001  
FXUS61 KPHI 170905  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
405 AM EST SUN FEB 17 2019  
   
SYNOPSIS
 
 
AN AREA OF LOW PRESSURE WILL MOVE ACROSS THE REGION LATER TONIGHT  
INTO MONDAY. HIGH PRESSURE WILL BUILDING ACROSS TO THE NORTH OF THE  
AREA TUESDAY, MOVING OFF TO THE NORTHEAST OF THE AREA TUESDAY NIGHT.  
A COMPLEX LOW PRESSURE SYSTEM WILL MOVE THROUGH THE REGION WEDNESDAY  
INTO THURSDAY. HIGH PRESSURE RETURNS FOR THE END OF THE WEEK.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
SURFACE RIDGE IS EXPECTED TO WEAKEN AS IT LIFTS NORTHEAST THROUGH  
THE DAY. AS THE RIDGE AXIS PROPAGATES SOUTHEAST OF OUR REGION, LOW  
LEVEL SOUTHEASTERLY FLOW IS EXPECTED TO DEVELOP, RESULTING IN  
MOISTURE ADVECTION AHEAD OF OUR NEXT SYSTEM TONIGHT.  
 
THANKS TO A COMBINATION OF INCREASING CLOUDS AND THE ON SHORE FLOW  
DEVELOPING, TEMPERATURES WILL LIKELY BE A FEW DEGREES LOWER THAN  
SATURDAY, WITH HIGHS IN THE 30S AND 40S ACROSS THE REGION.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/
 
 
A LOW IS FORECAST TO LIFT NORTH OF THE MID MISSISSIPPI VALLEY  
TOWARDS OUR REGION TONIGHT AND OVERNIGHT. IT IS A RATHER PROGRESSIVE  
SYSTEM, AND IS EXPECTED TO BE WELL EAST OF THE NEW ENGLAND COAST BY  
THE END OF THE DAY. NONE THE LESS, ALTHOUGH IT MAY NOT BE A LONG  
PERIOD OF PRECIPITATION, THIS SYSTEM HAS THE POTENTIAL FOR IMPACTS,  
ESPECIALLY FOR LOCATIONS NORTH AND WEST OF THE FALL LINE. AS FOR THE  
INDIVIDUAL ASPECTS OF THE SYSTEM:  
 
PRECIPITATION TIMING: PRECIPITATION SHOULD START THIS EVENING AND  
CONTINUE THROUGH MONDAY MORNING BEFORE A DRY SLOT DEVELOPS BY MID  
DAY MONDAY. AT THE ONSET, THERE IS A QUESTION HOW QUICKLY WE WILL  
SEE PRECIPITATION START GIVEN THE DRY BOUNDARY LAYER ALREADY IN  
PLACE (THERE HAVE BEEN A FEW CASES OVER THE LAST FEW DAYS WHEN THERE  
WERE RADAR ECHOS, BUT NOTHING WAS REACHING THE GROUND). THE  
SOUTHEASTERLY FLOW EXPECTED TO DEVELOP LATE TODAY AND RESULTING  
MOISTURE ADVECTION SHOULD COUNTERACT THIS A BIT. HOWEVER, WE WILL BE  
WATCHING CLOSELY TO SEE HOW QUICKLY THE MOISTURE ADVECTION DEVELOPS.  
ON THE BACK END OF THE SYSTEM, THE GFS IS THE MOST PROGRESSIVE IN  
CLEARING OUT THE PRECIPITATION, BUT OVERALL, MODEL AGREEMENT IN THE  
TIMING OF PRECIPITATION IS RELATIVELY GOOD.  
 
PRECIPITATION TYPE: WITHOUT QUESTION, THIS IS THE BIGGEST CONCERN  
WITH THIS SYSTEM. CURRENTLY, OUR FORECAST IS FOR MOSTLY RAIN ALONG  
AND SOUTHEAST OF THE 95 CORRIDOR (THOUGH THERE COULD BE A BRIEF  
PERIOD OF RAIN/SLEET MIX THIS EVENING). ALONG AND NORTHWEST OF THE  
FALL LINE, PRECIPITATION IS FORECAST TO START AS MOSTLY SNOW, BEFORE  
CHANGING TO A WINTRY MIX. HOWEVER, THIS IS NOT AS CLEAR CUT AS I  
WOULD LIKE, FOR A NUMBER OF REASONS. FIRST, THERE WILL ACTUALLY BE  
TWO SURFACE LOWS INITIALLY, WITH THE FURTHER SOUTH ONE EVENTUALLY  
BECOMING MORE DOMINANT. WITH THIS POINT, MODELS ARE HANDLING HOW  
THIS WILL EVOLVE VERY DIFFERENTLY. SECONDLY, AND POSSIBLY THE  
BIGGEST SOURCE OF UNCERTAINTY WITH THIS SYSTEM, IS HOW QUICKLY THE  
ELEVATED WARM LAYER WILL DEVELOP AND HOW FAR NORTH IT WILL BE. THIS  
WILL BE KEY IN THE TRANSITION FROM LIKELY A RAIN OR SNOW SITUATION  
AT THE BEGINNING TO WINTRY MIX FOR AREAS NW OF THE FALL LINE AND ALL  
RAIN ON THE COASTAL PLAINS. FINALLY, AS MENTIONED ABOVE, THE  
BOUNDARY LAYER IS CURRENTLY VERY DRY. IF THE MOISTURE ADVECTION IS  
SLOWER TO DEVELOP THAN CURRENTLY FORECAST, WE COULD HAVE WETBULB  
EFFECTS AT THE BEGINNING OF THE EVENT, LEADING TO A BRIEF PERIOD OF  
SLEET AT THE ONSET.  
 
RAIN, SNOW, AND ICE AMOUNTS: PRECIPITATION AMOUNTS FOR MOSTLY THE  
COASTAL PLAINS INCREASED, THOUGH THIS AREA WILL LIKELY SEE ALL RAIN,  
AND PRECIPITATION AMOUNTS STILL REMAIN WELL BELOW ONE INCH. FOR THE  
AREAS THAT WILL SEE A WINTRY MIX, LATEST FORECAST HASN'T CHANGED TOO  
MUCH WITH THE SNOW AND ICE AMOUNTS. HOWEVER, IT SHOULD BE NOTED THAT  
THE EXACT SNOW AND ICE AMOUNTS WILL BE HIGHLY DEPENDENT ON THE  
TIMING OF PRECIPITATION TYPE TRANSITIONS.  
 

 
   
LONG TERM /MONDAY NIGHT THROUGH SATURDAY/
 
 
HIGH PRESSURE WILL THEN BUILD DOWN FROM THE NORTHWEST, ACROSS THE  
MIDWEST AND INTO THE EASTERN UNITED STATES FOR TUESDAY, WHICH WILL  
GIVE US A BRIEF RESPITE BETWEEN SYSTEMS. THE HIGH WILL START TO  
SLIDE ACROSS TO THE NORTH AND EAST OF OUR AREA TOWARDS TUESDAY  
NIGHT. CONDITIONS ARE EXPECTED TO REMAIN DRY BUT COLDER AIR ARRIVES  
AND HIGHS WILL STRUGGLE TO WARM, REMAINING IN THE UPPER 20S ACROSS  
THE NORTHERN ZONES AND MID 30S TO NEAR 40 THROUGH THE REST OF THE  
FORECAST AREA.  
 
AS WE HEAD INTO TUESDAY NIGHT, THE HIGH SHIFTS TO THE NORTHEAST OF  
THE REGION, SETTING UP FOR SOME DECENT COLD AIR DAMMING TO TAKE  
PLACE. THE MODELS HAVE SHIFTED THE HIGH SLIGHTLY SOUTH AS IT MOVES  
OFFSHORE, WHICH MAY PREVENT THE CAD FROM FULLY SETTING UP. HOWEVER,  
THE HIGH RIDGES SOUTHWESTWARD ALONG THE APPALACHIAN FRONT AND THIS  
MAY PROVIDE JUST ENOUGH OF A BLOCK TO KEEP THE COLD AIR LOCKED IN AT  
THE SURFACE. WITH THE HIGH SHIFTING TO THE NORTH AND EAST, THE FLOW  
AT THE SURFACE WILL TURN MORE TO THE EAST AND THEN SOUTHEAST. THIS  
WILL INCREASE MOISTURE IN THE LOW LEVELS AND ALLOWS FOR SOME WARMER  
AIR TO TRY TO MOVE INTO THE AREA. WHILE PRECIPITATION IS POSSIBLE  
TUESDAY NIGHT AS WARM AIR ADVECTION AND LIFT INCREASES, THE MODELS  
CONTINUE TO SLOW THE ONSET AND WHILE OVERRUNNING MAY CAUSE SOME  
PRECIP TO MOVE IN EARLIER THAN THEY ARE SHOWING, CONFIDENCE IS SUCH  
THAT WE HAVE SLOWED THE ARRIVAL OF THE PRECIPITATION TO LATER TUESDAY  
NIGHT, WITH A BETTER CHANCE ACROSS THE SOUTHERN AREAS AND MUCH  
BETTER CHANCES AS WE HEAD CLOSE TO DAYBREAK ON WEDNESDAY.  
 
WEDNESDAY AND THURSDAY CONTINUE TO LOOK LIKE QUITE A MESSY SCENARIO  
FOR THE FORECAST AREA. A SURFACE LOW WILL TRAVEL UP FROM THE GULF  
COAST STATES AND UP INTO THE GREAT LAKES WITH A SECONDARY LOW  
DEVELOPING NEAR THE MID-ATLANTIC COAST. THE INITIAL LOW REMAINS TO  
THE WEST OF THE AREA AS THE COLD AIR DAMMING IN PLACE PREVENTS IT  
FROM MAKING MUCH HEADWAY INTO OUR AREA. THIS LEADS WAY TO THE SECOND  
LOW DEVELOPING NEAR OR JUST SOUTH OF OUR AREA. WITH THE COLD AIR  
REMAINING IN PLACE, WE ARE PRIMED FOR OVERRUNNING TO OCCUR AS THE  
WARMER AIR TO THE SOUTH TRIES TO OVERRIDE THE COLDER AIR TRAPPED IN  
THE LOWER LEVELS. THIS COMPLICATES THE FORECAST AS IT TENDS TO LEAD  
TO MULTIPLE PRECIPITATION TYPES, AND IN MANY INSTANCES CAN SIGNAL A  
RISK FOR ACCUMULATING ICE AND SNOW. WITH COLD AIR BEING IN PLACE AT  
THE SURFACE DURING THE ONSET, IT APPEARS LIKELY THAT PRECIPITATION WILL  
START AS SNOW. AS THE WINDS TURN MORE TO THE SOUTH AND SOUTHEAST,  
THE WARMER AIR WILL FLOW INTO THE MID-LEVELS, WHICH WILL RESULT IN  
THE PRECIP CHANGING OVER TO A WINTRY MIX OF SNOW/SLEET/RAIN THROUGH  
THE LATE MORNING AND INTO THE AFTERNOON, EVENTUALLY CHANGING TO ALL  
RAIN ACROSS DELMARVA. COLDER AIR IS LIKELY TO REMAIN IN PLACE IN  
PARTS OF THE REGION, ESPECIALLY ALONG THE I-78 CORRIDOR AND NORTH  
AND WEST. SNOW WILL EVENTUALLY MIX WITH SLEET AND THEN A CHANGE FROM  
SNOW TO FREEZING RAIN IS BECOMING INCREASINGLY LIKELY AS WE HEAD  
INTO WEDNESDAY EVENING. SOME COLD AIR LINGERING THROUGH THE I-95  
CORRIDOR MAY ALSO ALLOW FOR THE MIXED PRECIPITATION TO HANG ON THROUGH  
THE EVENING BEFORE ENOUGH WARM AIR MAKES IT TO THE SURFACE AND THE  
PRECIP STARTS TO CHANGE OVER TO PLAIN RAIN. AS THE LOW STARTS TO  
CROSS THE REGION WEDNESDAY NIGHT, THE RAIN/SNOW(MIX) LINE WILL START  
TO PUSH NORTHWARD, WITH EVENTUALLY THE ENTIRE FORECAST AREA ALL  
PLAIN RAIN BY THURSDAY MORNING.  
 
THE LOW MOVES QUICKLY OFFSHORE THURSDAY NIGHT AND ALLOWS FOR HIGH  
PRESSURE TO BUILD IN FROM THE WEST FOR FRIDAY. THE HIGH SLIDES  
ACROSS THE REGION AND OFFSHORE LATER IN THE DAY. ANOTHER SYSTEM MAY  
APPROACH OUR AREA LATER FRIDAY, TRAVELING ALONG A BOUNDARY THAT  
STALLS TO OUR SOUTH. THE MODELS DIFFER WITH THE STRENGTH AND TIMING  
OF THIS SYSTEM BUT SEEM TO SHOW WE SEE SOME PRECIPITATION MOSTLY  
CONFINED TO OUR SOUTHERN AREAS. HOWEVER, WITH SO MUCH TO TRANSPIRE  
BEFORE THE END OF THE WEEK, THERE IS STILL TIME FOR THE MODELS TO  
WORK OUT THE KINKS FOR THE NEXT SYSTEM. ONCE THAT SYSTEM MOVES OUT,  
THERE IS A RETURN TO HIGH PRESSURE FOR SATURDAY BEFORE ANOTHER  
POTENTIAL SYSTEM ARRIVES LATE IN THE WEEKEND.  
 

 
   
AVIATION /09Z SUNDAY THROUGH THURSDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
TODAY...VFR CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE DAY TIME  
HOURS. MID LEVEL CLOUDS BETWEEN 5000 AND 10000 FT AGL MAY BEGIN TO  
STREAM IN LATE IN THE DAY IN ADVANCE OF THE NEXT SYSTEM, BUT SHOULD  
STAY VFR. WINDS WILL BE LIGHT (LESS THAN 10 KT), AND VARYING FROM  
NORTHERLY TO SOUTHEASTERLY. HIGH CONFIDENCE.  
 
TONIGHT...CONDITIONS ARE EXPECTED TO DETERIORATE TO IFR BETWEEN 00  
AND 06Z (FROM WEST TO EAST) AS PRECIPITATION BEGINS TO MOVE IN. FOR  
KABE AND KRDG, A WINTRY MIX OF SLEET, SNOW, AND FREEZING RAIN IS  
LIKELY. FOR THE DELAWARE VALLEY SITES (KPHL, KILG, KPNE, AND KTTN),  
PRECIP MAY BEGIN AS A MIX OF SLEET AND RAIN, BEFORE CHANGING OVER TO  
ALL RAIN NEAR OR AFTER 06Z. AT KMIV AND KACY, PRECIPITATION IS  
LIKELY TO BE ALL RAIN. HAVING SAID THAT, THERE IS UNCERTAINTY IN THE  
PRECIPITATION TYPE AND THE TIMING OF ANY PRECIP CHANGE OVERS.  
CONSEQUENTLY, CONFIDENCE IN THE FORECAST IS LOW.  
 
OUTLOOK...  
 
MONDAY...CONDITIONS SHOULD SLOWLY IMPROVE TO VFR THROUGH THE DAY AS  
THE PRECIPITATION MOVES OUT OF THE REGION. NORTHWESTERLY WINDS WILL  
BE INCREASING TO 10 TO 15 KT WITH GUSTS TO 25 KT. HIGH CONFIDENCE ON  
MOST ASPECTS OF THE FORECAST, BUT LOW CONFIDENCE ON THE TIMING OF  
IMPROVEMENT TO VFR.  
 
MONDAY NIGHT THROUGH TUESDAY...MAINLY VFR CONDITIONS EXPECTED.  
NORTHWEST TO NORTH WINDS LESS THAN 10 KNOTS. HIGH CONFIDENCE.  
 
TUESDAY NIGHT THROUGH WEDNESDAY...VFR WILL BECOME MVFR BY TUESDAY  
NIGHT AND THEN BECOME MVFR/IFR AS SNOW, RAIN, AND A WINTRY MIX MOVE  
THROUGH THE TERMINALS. NORTHEAST TO EAST WINDS AROUND 10 KNOTS OR  
LESS. LOW CONFIDENCE WITH RESPECT TO PRECIPITATION TYPE.  
 
THURSDAY...MVFR OR LOWER CONDITIONS EARLY BEFORE POSSIBLY IMPROVING  
TO VFR LATER IN THE DAY AS THE PRECIPITATION MOVES OUT OF THE AREA.  
WEST TO NORTHWEST WINDS AROUND 10 KNOTS. MODERATE CONFIDENCE.  
 

 
   
MARINE
 
 
WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY  
CRITERIA TODAY AND TONIGHT. SOME VISIBILITY RESTRICTIONS IN RAIN ARE  
POSSIBLE, PRIMARILY LATE TONIGHT.  
 
OUTLOOK...  
 
MONDAY...WINDS AND SEAS WILL BEGIN TO BUILD, AND COULD REACH SCA  
CRITERIA BY MONDAY AFTERNOON. HAVE HELD OFF ON ISSUING AN SCA THOUGH  
AS CONFIDENCE IS BELOW NORMAL, BUT AN SCA MAY NEED TO BE ISSUED AS  
WE GET CLOSER.  
 
MONDAY NIGHT THROUGH TUESDAY...SMALL CRAFT ADVISORY CONDITIONS  
ARE POSSIBLE ON THE OCEAN WATERS MONDAY NIGHT. WINDS WILL  
GRADUALLY DIMINISH TOWARDS TUESDAY MORNING. SEAS GENERALLY  
AROUND 2 TO 4 FEET, SUBSIDING SOME THROUGH THE NIGHT.  
 
WEDNESDAY...INCREASING EASTERLY WINDS WITH GUSTS UP TO 25 KNOTS  
POSSIBLE WEDNESDAY NIGHT. SEAS WILL BUILD FROM 2 TO 4 FEET DURING  
THE DAY TO AROUND 3 TO 5 FEET WEDNESDAY NIGHT. A SMALL CRAFT  
ADVISORY MAY BE NEEDED.  
 
THURSDAY...MAINLY SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED. SEAS  
AROUND 3 TO 5 FEET EARLY WILL GRADUALLY SUBSIDE TO 2 TO 4 FEET  
THROUGH THE DAY. WINDS WILL BE WEST AROUND 10 TO 15 KNOTS.  
 

 
   
TIDES/COASTAL FLOODING
 
 
A SUBTLE ONSHORE WIND IS EXPECTED FOR MUCH OF SUNDAY AND SUNDAY  
NIGHT. ASTRONOMICAL TIDES ARE ON THE INCREASE AS WE NEAR  
TUESDAY'S FULL MOON. AS A RESULT, WE MAY EXPERIENCE SOME SPOTTY  
MINOR TIDAL FLOODING ALONG THE COASTS OF NEW JERSEY AND  
DELAWARE WITH MONDAY MORNING'S HIGH TIDE. IT DOES NOT APPEAR AS  
THOUGH THE FLOODING WILL BE WIDESPREAD ENOUGH TO WARRANT AN  
ADVISORY.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 10 AM EST  
MONDAY FOR PAZ054-055-060>062-105.  
NJ...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 10 AM EST  
MONDAY FOR NJZ001-007>010.  
DE...NONE.  
MD...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...MEOLA  
NEAR TERM...JOHNSON  
SHORT TERM...JOHNSON  
LONG TERM...MEOLA  
AVIATION...JOHNSON/MEOLA  
MARINE...JOHNSON/MEOLA  
TIDES/COASTAL FLOODING...IOVINO  
 
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