Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 281356
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
956 AM EDT SAT MAR 28 2015

.SYNOPSIS...
A HIGH PRESSURE SYSTEM OVER THE GREAT LAKES WILL SINK SOUTHEAST
AND REACH THE SOUTHEAST COAST SUNDAY. A COLD FRONT ASSOCIATED
WITH A LOW PRESSURE SYSTEM WILL MOVE THROUGH THE REGION ON
MONDAY. THIS WILL BE FOLLOWED QUICKLY BY AN ALBERTA CLIPPER
TYPE LOW PRESSURE SYSTEM PASSING NEAR OR THROUGH THE AREA
LATE ON TUESDAY. A HIGH PRESSURE SYSTEM SHOULD THEN BUILD INTO
THE REGION FOR WEDNESDAY. A COLD FRONT IS PREDICTED TO REACH THE
WESTERN GREAT LAKES ON THURSDAY MORNING AND APPROACH OUR AREA ON
FRIDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
HAVE INCREASED POPS ACROSS THE DELMARVA INTO THE LIKELY-
CATEGORICAL RANGE FOR THE NEXT FEW HOURS AS REGIONAL TRAFFIC
CAMERAS SHOW MINOR SNOW ACCUMULATIONS ON GRASSY SURFACES. THERE IS
STILL SOME DRY AND SLIGHTLY WARMER AIR THE FALLING SNOW HAS TO
OVERCOME AS THE RADAR IS SHOWING SOME SIGNS OF SUBLIMINATION BUT
AS WAS SAID ABOVE, THE GRASSY/MULCHY AREAS ARE SEEING MINOR
DUSTING/ACCUMULATIONS. THE CURRENT ACTIVITY WILL SLIDE TOWARDS THE
SOUTH AND EAST THROUGH THE MORNING HOURS BEFORE MORE ISOLATED TO SCATTERED
SNOW SHOWERS ARE EXPECTED THIS AFTERNOON. BASED ON SURFACE AND
BOUNDARY LAYER TEMPERATURES WE ARE NOT EXPECTING MUCH IN THE WAY
OF ACCUMULATION THIS AFTERNOON...THERE COULD ALSO BE SOME RAIN
MIXING IN FOR A TIME.

OTHERWISE, THE SYNOPTIC SETUP IS COMPRISED OF A STRONG UPPER-
LEVEL TROUGH ACROSS THE EAST. THE WATER VAPOR IMAGERY SHOWS THIS
FEATURE WELL. AT THE SURFACE, HIGH PRESSURE WILL BE BUILDING INTO
THE CENTRAL GREAT LAKES AND OHIO VALLEY DURING THE COURSE OF THE
DAY. MEANWHILE, LOW PRESSURE WILL CONTINUE TO DEVELOP WELL TO OUR
EAST.

AS THE UPPER-LEVEL TROUGH AXIS SETTLES OVERHEAD THIS AFTERNOON, A
RATHER COLD AIRMASS FOR THIS TIME OF THE YEAR WILL ARRIVE. THIS WILL
OCCUR AS STRONG CAA IS PRESENT. THE COMBINATION OF THIS CAA AND A
TIGHTENING PRESSURE GRADIENT WILL RESULT IN BREEZY CONDITIONS,
ESPECIALLY LATER THIS MORNING AND THROUGH THE AFTERNOON AS THE DEPTH
OF THE MIXING LAYER INCREASES. THE FORECAST SOUNDINGS INDICATE ABOUT
30 MPH WIND GUSTS SHOULD OCCUR ACROSS THE AREA.

SOME ENERGY SLIDING OFFSHORE WITHIN THE SOUTHWESTERLY FLOW ALOFT
AHEAD OF THE TROUGH IS MAINTAINING SOME LIGHT PRECIPITATION VERY
JUST OFF THE COAST. THIS APPEARS TO BE MOSTLY MID LEVEL MOISTURE.
OTHERWISE, SOME FLURRIES OR SNOW SHOWERS ARE JUST TO OUR WEST. THESE
APPEAR TO BE TIED TO HEIGHT FALLS AND SOME WEAK ASCENT ASSOCIATED
WITH THE ARRIVING UPPER-LEVEL TROUGH. WE CARRIED SOME FLURRIES FOR A
TIME THIS MORNING OUTSIDE OF THE DELMARVA ZONES. THE ARRIVAL OF A
STRONG SHORT WAVE WITHIN THE TROUGH AXIS IS FORECAST TO ARRIVE BY
LATE AFTERNOON. IT APPEARS THAT A SURFACE TROUGH WILL ALSO SETTLE
SOUTHWARD ACROSS OUR AREA THIS AFTERNOON. WHILE THE AIRMASS WILL
BE UNDERGOING A DRYING TREND, THERE IS ENOUGH MOISTURE FORECAST TO
BE PRESENT IN THE LOWER LEVELS. THE COMBINATION OF COLD AIR ALOFT,
SOME BOUNDARY LAYER HEATING AND WITH SOME LIFT FROM THE SHORT WAVE
AND SURFACE TROUGH THERE SHOULD BE SOME SNOW OR RAIN SHOWERS. SOME
OF THIS MAY INITIALLY NOT REACH THE GROUND AS THE LOWEST LEVELS
DRY SOME MORE. THERE DOES NOT APPEAR TO BE MUCH IN THE WAY OF
INSTABILITY AS ADDITIONAL DRYING IS FORECAST TO TAKE PLACE ABOVE
700 MB, THEREFORE A CONVECTIVE CONTRIBUTION LOOKS LOW. THERE ARE
SOME HINTS IN SOME OF THE HIGH RESOLUTION GUIDANCE THOUGH THAT
SOME NARROW BANDING OR WRAPAROUND MAY DEVELOP IN THE VICINITY OF
NORTHEASTERN NEW JERSEY LATER THIS AFTERNOON AND EVEN DOWN INTO
THE DELMARVA. OVERALL THOUGH, ANY PRECIPITATION SHOULD BE ON THE
LIGHTER SIDE.

AS FOR THE HIGH TEMPERATURES, WE USED A NAM/GFS MOS AND ECMWF BLEND
OVERALL WITH SOME TWEAKS. WE SHOULD MAINTAIN A DECENT AMOUNT OF
CLOUD COVER ACROSS THE AREA FOR MUCH OF THE DAY, AND THIS COMBINED
WITH THE STRONG CAA WILL RESULT IN A COLD LATE MARCH DAY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
AN UPPER-LEVEL TROUGH AXIS IS FORECAST TO SWING ACROSS OUR AREA
DURING TONIGHT. THERE IS QUITE A BIT OF SHORT WAVE ENERGY STRETCHED
OUT WITHIN IT AS IT SHIFTS ACROSS THE REGION, HOWEVER THE AIRMASS IS
FORECAST TO UNDERGO FURTHER DRYING. THE TAILEND OF THIS THOUGH MAY
RESULT IN A FEW NARROW STREAMERS OF SNOW SHOWERS ALTHOUGH IT IS
DIFFICULT TO PINPOINT EXACTLY WHERE THIS OCCURS IF IT WERE TO
HAPPEN. SOME OF THE HIGH RESOLUTION GUIDANCE SUGGESTS THAT OUR
SOUTHERN ZONES MAY GET A NARROW BAND OR TWO OF SNOW SHOWERS TO START
THE EVENING, AS STRONGER PVA MOVES THROUGH. OVERALL, THIS WOULD BE
RATHER LOCALIZED AND GIVEN THE DRYING NOT SURE IF IT ACTUALLY
MATERIALIZES INTO MUCH.

OTHERWISE, HIGH PRESSURE CONTINUES TO BUILD EASTWARD FROM THE OHIO
VALLEY HOWEVER ITS CENTER REMAINS TO OUR WEST. THIS ALLOWS A TIGHT
PRESSURE GRADIENT TO REMAIN OVER THE REGION. WHILE THE MIXING SHOULD
DECREASE SOME THROUGH THE EVENING, A BREEZE IS EXPECTED TO BE
MAINTAINED THROUGH THE NIGHT WITH THE MOST GUSTINESS OCCURRING IN
THE EVENING.

AS FOR THE LOW TEMPERATURES, A VERY COLD NIGHT IS EXPECTED WITH
TEMPERATURES DROPPING DOWN INTO THE 20S AND TEENS. THE WIND MAY HOLD
THESE UP SOME, HOWEVER IT WILL ALSO RESULT IN RATHER COLD WIND
CHILL VALUES. OVERALL, WE USED A MOS BLEND.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
AN ACTIVE LONG TERM WITH A COUPLE OF PCPN SHOTS POSSIBLE. THE
WRF-NMMB INITIALIZATION AT 500MB LOOKED BETTER THAN THE GFS, BOTH
MODELS WERE ABOUT THE SAME AT 850MB AND 925MB WITH ANY ERRORS
ON THE COLD SIDE BY ABOUT 1C. THE DP/DT WITH THE MODELS OVER
THE PAST 24 HOURS WAS SHOWING A DEEPER EAST COAST TROF. BASED
ON THIS MOVING FORWARD WE WERE SLOWER WITH THE EVOLUTION OF
EVENTS.

AN AIR MASS MODIFICATION WITH DECREASING WINDS IS PREDICTED FOR
SUNDAY. GIVEN THE COLD START, CHANCES ARE THAT THE MAX TEMPS
WILL OCCUR LATER IN THE AFTERNOON THAN USUAL. GIVEN FULL
SUN AND A DOWNSLOPING WIND, WE WENT FULL ADIABATIC
WITH MAX TEMPS CLOSE TO END OF THE AFTERNOON SOUNDING
SUGGESTED MAX TEMPS.

THE WEAKER OF THE NEXT TWO SYSTEMS WILL APPROACH OUR AREA ON MONDAY
NIGHT. THERE WILL BE DECENT MID LEVEL QVEC CONVERGENCE, BUT THE
PREDICTED ISENTROPIC LIFT AND FGEN FORCING ARE MORE MUTED. THE JET IS
NOT IN A BAD POSITION. GIVEN THE OVERALL DRYNESS OF THE INITIAL
AIR MASS, MODELS ARE NOT PREDICTING MUCH PCPN. BECAUSE OF THE DPVA
AND THE MID LEVEL QVEC CONVERGENCE, PCPN SHOULD BE FALLING FROM A
MID CLOUD DECK. NOT SURE IF IT WILL MAKE IT TO THE GROUND, BUT FOR
NOW WE WENT HIGHER THAN STAT GUIDANCE BECAUSE OF THE FORCING. WHILE
A LLJ WILL BE WARMING THE SUB CLOUD LAYER AND MIGHT BE ABLE TO OFFSET
EVAPORATIONAL COOLING EFFECTS, SNOW AS A PTYPE IS A POSSIBILITY IN
THE NORTHERN PART OF OUR CWA. BECAUSE QPF AMOUNTS ARE LOW, ANY ACCUMS
ARE EXPECTED TO BE LESS THAN AN INCH. MIN TEMPS WILL LIKELY OCCUR
EARLIER IN THE NIGHT AND RISE TOWARD MORNING.

USUALLY THE CASE WITH THESE WEAK SYSTEMS, ANY PCPN OCCURS IN THE WAA
PHASE WITH LITTLE IF ANY WITH THE CFP ITSELF. MODELS ARE PRETTY CLOSE
ON THAT DURING THE DAY ON MONDAY. WITH THE LAGGING STRONGER
CAA, THE DOWNSLOPING WINDS SHOULD MORE THAN COMPENSATE FOR COOLING ALOFT.
A STAT GUIDANCE COMBO LOOKS DECENT FOR MAX TEMPERATURES. IT WILL
BECOME WINDIER WIND PEAK GUSTS LIKELY REACHING AT LEAST 20 TO 30 MPH.

THE RIDGING FROM THE NEXT HIGH PRESSURE SYSTEM PASSES OVER OUR FORECAST
AREA ON MONDAY NIGHT. BUT WE MAY REMAIN IN A BIT OF A GRADIENT AND
DID NOT BOTTOM MIN TEMPERATURES.

AT LEAST ON PAPER TODAY, THE NEXT ALBERTA TYPE LOW PRESSURE SYSTEM
LOOKS MORE ROBUST. A MUCH BETTER PREDICTED COUPLET OF MID LEVEL FGEN
AND QVEC FORCING IN OUR AREA. THIS CAN BE SEEN WITH IN THE QPF
FIELD BY ITSELF. THERE ARE TRACK DIFFERENCES WITH DIFFERENCES
IN OPINION AS TO THE GREATER IMPACT. FOR NOW WE HAVE COMPROMISED
BETWEEN THE DATASETS, THUS ONSET OF UPPED PCPN CHANCES IS TUESDAY
AFTERNOON AND CONTINUING INTO TUESDAY NIGHT. WHILE THE BOUNDARY
LAYER WILL GET WARMED ON TUESDAY, IT IS STILL COLD ALOFT AND A
CHANGE TO SNOW, ESPECIALLY OVER THE HIGHER TERRAIN NORTH WOULD
BE THE LOGICAL OUTCOME FOR SUCH A SCENARIO. THIS ONE COULD BE
SNOWIER. BECAUSE OF DIFFERENCES WITH THE TRACK AND THE
INHERENT UNCERTAINTY OF TIMING, THERE EXISTS THE POTENTIAL
FOR SOME BIG ERRORS WITH MAX TEMPS ON TUE. WE ARE TOWARD THE
HIGHER END OF THE GUIDANCE SPECTRUM.

WEAKER HIGH PRESSURE SYSTEM TO FOLLOW ON WEDNESDAY WHICH MEANS LITTLE IF ANY
DROP IN MAXIMUM TEMPERATURES. THE REST OF THE LONG TERM WE SHIED AWAY
FROM THE FASTER GFS CFP TIMING. THUS OUR MAX TEMPS THURSDAY ARE HIGHER
THAN ITS STAT GUIDANCE. WE ALSO PUSHED BACK THE ONSET OF SHOWER CHANCES
CLOSER TO THE ECMWF`S TIMING AND PERSISTED IT THROUGH FRIDAY.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY, AND SURROUNDING AREAS.

TODAY...VFR WITH CEILINGS MAINLY AROUND 5000 FEET. NORTH TO
NORTHWEST WINDS INCREASING TO AROUND 15 KNOTS WITH GUSTS TO AROUND
25 KNOTS BY MIDDAY. A FEW SNOW OR RAIN SHOWERS ARE POSSIBLE, HOWEVER
WITH LOW CONFIDENCE ON ANY ORGANIZATION A MENTION WAS NOT INCLUDED
AT THIS TIME.

TONIGHT...VFR CEILINGS GENERALLY SCATTERING OUT. NORTHWEST WINDS 10-
15 KNOTS WITH GUSTS TO AROUND 20 KNOTS.

OUTLOOK...
SUNDAY...VFR. GUSTY NORTHWEST WINDS WILL BE DECREASING.

SUNDAY NIGHT AND MONDAY...SOME LOWER MVFR CIGS AND VSBYS IN
SCATTERED RAIN, HIGHER TERRAIN SNOW, SHOWERS. THERE IS A
CHANCE FOR LLWS AT SOUTHERN AIRPORTS. NORTHWEST WINDS
ON MONDAY SHOULD GUST TO AROUND 25 KNOTS.

MONDAY NIGHT...VFR.

TUESDAY AND TUESDAY NIGHT...POTENTIAL MVFR OR IFR RESTRICTIONS
IN RAIN AND POSSIBLY SNOW AT HIGHER TERRAIN AIRPORTS.

WEDNESDAY...VFR OR BECOMING VFR AS THE DAY PROGRESSES.

&&

.MARINE...
THE CAA WILL INCREASE THROUGH THE DAY AS THE PRESSURE GRADIENT
TIGHTENS BETWEEN LOW PRESSURE ORGANIZING WELL OFFSHORE AND HIGH
PRESSURE BUILDING INTO THE OHIO VALLEY. THIS WILL RESULT IN NORTH TO
NORTHWEST WINDS INCREASING TO SMALL CRAFT ADVISORY LEVELS. THE
FORECAST SOUNDINGS INDICATE THAT THE MIXING DEPTH WILL INCREASE INTO
TONIGHT WITH GUSTS UP TO 30 KNOTS. THIS WILL CONTINUE TONIGHT AS
WELL. THE UPTICK IN THE WINDS WILL ALLOW THE SEAS TO BUILD SOME ONCE
AGAIN, ALTHOUGH GIVEN THE OFFSHORE COMPONENT THE HIGHER SETS WILL BE
NEAR THE MOUTH OF DELAWARE BAY AND ALSO FARTHER OFFSHORE. AS A
RESULT, THE SMALL CRAFTS ADVISORY REMAINS IN EFFECT.

OUTLOOK...
SUNDAY...THE SMALL CRAFT ADVISORY WAS EXTENDED INTO
SUNDAY MORNING. WINDS AND SEAS SHOULD BE BELOW SCA CRITERIA BY
THE AFTERNOON AS THE GRADIENT RELAXES.

SUNDAY NIGHT AND MONDAY...ANOTHER ROUND OF SCA CONDITIONS
IS POSSIBLE IN THE INCREASING SW FLOW PRECEDING THE NEXT
CFP. WHILE AIR TEMPERATURES WILL BE WARMING MONDAY, MIXING NEAR
COASTAL AREAS COULD KEEP SCA CONDITIONS PERSISTING EVEN AFTER
THE CFP.

MONDAY NIGHT...SUB SCA CONDITIONS OUTLOOKED TO RETURN AS THE
PRESSURE GRADIENT WEAKENS AGAIN.

TUESDAY THROUGH WEDNESDAY...PRIMARILY SUB SMALL CRAFT ADVISORY
CONDITIONS ARE OUTLOOKED. THE ONE CAVEAT IS THAT WITH A CLIPPER LOW
PRESSURE SYSTEM PASSING THROUGH OR NEAR OUR COASTAL WATERS, WE
WILL HAVE TO MONITOR A STRONGER OVERALL LOW THAT MIGHT INCREASE
BOTH WINDS AND SEAS INTO SMALL CRAFT ADVISORY CRITERIA.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT SUNDAY FOR ANZ430-431-
     450>455.

&&

$$
SYNOPSIS...GAINES/GIGI
NEAR TERM...GORSE/HEAVENER
SHORT TERM...GORSE
LONG TERM...GIGI
AVIATION...GAINES/GIGI/GORSE
MARINE...GAINES/GIGI/GORSE



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