Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 192350 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 750 PM EDT Sat May 19 2018 .SYNOPSIS... A warm front will continue lifting northward through our region this evening. A cold front approaching from the northwest is forecast to arrive late on Sunday. The boundary is anticipated to stall to our south on Monday. Weak low pressure is expected to move from the eastern Great Lakes to New England on Tuesday and Tuesday night and it should pull another cold front through our region early on Wednesday. The front is forecast to stall to our south as weak high pressure influences our weather on Thursday and Friday. The boundary may return northward as a warm front next weekend. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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730 pm update: Flood watch was dropped at 630 pm, as the more widespread rain has ended. Still some scattered showers moving SSW to NNE through eastern portions of the area, but these are not expected to produce widespread heavy rain. Of more pressing concern now is the fog, with several sites to the northwest of the Fall Line with visibilities falling near/below a quarter mile. These conditions will likely persist at least for a few hours and may worsen before the warm front moves northward. Speaking of, the northward progression of the front is likely overdone in the guidance, so I am quite skeptical of the hi-res model guidance improving visibilities later tonight. This may not happen until after sunrise. With this in mind, issued a special weather statement addressing the current fog, and updated the hazardous weather outlook to mention the possibility of a need for a dense fog advisory. This will be determined by the 930 pm update at the latest. Previous discussion... As of mid afternoon, the persistent pattern we`ve been in continues. Low pressure centered to our west near Michigan with a warm front extending eastward from it across the Delmarva. This boundary is separating warm and very humid air with dew points near 70 from a much cooler airmass to the north. Deep layer southerly flow continues east of the aformentioned low and around a high in the western Atlantic as it continues to pump rich moisture northward with PWATs near 2.0 inches. This moisture interacting with the front is leading to periods of heavy rainfall over the Delmarva with the latest batch moving in and showing some signs of training as it`s oriented in a south- north axis...the same as the cell motion. As such, we`ve extending the Flood Watch for southern NJ and the Delmarva to 9 pm but have removed SE PA zones where the threat for flooding has diminished. As we head through the late afternoon into this evening, big concern will be watching rain/showers continuing to move north and potentially producing continuing periods of heavy rainfall with embedded thunder possible with amounts of a half inch to an inch or more possible within a brief period. Area of greatest concern again looks to be the Delmarva especially from Talbot and Caroline Counties in Maryland into Kent Co. Delaware and points north...especially since these areas so such much rain Friday. Urban and small stream flooding will the most likely type of flooding but flash flooding will also be possible. The good news is, is that as we head through this evening, warm front will continue to lift northward through the area and this along with the loss of diurnal heating will lead to rain/showers diminishing...becoming lighter and more scattered across the area in the warm sector. Concern will then shift to areas of patchy fog and drizzle that may form in the increasingly muggy airmass as it advects in. In fact, as this airmass moves in, much of the area will continue to warm into this evening and then see temperatures hold fairly steady in the 60s or even rise overnight along with increasing dew points. Late at night, a cold front will begin to approach from the north and west along with some shortwave energy in the upper levels and this may tend to increase the chances for showers and even some isolated thunder mainly N/W of I-95.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... For Sunday, area will be firmly in the warm sector to start the day as low pressure moves northeast through Quebec. Don`t really expect any sun though as low levels will remain quite saturated in southerly flow and there will continue to be some showers, mist, and drizzle around. Heading into the late morning through the afternoon, the cold front will push south with time...reaching the I-95 corridor by mid afternoon and southern NJ across the Delmarva by evening. This front will be the focal point for more scattered showers and storms to develop...especially during the afternoon from the I-95 corridor S/E. Some good news is the the mid and upper levels will be drying out and the upper forcing will be shifting off to the east. This may tend to limit the coverage of showers and storms but nevertheless, PWATs will still be quite high (1.7+ inches) and with the saturated ground any showers/storms will be a concern for additional hydro issues...mainly of the urban and small stream variety. Temperatures will be much warmer as there will also be some sun developing by afternoon...highs will be mainly in the upper 70s to low 80s except cooler in the far north across the southern Poconos. Dew points will also be in the upper 60s ahead of the front so it will feel very humid until the front clears the area by tomorrow night. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... The long-term forecast period will begin with a mid level trough over eastern Canada and the northeastern states on Sunday night. The feature is expected to progress slowly eastward during the course of the week. A ridge is anticipated to build overhead from the west on Friday and Saturday. Conditions are expected to remain in flux during the first half of the work week. Dry air is forecast to push down from the north for Monday in the wake of a frontal boundary. However, the boundary and moisture should build back to the north on Monday night and Tuesday. We will keep the forecast rain-free for Sunday night and most of Monday, then we will indicate a chance of showers and an increasing potential for thunderstorms from Monday night into Tuesday. Weak low pressure is forecast to pass to our north on Tuesday night and it should pull a cold front through our area early on Wednesday. We will keep a chance of showers and thunderstorms for Tuesday night in advance of the front. A more substantial shot of dry air is expected for the second half of the work week. We are not anticipating any precipitation from Wednesday through Friday as the frontal boundary stalls well to our south and as ridging begins to build overhead from the west. The forecast for Saturday could go either way at this point. We will not mention any precipitation at this time. However, with a southerly flow becoming established and with the mid level ridge axis moving to our east, we may eventually need to introduce a chance of afternoon showers and thunderstorms. Temperatures for the period from Sunday night through Saturday are expected to be typical for this time of the year with highs mainly in the 70s and lower 80s, and lows in the 50s and 60s. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...IFR/LIFR CIGs/VSBYs with potential for some dense fog, especially at RDG/ABE. Light/variable winds may become predominantly southerly late. Moderate confidence. Sunday...IFR CIGs may persist through much of the morning, though VSBYs are forecast to improve gradually to MVFR/VFR after 12Z. MVFR to VFR conditions are expected everywhere by mid afternoon (though exact timing is quite uncertain) as southwest winds increase to 10 to 15 kts with occasional gusts to 20 kts possible. Low confidence. OUTLOOK... Sunday night and Monday...Mainly VFR. Some late night and early morning visibility restrictions are possible. Monday night through Tuesday night...A chance of showers and thunderstorms. Conditions varying between VFR and MVFR. Brief periods of IFR may occur in precipitation. Wednesday through Thursday...Mainly VFR. Some late night and early morning visibility restrictions are possible.
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&& .MARINE...
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730 pm update: Dense fog advisory issued for the coastal NJ zones, as webcams are indicating dense fog hovering just off the coast. With dew points increasing atop the cold ocean waters, do not expect this fog to dissipate through much of the morning tomorrow. Previous discussion... A Small Craft Advisory remains in effect. While winds continue to see a lull in many areas expect them to increase again by later this evening through tonight. Also, there will be some showers around tonight along with patchy fog, especially for the northern waters, and this may lead to reduced visibilities. For Sunday, SCA conditions continue over the ocean waters as SW winds gust up to 25 knots and seas will be around 5 ft. Conditions should be below SCA levels over the Delaware Bay. There will be some scattered showers around with the chance of thunderstorms, especially in the afternoon. OUTLOOK... Sunday night...A Small Craft Advisory is in effect until 10:00 PM Sunday for our ocean waters to allow wave heights to fall below 5 feet. West wind around 10 knots becoming north. Monday through Thursday...No marine headlines are anticipated.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Dense Fog Advisory until noon EDT Sunday for ANZ450>453. Small Craft Advisory until 10 PM EDT Sunday for ANZ450>455. Small Craft Advisory until 6 AM EDT Sunday for ANZ430-431.
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&& $$ Synopsis...Iovino Near Term...CMS/Fitzsimmons Short Term...Fitzsimmons Long Term...Iovino Aviation...CMS/Iovino Marine...CMS/Fitzsimmons/Iovino

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