIS PERIOD AS IT APPEARS TO BUILDING TOO MUCH SWELL. && .HYDROLOGY... 1/4 TO 3/4 INCH LIQUID EQUIVALENT PRECIPITATION IS LIKELY TONIGHT INTO THURSDAY. MOST OF THIS WILL BE FROZEN...SO HYDROLOGIC IMPACTS ARE NOT EXPECTED. NO SIGNIFICANT PRECIPITATION IS EXPECTED FROM THURSDAY NIGHT THROUGH THE MIDDLE OF NEXT WEEK. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR CTZ009>012. NY...WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR NYZ072>075-078>081-176>179. WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR NYZ069>071. NJ...WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR NJZ006- 106>108. WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR NJZ002- 004-103>105. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ350- 353-355. && $$ SYNOPSIS...JC/DS NEAR TERM...DS/DW SHORT TERM...DS LONG TERM...JC AVIATION...MPS MARINE...JC/DS HYDROLOGY...JC/DS

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