Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 240121 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 921 PM EDT Sun Jul 23 2017 .SYNOPSIS... A frontal boundary will remain over our area overnight. Low pressure will ride eastward along the front and it should pass through our area on Monday. A second low will follow on Monday night and Tuesday as the boundary sinks slowly to the south. High pressure is forecast to build down from the northwest for the middle part of the week. A cold front from the northwest is anticipated to arrive on Friday. The front is expected to move slowly to our southeast over the weekend as areas of low pressure travel along it. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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**A Flash Flood Watch is in effect for the I-95 corridor and areas to the north and west for tonight through early Monday morning.** 919 PM Update...The focus for convection this evening has been north of a stationary boundary. The boundary at the present has become ill-defined due to cooling from convection but based on Theta-E analysis from the LAPS which shows a packing of contours just north of the boundary was still floating around across southern DE to the central parts of the Maryland Eastern Shore. Overall the intensity of the convection in the last hour has trended down and radar has the look of a stratiform type precipitation more than convective overall. Models are not doing too well this evening with respect to the placement of QPF, so I made adjustments to the grids for the next few hours largely based on radar interpolation. My thought is in the next 2-3 hours that most of the focus will remain along and northwest of I-95 towards the Fall Line. The slow movement to the northeast will keep the flood threat going. Rainfall rates will generally be under an inch per hour except in heavier pockets of rain. My thought on the far northwest part of our area is the flash flood threat here is not as great, but the watch will stay up for now and can be adjusted as the night unfolds. The next area to watch will be over central/southern Virginia which is potentially where convection may work into our area from later on tonight. Any additional rounds of heavy rain where we saw issues earlier (far northeast Maryland - mainly Cecil County, Berks County and points west of Philadelphia) will need a close eye if any more heavy rain falls as it will not take much to cause more flooding. Temps were adjusted as well based on the latest hourly temps and I also did a broad 1-2 degree bump in lows down as many spots were already at forecasted lows for tonight. Please follow any short fused products for more details on specific storms and area hazards. The boundary may move slightly north tonight but will remain nearly stationary into Monday. A low pressure system will develop along the boundary and move into our area late tonight. Heavy rain and thunderstorms will accompany the system. This second batch of rain is more problematic than the convection we will see this afternoon and evening. A good swatch of 1-2 inches of rain fell last night. We have not had ample time to dry out so the ground will be unable to absorb nearly as much precipitation as it otherwise would. Models have trended wetter with the latest runs and put a bullseye, or more of a heavy swath, of rain across our area. The focus looks to be more along the I-95 corridor but some of the models show a slight shift to the north and west of I-95. With PWATS still running around 1.5-2.0 inches across the region, we will have plenty of moisture to feed into showers and thunderstorms and torrential rainfall will occur. While the models are outputting pretty high, and what look like unreasonable, amounts it seems likely that a good 2-4 inch rainfall will occur within our CWA. A lack of strong flow at the surface and aloft shows that storms may not move very quickly (or at all), enhancing the flash flood threat. With higher confidence that flash flooding will occur somewhere in the CWA, we have issued a Flash Flood Watch for the I-95 corridor and areas to the north and west through Monday morning. Temperatures have certainly been cooler today than of late but expect a decent amount of cloud cover to remain over the region through tonight. This will keep the temperatures more moderate overnight tonight. Expect lows to range from the upper 60s across the southern Poconos to the low to mid 70s across the region.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... The boundary remains in the area with the low pressure system moving through the region on Monday. A cold front will drop down from the the north on Monday, taking its time as it makes its way through our area. A continued chance for showers exists through much of the day with a chance for some thunderstorms as well. Heavy rain will remain a threat in some of the stronger showers and in thunderstorms. Some clearing may occur during the afternoon, mainly southern areas, with more clearing expected towards evening. Highs will rebound slightly and dewpoints should start to drop, although that may be a slower process. It will still feel humid, especially across Delmarva and extreme southern New Jersey. Expect highs to be in the lower 90s from I-95/Philadelphia and points to the south and in the mid to upper 80s through central New Jersey. Lehigh Valley, Pocono and northern New Jersey will remain cooler with highs in the 70s to around 80. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... A chance of showers and thunderstorms will linger into Monday night. Based on the latest model guidance, drying may be delayed a bit. It now appears as though the mid level short wave trough from the northwest will not arrive until late Tuesday. As a result, we will keep some clouds and a slight chance of showers for Tuesday. Dry air is anticipated to follow the mid level trough for Tuesday night through Wednesday night. A cold front is expected to approach from the northwest on Thursday and it should pass through our region on Friday. We will indicate an increasing chance for showers and thunderstorms at that time. The forward progress of the front is expected to slow over the weekend as waves of low pressure travel along the boundary. We will continue to carry a mainly dry forecast for Saturday and Sunday, but that could change if the front starts to trend toward being even less progressive. Temperatures are expected to be seasonable during the period from Monday night through Sunday. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Scattered convection across the region through tonight with showers continuing through the overnight hours. Periods of heavy rain with IFR conditions possible, especially from KILG/KPHL and terminals to the north and west. There remains the potential for strong to severe storms today with gusty to damaging downburst winds and torrential rainfall. VFR/MVFR conditions have prevailed through much of the day and we should see mainly VFR conditions at the terminals outside of showers and convection. Conditions will deteriorate as storms arrive and ceilings and visibilities will remain MVFR, possibly IFR, through much of the night and into Monday morning. Conditions will be slow to improve on Monday but are expected to return to VFR by late morning/early afternoon. Winds...Easterly winds at the terminals today have remained light, around 10 knots or less across the region. Winds will become light and variable overnight and then become mainly west to northwest for KPHL/KILG/KMIV/KACY/KRDG and more north to northeast for KTTN and KABE for Monday. Winds speeds are expected to remain around 10 knots or less. OUTLOOK... Monday night...Conditions lowering to MVFR and possibly IFR. A chance of showers and thunderstorms. Tuesday...MVFR and IFR conditions possible in the early morning, then VFR. Tuesday night through Wednesday night...Mainly VFR. Thursday...Mainly VFR. A chance of afternoon showers and thunderstorms. Thursday night and Friday...MVFR and IFR conditions are possible in showers and thunderstorms. && .MARINE... Sub-advisory conditions are expected to continue on the area waters through Monday. Seas are 2 to 4 feet on the ocean and around 2 to 3 feet on the Delaware Bay. While seas are expected to remain below 5 feet, they may near 5 feet late tonight/early Monday, mainly our northernmost waters. Additionally, winds will pick up some overnight our of the east in response to a surface low moving over the area and a tightening pressure gradient. The gradient doesn`t look to fully wrap up until the surface low is to the east of our area. Winds may gusty briefly near 25 knots but confidence is low that a small craft advisory will be needed. Showers and thunderstorms will impact the area waters through tonight, with locally higher seas and gusty winds. OUTLOOK... Monday night through Friday...No marine headlines are anticipated. RIP CURRENTS... A low risk remains is expected for Monday for rip currents with a possible moderate risk along the Monmouth and northern Ocean County beaches. && .TIDES/COASTAL FLOODING... There is Coastal Flood Advisory in effect for this evening`s high tide along the New Jersey and Delaware coasts and along Delaware Bay. An onshore flow along the coast from Sandy Hook down to around Atlantic City almost guarantees minor flooding for the New Jersey coast. Conditions may be a bit marginal for Delaware. The astronomical tides will remain high for Monday evening`s high tide and another Coastal Flood Advisory may be needed at that time. && .EQUIPMENT... Dew point readings at KDOV continue to measure too high compared to surrounding locations and should be treated as unrepresentative of the area. Hamburg NJ transmitter is off the air. No known rts. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flash Flood Watch until 6 AM EDT Monday for PAZ054-055-060>062- 070-071-101>106. NJ...Flash Flood Watch until 6 AM EDT Monday for NJZ001-007>010-012- 013-015>019. Coastal Flood Advisory until 1 AM EDT Monday for NJZ012>014- 020>027. DE...Flash Flood Watch until 6 AM EDT Monday for DEZ001. Coastal Flood Advisory until 1 AM EDT Monday for DEZ002>004. MD...Flash Flood Watch until 6 AM EDT Monday for MDZ008. MARINE...None. && $$ Synopsis...Iovino/Stachelski Near Term...Meola/Stachelski Short Term...Meola Long Term...Iovino Aviation...Iovino/Meola Marine...Iovino/Meola Tides/Coastal Flooding...Iovino Equipment...PHI is the U.S. government's official web portal to all federal, state and local government web resources and services.