Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 222255 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 655 PM EDT Sat Jul 22 2017 .SYNOPSIS... A frontal boundary extended from the southern Great Lakes to our region this afternoon. Low pressure will ride eastward along the front and it should pass through our area tonight. Another low is expected to follow on Monday. The second low is forecast to pull the boundary southward and away from our region allowing high pressure to build down from the northwest for the middle part of the new week. A cold front from the northwest is anticipated to arrive on Thursday night. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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655 PM Update...Did some tweaks to hourly temps/dewpoints to lower temps and raise dewpoints where convection has hit in the last hour or so. Also bumped up PoPs in areas of Central/South Jersey based on latest radar trends in the last hour. Main threats continue to be gusty winds and downpours in the next few hours and short fused products will handle these. We are concerned about the heavy rain potential for Central and North Jersey tonight as well as parts of East-Central PA, mainly from Bucks/Mercer/Monmouth Counties on north. Higher resolution short term models are showing a heavier rain somewhere in this area resulting from lift from this afternoon`s sea breeze, the moisture boundary in place in that area and the approaching remnant MCV over eastern PA heading east. Larger scale global models, except the GFS, also show a threat for this but have it further north across North Jersey toward the New York border. We will keep an eye on radar trends but Flash Flooding may increase as a threat in these areas tonight if things all come together. PWATs are very juicy so the unload factor will be there if anything can ring it out of the clouds. 538 PM Quick Update...Bumped up PoPs and adjusted timing for the next 3 hours for southeast PA/west-central NJ based on the latest radar trends. Activity over Chester County as of writing should work into much of Philadelphia and the northern and western suburbs. Gusty winds and downpours causing water to collect are the main hazards with this line. Follow any short fused products for more details. A couple of convective complexes will impact the region through tonight. The first complex is a persistent MCS that is moving through the region this afternoon. The strongest portion is moving across Delmarva, where the greatest threat for severe presently exists. Good shear along with high CAPE values supports the potential for severe storms. SPC continues the slight/marginal risk across our forecast area with the greatest threat being damaging winds. Additionally, PWATs have been creeping up through the day as low level moisture is on the rise. Dew points into the mid 70s, especially across Delmarva, are present and any convective development will have some heavy rainfall rates. This combined with the deep shear and a well mixed boundary layer indicates that there is the potential for wet microbursts to occur. Poor drainage and urban flooding looks like the most likely outcome of the heavy rain but if the flow slows in any way, we could see some slow movers or training cells and flash flooding may become more of a threat and needs to be monitored. More convection is expected to arrive in our area through tonight as a second complex/boundary arrives. However, there is some uncertainty as to how much we will see across the region as atmosphere gets a bit cleansed from the first round of convection. Confidence is lower as to the coverage of the second batch of convection and have kept pops low across the region overnight and into the early morning hours. The convection will start to move offshore late tonight/early morning but we won`t feel all that much relief from the humid conditions. Temperatures overnight will be mild as cloud cover increases across the region. Fog may start to develop in some areas towards late tonight/early morning, especially where heavy rain has fallen. Lows will drop down into the low to mid 70s across the region, with some mid to upper 60s across parts of the southern Poconos and northwest New Jersey.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... Another slightly muggy day on tap for the region but temperatures will not be quite as high as they have been recently. Sky conditions will be pretty cloudy which should help to keep the temps a bit lower. With a boundary across the region it may be the tale of two cities (or parts of the forecast area). Areas to the north of the boundary should remain slightly cooler than those areas to the south of the boundary. For now, anticipate that the boundary will remain just south of or along the Mason-Dixon line. Areas to the north will remain in the 80s, while areas to the south look likely to reach into the lower 90s. Low pressure is slated to travel along the boundary and another round of showers and thunderstorms is expected, mainly during the afternoon and evening hours. Once again the abundance of moisture across the region will bring the threat for heavy rain and we will need to monitor it closely, especially for those areas that see heavy rain today. SPC continues the slight/marginal risks across our forecast area for Sunday with damaging winds being the greatest threat. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... Unsettled conditions are forecast to continue from Sunday night into Monday night. The frontal boundary is expected to remain in our region on Sunday night with another low expected to pass through our area on Monday. We are anticipating the likelihood of showers and thunderstorms associated with another convective complex on Sunday night. Precipitable water values should be in excess of 2 inches across the central and southern parts of our forecast area. As a result, we will mention the potential for heavy rain at that time. The chance of showers and thunderstorms will continue into Monday and Monday night with the passage of the low. The low is expected to begin pulling the front to our southeast and south on Monday night. The axis of a mid level short wave trough approaching from the northwest is anticipated to pass overhead on Tuesday afternoon and it will be followed by a shot of dry weather for the mid week period. A cold front is expected to approach from the northwest on Thursday and it should pass through our region from Thursday night into early Friday. We will mention a chance of showers and thunderstorms with the front. Dry weather is forecast to return for next weekend. Temperatures are expected to be seasonable during the new week with no excessive heat events in sight. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Scattered convection across the region through tonight. Timing is difficult as the lines are breaking up as they near our area but most likely time to affect the terminals is between 21-03Z. Additional showers/storms may follow in the wake of convection but confidence is lower as to timing and coverage. MVFR/IFR ceilings and visibilities are likely to occur in the wake of the convection and persist into the morning hours. Best chances will be at those locations that see heavy rain. There is potential for strong to severe storms today with gusty to damaging downburst winds and torrential rainfall. Sunday...Fog/low clouds early should clear into the afternoon but skies are expected to remain pretty overcast. VFR conditions are expected to return late morning/early afternoon but confidence is low that we see significant clearing through the day. Another round of showers and thunderstorms is expected, mainly during the afternoon/evening hours. Winds...light southerly winds today will become more west to southwest overnight and then will become more north to northeast on Sunday morning. Winds speeds are expected to remain around 10 knots or less. OUTLOOK... Sunday night...MVFR and IFR conditions in showers and thunderstorms. The rain may become heavy. Monday...A chance of showers and thunderstorms with conditions improving to VFR outside of any areas of rain. Monday night...Conditions lowering to MVFR and possibly IFR. A chance of showers and thunderstorms. Tuesday...MVFR and IFR conditions in the morning improving to VFR. Tuesday night through Thursday...Mainly VFR. && .MARINE... Sub-small craft advisory conditions are expected to continue on the area waters. Winds will generally be south to southwest through this evening around 10 knots. Winds will become more west tonight and then northerly into Sunday. Seas are 2 to 3 feet on the ocean today and will gradually rise to 3 to 4 feet on Sunday. While seas are expected to remain below 5 feet, they may near 5 feet on the outer waters late tonight into Sunday. Showers and thunderstorms will impact the area waters through tonight, with locally higher seas and gusty winds. OUTLOOK... Sunday night through Thursday...No marine headlines are anticipated. RIP CURRENTS... A moderate risk for risk currents is expected to continue through this evening. The underlying 10-12 second period continues to show up on guidance and is impacting the rip current risk. Additionally, with the new moon is occurring on Sunday, and a moderate risk looks likely for New Jersey with a low risk for Delaware for Sunday. && .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. The surge at this morning`s high tide was about +0.4 to +0.6 feet. There will be an onshore component to the wind today and it should bring the surge up around +0.6 to +0.7 feet by evening. The astronomical tides with the upcoming new moon are quite high, as was the case with the new moon in both May and June. As a result, the somewhat unimpressive surge values will likely result in some minor flooding. If heavy rain occurs coincident with the high tide, the potential for flooding will increase. Conditions may be similar for Sunday evening`s high tide. An onshore flow is anticipated for Sunday, especially in areas from Atlantic City up to Sandy Hook. && .EQUIPMENT... Dew point readings at KDOV continue to measure too high compared to surrounding locations and should be treated as unrepresentative of the area. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Coastal Flood Advisory until midnight EDT tonight for NJZ012>014-020>027. DE...Coastal Flood Advisory until midnight EDT tonight for DEZ002>004. MD...None. MARINE...None. && $$ Synopsis...Iovino Near Term...Meola/99 Short Term...Meola Long Term...Iovino Aviation...Iovino/Meola Marine...Iovino/Meola Tides/Coastal Flooding... Equipment...

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