Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 191622 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1222 PM EDT Wed Apr 19 2017 .SYNOPSIS... High pressure from near the Canadian Maritimes and extending down the East Coast shifts eastward today and tonight. Low pressure tracks from the Great Lakes to New England today and tonight and weakens, however its frontal boundary settles into our area. Another low moves east across the Great Lakes into the Northeast Thursday and Friday, with the main cold front moving through our area during Friday. A storm system approaching from the Ohio Valley Saturday night will track to our south Sunday into Monday resulting in unsettled weather. High pressure builds in from the north for Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure centered over Atlantic Canada today will maintain an east to south surface flow in our region today. Clouds with bases in the 2000 to 3000 foot range will remain over parts of our region into the early afternoon. Spotty light showers from the west may continue to affect the Poconos, Berks County, the Lehigh Valley and northwestern New Jersey early this afternoon. A deck of altocumulus is forecast to overspread our region from the west this afternoon in the warm advection ahead of a frontal boundary approaching from the eastern Great Lakes. Scattered showers in advance of the front may again affect our northern counties late in the day. The flow off the ocean should keep maximum temperatures mainly in the 55 to 65 degree range in our region. Readings may not get above the lower 50s right along the coast.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... Mostly cloudy. Stratus should develop by midnight over parts of eastern PA and develop sewd to near I95. Instability aloft is increasing and there should be a few showers near and N of I-80 in the proximity of a slowing southward developing cool front. The far south the shower risk tonight...for now the NSSL WRF and SPC WRF both suggest cutting off the srn extent of the showers near I-78. The 00z/19 EC showers extend a little further south of I-78. Lows will be milder...8 to 13 degrees above normal. Light south to southwest wind. This part of the forecast was a 50 50 blend of the 00z/19 GFS/NAM MOS. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Summary...Much warmer for most of the area Thursday and especially Friday; unsettled weather mainly Sunday into early next week along with some cooling. Synoptic Setup...A ridge slides across the area Thursday with a trough moving across the Great Lakes into Friday then the Northeast Saturday. A secondary short wave sharpens a trough in the Central Plains Friday night into Saturday, which then moves eastward to the East Coast Sunday night. This feature may be slow to exit eastward early next as it closes off to our south. The next short wave trough quickly moves from the Midwest and Great Lakes region Tuesday to near northern New England Wednesday however this may weaken as more energy ejects into the Plains. This will all translate to changeable weather across our area, featuring a significant warmup for much of the area along with the potential for a widespread rainfall during the second half of the weekend. We used a model/continuity blend for Thursday through Friday night, then blended in the 00z WPC Guidance. Some adjustments were then made following additional collaboration with our neighboring offices. For Thursday and Friday...Low pressure is forecast to be exiting New England and weakening Thursday morning, however a cold front will be trailing to its southwest and down into a portion of our area. There should be plenty of low-level moisture in place and with incoming warm air advection, low clouds should be around for at least Thursday morning. Some fog is also possible. A short wave trough moving across the Great Lakes region will drive surface low pressure eastward, and the aforementioned front ties into this low as a warm front. Some showers and perhaps some thunder moves through mostly the northern half of the area Thursday morning then there may be a break. Some additional showers/thunder should develop Thursday afternoon to our west with an incoming warm front and associated lift. This activity at least in a weakened state should slide across the region later Thursday afternoon and especially Thursday night. The main forcing associated with a stronger wind field and warm air advection is forecast to be sliding by to our north Thursday night into Friday morning, therefore the heavier and more organized showers and thunder should be north of us. The cold front looks to move through prior to midday Friday, and with most of the forcing weakening there should be limited convection outside of early morning activity. Given the track of the surface low and timing of the front, looks like any convection should be the more typical variety. Clearing should take place during Friday afternoon as the cold front shifts east and the winds shift to the west and northwest along with drier air advecting in. The main cold air advection looks to be delayed especially below 850 mb therefore Friday is expected to be rather warm. For Saturday and Sunday...The cold front from Friday looks to stall to our south. As energy slides eastward, a surface low tracks into the Ohio Valley Saturday afternoon. This will result in increasing clouds and warm air advection up and over the low-level boundary. Some showers may develop across the southern areas Saturday afternoon, however stronger and more organized lift arrives later Saturday night and especially Sunday. While the surface low is forecast to track to our south Sunday and Sunday night, plenty of ascent should drive an area of rain. There is the potential for a widespread rainfall on Sunday, some of which can be moderate/heavy. There will be a low-level onshore flow (breezy at the coast), allowing for much cooler conditions on Sunday. This will also keep any instability elevated, however as of now thunder was not added to the forecast. PoPs were increased later Saturday night and Sunday for much of the area. Some guidance hinting at convection to our south Sunday, which may keep the deeper moisture inflow from getting as far north as our area. The system should shift offshore later Sunday night with some improving conditions. For Monday and Tuesday...A closed low may develop Monday across the Southeastern States, which would slow the departure of low pressure along a frontal zone. This appears to occur far enough south and east to keep the associated main rain shield offshore. However, there still could be some showers especially Monday. Meanwhile, high pressure is forecast to build down from eastern Canada and combined with low pressure to our south will produce an onshore flow. This may keep clouds in place especially if enough drying/subsidence with the surface high remains farther to our north, along with cooler temperatures particularly along the coast. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...After early cigs 2000 to 3000 feet dissipate...VFR with cigs near 7000 ft developing this afternoon and lowering late in the day. Southeast wind should gust 15-20 kt this afternoon. Tonight...VFR cigs with probable cigs 500-1500 ft developing late over eastern PA (KRDG/KABE)...possibly into KPHL toward 10z Thursday. scattered showers in vcnty of KABE/KRDG/KTTN. Light south wind. OUTLOOK... Thursday...MVFR or IFR ceilings (some fog possible) should improve to VFR ceilings in the afternoon. Some showers or a thunderstorm are anticipated especially in the morning then again late day and at night, which can result in brief IFR conditions. Southwesterly winds mainly 5-10 knots. Friday...Mainly VFR ceilings which should clear out in the afternoon and at night following the passage of a cold front. A few showers or a thunderstorm possible especially through midday. Southwest winds 5- 10 knots in the morning becoming west-northwest 10-15 knots and potentially gusty in the afternoon. Saturday...Mainly VFR during the day as clouds increase, then sub- VFR ceilings may develop at night with some rain arriving late. Northwest to north winds less than 10 knots. Sunday...MVFR/IFR conditions probable with periods of rain. Some fog possible. East-northeast winds around 10 knots with some gustiness especially closer to the coast.
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&& .MARINE... We have issued a Small Craft Advisory for our waters from Little Egg Inlet south to Fenwick Island. The east to southeast flow should keep seas around 4 to 5 feet in that area into the afternoon. A general east southeast flow prevails today...gusting around 20 kt. Isolated gusts possible to near 25 kt. Winds turn south tonight and then southwest by dawn Thursday. OUTLOOK... Thursday and Friday...The conditions are expected to be below Small Craft Advisory criteria. Some fog possible especially each overnight and morning. Saturday...The conditions are anticipated to be below advisory criteria. Winds become light for a time, then turn northeast and increase some at night. Sunday...Small Craft Advisory conditions should develop as a northeasterly wind increases and allows seas to build into the 4-6 foot range on the ocean zones. Periods of rain are forecast to occur. && .CLIMATE... April will probably be a top 10 warmest in the period of record for multiple long term climate stations and depending on the warmth of this Thursday-Friday and how cold it is on Sunday when there is a potential chilly washout for at least part of the day...we could be heading for a top 2 warmest april on record. The usual analysis process first 18 days done, the 19th-25th per our 330 am fcst, the 26-29th from FTPRHA and the last day, normal max/min for the date. PHL projects #2, 4.9 above normal and 0.5degs from record. POR 1874 ABE projects #2, 5.9 above normal and 0.6degs from record. POR 1922 ACY projects rer 5.0 above normal,0.4F above prev 2010 56.3 POR 1874 So, there could be some slippage but its unlikely that any of these locations can slip below #10. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ452>455. && $$ Synopsis...Gorse Near Term...Iovino Short Term...Drag Long Term...Gorse Aviation...Drag/Gorse Marine...Drag/Gorse Climate...Drag is the U.S. government's official web portal to all federal, state and local government web resources and services.