Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 231951
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
351 PM EDT MON MAR 23 2015

.SYNOPSIS...
HIGH PRESSURE CENTERED NEAR THE NORTHERN GREAT LAKES WILL CONTINUE
TO SLOWLY BUILD SOUTHEASTWARD AND OVER OUR AREA THROUGH TUESDAY. A
WARM FRONT IS THEN FORECAST TO LIFT NORTH THROUGH THE REGION
WEDNESDAY, FOLLOWED BY A STRONG COLD FRONT THURSDAY NIGHT. HIGH
PRESSURE BUILDING DOWN FROM CENTRAL CANADA FRIDAY WILL GRADUALLY
BUILD EAST TOWARD THE MID ATLANTIC OVER THE WEEKEND, WITH ANOTHER
COLD FRONT POSSIBLY CROSSING THE REGION MONDAY.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
HIGH PRESSURE AT THE SURFACE CENTERED OVER THE GREAT LAKES REGION,
WHICH THEN STRETCHES SOUTHEASTWARD ACROSS OUR AREA. THIS IS FORECAST
TO REMAIN IN PLACE THROUGH TONIGHT. AS WE LOOK ALOFT, AN UPPER-LEVEL
TROUGH IS MAINTAINED ACROSS THE EAST. THERE ARE SOME SHORT WAVES
EMBEDDED WITHIN THE ASSOCIATED FLOW.

THE ABUNDANCE OF DRY AIR AND SUBSIDENCE, ALONG WITH A SHEARING OUT
SHORT WAVE WELL TO OUR SOUTH, IS HELPING TO PROVIDE PLENTY OF
SUNSHINE THIS AFTERNOON. THE WATER VAPOR IMAGERY HOWEVER SHOWS A
POTENT SHORT WAVE EXITING THE CHICAGO AREA AS IT TRACKS EAST-
SOUTHEASTWARD. AN UPPER AIR ANALYSIS INDICATES STRONG WAA OCCURRING
WITH THIS FEATURE, WHICH IS HELPING PRODUCE AN AREA OF HEAVIER SNOW
ACROSS PORTIONS OF ILLINOIS, INDIANA AND INTO OHIO. THE ASSOCIATED
WAA HOWEVER IS FORECAST TO DECREASE EAST OF THE MOUNTAINS LATE
TONIGHT. SOME OF THE GUIDANCE DOES MAINTAIN ENOUGH LIFT AND MOISTURE
THOUGH TO PRODUCE SOME OVERRUNNING LIGHT SNOW ACROSS MAINLY PORTIONS
OF OUR DELMARVA ZONES LATE TONIGHT. THE FORECAST SOUNDINGS SHOW THE
AIRMASS SATURATING IN THE MID LEVELS FIRST THEN WORKING DOWNWARD.
THE LOW LEVELS MAY REMAIN TO DRY FOR ANY PRECIPITATION TO REACH THE
SURFACE, HOWEVER SOME OF THE SAME FORECAST SOUNDINGS DO MOISTEN UP
THE LOWER LEVELS ENOUGH.

SINCE THE INITIAL SHORT WAVE MAY START TO SHEAR OUT SOME PLUS IT IS
RUNNING INTO MORE OF A CONFLUENT FLOW OVER OUR REGION, WE ARE NOT
REAL CONFIDENT ABOUT PRECIPITATION LATE TONIGHT THIS FAR EAST. FOR
NOW, ADDED AN AREA OF 20-40 POPS ACROSS PARTS OF DELAWARE, EASTERN
MARYLAND AND INTO CHESTER COUNTY FOR THE POTENTIAL FOR SOME LIGHT
SNOW. THIS WAS COLLABORATED WITH WFO`S STERLING AND STATE COLLEGE.

OTHERWISE, INCREASING CLOUDS ARE EXPECTED AS AT LEAST SOME WAA
OCCURS AHEAD OF THE AFOREMENTIONED SHORT WAVE. THIS WILL BE MID TO
HIGH LEVEL CLOUDINESS FIRST, WHICH WILL THEN TEND TO SETTLE INTO A
STRATOCUMULUS DECK NEAR THE SUBSIDENCE INVERSION LATE. THE TIMING
AND THICKNESS OF THE CLOUD COVER WILL HAVE SOME INFLUENCE ON OUR
TEMPERATURES THROUGH THE NIGHT. WE DID USE A NAM/GFS MOS BLEND FOR
THE LOW TEMPERATURES, BUT THEN ADJUSTED THEM DOWN A LITTLE FOR SOME
OF THE COLDER LOCALES GIVEN THE LOW DEW POINTS AND LACK OF CLOUDS TO
START.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
A SHORT WAVE IS FORECAST TO MOVE ACROSS THE AREA IN THE MORNING.
THIS FEATURE MAY HAVE JUST ENOUGH MOISTURE ACROSS MAINLY PORTIONS OF
THE DELMARVA TO SQUEEZE OUT SOME LIGHT SNOW. AS A RESULT AND BASED
ON WHAT WAS MENTIONED IN THE NEAR TERM, WE CARRIED SOME LOW POPS FOR
THE MORNING. A DECENT AMOUNT OF CLOUD COVER IS EXPECTED ESPECIALLY
FOR THE SOUTHERN HALF OF OUR CWA AS THE SHORT WAVE MOVES THROUGH.

A SECONDARY AND STRONGER SHORT WAVE MOVES THROUGH DURING THE MIDDAY
AND AFTERNOON HOURS. THIS IS ASSOCIATED WITH AN UPPER-LEVEL TROUGH
AXIS. THERE APPEARS TO BE LITTLE MOISTURE WITH THIS FEATURE OTHER
THAN SOME CLOUDS. AS THIS FEATURE MOVES THROUGH AND THE ASSOCIATED
VORTICITY BECOMES MORE CHANNELIZED, WE SHOULD SEE AN EROSION OF THE
CLOUD COVER FROM NORTH TO SOUTH DURING THE COURSE OF THE AFTERNOON.

AS FOR THE HIGH TEMPERATURES, WE WENT A LITTLE COOLER THAN GUIDANCE
WITH THE IDEA OF NOT MUCH MIXING AND ALSO A LOT OF CLOUDS. THIS IS
ESPECIALLY FOR THE SOUTHERN HALF OF THE CWA.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
A QUIET BEGINNING TO THE LONG TERM TUESDAY NIGHT WILL TRANSITION
INTO A MORE ACTIVE AND UNSETTLED PATTERN INTO THE MIDDLE AND END OF
THE WORK WEEK. TO START OFF, AN AREA OF HIGH PRESSURE OVER THE
NORTHEAST TO NORTHERN MID ATLANTIC DURING THE DAY TUESDAY WILL
GRADUALLY BE MOVING OFFSHORE GOING THROUGH TUESDAY NIGHT. OTHER THAN
SOME INCREASING CLOUDS ARRIVING FROM THE SOUTHWEST TOWARD DAYBREAK
WEDNESDAY, LIGHT WINDS AND DRY WEATHER ARE ANTICIPATED THROUGH
TUESDAY NIGHT, WITH OVERNIGHT MINIMUM TEMPERATURES RUNNING A LITTLE
BELOW AVERAGE AS TEMPS BOTTOM OUT MAINLY IN THE 20S ACROSS THE
REGION.

INTO WEDNESDAY, THE MAIN FEATURE TO WATCH WILL BE SURFACE LOW
PRESSURE AND AN UPPER LEVEL SHORTWAVE LIFTING NORTH INTO THE GREAT
LAKES, ALLOWING AN ASSOCIATED WARM FRONT TO ALSO APPROACH AND LIFT
NORTH THROUGH OUR REGION DURING THE COURSE OF THE DAY. THERE
CONTINUES TO BE SOME TIMING DIFFERENCES BETWEEN THE NAM, GFS, ECMWF,
AND CMC WITH REGARDS TO THE FRONTAL PASSAGE AND HOW MUCH MOISTURE
AND PRECIP MAY OCCUR. BASED ON A CONSENSUS OF THE 12Z RUNS, WE KEPT
POPS AND QPF RELATIVELY LOW DURING MUCH OF THE DAYTIME WEDNESDAY,
THEN BRINGING SOME HIGH CHANCE POPS ACROSS THE AREA FOR LATER
WEDNESDAY NIGHT.

IN FACT, FROM LATE WEDNESDAY NIGHT INTO THURSDAY, ANOTHER SURFACE
LOW WITH A SUPPORTING UPPER LEVEL SHORTWAVE IS PROGGED TO BE
TRACKING NORTHEASTWARD UP THROUGH THE OHIO VALLEY, WITH A BROAD AND
MOIST SOUTHWESTERLY FLOW ACROSS OUR REGION. AS A RESULT, WE RAMP UP
POPS TO LIKELY THROUGH THURSDAY AS WIDESPREAD RAIN/SHOWERS ARE
EXPECTED. IN ADDITION, FORECAST SOUNDINGS DO SHOW UP TO A FEW
HUNDRED J/KG OF CAPE DEVELOPING THURSDAY ACROSS MUCH OF THE FCST
AREA, ALONG WITH BULK SHEAR FROM 0-6 KM RANGING BETWEEN 40 TO 50 KT
AS THE COLD FRONT NEARS THE REGION INTO THURSDAY EVENING. WITH THE
MARGINAL FORECAST INSTABILITY, WE HAVE KEPT A SLIGHT CHANCE FOR
TSTORMS IN THE PICTURE FOR THURSDAY, AND IF ANY STORMS DO DEVELOP, A
STRONGER STORM OR TWO CANNOT BE RULED OUT, BASED ON THE FORECAST
BULK SHEAR. THE COLD FRONT IS EXPECTED TO TRACK QUICKLY EAST AND
OFFSHORE THEN INTO THURSDAY NIGHT, AND WE GRADUALLY STEP-DOWN POPS
FROM WEST TO EAST ACROSS THE FORECAST AREA THROUGH THE NIGHT.

INTO FRIDAY, THE SYNOPTIC SET-UP LOOKS TO FEATURE THE OFFSHORE COLD
FRONT, WITH STRONG HIGH PRESSURE BUILDING DOWN FROM CENTRAL CANADA
INTO THE PLAINS AND MIDWEST STATES, AND A PRONOUNCED LONGWAVE TROUGH
ACROSS THE EAST. OVERALL, A DRYING NORTHWEST SURFACE FLOW LOOKS TO
BE SETTING UP, WITH EVEN THE 12Z CMC NO LONGER SHOWING POSSIBLE
COASTAL LOW PRESSURE DEVELOPING ALONG THE DEPARTING FRONTAL
BOUNDARY. THE CMC IS NOW MORE IN LINE WITH THE GFS AND ECMWF,
LOOKING MORE PROGRESSIVE IN NATURE, WITH ANY DEVELOPMENT WELL
OFFSHORE. THEREFORE, WE CONTINUED THE DOWNWARD TREND OF POPS.

OVER THE WEEKEND, THE PREVIOUSLY MENTIONED STRONG HIGH PRESSURE IS
PROGGED TO BUILD SLOWLY SOUTH AND EASTWARD, WITH GENERALLY DRY, BUT
COOL CONDITIONS IN STORE FOR OUR FORECAST AREA. THEREAFTER, A LOW
PRESSURE SYSTEM MOVING ACROSS SOUTHERN CANADA MAY SEND A COLD FRONT
ACROSS OUR REGION MONDAY, BUT PRECIP AMTS LOOK TO BE LIGHT AT THIS
TIME AS MOST OF THE FORCING WITH THIS SYSTEM IS EXPECTED TO BE WELL
TO OUR NORTH.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

REST OF THIS AFTERNOON...VFR WITH A LITTLE HIGH CLOUDINESS.
NORTHWESTERLY WINDS AROUND 10 KNOTS, DIMINISHING TOWARD EVENING..

TONIGHT...VFR, WITH INCREASING CLOUDS AND A CEILING DEVELOPING AND
LOWERING TO NEAR 5000 FEET FOR MOST AREAS. NORTH-NORTHEAST WINDS
LESS THAN 10 KNOTS.

TUESDAY...VFR CEILINGS THINNING OUT FROM NORTH TO SOUTH DURING THE
MIDDAY AND AFTERNOON. THERE COULD BE SOME LIGHT SNOW IN THE MORNING
SOUTHWEST AND WEST OF KILG, HOWEVER THIS IS LOW CONFIDENCE.

OUTLOOK...
TUESDAY NIGHT...VFR CONDITIONS ARE EXPECTED.

WEDNESDAY...CONDITIONS MAY GRADUALLY LOWER TO MVFR WITH RAIN.

THURSDAY...MVFR TO POSSIBLE IFR AT TIMES IN RAIN SHOWERS AND
ISOLATED TSTORMS. A COLD FRONT PASSAGE THURSDAY EVENING/NIGHT WILL
DELIVER SOME GUSTY WINDS, WITH THE WINDS SHIFTING FROM SOUTHWEST TO
NORTHWEST.

FRIDAY...CONDITIONS IMPROVING BACK TO VFR WITH NORTHWEST WINDS.

SATURDAY...VFR CONDITIONS.

&&

.MARINE...
HIGH PRESSURE AT THE SURFACE WILL DOMINATE OUR WEATHER THROUGH
TUESDAY. THE POSITIONING OF THE SURFACE HIGH TO OUR NORTHWEST AND
NORTH WILL ALLOW FOR A NORTHERLY FLOW. THE FLOW THROUGH THIS EVENING
LOOKS LIGHT ENOUGH ESPECIALLY FOR THE SOUTHERN WATERS, FOR SOME
ONSHORE FLOW COMPONENT TO OCCUR. THIS EAST OR NORTHEAST FLOW SHOULD
PERSIST INTO TUESDAY AS WELL. AS THE BOUNDARY LAYER COOLS AGAIN
TONIGHT, SOME BETTER MIXING MAY DEVELOP. HOWEVER, THE FLOW LOOKS
LIKE ENOUGH AND THEREFORE THE CONDITIONS ARE ANTICIPATED TO BE BELOW
SMALL CRAFT ADVISORY CRITERIA THROUGH TUESDAY.

OUTLOOK...
TUESDAY NIGHT AND WEDNESDAY...WINDS AND SEAS ARE EXPECTED TO REMAIN
BELOW SCA CRITERIA.

THURSDAY AND FRIDAY...SCA CONDITIONS ARE EXPECTED TO DEVELOP EARLY
ON THURSDAY AND LAST INTO FRIDAY WITH THE APPROACH AND PASSAGE OF A
COLD FRONT. WIND GUSTS WILL REACH INTO THE 25 TO 30 KNOT RANGE, WITH
A WIND SHIFT FROM SOUTHWEST TO NORTHWEST OCCURRING AS THE COLD FRONT
PASSES OVER THE WATERS LATE THURSDAY NIGHT. IN ADDITION, SEAS WILL
STEADILY BUILD INTO THE 5 TO 8 FOOT RANGE FOR THE COASTAL WATERS
DURING THURSDAY AND THURSDAY NIGHT, BEFORE GRADUALLY SUBSIDING ON
FRIDAY.

SATURDAY...SUB-SCA CONDITIONS ARE EXPECTED. SOME NORTHWEST WIND
GUSTS TO AROUND 20 KNOTS POSSIBLE FOR THE COASTAL WATERS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...KLINE
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...KLINE
AVIATION...GORSE/KLINE
MARINE...GORSE/KLINE


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