866
FXUS61 KPHI 181946
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
346 PM EDT TUE JUN 18 2013
SYNOPSIS
A COLD FRONT WILL MOVE OFF THE COAST TONIGHT AS WEAK LOW PRESSURE
MOVES ALONG IT. HIGH PRESSURE FROM THE GREAT LAKES REGION WILL THEN
BUILD INTO THE NORTHEAST AND MID-ATLANTIC TOMORROW. THE CENTER OF
THIS HIGH WILL SHIFT OFFSHORE ON THURSDAY. A REINFORCING SHOT OF
CANADIAN HIGH PRESSURE MOVES TOWARD THE REGION ON FRIDAY...THEN OFF
THE COAST ON SATURDAY. A RETURN FLOW AROUND THIS HIGH WILL BRING AN
INCREASE IN HEAT AND HUMIDITY AND A THREAT OF SCATTERED SHOWERS AND
THUNDERSTORMS THIS WEEKEND AND INTO EARLY NEXT WEEK.
NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/
VERY TROPICAL-ISH AIRMASS IN PLACE THIS EVENING AND TONIGHT AS A
WEAK FRONTAL BOUNDARY SAGS ACROSS THE MID-ATLANTIC STATES. THERE IS
AMPLE ELEVATED INSTABILITY AROUND THE REGION TO MAINTAIN THE
CURRENT SHOWER/THUNDERSTORM ACTIVITY EAST ACROSS OUR REGION. WITH
THE WEAKENED FLOW ALOFT ANY MORE STORMS THAT INITIATE WILL MOVE VERY
SLOWLY AND INUNDATE THE AREAS THEY PASS OVER. WE HAD SEVERAL FLASH
FLOOD WARNINGS ISSUED THIS AFTERNOON AND SAW HOURLY RAINFALL RATES
EXCEED 1.5+ INCHES FROM EASTERN PENNSYLVANIA INTO SOUTHERN NEW
JERSEY.
EVERYTHING WILL BE SLIDING OFFSHORE OVER THE NEXT COUPLE OF HOURS
THOUGH THE COLD FRONT TO OUR NORTH MAY TOUCH OFF EVEN MORE WIDELY
SCATTERED SHOWERS. COULD NOT REMOVE ALL CHANCES THROUGH THE EVENING
HOURS AS SOME OF THE HI-RES MODELS SHOW THESE SHOWERS TRAVERSING THE
REGION. NOT EXPECTING THE TORRENTIAL DOWNPOURS AND CONVECTION TO BE
AN ISSUE AS HEATING TO OUR NORTH AND WEST HAS BEEN WEAKENED WITH THE
EXTENSIVE MID AND HIGHER LEVEL CLOUDS. THE CU FIELD WELL TO OUR
NORTHWEST IS REALLY FLAT LOOKING AS DEWPOINTS BEHIND THE FRONT ARE
IN THE MID TO UPPER-50S. THE FRONT COULD HOWEVER POSE AN ISSUE IN
TERMS OF FOG/STRATUS FORMATION LATE TONIGHT. DEPENDING ON HOW FAST
IT SLIDES THROUGH AND WE GET THE DRIER DEWPOINTS MIGHT ALLOW A
WIDESPREAD FOG TO FORM UNDER A BUILDING INVERSION (NEAR THE FRONT)
AND WITH THE ADDED MOISTURE FROM TODAYS RAIN. DO NOT THINK IT WILL
DENSE ENOUGH TO HAVE TO WORRY ABOUT HEADLINES, BUT IT COULD BECOME
THICK IN SOME SPOTS.
OVERNIGHT LOWS WERE A STRAIGHT BLEND OF THE MET/MAV.
SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/
THE COLD FRONT WILL CONTINUE TO PUSH FURTHER SOUTH AND EAST AND THE
DRYING NORTHERLY FLOW BEHIND THE FRONT INCREASES. MID-LEVEL AND
SURFACE RIDGING START TO RE-ENTER THE REGION FROM THE
WEST-NORTHWEST WHICH HELPS TO KEEP OUR REGION DRY FOR THE MOST
PART. CONTINUE WITH SOME SLIGHT CHANCE POPS ACROSS THE EXTREME
SOUTHERN DELMARVA WHERE SOME LOW-LEVEL CONVERGENCE ALONG THE FRONT
MAY STILL EXIST AND WHERE DEWPOINTS WILL CONTINUE TO POOL IN THE
UPPER-60S. TEMPERATURES WILL BE A COUPLE DEGREES COOLER TOMORROW
BEHIND THE FRONT AND A BASIC BLEND OF THE MET/MAV WAS USED FOR HIGHS.
LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/
SURFACE HIGH PRESSURE IS EXPECTED TO BUILD OVER THE REGION WEDNESDAY
NIGHT...WITH THE CENTER OF THE HIGH MOVING OFF THE COAST ON
THURSDAY. A REINFORCING SHOT OF CANADIAN HIGH PRESSURE MOVES TOWARD
THE REGION ON FRIDAY...THEN OFF THE COAST ON SATURDAY. THIS HIGH
SHOULD THEN INFLUENCE WEATHER OVER THE AREA INTO NEXT WEEK AS A
SOUTHWEST FLOW ON ITS WESTERN SIDE BRINGS IN WARM AND HUMID AIR.
A CHANCE OF SHOWERS OR THUNDERSTORMS ARE POSSIBLE JUST ABOUT
EVERYDAY FROM SUNDAY INTO EARLY NEXT WEEK...BUT MOST OF THE TIME
SHOULD BE RAIN FREE. THIS LOOKS MORE LIKE A TYPICAL SUMMER TIME
PATTERN IN THE MID PORTIONS OF THE ATMOSPHERE AS A RIDGE TRIES TO
BUILD EAST FROM THE HIGH PLAINS. TEMPERATURES WILL START OFF IN THE
NORMAL RANGE....THEN CLIMB ABOVE NORMAL LATE IN THE WEEKEND AND
EARLY NEXT WEEK.
AVIATION /20Z TUESDAY THROUGH SUNDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
THIS EVENING...VERY COMPLEX FORECAST WITH MOSTLY VFR EXPECTED.
NUMEROUS SHOWERS AND THUNDERSTORMS WILL CONTINUE TO PLAGUE OUR
TERMINALS OVER THE NEXT COUPLE OF HOURS AS A WAVE OF LOW PRESSURE
MOVES THROUGH. THE HEAVIER SHOWERS AND THUNDERSTORMS WILL CAUSE
LOCAL IFR CONDITIONS WINDS WILL PREDOMINANTLY BE OUT OF THE
EAST-SOUTHEAST AND REMAIN LIGHT FOR THIS AFTERNOON. MULTIPLE OUTFLOW
BOUNDARIES AND HEAVIER SHOWERS WILL CAUSE TEMPORARY GUSTS WITH
VARIABLE DIRECTIONS.
TONIGHT...WEAK COLD FRONT TO THE NORTHWEST WILL SLOWLY DRAG ITSELF
TOWARDS THE REGION TONIGHT AND TRIES TO PUSH THROUGH. WINDS SHOULD
BACK TOWARDS THE SOUTHWEST AND THEN NORTH BEHIND THE FRONT. IF THE
FRONT SLOWS EVEN FURTHER OR STALLS JUST TO THE NORTH WE COULD HAVE
ISSUES WITH STRATUS AND FOG THROUGH THE MORNING HOURS....IFR/MVFR
POSSIBLE.
WEDNESDAY...VFR WITH SCATTERED CIGS. WILL MAINTAIN A NORTHERLY WIND
BEHIND THE FRONT AROUND 10KTS.
OUTLOOK...
WEDNESDAY NIGHT THROUGH SUNDAY...VFR EXCEPT IN MORNING FOG/HAZE OR
MAINLY AFTERNOON AND EVENING SHOWERS/THUNDERSTORMS.
MARINE
SUB-ADVISORY CONDITIONS LOOK TO PERSIST ACROSS OUR WATERS TONIGHT
AND TOMORROW. A WEAK COLD FRONT WILL MOVE THROUGH LATE TONIGHT INTO
WEDNESDAY MORNING AS HIGH PRESSURE SINKS TOWARDS THE SOUTH. WINDS
WILL START OFF EASTERLY AND THEN TURN NORTHERLY BEHIND THE FRONT
TOMORROW. THE PRESSURE GRADIENT MAY BECOME TIGHT FOR A PERIOD
TOMORROW AFTERNOON AND COULD PRODUCE SOME MARGINAL SMALL CRAFT GUSTS
BUT DID NOT HAVE THE CONFIDENCE OR LONGEVITY OF THE EVENT TO PUT UP
A FLAG. SEAS WILL CLIMB UPWARDS OF 4 FEET THROUGH TOMORROW AS
CONDITIONS BECOME MORE TRANQUIL LATER IN THE DAY.
OUTLOOK... NO HEADLINES ARE EXPECTED THROUGH SUNDAY.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.
SYNOPSIS...MIKETTA
NEAR TERM...HEAVENER
SHORT TERM...HEAVENER
LONG TERM...MIKETTA
AVIATION...HEAVENER
MARINE...HEAVENER
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