Area Forecast Discussion
Issued by NWS Upton, NY

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000
FXUS61 KOKX 310528
AFDOKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
128 AM EDT TUE MAR 31 2015

.SYNOPSIS...
A COLD FRONT MOVES OFFSHORE TONIGHT...FOLLOWED BY A QUICK MOVING
LOW PASSING TO THE SOUTH ON TUESDAY. HIGH PRESSURE WILL BUILD
ACROSS THE AREA ON WEDNESDAY AHEAD OF A FRONTAL SYSTEM MOVING INTO
THE PLAINS. THE FRONTAL SYSTEM WILL THEN PROGRESS SLOWLY ACROSS
THE AREA FROM LATE THURSDAY INTO EARLY SATURDAY. HIGH PRESSURE
WILL RETURN LATER THIS WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
INITIAL COLD FRONT MOVED OFFSHORE EARLIER THIS EVENING.
HOWEVER...A SECONDARY COLD FRONT IS CURRENTLY MAKING ITS WAY
ACROSS THE REGION. THIS FRONT IN COMBINATION WITH A MID LEVEL
SHORTWAVE HAS ALLOWED ISOLD/SCT SHOWERS TO MOVE INTO PARTS OF NE
NJ...NYC METRO AND SOUTHERN. THESE RAIN SHOWERS SHOULD DIMINISH
BY 06Z. THEREAFTER EXPECT CLEARING SKIES...AND DIMINISHING W TO
WNW FLOW. LOWS WILL BE IN THE UPPER 20S INLAND AND IN THE LONG
ISLAND PINE BARRENS...30-35 MOST ELSEWHERE...AND MID/UPPER 30S
INVOF NYC.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
ALBERTA CLIPPER LOW NOW MOVING FROM THE NRN MISSISSIPPI VALLEY
TOWARD THE UPPER GREAT LAKES WILL CONTINUE SE...REACHING THE NRN
MID ATLANTIC BY TUE AFTERNOON. EXPECT TUE MORNING TO BE DRY WITH
INCREASING CLOUDS...THEN PRECIP SHOULD OVERSPREAD THE AREA IN THE
AFTERNOON. HAVE LIKELY/CAT POP FOR NEARLY THE ENTIRE CWA...EXCEPT
FOR SOUTHERN CT AS THERE IS SOME UNCERTAINTY AS TO HOW FAR NORTH
THE ASSOCIATED PRECIP SHIELD WILL EXTEND SINCE NWP GUIDANCE SHOWS
BEST WAA AND H5 FORCING PASSING MAINLY OVER NYC METRO/LONG ISLAND
AND POINTS SOUTH.

PRECIP DURING THE DAYLIGHT HRS SHOULD BE MAINLY RAIN FOR NYC
METRO AND LONG ISLAND...BUT INLAND THERE IS SOME UNCERTAINTY AS TO
PRECIP TYPE. ATTM EXPECT AN ELEVATION-DEPENDENT SNOWFALL...WITH A
COLD RAIN OR A RAIN/SNOW MIX IN THE LOWER ELEVATIONS...AND MOSTLY
SNOW IN THE HIGHEST ELEVATIONS. P-TYPE SHOULD TREND MORE TOWARD
SNOW THROUGHOUT BEFORE ENDING AS THE BOUNDARY LAYER COOLS VIA
WET-BULB COOLING AND AN INCREASING COLDER NORTHERLY FLOW. ATTM
EXPECT LITTLE TO NO ACCUMULATION IN NYC METRO...NO MORE THAN A
COATING MOST ELSEWHERE AND UP TO AN INCH IN THE HIGHEST
ELEVATIONS. THE WORST-CASE SCENARIO WOULD BE A COATING OF
ACCUMULATION IN NYC...UP TO AN INCH MOST ELSEWHERE...AND 1-2
INCHES IN THE HIGHER ELEVATIONS.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
A PROGRESSIVE...YET SOMEWHAT AMPLIFIED UPPER FLOW ACROSS THE LOWER
48...WILL BE FEATURED DURING THE PERIOD.  THIS WILL RESULT IN
SEVERAL SWINGS IN THE TEMP REGIME AS WE GO FROM BELOW NORMAL AT THE
START OF THE PERIOD...TO ABOVE NORMAL AHEAD OF AN APPROACHING
FRONTAL SYSTEM AT THE END OF THE WEEK...FOLLOWED BY YET ANOTHER SHOT
OF UNSEASONABLY COLD AIR AT THE END OF NEXT WEEKEND. THERE ARE ALSO
SOME TIMING ISSUES...IN PARTICULAR WITH THE FRONTAL SYSTEM AT THE
END OF THE WEEK. THE GFS IS MORE AGGRESSIVE WITH A RAINFALL WITH A
FRONTAL WAVE...WHILE THE ECMWF HAS THAT WAVE DISPLACED FARTHER NORTH
AND WEST. EVEN SO...BOTH THE 12Z GFS AND ECMWF DRY CONDITIONS OUT
BEHIND THE COLD FRONTAL PASSAGE ON SAT. THE DIFFERENCES ARISE DUE TO
THE TIMING OF THE PAC SHORTWAVE ENERGY. THE SPECIFICS OF SUCH CAN
NOT BE WORKED OUT THIS EARLY IN THE FORECAST PROCESS. PREFERENCE WAS
TO TAKE A MIDDLE GROUND APPROACH WITH THE TIMING OF THE LATE
WEEK SYSTEM.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
LOW PRES APPROACHES FROM THE W TODAY AND PASSES S OF LONG ISLAND
TNGT.

VFR TIL THIS AFTN WHEN CIGS LWR AND PCPN OVERSPREADS THE REGION.
THE PCPN STARTS AS A MIX OF RASN OR ALL RAIN...THEN CHANGES TO
SNOW INTO THE EVE.

LIFR POSSIBLE IN THE 22-04Z TIME PERIOD WHEN POTENTIAL WILL BE
HIGHEST FOR 1/2SM SN.

IMPROVEMENT FROM W TO E TNGT.

WINDS VEER THRU THIS AFTN...THEN VRB DIRECTION BECOMES NE AS THE
LOW APPROACHES THE METRO. THE NE FLOW THEN VEERS TO THE NW AS THE
LOW PASSES E OF THE REGION.

.OUTLOOK FOR 06Z WEDNESDAY THROUGH SATURDAY...
.TUESDAY NIGHT...VFR WITH NW FLOW 10-15KT.
.WEDNESDAY-THURSDAY...VFR.
.THURSDAY NIGHT-FRIDAY NIGHT...MVFR IN RAIN SHOWERS.
.SATURDAY...SUB VFR POSSIBLE IN SHOWERS EARLY...THEN VFR LATE.

&&

.MARINE...
SCA CONTINUES ON THE OCEAN WATERS...EASTERN SOUND...AND PECONIC
AND GARDINERS BAYS. OCEAN SEAS 4-6 FT AND MAY INCREASE ANOTHER FT
BY DAYBREAK. GUSTS OUT EAST AFTER FROPA SHOULD REACH SCA LEVELS.
GUSTS TO 25 KT LOOK TO BE ONLY BRIEF/OCNL IN NATURE THIS EVENING
ON THE WRN SOUND AND SOUTH SHORE BAYS.

SCA CONDS COULD LAST ON THE OCEAN THROUGH TUE NIGHT...AND ALSO
RETURN TO THE ERN WATERS TUE NIGHT...AS LOW PRESSURE PASSES TO THE
S AND NORTHERLY FLOW INCREASES IN ITS WAKE. THEN EXPECT SUB-SMALL
CRAFT LEVEL CONDITIONS WED THROUGH THU AS A WEAK PRESSURE GRADIENT
REMAINS OVER THE REGION. WIND GUSTS AND WAVES INCREASE TO SMALL
CRAFT LEVELS AHEAD OF THE NEXT SYSTEM APPROACHING THE OCEAN
WATERS THURSDAY NIGHT INTO SATURDAY.

&&

.HYDROLOGY...
QPF OF 1/10 TO 1/4 INCH EXPECTED TUE AFTERNOON AND EVENING.

THERE IS THE POTENTIAL FOR WIDESPREAD RAINFALL AT THE
END OF THE WEEK WITH A FRONTAL WAVE ALONG A SLOW MOVING FRONTAL
SYSTEM.

RIVERS AND STREAMS ARE EXPECTED TO REMAIN BELOW BANK FULL...BUT
INCREASED RIVER/STREAM FLOW ACROSS THE LOWER HUDSON VALLEY AND
SOUTHERN CONNECTICUT WILL CONTINUE ICE BREAKUP AND MOVEMENT INTO
THIS WEEKEND. ISOLATED ICE JAMS ARE POSSIBLE...WHICH IF THEY
OCCUR...COULD RESULT IN LOCALIZED FLOODING. SINCE ICE JAM FLOODING
IS UNPREDICTABLE AND SUDDEN...INTERESTS ALONG ICE COVERED RIVERS
SHOULD MONITOR NWS FORECASTS FOR THE LATEST INFORMATION.

FOR DETAILS ON SPECIFIC AREA RIVERS AND LAKES...INCLUDING
OBSERVED AND FORECAST RIVER STAGES AND LAKE ELEVATIONS...PLEASE
VISIT THE ADVANCED HYDROLOGIC PREDICTION SERVICE /AHPS/ GRAPHS ON
OUR WEB SITE.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
NY...NONE.
NJ...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT TODAY FOR ANZ330-340-350-
     353-355.

&&

$$
SYNOPSIS...GOODMAN/DW
NEAR TERM...GOODMAN
SHORT TERM...GOODMAN
LONG TERM...DW
AVIATION...JMC/PW
MARINE...GOODMAN/DW
HYDROLOGY...GOODMAN/DW


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